Temporal bone dissection (house)

l-.
F
F
ft
ah
a
ft
F
EF
3
3
3
t'?
3
7
3
34
14
1
4
4
4
-{
1,.-a
L;l-
TemporalBoneSurgicalDissectionManual
by
RalphA. Nelson,M.D.
HouseEarInstituteandotologicMedicalGnoup,lnc.,LosAngeles
Publishedby HouseEar Institute, Los Angeles

Tableof Gontents
F
F
EF
i-e
P
P
F
F
rc
?
lo
?rc
F
P7o
i'-
i-o
i-3
i3
ie
i'?
F
F7
z1i
7
?a
-a?a
4
4
4
4
a
D
,t
b)
Introduction: Equipment, General Considerations. . I
1. Basic Mastoidectomy T
2. FacialRecess,Epitympanum. ......19
3. Postauricular Facial Nerve Decompression . . ,26
4. Endolymphatic Sac and Extended
FacialRecessDissections. ......96
5. TympanicRingRemoval ......42
6. PostauricularLabyrinthectomy ....49
7. InternalAuditory Canal. ......52
8. MiddleFossaApproach... ....62
9. Middte Ear Dissection ...29
lO. WallDownTechniques. ......9b
Index ...91

Basic Mastoidectomy
Step 1tFig. 3l:
Topography
Surface topography on exposure of the lateral surface of the mastoid bone
before dissection is the external acoustic meatus (ear canal) anteriorly'
the suprameatal spine (of Henle) at the superior posterior portion of the
canal, and the suprameatal triangle (of Macewen) immediately behind the
spine of Henle, where subperiosteal abscesses mi$ht form secondary to
mastoid infection. The temporal line, forming a ridge continuous from
the superior border of the zygomatic arch posteriorly onto the mastoid
cortex, is the inferior limit of the temporalis muscle insertion. The lateral
wall of the mastoid process (tip) is the point"of insertion of the
sternocleidomastoid muscle.
The largest available burr and the largest available suction-irri$ator
shouldbe used during initial cortical exposure. An absence of important
structures in the cortex allows safe and rapid removal of this bone,
conserving the surgeon's time and energy for more tedious and delicate
dissection elsewhere. A high rate of irri$ation is necessary to prevent
overheating of the burrs and clogged burr flukes, which decrease cuttin$
abilitv.
External auditory canal Macewen's triangle
y
!-
a
-
a
ts1
Fj
,J
-
P
ts
er
ei
Landmarks:
External auditory canal
Spine of Henle
Macewen's triangle
Temporal line
Mastoid process e.
t.
e-
F
ts
e-
t-
F
e
-
F
l}
F
3
7
-
>
>
g
t
e
tr
t:
b
tt
t,
e
ts
b
I
t!
^l
Spine of Henle
Figure 3

step 2 tFig.4l:
t
i
-a
-t
'{
-t
-1
J
a
a
a
.a
.a
a
.a
2
I
_-
-t
Removalof Gortex
The surface of the bone is wet with irri$ation fluid from the suction-
irrigator and the drill is applied to the mastoid cortex immediately
posterior to the spine of Henle. A straight cut drawn along the temporal
line posteriorly into the sinodural angle delineates the upper portion of
the dissection. A second cut is made perpendicular to the first and
toward the mastoid tip. This cut is immediately posterior to the posterior
canal wall. The mastoid cortex is then removed in a systematic fashion of
saucerization, with the deepest portion of penetration at the junction
between the two perpendicular lines. This area behind the spine of Henle
which actually overlies the mastoid antrum is called the suprameatal
triangle of Macewen.
External auditory canal Temporal line
Spine of Henle
Mastoid tip
Landmarks:
Spine of Henle
Macewen's triangle
Mastoid tip
Temporal line
Figure 4
4f
<
4
4
a
4
-a
a
-a
4
a
a
a
a
a
A
2
2
2
)
2
2
2
2
l

Step 3 tFig.5l:
Gavity Saucenization
To avoid a constricted dissection that prevents adequate angular
visualization of deeper-lying structures, wide cortical removal should be
completed before aeepei penetration into the antrum. The mastoid cortex
snouta be unroofed fiom the posterior canal wall back to and slightly
beyond the sigmoid sinus and at an adequate distance into the mastoid
tip. fn. poste-rior canal wall should be thinned so that the shadow of an
instrument can be seen through the bone when the canal skin is
elevated. This wide saucerization cannot be emphasized enough.
Insufficiently wide saucerization is the singlg most, common reason for
inadequate recognition of landmarks and awkward exposure during
deeper dissection.
When adequate cortical removal has been accomplished, a kidney bean-
shaped
".rrity
will result. The inferior portion of the shape is formed by
the^mastoid iip below the sigmoid sinus and ear canal. The upper portion
is above the sigmoid sinus, extending posteriorly into the sinodural angle
and anteriorly'into the zygomatic root. Anteriorly, the posterior bony
canal wall wiil constrict tlie center of the cavity. This type of cortical
removal is basic to all posterior approach procedures on the mastoid
cavity. Again, be reminded that failure to perform this type of exposure
while deJpening the dissection toward the antrum can lead to a
bothersome constriction of the cavity at more medial levels.
Posterior canal wall Tegmen tympani
Landmarks:
Posterior canal wall
Tegmen tympani
Mastoid tip v
e
O-
e-
e-
F
v
e-
F
>f
FD
/f
Ft-
F
F
F
F
>
)-
F
>
F
F
ts
ti
t,
ti
ti
t:
Figure 5
ti
e
b
I I
tia
a-
Zygomatic root
10
Koerner's sePtum

step 4 tFig.6l:
J
a
€
-a
4
€
a
)
)
ldentificationof the MiddleFossaDunalPlate
During mastoidectomy, it is important to exposethe middle fossa dural
plate (tegmen tympani) for best possible accessinto the antrum and
ipttympanic areas. This exposure is critical to a well dissected sinodural
angie, which provides visual access into the internal auditory canal,area
after tabyrinthectomy. Failure to locate the middle fossa plate usually
leads to insufficient removal of cells along the superior border and causes
compromised exposure and decreased accessto the epitympanum and
hard angle.
We have found that the best way to expose the middle fossa plate is to
burr the cortex into the area of the linea temporalis until bone color
changes indicate that the middle fossa dura has been reached. The
dissection should round off the edge of the superior lip roughly
paralleling the curve of the dura. This plate exposure can be followed into
the antrum without lacerating the dura. At this stage of the dissection,
do not use #24 burrs for extensive thinning of the plate, since larger
cortical burrs tend to fracture the thin plate and create large dural
dehiscencesthat may become lacerated. Once the heavier bone is
removed, thinning can be performed with a diamond, which results in
less bleeding.
t.
-a
)
)
aa,-
p
t)
h
14
l;
14
ts
F
t'
F,-
F
ir
ir,-
,-
,-
,-
,-
,t
,2
,2
P
t2
t2
2t9
Tegmen tympani (middle
fossa dural plate)
Mastoid tip
Sinodural angle
Tegmen (middle fossa plate)
Figure 6

Step 5 tFig.7ll.
ldentificationof the Lateral Sinus
When the middle fossa plate is well established, the surgeon locates the
sigmoid sinus by drilling out the posterior portion of the mastoid cavity a
sufficient distance from the bony canal wall. Well aerated mastoid bone is
frequently found in neurotologic dissections, and it is possible to
continue drilling in the posterior direction until the occiput is exposed. If
a sufficient amount of bone has been removed posteriorly, the dissection
may proceed deeper into the mastoid cavity in an attempt to find the
sigmoid sinus. The sigmoid sinus generally appears in the posterior
portion of the dissection as a blue discoloration of smooth dural bony
plate. Dural plate of both the middle fossa and the posterior fossa tends
to be somewhat uniform and is not cellular; therefore, one should inspect
any area of smooth plate carefully for color changes that indicate an
underlying soft structure, such as the si$moid sinus. Because this plate
can be quite thin, one proceeds with caution. Thinned dural plate usually
can be identified by changes in the sound of the burr vibrating on it.
Once the sigmoid sinus has been located under its plate, the area
between the sigmoid and the middle fossa plate, the sinodural angle, can
be fully evacuated of air cells. In dissection of the sinodural angle,
penetration of the plate results in exposure of the superior petrosal sinus.
This sinus lies immediately deep to the sinodural angle in its entire
extent, and represents the posterior superior lip of the temporal bone
where the middle fossa and posterior fossa meet. The sigmoid sinus
usually lies a few millimeters deep to the cortex in the mastoid cavity.
This structure is the posterior limit of the standard mastoid dissection. It
is not more widely exposed unless the posterior fossa is to be entered.
Inferior to the sigmoid sinus lies the largely air-containing mastoid tip.
Laterally, there is no danger of entering any vital structures, so the tip
may be cleaned of air cells to gain better exposure in the jugular bulb
area.
The areas dissected and the structures identified thus become landmarks
for deeper penetratiori into the temporal bone. The cortical landmarks of
the external canal, spine of Henle, linea temporalis, and mastoid tip now
become the mid-level landmarks of the middle fossa plate, sinodural angle
plate, sigmoid sinus plate, mastoid tip air cells, and the thinned posterior
external canal bony wall. Knowledgeable and safe penetration deeper in
the temporal bone depends upon complete identiflcation of these
structures. The principle of temporal bone surgery is to move from one
known landmark to the next, guided by the relationships between each.
Only in this way can the temporal bone surgeon avoid the danger of
being lost within a nebulous network of vital structures.
Landmarks:
Tegmen tympani
Sinodural angle
Mastoid tip
rlz
{
tsD
F
=
tF!
F
-
P
U
U
v
U
v
U
U
P
U
U
E
-
-
!t
tsID
2
=
tstt
Ftt
-
F2
>V
--
tsv
,J
-
Y
E
V
a
ts
v
g
ti
,
I
lJ
i
F/
II
E
a
!
L2

ldentification of the Lateral Sinus
Posterior canal
Sinodural angle
Figure 7
Sigmoid sinus

srep 6 tFig.8l:
TheMastoid Antrum
The most important landmark at the next level of this dissection is the
mastoid antrum. Although the size of this air-containing pocket varies
considerably between pneumatized and nonpneumatized bones, one
rarely encounters a totally absent antrum. The antrum lies immediately
below the deepestpoint of penetration into the temporal bone posterior to
the spine of Henle and the zygomatic root. Koerner's septum (Fig. 5) often
lies deep to the mastoid cortex within the air cells of the well
pneumatized temporal bone. It is a segment of the petrosquamous suture
iine representing the fusion of the squamous and petrous bones. It is
usually a solid wall of nonpneumatized bone extending across the entire
mastoid cavity separating the more superficial mastoid cortex (squamous)
cells from the deeper (petrous) cells and antrum. It extends from the
posterior canal wall at the tympanomastoid suture line and blends with
the air cells in immediate approximation to the middle fossa plate,
sinodural angle, and sigmoid sinus plate. This structure is often initially
mistaken forlhe hard bone of the labyrinth and horizontal semicircular
canal. These structures, of course, lie deep to Koerner's septum. After the
septum is penetrated in the anterior superior quadrant of dissection, the
true antrum will be seen as a very large air-containing cavity. By keeping
the canal wall bone thin and avoiding the nearby middle fossa dura,
progressively deeper penetration will reveal the antrum. Normally, the
antium can be identified as a larger air-containing space at whose
bottom lies the basic landmark of the smoothly contoured, hard,
labyrinthine bone of the horizontal lateral semicircular canal.
Location of the horizontal semicircular canal (lateral canal) allows
exposure of the fossa incudis, the epit5rmpanumanteriorly and
superiorly, and the external genu of the facial nerve medially and
inferiorly. The hard labyrinthine bone extends posteriorly from the
horizontal canal to the posterior canal, which lies anterior and medial to
the sigmoid sinus. By removing cellsbetween the horizontal canal and
the sinodural angle, one encounters the hardest bone of the body, the so-
called "hard angle," which is part of the otic capsule. Posterior to the
labyrinth there may be some air cells in continuity with the petrous apex.
Inferior to the posterior canal, the posterior fossa dural plate overlies the
endotymphatic sac. More inferior to this area the bone of the mastoid tip
may be thinned to exposeperiosteum of the digastric muscle. The
digastric ridge runs in a posterior-to-anterior and lateral-to-medial
diiection, starting inferior to the si$moid and ending at the stylomastoid
foramen where the mastoid segment of the facial nerve exits the temporal
bone. The periosteum $enerally is arranged in a semi-lunar shape and
seems to turn superiorly to blend with the facial nerve sheath at the
foremen. Finding the digastric is one method of locating the facial nerve
in the mastoid cavity. Cells medially lead through the retrofacial area
above the jugular bulb. After the mastoid portion of the facial nerve
(discussed laler) has been definitively identified, the continuity between
the jugular bulb and sigmoid sinus can be followed along the smooth
dural-type plate.
Landmarks:
Tegmen tympani
Sinodural angle
Sigmoid sinus
Lateral semicircular canal
*
-tt
r,.J
I
FJ
It
lr.J
llt
4
st
P.!t
€
V
)4
v
v
v
ts
Fv
v
v
P:t
-
!t
Fg
ts!g
-
It
-
!p
F]!t
F!t
tsrg
Fg
€
F
v
F:
V
U
V
V
I
j.r
:l
g,
J
I
D'
;l:l

TheMastoid Antrum
Dr.,gastric ridge Fossa incudis
Horizontal semicircular canal

Step 7 [Fig.9l:
Gompletingthe Basic Mastoidectomy
The fossa incudis is most easily identified by removing bone in the
zygomatic root overlying the antrum. The incus can normally be seen
U.Tot. actual exposure 6ecause of the light-bending refraction of the
irrigating fluid (Fig. 9A). As the fluid is removed, the incus appears to
disippeai. As fluid fills the antrum, the incus once again appears.
The facial nerve is normally located inferior and slightly medial to the
horizontal semicircular canal by thinnin$ the posterior canal wall bone
and carefully removing bone in the facial recess area. The facial recess is
delineated by the fossa incudis, the chorda tympani, and the facial nerve
(Fig. 9B). Generally, under increased magnificaligt: 3
cutting burr is
usjd during irrigaiion with copious amounts of fluid to remove bone dust
and to p.o'o'id. oltimat visualiZation of underlying bone. In this way, the
blood vlssels and sheath of the facial nerve will impart discoloration to
the bone, normally pink in the living specimen and stark white in the
cadaver. Upon tocition of this discoloration, the sheath of the nerve can
be followed inferiorly toward the mastoid tip and superiorly and anteriorly
into the facial recess.
We have now delineated a new set of landmarks that are used for further
dissection of the temporal bone. The dissection thus far has created what
is commonly called a simple mastoidectomy.
Landmarks:
Tegmen tympani
Lateral semicircular canal
Fossa incudis and incus
Sinodural angle
Digastric ridge
Posterior semicircular
canal
.3 1
.r I
+,rl
--1,
'l4,
irI
4
-.1
t4
vl
E
c
e
e
e
U
F
E
e
Et
-
tl
J
It
4
-
tsv
-
-
IJ
lE
q
!-
a-
IE
e
e
e
e
v
v
U
I
j/
I
el
J
T
"l

Completingthe Basic Mastoidectomy
Digastric ridge
Fn
?3
3
3
?
?
3
3
?
3
?
3
3
?4
?
7
7
7
3
3
?
i'?
i'e
?
?
i-r
if
i-a
it
?
?q
lA
lA
lA
1.,
t,
l/)
t/)
I
{.
,
aa

Figure 9

C
-1
a,
4tl,
-/le
rr
t/
/al
/
F
F
F
7
ai
/
I
3!
I
'1E
-1F
-1t
tl
,f
Y)
I
,
I
,J
tr
/

/

a

t
,

a
,
f
,
,I
,
J
t
I
I
I
I
(
{
I
Notes

FacialRecess'EPitYmpanum
Step 1tFig. 1Ol
Topognaphy
The facial recess is a collection of air cells fyil$ immediately lateral to the Landmarks:
facial nerve at tnelxteinat genu' It occasionally serves as a route for Horizontal canal
middle ear diseas. lo .*i"ttE ittto the mastoid area via cells other than Fossa incudis
the antrum. cnoresteatoma that frequently invades these cells will be Posterior canal wall
extremely difflcult to remove via staridard iranscanal approaches. w9 f.':1^ External genu of VII
;ii;i;#ing or the facial recess in arry chronically diseased ear is of value
in providing an additional avenue of mastoid aeration' This exposure also
allows better visualization of the middle ear cavity in chronic ear disease
"rra
.*po*ure of the horizontal portion of the facial nerve during facial
nerve decompression. It is also ihe route to the round window for
insertion of the
"o"t
i"", implant electrode.The landmarks used to
expose the facial recess are the external genu of the facial nerve medially'
the fossa incudis s-riJ*i"irv, ihe chordaTympani nerve laterally, and the
tympanic membrane anteriorly and laterally'
sl
F.J,
rDl
-,
Ul
t-,
.'l
rll
F3
?
ts
ts
V
V
V
ts
;4
V
I
ts
-l
'J
v'l
Iaz
/
t?
r'It? |
)tz
1
I
u,
,/t/
c
C
C
€
d
/
Jul
J.
-1a
1J
1J
lII
'1
I
'l
t
'l
tl
;
I
a
i
Chorda tYmPani (roof) Posterior canal wall Fossa incudis
Mastoid tiP Incus buttress (wall)
Sigmoid sinus Tegmen
Zygoma

tic root
Sinodural angle
Facial nelve (floor)
Figure 1O

Step 2 tFig.111:
Openingthe FacialRecess
One begins dissection of the facial recess by identifying the external genu
or the descending portion of the facial nerve in the mastoid cavity. As
previously indicated, a free flow of irrigating fluid is used to allow clear
and constant visualization of the underlying bone so that color variations
in it may be easily identifled. The microscope is turned to 10 power. The
color of the facial nerve is pearly white in the preserved bone and pinkish
(from the vascularity of the facial canal and the nerve sheath) in a living
specimen. Generally, this dissection is accomplished with a cutting burr
until a change in bone. character is identified; further dissection is
performed with a diamond burr. A thin layer of bone is preserved over the
facial nerye and, because color changes in the bone will occur before the
facial sheath is uncovered, the soft tissue is not injured.
Identification of a facial recess cell tract is often possible by thinning the
posterior canal wall enough to see the shadow of an instrument through
the bone. One must not perforate the canal wall, disrupt the chorda
tympani, or transect the annulus.
Facial recess
Zygomatic root
Incus
Incus buttress
Landmarks:
Horizontal canal
Fossa incudis
Facial recess cells (if
present)
External genu
Cell tract
Posterior canal
Mastoid tip
wall
Sigmoid sinus
External genu Horizontal semicircular canal
Figure 11

srep 3 tFig.121=
Gompletingthe Recess
With the new landmark of the facial sheath, the nerve is skeletonized
distally along its descending portion in the mastoid and then medially as
it foUows thJ floor of the facial recess into the middle ear space. Smaller
burrs will be necessary to accomplish most of the dissection in the facial
recess since the recess itself rarely exceeds two or three millimeters.
Inferiorly the chorda tympani nerve is detected as it leaves the facial
nerve. Dissection does not sacrifice this structure. The chorda t5rmpani
nerve joins with the tympanic membrane anteriorly and laterally at the
annulir edge; thus, following the chorda t5rmpani generally prevents
disruption of the tympanic membrane.
Landmarks:
Facial nerve
Incus
Fossa incudis
Chorda tympani
Stapes
Horizontal canal
Figure 12
{
4tD
)€3
F12
,t1
2,
F2,
r
S4
V
14
V
V
r
r)
"l
4,vl
J
:)
7lri
4lz, I
J,u-l
/,
u, l
/tra
I
I
v-l
J
ol
I
ol
-l
2, 1
)
:)
3
:J
:J
Chorda
Descending segment of facial nerve
Digastric muscle
Posterior canal wall Long process of incus
Buttress
Fossa incudis
Stapes Tegmen
External genu Horizontal semicircular canal
Posterior semicircular canalSigmoid sinus

Step 4lFig. 131:
TheMiddleEar Thnoughthe FacialRecess
With the facial recess fully opened, one can easily visualize the horizontal
portion of the facial nerve, the lenticular process of the incus, the
incudostapedial joint, the capitulum of the stapes, the stapedial tendon,
and, with proper angulation, the cochleariform process.
The round window may be easily identified inferior to the stapedial
landmarks. Superiorly, a buttress of bone is preserved between the short
process of the incus and the facial recess. This is commonly termed "the
buttress." Drilling through the buttress causes disruption of the
ligaments to the short process of the incus and incudal dislocation is a
possibility.
Landmarks:
Facial nerve
Incus
Lenticular process
Incudostapedial joint
Stapes
Round window
Cochleariform process
Chorda tympani
Horizontal canal
,"1
Incudostapedial joint Incus
Figure 13
Chorda tympani
Round window
Promontory
Pyramidal process
Stapedius tendon
rnal genu
Tegmen
Buttress
Horizontal canal
Lenticular process

step 5 tFig.141=
Unroofingthe Epitympanum
In chronic otitis media, the epitympanum is a common repository for
cholesteatoma. It often has destroyed ossicles; more frequently it has
involved the body of the incus and the head of the malleus without
complete destruCtion. Complete exposure of the epitympanum without
dest-ruction of the scutum can be obtained by removal of additional air
cells in the root of the zygoma. This is done with use of the middle fossa
dura and the thinned posterior canal wall as landmarks'
Often a small diamond burr is necessary if the middle fossa dura and its
underlying bony plate, the tegmen tympani, lie low.-A small burr also
pr..r.ttl" iirattering of the thin plate. If necessary, this dissection may be
iarried anteriorly through the zygomatic root to the glenoid fossa. The
floor of the dissection is the horizontal canal, the superior sernicircular
canal. and the facial nerve.
Landmarks:'
Incus
Malleus
Tegmen
Horizontal canal
Facial nerre
Figure 14
V
V
€
Posterior canal wal
Buttress
Lenticular process
Stapes
Incudomallear joint
Head of malleus
?
,-'l
-i
Ll
J
2
:J
2
2
2
Y
:)
3
2
7rl
Ja, I
Epitympanum
Tegmen
Incus Superior ligament
,1tt
Horizontal segment of VII Ligament of short Process

Step 6 tFig.151:
Removingthe Buttress
In chronic disorders in which cholesteatoma involves the incus, the facial
recess may be connected to the attic and the epitympanic exposure by
removing the buttress after the incus has been disarticulated from the
stapes. This continuity between atticus and facial recess gives an
extensive view of the middle ear from behind. In cases in which
cholesteatoma involves the stapes, this technique can be used to provide
both an anterior and a posterior exposure of the stapes. This allows more
complete and safer removal of the cholesteatoma from these difficult
areas. With this approach, exposure of the facial recess is so complete
that the surgeon rarely has doubt about complete removal of
cholesteatoma in facial recess cells.
Cochleariform process Superior ligament
Chorda tympani Malleus head
Promontory Zygomatic root
Jacobson's nerue Tegmen
Round window Tympanic segment of VII
lvramidaf Process Horizontal semicircular canal
Landmarks:
Facial nerve
Horizontal canal
Chorda tympani
Stapes
Figure 15
Articular process
Stapedius tendon Anterior stapedial crus

Step 7 tFig.161:
@he Antenior EpitYmpanum
{
,-a
L
,tt
a.
;1
L
11
t4
14
a-
,-rr./
€
€
€
V
Y
€
i-/*i
/*l
,J:
J
:)
t.rl
J
./l
d
fr1
r'rrl
I
-l/
l.rr.
/
a
I
Y
ts
Y
a
'1i-
:1u
'12
.1
t-
:1
-'1a
"1
tl
:a
:I
l
I
l
ll
t
After removal of the head of the malleus and body of the incus, this
dissection allows unimpeded inspection of all epitympanic areas' In a well
pneumatized bone, air cells extending anteriorly into the petrous apex
may also be seen.
The figure shows the expansive e_xposureobtained with this technique'
trlote tLe cog, a bony ledge extending into the epitympanum from the
tegmen antErior to itre almputated h-eadof the malleus' This spicule may
"!!"r"t.
the epit5rmp.nrrrriirrto posterior and anterior compartments.
Removal of ctr-otesteito-u that is harbored anteriorly, which is common'
requires careful burring away of the cog'
This step completes dissection of the facial recessand epit5rmpanum'
root
I
Cochleariform Process ZYgomatic
Chorda tYmPani
cog
Landmarks:
Stapes
Facial newe
Cochleariform Process
Long process of malleus
Eustachian tube
cog
Figure 16
Manubrium
Umbo
J
,
l
'
HypotYmPanum
Peritubular cells
Tegmen
Promontory Facial neffe
26
Eustachian tube Canal of tensor tYmPani

PostauricularFacialNerue Decompression
Step 1= SimpleMastoidectomytseeGhapter1l
Tympanic membrane
Descending segment
Figure 17
Stylomastoid foramen External genu
Chorda tympani Tympanic segment of VII
Step 2= Openingthe FacialRecesstseeGhapter2l
Orientation: Fig. 17 shows the general orientation of the facial nerve.
Notice the posilion of the nerve in relation to the posterior canal wall, the
fossa incudis. and the horizontal semicircular canal. The facial recess is a
key to facial nerve decompression.
)-!l
r
F
5
,-tt
?;-J
l,
Fr,
Ft
)tJ
F
V
V
V
V
J-r
;.J
jJ
I
F
-l
>tl
-l
4
t
/,,
€
/
4
r-
€
,J
/
tJ
)
-l
Y.
-l
-l
;l
l
- t
J
J
l
l
J
J
J

step 3 tFig.181:
Skeletonizingthe DescendingPontion of Vll
During complete simple mastoidectomy, most of the facial nerve has been
u'ell delineated. For decompression, the nerve is followed from the
exposed external genu and the mastoid segment to the stylomastoid
foramen. As the stylomastoid foramen is approached, the periosteum of
ttre digastric muscle will blend with the sheath of the facial nerve. This,
in essence, is the stylomastoid foramen. The digastric itself is
occasionally used as a landmark to find the descending portion of the
facial at the stylomastoid foramen. In this method, after the nerve is
located at the foramen, the mastoid segment is followed superiorly back
to the area of the external genu and facial recess. However, this method
is generally not as reliable as locating the nerve at the level of the genu or
descending portion. The bone over the descending portion is thinned
u.ith use of a diamond burr and profuse irrigation to prevent frictional
heating of the nerve. An eggshell covering of bone is preserved over the
posterior one-half of the descendin$ portion of the nerve. This is
necessary to decompress the nerve satisfactorily and to prevent its
extrusion through a narrow opening in the bone. This part of the nerve
is not routinely uncovered anteriorly because of the external auditory
canal, laterally because of the chorda tSrmpani, or medially because it is
not necessary.
Descending segment of VII Long process of incus
Mastoid tip Chorda tymPani Posterior canal wall
Digastric muscle Facial recess Body of incus
Sigmoid sinus Stapes ntal semicircular canal
Landmarks:
External genu
Vasa vasorum of facial
nerye
Chorda tympani
Stylomastoid foramen
Digastric muscle
29Stylomastoidforamen Externalgenu Posterior semicircular canal
Figure 18

Step 4 tFigure.191:
TheHorizontalPortion of UII
The nerve is further exposed medial to its external genu into the facial
recess,as in the approach to the facial recessfor chronic otitis media.
This exposure allows visualization of the horizontal portion of the nerve
anteriorly toward the cochleariform process and then superiorly to the
tegmen, where the geniculate ganglion is located. Dissection of the
epitympanic space through the normal antrum-attic approach frequently
allows some exposure of the more medial portions of the horizontal
segment. The bone over the nerve is thinned enough so that the bone can
be easily lifted off the nerve with an elevator. The facial recess area will
normally admit the smallest diamond burrs (OOand OOO)under the incus
without dislocation of the ossicular chain. Rarely must the incus be
disarticulated from the stapes. A very small suction-irrigator removes
bone dust and debris from the tiny facial recessopening. Again,
irrigation must be adequate to prevent frictional heating of the nerve.
Suction may be inserted through the epitympanic spaceto provide
circulation of irrigating fluid while the burr is used in the facial recess.
The surgeon may choose to change the burr to the opposite hand for
proper angulation into the recess.
Bone should be thinned 18Odegreesacross the lateral aspect of the
external genu, and over the entire inferior one-half of the horizontal
(tympanic) part of the facial.
Cochleariform Process Buttress
Incus
Landmarks:
Facial nerve
Chorda tympani
Incus buttress
Fossa incudis
Incus (long process)
Stapes
Horizontal canal
-,/1L
t-
ft
-J
b
t1
l-
4
l-
lJ
!.
FJ
iJ
F
F
ts
F
I'r
14
r-'
}J
t4
!r.
F/
t/
att
1,
,1
tt
/tr,
t4
v
,4
!/
i4
!/
t4
t/
4
!/
IJ
tJ
t/
t4
v
i-
.4
.F
.t4
,
,?|
.l
,t.
,,J
J
:l
.;.
JI
G.
, ' .
Descending segment of VII
BO
Stapes Tympanic segment of VII
Figure 19

Step 5 tFig.2Ol:
"Barber Poling"the FacialNerve
Bone thinning for bone removal is performed in a "barber pole" fashion.
This effect is produced when: (1) the descending portion of the mastoid
segment between the stylomastoid foramen and the external genu is
unroofed on the posterior aspect; (2) the external genu and facial recess
portion of the nerve is unroofed on its lateral aspect; and (3) the
horizontal segment of the nerve is unroofed along its inferior border to
the level of the cochleariform process. This rotation of the unroofing
process from posterior to lateral to anterior allows safe removal of bone
without injury to the surrounding structures. In the descending portion,
decompression on the lateral side will result in sacrifice of the chorda
tympani. At the level of the external genu, removal of bone on the
posterior side will lead to fenestration of the horizontal canal. Burring
posteriorly or superiorly in the horizontal segment will lead to injury of
the horizontal canal. This thinning process should be completed over the
entire mastoid and middle ear segments of the facial nerve. Then the
burr is set aside.
Chorda tympani Fossa incudis
Posterior canal wall Buttress
Digastric muscle
Swlomastoid foramen Horizontal semicircular canal
Landmarks:
Facial nerve
Horizontal canal
Stapes
Chorda tympani
Incus
Figure 20
Posterior semicircular canal

Step6 tFigs.21,22l=
Uncoveringthe Sheath
The eggshell-thin bone is gently pried off the sheath of the facial. Any
thin, sharp pick may be used; a small dental excavator, with its twist like
that of the "whirlybird" of middle ear surgery, works extremely well.
Right- and left-hand excavators must each be available for optimum
angulation. One should not use another portion of the facial as a
fulcrum; rather, brace the elevator against nearby bone. Complete control
of the tip of the pick can be maintained at all times by proper use of a
fulcrum. The accompanying figures show the more familiar Rosen needle
being used to elevate the bone.
Landmark:
Facial nerve
Figure 21
---z
l9r
llt
/-J
llt
-
tf/
7J
l,
r--v
s1v
e-J
ts
F
H
ts
F
F
S-
F
>
lr
External genu
Buttress
l
tJ
t4
tl,
rJ
t
l1
!,
f4
l,
11
v
I
t?..:at::*t:;€*,:tl43t lij's*..lr:t:'a:,':; at:,i:l::,:rt:rrr.- I I
'
l;r
til
F
l-
l-
-
,4
4
e
q
€
I
rt
ct
;
;t
J
JI
(=.1

Figure 22
Uncoveringthe Sheath
Digastric muscle
Chorda tympani
Stylomastoid foramen

Step 7 tFigs.23, 241=
Openingthe Sheath
The sheath is opened with a #59 BeaverRknife. It is shaped like u."igkt'
knife with slightly less curve. Because it is disposable.' it is never dull' A
drrllblademight""*.tuggingonthenerveduringslicingofthes|3trt
because ttre sfreaitrl; q;i6 toirgtr and relatively thick' It has the white
color of connective tissie and the nerve fibers it contains are gray.
Becertaintoexaminethenerveforcircularfibrousbandsthatwill
constrict the nerve flbers' These bands must be lysed'
Themastoidandmiddleear.portionsofthefacialnervearenow
decompressed.FurtherdecompressionofttrelabyrinthineSegmentmust
be carried out trriouan ,n" middte fossa. Although some of the
labyrinthi.r. po.aiorro.rr"y be decompressed v].a
itre
mastoid, it is a tedious
and difficutt aisseciiorr. in addition, the medial po_rusof the fallopian
canal cannot b. ;;;a iioln tt i" approach,.ln{ this is the narrowest
;;;iiht canal ind the area most susceptible to constriction.
Landmark:
Facial neffe
Figure 23
Buttress
Descending segment of Vtl
Tympanic segment of VII
34

Stvlomastoid foramen Chorda tympani
Openingthe Sheath
Mastoid tip
Figure 24
Sigmoid sinus

Notes
4lr-
{
2-J
]
FJ
L,
/
-/
-
/
-
t4
-
V
V
>
e
e.
F
E
E
E
sr
s--3
FJ
3
,1
rb
I
3
€
11f
tsY
€
.J
rtt
t-
v
eY
J
ts
V
V
V
t-
Y
et
€/
I
FJ
elj
I
ET
i
tfi
k-

l-
I enOolymphaticSac Dissection
Step 1tFig. 251:
Topography
The endolymphatic sac is located in a thickened portion of posterior !f""
Landmarks:
dura medial io the si$moid sinus and inferior to the posterior canal. The
Horizontal canal
sac is readily found by performing a simple mastoidectomy with
- Posterior canal
particular aitention to sketetonizlng the si$-moid sinus and thinning the
b;;e;;t t tit
"^posterior
fossa dural plate immediately medial to the sinus' Although
Sinodural angle
tlue-lining the posterior semicircular canal was once routine, it is only
Sigmoid sinus
rarely reqiired ind is usually avoided because it carries greater incidence gL-* f"lf"pian canal
of hearing loss. The area of ihe sac extends from the medial aspect of the
M;;i"id tii-""ff"
sigmoid s-inus anteriorly into the retrofacial area inferior to the posterior
b"r"f ff"tl
calal and superior to the jugular bulb. The exact location of the sac,
which varies, is usually idenlified by the presence of thickened white
dura next to the normally darker, single-layered dura, or by the presence
of hypervascularity on the surface of the sac. The sac also has been
known to occupy lhe medial wall of the jugular bulb. The most likely
cause of inability to locate the endolymphatic sac is that the dissection is
not carried far enough into the retrofacial recess. Of course, to delineate
the sac safely in this area, the descending portion of the facial nerve
must be located and carefully preserved' Donaldson's line is an ima$inary
line in the plane of the horizontal canal back to the sigmoid sinus. It
often marks the top of the endolymphatic sac'
13
{
tb
!b
b
,4
3
l-
=
-F
F
-
ts
,2r
F
?.J
It
,
a
Area of facial nerve
Retrofacial cells
Mastoid tiP
a
t
Y
tJ
iJ
j-
rj
rF
?
F
E
i
€J
II
FI
.J
F{
Tegmen
38
Donaldson's line Sinodural angle
Figure 25

Step 2 tFig.261:
Uncoveningthe Sac
The dural plate over the sac is thinned with a diamond burr. Wide
exposure is performed so that sutures may be placed in the dura to
secure a muscle plug at the end of the procedure. Retrofacial and mastoid
tip cells may be opened for wide exposure and dural plate bone is thinned
next to the posterior canal. Again, do not blue-line this canal. The
endolymphatic duct may be seen as the apex of a fan-shaped extension of
the sac under the posterior canal. This apex is often tented from the
labyrinthine bone where the duc't exists deep to the canal when the sac is
depressed with an elevator. The eggshell-thin dural plate is then picked
away from the dura.
Facial
Retrofacial cells Fossa incudis
-l
Endotymphatic sac Tegmen
Sinodural angle
Landmarks:
Sigmoid sinus
Labyrinthine bone
Dura
Sigmoid sinus
Figure 26

I
Step 3 tFig.271=
Incisingthe Sac
The lateral wall of the sac is incised and the interior exposed. There is a
smooth, glistening lining which, in the living specimen, is moist. The
incision 5n the laleral srJrface of the sac can be made with any relatively
sharp instrument that will not penetrate deeply into the sac and beyond
into ihe subarachnoid space. The incision into the medial wall of the sac
under higher power magnification may be accomplished with a small
hook so as to avoid injury to underlying vessels. This medial incision is
generally at right angl-es io the lateral wall incision and further under the
fiap to facilitaie closire. The medial incision is only a separation of dural
fibers allowing the arachnoid to bulge into the sac. This, of course, does
not occur with a cadaver specimen.
The shunt tube is inserted through the medial incision into the
subarachnoid space, allowing the flange to remain-in-the sac lumen' The
flap is then used to cover the-flange. A silk suture holds a muscle plug
agiinst the lateral incision of the sac wall'
Facial nerve
Retrofacial cells
Sigmoid sin
Fossa incudis
Sinodural
Landmarks:
Endolymphatic sac
Sac lumen
Subarachnoid sPace
il
I
{l
f
l
|}
-
!}
,1tD
/!
ts
F
7
ts
F
ts
F
s-'
F
-
-
3
It
lfr
rb
rL,
rJ3.
J4
b
t1
tj
tj
t4
rJ
}J
/
F
?
7
-
?r
I
I
IE
I
a.l
-l
j
!{
40
Lumen of endolYmPhatic sac Shunt tube
Figure 27

ExtendedFacialRecessDissection
Step 1tFig. 281:
Topography
Inferiorly, the facial recess dissection may be extended with sacrifice of
the chorda tympani. Such an exposure provides visualization of the
hypotympanic area and access to the so-called "crotch" where the jugular
bulb meets the carotid artery. The primary landmarks for this dissection
are the descending portion of the facial nerve as the medial limit of
dissection, the annular ligament of the tympanic membrane laterally, and
the jugular bulb inferiorly. This approach is the commonest for smaller
glomus tumors. Further dissection in the inferior portion of the mastoid
cavity may be carried out in the retrofacial area, which is inferior to the
posterior canal and medial to the facial nerve. This approach enables
complete exposure of the hypotympanum if it has been invaded by
hypotympanic and retrofacial cholesteatoma. This also is a route for
exposure of larger glomus tumors. Limits of this dissection are the
posterior canal and cochlea superiorly, posterior fossa plate posteriorly,
and the jugular bulb inferiorly and anteriorly. This approach can be
combined with transcochlear and translabyrinthine approaches to
reroute the facial nerve in cases of large congenital cholesteatoma or large
glomus jugulare tumors.
Zygomatic root
Posterior canal wall Buttress of incus
Fossa incudis
Landmarks:
Fossa incudis
Incus buttress
Facial recess
Facial nerve
Chorda tympani
Stapes
chorda.*"1
/
Facial nerve
Stapes
Figure 28

Step2 tFigs.29,3OI:
Extendingthe FacialRecess
The facial recess is extended at the lateral aspect of the facial nerve by
sacrificing the chorda tympani. This allows the recessto be opened
inferiorlybetween the facial nerve and the annulus fibrosis. As the
annulus turns anteriorly, it moves away from the facial nerve, which
permits the surgeon to remove more bone. The annulus then becomes
the prime landmark. As the dissection continues forward through
hypotympanic bone, a new structure is encountered: the jugular bulb as
it iises into the hypotympanum. This provides the exposure necessary to
remove a small glomus tumor or extensive hypotympanic cholesteatoma.
Pyramidal process
Chorda tympani
lncus buttress
Fossa incudis
Facial nerve Horizontal semicircular canal
Landmarks:
Facial nerve
Chorda tympani
Annulus
Tympanic membrane
Figure 29
{l
c']
{l
a1
I
21r
t
a1
1
/l
7
7
r
r
V
V
r
7
r
V
tsa
Fa
FJ
L
/

/lr.
|1
a
F
a
t4
l"
F
t
11rL
(
a
(
/3
/a
C
r
r
F
i
I
ut
J
..
J
J
J
Stapes

Extendingthe FacialRecess
E
E
E
)4
)2
)D
)D
V
w
Figure 3O
Medial side of tympanic
Annulus fibrosis
Umbo
membrane
Facial nerve
Incus buttress
43

Step 3 tFigs.31, 321:
JugularBulb/GarotidArtery
If the surgeon extends the dissection, the bone of the inferior portion oI
the tympanic ring and mastoid tip may be removed lateral to the facial
nerve. This gives wide exposure of the hypotympanum to the level of the
eustachian tube.
Removal of retrofacial cells that extend from the mastoid into the middle
ear allows one to follow the sigmoid sinus in its continuity with the
jugular bulb. Carrying the dissection even more anteriorly, one
encounters the carotid artery and sees the confluence of the two large
vessels leaving the carotid sheath and entering the base of the skull. The
bone occupying the part of the skull base where the carotid turns
anteriorly and the jugular turns posteriorly is called the "crotch"
(jugulocarotid spine). Follow these vessels. The jugular bulb can be
opened and IX, X, XI found in proximity to the multiple openings of the
inferior petrosal sinus.
Stapedial tendon Buttress
Annulus fibrosis
Hypotympanum Stapes
Extended facial recess Horizontal semicircular canal
Landmarks:
Facial nerve
Annulus fibrosis
Sigmoid sinus
Jugular bulb
Carotid artery
Figure 3l
-J
v,.
C
It
-
tlt
/-1
rD
,4
D
,|J
D
Ft
-
g
r
14
?
F
-
F1
-
7
-
!
2
FJ
L
F
?
FrD
FJ
t
rJ
L
-
L
/rD
,1
3
F
IL
/rD
4
t
F
?
/t,
C
€
€
e
r
F
-
V
ts>
F!
P/v
-i
:
F.
-
}..
Retrofacial cells Facial nerve

Round window
JugularBulb/GarotidArtery
Jugulocarotid septum
Jugular bulb (ghost)
r:{4W
Sigmoid sinus
Retrofacial cells
Figure 32
Carotid artery (ghost)

Notes
4tL-
{
l,
t
L
|1
r/
F-
a
{
€
;'1
a
>4v
s1
V
€
>1
a/
€
C
-
!-
l;l
t-
rL
tl-
-
,/
t-
,.r
-
=
v
J
-
,/
i
FJ
,-
,-
/
)
l-
l)
,-
7
i
J
ts
I
|.
:
=46

TympanicRingRemoval
Step 1tFig. 331:
Removingthe TympanicBone
Removal of the t5rmpanic ring is often indicated when there is a
carcinoma of the conchal area of the ear or the external ear canal. A
procedure for cancer must be performed in an en bloc fashion with the
skin of the ear canal, the tympanic membrane, and the bony canal walls
removed together. This can be done by a combination of some procedures
described pleviously and a dissection through the area of the zygomatic
root and the temporomandibular joint. A standard postauricular simple
mastoidectomy is performed, followed by an extended facial recess
dissection under the posterior canal wall but lateral to the facial nerve.
More anteriorly, the lateral portion of the jugular bulb is the most medial
part of the dissection. The lateral wall of the jugular bulb will eventually
intersect with the posterior wall of the internal carotid artery in the
anterior hypot5rmpanum medial to the eustachian tube. Superiorly, the
dissection started in the antrum continues through the epit5rmpanum
and zygomatic root below the middle fossa dura until the area of the
temporomandibular joint is entered. The auricle or the concha is then
rembved en bloc with a sleeve of tissue representing the bony and
cartilaginous external auditory canal, including the tympanic membrane
and malleus. The incus will normally be attached to the malleus and it
must be disarticulated from the stapes'
Tlmpanic ring sleeve Canal of tensor tymPani
Zygomatic root
Temporomandibular j oint space Tegmen
Landmarks:
Zygomatic root
Jugular bulb
Temporomandibular joint
,}J
3'
dl
,-J
l}
-.J3
r.,.J
ff/
,J
3
s-J
tl/
|1
v
i4II
-
a/
--
€
P
-
€
a/
,FY/
-
v
-
v,
4
-3
tJ
dr,
-
{r,
-
',t1,
,1
'l/
F
{9
,.J
s,
aitl
s/
-
S,
.'Si1
S,
Pa'!S/
i'ia
s,
:F
!,
pt
:l,
ts!,
F
>
.f
tY'S/
l '
Extended facial recess
Jacobson's nerve
Epitympanum
ittv
,J
)!/
ivv
g
St
I.
'J
i'L
Promontory Eustachian tube
Figure 33
,tr

PostauricularLabyrinthectomy
Step 1tFig. 341:
Topography
The postauricular labyrinthectomy is designed to eradicate labyrinthine
vertigo by complete removal of the semicircular canals and all soft tissue
of the vestibule. It is also the commonest surgical route to the internal
auditory canal. A complete simple mastoidectomy is performed with the
posterior canal wall left intact. The sinodural angle must be completely
drilled out to provide adequate exposure of the area of the vestibule later.
The middle fossa plate must be thinned completely to provide access to
the superior semicircular canal. A large cutting burr is used to open the
sinodural angle posterior to the labyrinth. In this way, the flukes on the
side of the cutting burr may be used to better advantage in removal of the
extremely hard labyrinthine bone anterior to it.
-r7
Tegmen
Landmarks:
Incus
Horizontal semicircular
canal
Posterior semicircular
canal
Tegmen tympani
Facial nerye
Sigmoid sinus
Sinodural angle
L
L
L
L
rt,
rt
-
!-
!,
F3
-
€
ts
€
tsI,
€
ts
tj
t-
-
L

rL
rL
rt
tl"
,1
l,
-
t-
,t1
!4,
1,
t
C
{
-
t
;r
r
F
ts
>
>
Frf
h-
ts
e.

Mastoid tip
Labvrinth
Figure 34
50
Mastoid cortex
Sigmoid sinus Sinodural angle

step 2 tFig.351:
E
H
F
a
3)D
V
V
)a
b
Openingthe SemicircularGanals
By cutting into the labyrinth, one should be able to fenestrate the
horizontal semicircular canal and, by enlarging this dissection, unroof
the posterior canal and the anterior portion of the superior canal as well.
The fenestrated canals are followed in their extent to provide continuing
landmarks. The surgeon should eventually have a dissection that shows
the orientation of each canal to its neighbors. Anterior to the horizontal
canal, the external genu and horizontal portions of the facial nerve can be
skeletonized. Preservation of the anterior wall of the horizontal canal
seryes as a protection for these portions of the facial nerve until further
thinning over the facial is necessary to expose more of the vestibule.
Profuse irrigation is necessary to remove vast quantities of bone dust and
also to prevent frictional burning of nearby bone. The largest burr that is
comfortable should be used to enable quick bone removal, decrease
frictional heat, and prevent burr clogging.
Posterior canal wall Incus
Facial nerve Tegmen
Landmarks:
Semicircular canals
Facial nerye
Incus
Tegmen
Sigmoid sinus
Superior semicircular canal
Figure 35
51

step 3 tFig.361:
Followingthe SemicirculanGanals
The semicircular canals must be followed as they are highways into the
vestibule. Transection without following will leave "snake eyes" and create
confusion about which direction to continue the dissection. Try to
develop a three-dimensional concept of the canal planes.
Superiorly, the superior semicircular canal arches in a posterior-medial
direction underneath the middle fossa plate. This canal is traced
posteriorly and medially until it becomes the common crus in its junction
with the posterior semicircular canal. The subarcuate artery usually
penetrates the hard labyrinthine bone in the center of the circle inscribed
by the superior canal. The posterior canal is then followed inferiorly and
anteriorly under the descending portion of the facial nerve. Look for the
endolymphatic duct as it courses from its opening in the medial wall of
ttre vestibule next to the common crus. It travels posteriorly in the medial
wall of the common crus and then curves inferiorly and laterally as it
passes under the posterior canal to enter the endolymphatic sac in the
posterior fossa dura. There is frequently a bony operculum or small bony
cap overlying this portion of the sac as the duct enters it. The sac often
causes confusion by appearing to represent torn dura until the true
nature of the soft tissue is recognized. The endolymphatic duct appears
as a pearly white, thread-like discoloration in the hard labyrinthine bone.
Landmarks:
Facial nerve
Tegmen
Semicircular canals
Sigmoid sinus
F
t
d
/-J
3
..-J
3
a-J
3
F
3
14
13
t3
S,J
-
4
Y
a4
Y
€
ts
tsU
/f
Ff
€
?4
f
St
3
,4
t
a4
t
,-J
f
r-a
3
F
3
F
3
t4
f
FtL
e
/f
F
a
€
€
€
Y
V
e
)/
- I
H
-l
>/
-,l
h/
li
t
t!.

Followingthe SemicircularGanals
""*-"" "r"lEndolymphatic duct Subarcuate arterv
Endolymphatic sac Superior semicircular canal
Incus
lE
)n
n)a
T*'"
Figure 36
Facial nerve Horizontal semicircular canal
53

Step 4 tFigs.37,381:
OpeningandGleaningthe Vestibule
The surgeon follows the common crus forward into the vestibule and
opens it widely. The bone over the facial nerve is then thinned well to
provide good visual access to the vestibule. A11the semicircular canals are
completely connected, and any soft tissue is removed from the vestibule
and semicircular canals to eliminate any remaining vestibular function.
Before removing the soft tissue, note the maculae of the utricle and
saccule. Note the spherical recess of the saccule in the anterior portion of
the vestibule and the elliptical recess for the utricle posteriorly. Probe the
opening of the endolymphatic duct at the anterior end of the common
crus. Palpate the stapes footplate from its medial side and notice its
proximity to the saccule and utricle. The postauricular labyrinthectomy is
now complete.
Elliptical recess of utricle
Landmarks:
Facial nerve
Tegmen
Semicircular canals
Elliptical recess
Spherical recess
Footplate of stapes
Endolymphatic duct
Figure 37
-
t
(
llt
,'r-
!
-
ll
FJ
3
f1
a
s.J
-
F
-
-
s1
?
?
;-r!
Ff
I
,'r'
-lts
-l
-,
!'l
r-J
3
.J
tb
rl
tJ
t
tJ
rL
€t
).J
!
,1
!
-
!
t.'J
t
tD-
I
€
tlj
!
€
7
€
V
I
H
IH.
-l
)4.
-l
ts
-l
l:J
I
ts I
t!
FJ I
r{
Spherical recess of saccule
l
Membranous labyrinth remnant

OpeningandGleaningthe Vestibule
Ampulla of posterior semicircular canal
Ampulla of horizontal semicircular canal
Ampulla of superior semicircular canal
:. :)t,
Endolymphatic duct Superior semicircular canal
Common crus
Posterior semicircular canal Subarcuate artery
wall
l
Posterior canal
)a
)4
)-
wwb
w
Figure 38
cc

lnternal AuditonyGanal
Step 1tFig. 391:
Topography
The simple mastoidectomy and postauricular labyrinthectomy are the
first twostages of the approach to the internal auditory canal. This new
and much deeper dissection requires that all the previous steps be
accomplished properly to provide wide access for adequate visualization
and working room deep within the petrous bone. During labyrinthectomy
in this procedure, the ampulla of the superior semicircular canal is
preserved as a landmark to find the end of the superior vestibular nerve,
Bill's bar, and the facial canal. In approaching the internal auditory
canal, one must remember that the medial wall of the vestibule
represents the lateral wall of the internal auditory canal fundus, where
the nerves enter the inner ear structures. Therefore, minimal bone
removal on the medial wall of the vestibule will expose the internal
auditory canal. Posteriorly, at the posterior fossa dura, the route to the
porus acusticus is much deeper because the internal auditory canal is
slanting away from the dissector. The plane of the canal, in an anterior-
posterior direction, is roughly from the external genu to the sinodural
ingte. The superior bordei of the internal auditory canal extends from
thJfacial canal to sinodural angle. The inferior border of the internal
auditory canal is at a point approximating the junction of the external
genu and descending portion of the facial nerve and parallels the superior
border posteriorly to its junction with the posterior fossa.
A sharp pick is often used to perforate the very thin bone of the internal
auditory-canal fundus in the area of the elliptical recess. Frequently a
blue-line discoloration appears.
Inferior border of internal auditory canal
Vestibule
External genu of VII
Tegmen
Sigmoid sinus
Sinodural angle
Landmarks:
Facial nerye
Vestibule
Tegmen
Posterior fossa plate
Superior canal ampulla
.lrl
l
F-l
I
ttJ
3
--1
if
FJ
,tf
aj'f
F-r
t
11t
F'-
lE
v
t4
Y
Ft
-
t,
)
-lJ,
-l,r-J,
-l1
:l
F
fl
,-J
j
4
t
/
l}
tJ
l}
-
r}
Frly
-
3
f
t1
D
U
3
tl/
FDJ
lr,
{
€
€
ts!
lr'
-iF-J
!, I
J
3
;.1
TI
H
s{
Subarcuate artery
58
Superior border of internal auditory canal
Figure 39

Step 2lFig. 4Ol:
E
E
n
a
2
a
3V
b
b
b
RemovingBoneover the InternalAuditory Ganal
As seen from above, the bone to be removed for extrrosure of the internal
auditory canal forms a wedge or triangle. One side is the roof of the
internal auditory canal and the medial portion of the dissection; the
second side is the floor of the labyrinthectomy dissection; and the third
side is the posterior fossa dura as it extends between the other two sides.
The thicker posterior portion of the bone is usually more difficult to
remove because it is composed of hard labyrinthine bone. The internal
auditory canal can be recognized by color changes in the bone. In the
cadaver specimen or the living surgical specimen without a tumor, the
color of the canal will be dark blue as in blue-lining of any hollow
structure. In the specimen with a tumor, the color is usually ruddy from
the vascularity of the tumor and overlying structures.
Posteriorly in the sinodural angle, the blue-line of the superior petrosal
sinus will show as it runs along the posterior superior border of the
temporal bone frorn the apex to its entrance into the transverse sinus.
Facial nerve Superior semicircular canal ampulla
Vestibule Superior border of internal auditory canal
Landmarks:
Tegmen
Sinodural angle
Vestibule
Ampulla of superior canal
Sigmoid sinus
Internal auditory canal
Posterior fossa dural plate Bone wedge
Inferior border of internal auditory canal Subarcuateartery
Figure 4O

srep 3 tFig.4111.
Blue-liningthe lnternal Auditory Ganal
Skeletonization of the internal auditory canal for dissection purposes is
accomplished through removal of bone for 18O degrees around the
posterior portion of the canal extendin$ from the area of the fundus to
ihe porus acusticus. Such extensive surgical exposure is to prevent the
bony overhang that would make work within the canal difficult. Blind
dissection under bony ledges carries the possibility of injury to a nerve or
blood vessel within the canal. For such extensive exposure, the surgeon
must remove all bone superior to the canal extending from the area of the
facial canal and petrous apex to the superior midpoint of the porus
acusticus. This dissection is usually performed with small diamond burrs
and a small suction-irrigator, which prevents the accumulation of bone
dust from obscuring the underlyrng dissection area. The middle fossa
dura is located and followed in an ever-deepening trench, with
preservation of a thin layer of bone over the superior portion of the
internal auditory canal.
At the deepest portion of this dissection, which is at the superior lip of
the porus
-acuslicus,
exposure is extremely limited. With patience and
perslstence, however, the posterior superior portion of the internal
iuditory canal can be well exposed. With the posterior portion of the
porus atusticus well defined at the junction of the posterior fossa dura
ind internal auditory canal, the inferior border of the internal auditory
canal can be better defined. A trench with the jugular bulb inferiorly and
the internal auditory canal superiorly is constructed between the
posterior fossa dura and hard labyrinthine bone anteriorly. This
dissection is carried anteriorly until a small white discoloration in the
bone appears. This represents the cochlear aqueduct which, when
entered, will often release cerebrospinal fluid. Extension of the dissection
anterior to the cochlear aqueduct will involve the jugular bulb and the
ninth. tenth, and eleventh cranial nerves. If proper removal of bony
covering has occurred throughout the exposure of the internal auditory
canal, t-here should now be an eggshell-thin covering of bone from the
fundus of the canal to the area of the jugular bulb inferiorly, to the
superior petrosal sinus and middle fossa dura superiorly, and to the
sigmoid sinus posteriorly. This bone may be removed for a wide exposure
of-the internal auditory canal and the posterior fossa dura. For
procedures involving section of the vestibular nerve, such extensive
exposure is not necessary. However, we encourage wide exposure to
ethinate blind dissection through a small keyhole into the internal
auditory canal fundus. Limited exposure also precludes the ability to deal
with th-e potential problem of a bleeder from the sectioned nerve.
Landmarks:
Superior petrosal sinus
Superior canal ampulla
Vestibule
Facial nerve
Cochlear aqueduct
Tegmen
Jugular bulb
Sigmoid sinus and
posterior fossa plate
tJl
rDl
4)
v
72
J,
rl
€l
q
q
nq
n
7q
?l
t1
rl
F.l
rl
{l
{l
{l
{l
tla
fi
,1
f
.4
rl,
d
C
€
€
€
r
€
V
ei
€t
F.1
)
;t
;r
c
cJ
s{

egmen
/
Blue-liningthe InternalAuditoryGanal
Superior semicircular canal ampulla
Vestibule
Figure 41
Internal auditorv canal "blue-lined"
Cochlear aqueduct Sinodural angle

Step 4 tFig.421=
The bone removed, the exposed dura of the internal auditory canal is slit
along the long axis of the canal at its inferior border. This precludes
injufir to the Iacial nerve superiorly in the occasional cases of variation
(sombtimes a tumor pushes the nerve posteriorly).
Within the internal auditory canal, the vestibular nerves are both
posterior, whereas the facial nerve is anterior superior and the auditory
^rt.*.
anterior inferior. To locate these structures from a lateral
dissection approach to the internal auditory canal, w_euse the facial nerve
as the principal landmark. The facial nerve is located anterior to the
superior nesfibular nerve. Therefore, we ordinarily preserve the ampulla
to ttre superior semicircular canal, which makes for easier identification
of the suierior vestibular nerve. A diamond burr is used to penetrate the
medial wall of the superior ampulla. The thinned bone then exposes the
superior vestibular n-erveas it enters the labyrinth
-at-
that point. If the
bone has been removed from the superior border of the internal auditory
canal far enough anteriorly, the facial canal may be seen descending
-
through its lab]rrinthine portion from the geniculate into the internal
auditory canal.
t-J
lD-
C1
D
4
D
/'J
rD
;J
rD
FJ
2
-.42
l:-l
v-
"1
Y,
s.Ja-
;4
Y.
€
/a-
,-J
-i;1
*l
;-J
*l
4
Ll
JtL,
I
rL
/
e.
/
rL
/
rL
4rL
la
1-
/It-
/It-
/It-
/
t-
,4
t/
C
C
tJ
-i,1
"{
4
-lL
3
l
l
l
J
J

Openingthe InternalAuditory Ganal
Transverse crest Superior vestibular nerve
Facial nerve Superior semicircular canal ampulla
Jugular bulb
V
b
b
Figure 42
Internal auditory canal dura
Singular nerve
Porus acusticus
Inferior vestibular nerve
63

Step 5 tFigs.43, 441=
ldentificationof the Nerves
When the superior ampulla is preserved, its medial wall represents the
last remaining bone over the superior vestibular nerve at its termination
in the ampulla. When this bone is removed, a brush-like ending of the
nerve is encountered.
After the superior vestibular nerve is identified, a one-millimeter hook
may be inserted deep to the vestibular nerve directly anterior and medial
to the superior vestibular nerve to palpate the shelf of bone that separates
the superior nerve from the facial canal. The superior vestibular nerve
occupies a recess medially. The recess may be safely probed and the
posterior edge of it palpated. Bill's bar, as this shelf of bone is called,
represents the posterior wall of the fallopian canal. With identification of
the bar and the fallopian canal, the superior vestibular nerve may then be
avulsed from its attachments in the ampulla area. When gently lifting the
superior vestibular nerve, one should carefully look for the facial nerve as
it exits the fallopian canal into the internal auditory canal. Vestibulo-
facial anastomoses that occur here should be carefully sectioned.
Directly inferior to the superior vestibular and facial nerves, a bony
prominence protrudes into the fundus of the internal auditory canal.
This shelf of bone. called the transverse crest, falciform crest, or crista,
divides the canal into superior and inferior portions. It is evident during
exposure of the fundus and allows easy identification of the inferior
vestibular nerve laterally and the auditory nerve medially. The singular
nerve to the posterior semicircular canal is an offshoot from the inferior
vestibular nerve within the internal auditory canal. This method of
internal auditory canal exposure is used for translabyrinthine vestibular
nerve sections and the translabyrinthine approach for acoustic neuroma
removal.
If bone is removed from the fallopian canal starting at Bill's bar, the facial
nerve may be decompressed to the geniculate ganglion and internal genu
a few millimeters anteriorly.
Landmarks:
Falciform crest (tranverse)
Superior vestibular nerye
Bill's bar (vertical crest)
Facial nerve
-fLt
.-J
L
4
t!
rL
FJ
rL
3
-,
3
F4,
F
a.
s1l-
€
€
€
tst
F
f
l-J
l
s1l
tsrl.
tj
F-i
rL
-J
rL
,J
le
/rL
/
3
F
lt'
-
lL
-
ra,
a1
!L
-
3
tlJ
3
,4
lr.
,4
3
3
ts3
ts],
I
F
-l I
g
f/
J
-lFJ,rl

Transverse crest Recess of superior vestibular nerve
Bill's bar
ldentification of the Nerves
Porus acusticus
Facial nerve Transverse crest
Facial nerve
ar nerve

Inferior vestibul
)4
)4
)4
12
V
)t
w
Figure 43
Recess of superior vestibular nerve
Fallopian canal
Bill's bar
Facial nerve
Superior vestibular nerye
Inferior vestibular nerve
65
Figure 44
Porus acusticus

l-
Notes
/,
9l
{1
l}
tD
F
a
2--
j
i1
tD
,r-J
-
3
7
7
?
e
7
ts
-
€
/
I
)rbl
F1j
a
rL
/tl'
,1
L
F!L.
-
t-
{
{
€
{
{
{
-
t
{
€
V
)rt
-l
--l
-'-l
>'
-l
J
-l
tJ-l
LJ-l
Fi
I
ql
66

MiddleFossaApproach
srep 1tFig.45A,Bl:
MiddleFossaToPography
In the middle fossa dissection of the temporal bone,^placementof the
tor. within the bone cup usually presents some difficulty. The dissector
should visualize the boni as if looking through a-craniotomy window that
has been inscribed in the squamosal portion of the temporal bone (Fi€'
45A). This is from the vertei of the head (the surgeon sits at the head of
the table, not at the side as in the standard postauricular approach)' The
bone is positioned so that the surgeon looks directly down upon the-
.rriOat. fbssa floor. Then dura shoild be stripped back from the roof of
itr. t.-poral bone, as in the surgical procedu-refor this approach. The
t.p"gr"ptl should be studied 1ri-g.+5n). As dura is reflected away from
thi s-quamosalportion of the bonE, the floor of the middle fossa is
revealld. Laterally, this is the tegmen overlying F9 aerated mastoid
ptrtion of the bone and epitympanum. Anteriorly beyond the
lpity-p"trum, thin bone
"overs
the eustachian tube. More anteriorly, the
middle meningeal artery is the first major landmark.to be encountered in
.f.""iitrg the d'ura. Thgforamen spinojum is located where the flat lateral
portion"of the squamosa intersects with the floor of the middle fossa'
Fosteriorty the flbor of the middle fossa drops abruptly into the posterior
fossa where the tentorium intersects with the temporal bone. The
superior petrosal sinus is located in the reflected dura. Medial to the
aerated epitympanic bone, the arcuate eminence of the superior canal is
the seconldi""jo.landmark. Anterior to the arcuate eminence and
approximately"one centimeter medial to the middle meningeal artery is
the greater superficial petrosal nerve running anterior to posterior into
the Iacial hiatus, wher^eit will join the facial nerve and geniculate
g;t gliott. This key landmark ailows the surgeon to locate the geniculate
E"nEtion for unro"ofing the facial nerve. It evlntually will become the
Frifie landmark in the middle fossa dissection'
Landmarks:
Squamosa
Arcuate eminence
Middle meningeal artery
Superior petrosal sinus
€l
Cl
Cl
--J,
rl
--J,
rl
rDl
,.J
3
r-Jt,
?-J3
€
V
€
V
;.J
l/
s1v
tJv
I
?-J
-ll.J
r/i
IaJ
r't-,
/
t,
/
t/
-4
tr
I
t-/
4
f./
tl
-/
,l
-lf-r1
^z
rl
4
rl
4
x7
l
l
l
l
l
l
l
l
J
J

I
4
-t
-t
-t
-
-
-4
4
4
4
4
4
4
4
4
4
-t
-,
-,
-t
a
-4
-
-
-4
-4
4
4
4
4
4
4
4
,1
.t
t.'
t.'
'?.:'::,.'.,.,2
(,
{''"a
'
Middle FossaTopography
Styloid process
llastoid tip
Foramen spinosum
ygomatic process
Petrous apex
Greater superficial
petrosal nerye
Z
I
*:
Temporoparietal suture
Arcuate eminence
Suoerior semicircular canal
(ghost)
Superior petrosal sinus groove
Superior vestibular nerve (ghost)
Inferior vestibular nerve (ghost)
Arcuate eminence
(ghost)
Facial nerve (ghost)
Cochlear nerve (ghost)
Foramen spinosum
Figure 45A
'2
|t
V.
'tA
Vr
Greater superficial petrosal nerve
Tegmen
Figure 45B
69

Step 2 tFig.46A, B, Cl
SuperficialDissection
The first pcrtion of the dissection involves unroofing the geniculate
ganglion and tracing the facial nerve from the internal genu into the
middle ear space. The greater superficial petrosal nerve should be
followed to the geniculate ganglion (Fig. 46.4'). The geniculate ganglion
will be superficial; therefore, a minimum of bone should be removed. The
largest diamond burr is used for this procedure with copious amounts of
irrigating fluid to remove the bone dust. At the geniculate ganglion the
nerve turns laterally, posteriorly, and inferiorly into the epitympanum.
Although the nerve can be followed for quite a distance through this
approach, the cochleariform process is the normal limit of dissection.
Lateral to the facial nerve, the ossicular chain will be noted with the head
of the malleus particularly prominent. Because the ampullated end of the
superior canal is close to the medial portion of this dissection, one must
be careful not to fenestrate the canal through the hard labyrinthine bone.
The canal is usually blue-lined for definitive identification. From the
geniculate ganglion, the labyrinthine portion of the nerve may be followed
posteriorly, medially, and inferiorly, past the ampullated end of the
superior canal as it turns deep into the anterior superior portion of the
internal auditory canal (Fig. 468). With adequate thinning of bone over
the medial end of the facial nerve, one can identify the shelf of bone that
separates the superior vestibular nerve as it enters the superior ampulla
next to the facial nerve. This is Bill's bar (Fig. 46C).
Malleus
Facial nerve Stapes
Vestibule Middle meningeal artery
Landmarks:
Greater superficial petrosal
nerye
Geniculate ganglion
Superior semicircular
canal
Epitympanum
l}

I
a
rL
a
-
a
-
a
a
)-J
!
L
-
?
!
Fl-
ts:
14:
-
t
-
a
L
a
a
a
tL
-
a
a
,1
IL
f
,4
f
1
tsL
;1
l
,1
L
{
,1t
- l
F,
El
,
:i
-lF,
-l
r.J
-t
-l
I
h-J
-l
h.J
-l
H
70
Geniculate ganglion Greater superficial petrosal nerye
Figure 46A

Figure 468
Facial nele
Internal auditory canal
Superior semicircular canal Cochleariform process
Malleus acial nerve
SuperficialDissection
Geniculate ganglion
Cochlea (opened)
Geniculate ganglion Eustachian tube
14
)4
)2
ww)4
)a
7L
Figure 46C
Greater superficial petrosal nerveBill's

Step 3 tFig.471=
DeepDissection
During blue-lining of the internal auditory canal, the exposure may be
widened as the posterior fossa is approached. This is possible because
the cochlea lies anteriorly and laterally under the geniculate ganglion,
and the superior canal turns more posteriorly away from the area of the
internal auditory canal as the posterior fossa is reached. Becausethe
internal auditory canal can be widely exposed and well delineated, there
is no reason to work under a bony shelf when entering the canal, and the
same principle for wide exposure in the posterior approach to the canal is
used here. Medial to the internal auditory canal is the petrous apex,
which is frequently filled with open air cells. Anterior to these apex cells
and anterior to the cochlea is the carotid artery. The middle fossa
approach can be used for ligation or packing of the medial portion of the
carotid artery in uncontrolled bleeding. Laterally the eustachian tube
extends from the middle ear cavity forward medial to the middle
meningeal artery and lateral to the carotid artery as the tube descends
into the nasopharynx.
Greater superficial petrosal nerve
Cochlea (opened)
Superior semicircular canal Carotid siphon
Porus acusticus
Landmarks:
Superior semicircular
canal
Bill's bar
Facial newe
Cochlea
Superior vestibular nerve
Carotid artery
Figure 47
4
9l
-J,
Dl
F-J,
bl
I
rl
;.J
l}l
/rl
trzl
D
i,-J
U
j
U
F.J!
4
-
ts
r
)J
f
rDjf
?f{
I
a4t,
IE
fl
;J
tl'
rJ
f
-J
rl,
(
(
{
t-a
f
C
4
a
C
4
j
Ff
4
3
€
C
r
t''iI
r,
I
E
-lg.
-l
E
-l
bJ
-l
lrJ
h.l-l
ttl
Geniculate ganglion
Superior vestibular nerve
Petrous apex cells

MiddleEanDissection
Step 1tFig. 481:
Topography
Middle ear procedures can be practiced through a canal approach or a
postauricular approach on the temporal bone as easily as in the patient.
These techniques will familiarize the surgeon with actual operating room
procedure and increase dexterity in procedures that are among the most
demanding of the otologist's armamentarium. With the temporal bone in
the surgical position, the dissector operates through a speculum placed
within the external auditory canal. The skin in the canal and the
tympanic membrane of preservedbones tends to be like leather and does
not simulate the feel of skin of patients. Therefore, frozertbones are
useful because thawing will often produce conditions that more closely
approximate actual surgery.
Landmarks:
Zygomatic root
Spine of Henle
Mastoid tip
Tympanic ring
-,
r>rl
€l
tJ
lDl
//
D
,1
rD
14
rD
;.4
!
rt
4
-4
U
?
E
rt
V
C
4
J
€,
I
V' I
el
t4
lDi
tJ
|D
C
C
C
C
4
rt
C
C
C
{
C
C
C
C
V I
si I
si I
t4,EI
I
E.
-l
ts,4
-J-l
r.J
!
bJ
s{

; Topography
;?
,,
f - rymPanis ring
4
-
Figure 48

Step 2 tFigs.49,5O1:
ExternalAuditory Ganal
An injection of the vascular strip should be attempted to define this area
of thickened posterior canal wall soft tissue. The injection will expand the
soft tissue between the tympanosquamous and tympanomastoid suture
lines. They are prime landmarks for making incisions in an overlay graft
technique. Tympanomastoid and tympanosquamous suture line incisions
should then be made with a #1 knife. The incisions should be connected
medially along the annulus with a #2 knife and laterally along the bony
cartilaginous junction with a scalpel. The sleeve of canal skin which is
then removed is the same as in the standard overlay technique' It is
removed with a round knife that is constantly kept against bone to avoid
perforations of the very thin canal skin. The epithelial layer of the
tympanic membrane is removed en bloc with the canal skin preserving
the underlying fibrous layer. Then enlargement of the external auditory
canal for excision of exostoses, for the lateral graft technique, or for
canaloplasty can be practiced. The dissector should also practice
suctioning against the instruments, not the soft tissue, to prevent
trauma to flaps and other soft tissue structures.
Umbo
Short process of malleus
rb
L
L
rL
rb
a
-
L
t4
t
14a
f-J
!
F
-
r
r
r
I
I
/a
f
t4
f
t
lL-
L
t-
t-
L
t-
tl-
1-
a-
t-
t-
t-
l-.
L
C
r
V
-
V
I
h-r
.l
Li
;
f-
tt'
Landmarks:
Bony-cartilaginous
junction
Vascular strip
$mpanosquamous suture
Tympanomastoid suture
Annulus fibrosis
Malleus
Figure 49
76

ExternalAuditory Ganal
Annulus fibrosis Tlmpanosquamous suture
Vascular strip
Figure 5O
Bony-cartilaginous j unction

Step 3 tFig.511:
RemovingAnteniorGanalBulge
In the lateral graft technique, the anterior canal wall bulge overlying the
glenoid fossa is usually removed. Superiorly, just anterior to the
tympanosquamous suture line, the excessbone is removed to achieve a
smooth contour from the cartilaginous external auditory canal to the level
of the annulus. This bony removal helps prevent blunting that
occasionally occurs with this technique. The removal also allows one to
determine how deep the temporomandibular joint actually lies without
entering the joint capsule. Bone is then removed inferiorly anterior to the
tympanomastoid suture, again to form a smooth contour from the
cartilaginous external auditory canal to the level of the annulus. This
eliminates any overhang that might prevent adequate visualization of the
sulcus inferiorly. These two areas of bone removal are then connected
across the anterior canal wall bulge. Usually the chance of entering the
temporomandibular joint is minimal since the depth of the joint has been
established. Ultimately, enough bone should be removed so that in a
transcanal view through the microscope, the entire annulus can be
observed.There should be no need to readjust the microscope to seethe
anterior sulcus and the posterior annular area.
Landmarks:
Annulus
Bony-sartilaginous
junction
Malleus
Temporomandibular joint
Fa,
l}l
tl
-J]l
FJ
3
FJ
f
-
l]
.J
l
t-J
U
4
5
r
:
t4
-
€
€
rJ
lr
€
€
ts!
Ij
1
tD
(
{
€
€
{
€
t
€
€
€
€
€
r
r
V
l
F
-l I
)-1
;J
;J
J
d
c
SI

RemovingAntenior GanalBulge
r grooves (drilled)
Annulus fibrosis
a
Vascular strip
Figure 5l

Step4 tFigs.52,53l:
MiddleEar Dissection
After the anterior canal wall bone is removed, the annulus may be
elevated posteriorly in a standard tympanoplasty approach. The tympanic
membrane is then folded forward to exposethe middle ear structures.
Now it is worthwhile to do a standard stapedectomyto become familiar
with middle ear structures. During palpation of the malleus, one should
be able to see movement of the stapes fogtplate along with the ossicular
chain and. if fluid remains in the inner ear. a round window reflex can
be obtained. Observethe topography of the promontory and note that
Jacobson's nerve usually crossesthe promontory in a bony groove or
canal. Severalbranches of the tympanic plexus, which includes this
nerve, can be seen. The scutum should be curretted for exposure. One
can now incise the incudostapedial joint, cut the stapedial tendon, and
attempt to fracture the superstructure of the stapes onto the promontory.
Unfortunately, in a cadaver bone, these steps will normally result in
complete avulsion of the stapedial footplate with its superstructure. One
may then practice placing various prostheses upon the incus as in
standard stapedectomy. This tympanotomy approach is also used for
insertion of an incus replacement prosthesis around the malleus in cases
in which the incus is missing following a previous stapedectomy.
Long process Manubrium lncudostapedial j oint knife
Chorda tympani
Landmarks:
Malleus
Incus
Stapes
Chorda tympani
Jacobson's nerve
Round window
Oval window
!Ll
.1,
l
I,
l
rl
rl
t
L
/
a
t4
!
a
F1
a
a
/:
;4
f
!l
rl
F
al
l}l
rJlll
rb
L
L
rL
rt
3
rL
!L
r
rL
11
!
{
t4j
fz
l
{t
l
(t
I
ts
-l|--r,
)fl
>.
-lF-J
;l
*l-l
H I
r
I
:
.i
i ,
Anterior crus Posterior crus
Figure 52

b
4
-t
-t
-t
-
4
4
4
4
4
4
4
4
4
MiddleEar Dissection
Manubrium
Tl-mpanomeatal flap
Promontory
Chorda tympani
Scutum
Stapes wire
Figure 53
4
4
-t
-J
-t
a
-
4
4
4
4
3
3
4
4
4
4
14
la
la
l2
ln
la
1.4
m
Soft tissue
Crimper
81

Step5 tFigs.54,55, 561:
MiddleEar DissectionlGont.l
The incus is removed by insertion of a three-millimeter hook in the
incudomalleal joint and rotation of the hook so that the ossicle is brought
out through the ear canal. A myringoplasty knife is used to incise the
mucosa and fibrous attachments to the malleus from the underside. A
tunnel is made under the mucoperichondrium of the malleus handle so
that the incus replacement prosthesis (I.R.P.) hook can be placed over the
malleus without perforation of the tympanic membrane. The loop end of
the I.R.P. is then rotated into the oval window. With use of smooth
alligator forceps to stabilize the wire, a hook is used to pull the wire into
a crimped position around the malleus.
Another procedure that can be performed is transcanal labyrinthectomy
in the oval and round windows. The stapes is removed and the round
and oval windows are connected with use of a small burr. This larger
opening allows insertion of a three-millimeter hook into the vestibule to
remove the ampullae of the semicircular canals.
3mm hook
Scutum
..i:.; ,.
Stapes
Landmarks:
Malleus neck
Incus
Icudomallear joint
Chorda tympani
Figure 54
/'
]l
q
.-a
lli
,-/
3
-J
rl,
/-A
rf.
]
f
,>-
!
€
€
r
r
r
ts
-
(
€
f
-
t
z
a
I
f
?J
a
-
3
a4
I
-
f
,1
j
,1
!
tsl'
,-a
!
ts!}
C
(
€
r
r
t-r/
-lr
-l/.
-l
J
J
bJ
I
b'l
I
Gr
82

MiddleEar DissectionlGont.l
Ivtyringoplasty knife
l)
I
3?)
-'
a
4
4
4
4
4
4
4
4
4
4
1
a,7
7
7
7
?
?
3
?
3
?
?
3
3
?
3
3t4
14
11
w
V
w
V'
1.1.
Figure 55
Footplate
Manubrium
Tunnel
Oval window
83
Figure 56

Wall DownTechniques
Step 1tFigs.57, 581:
Topography
We begin the canal wall down (open cavity) procedures in the same
manner as the intact canal wall operations: with the postauricular
approach. The essential difference between the two procedures is removal
of the posterior bony canal wall. Thus, you may use a bone with a
completed intact canal wall for this dissection.
The usual problems with open cavity mastoidectomy are incomplete
removal of the posterior canal wall and poor meatoplasty. An incompletely
removed buttress or a poorly lowered facial ridge frequently leads to
cicatrix formation, which further reduces cavity access.Incomplete
cleaning of the cavity is the usual consequence,and new cholesteatoma
may form.
Fossa incudis
Mastoid tip
Sigmoid sinus Sinodural angle
|br/|
.,/
L
I
l,
/-J
|L
4
l,
rL
F1
j
rJj
,-1
L
f1
3
]
Sr'-
-
€
,1
3
{
,4
!}
f
-1a
-
L
L
rL
rly
/4
rL
F
rL
-
rL,
-
rL
C
{
C
)1
t
'1
3
tsL
(
tsl
r
v
)
-l
F
-l
rJ
;
-l
ei
I
t/
s
Landmarks:
Posterior bony canal wall
canal
Sigmoid sinus
Incus
Tegmen
Figure 57
86
Horizontal semicircular canal Tegmen

Topography
b
l'"
I'i"
i'"
i?
3
3
3
3
3p
>,'
V5
b
fr
h
14
h
i-3
i-o
fO
frfr
?
?
?
3
?
?
33
?t4
l-a
lA
lA
12
lD
lD
)n
.ic root
/
Malleus
Figure 58

Step 2lFigs. 59, 6O,611:
Removingthe Posterior GanalWall
If you are using a fresh temporal bone, proceed through a standard
posterior approach to identiff a thinned posterior bony canal wall, the
skeletonized sigmoid sinus posteriorly, a thinned middle fossa dural
plate, and the prominence of the horizontal (lateral) semicircular canal.
The fossa incudis and horizontal semicircular canal are then used to
begin dissection of the facial recess.The floor of the recess,which is the
lateral wall of the fallopian canal at the external genu, will be the most
medial part of the dissection.
The anterior buttress is that bone where the posterior bony canal wall
meets the tegmen. Removeit totally to achieve a smooth continuum
between the middle fossa tegmen and the middle ear epitympanic
tegmen.
The posterior buttress is where the posterior canal wall meets the floor of
the external auditory canal lateral to the facial nerve. This area is
especiallyprone to cicatricial blunting and, if not openedwell, will result
in, a deep "blind" pocket at the mastoid tip. The best way to eliminate the
area of the posterior buttress is to lower the facial ridge by skeletonizing
the facial nerve laterally. Then the floor of the external auditory canal
slopes off into the mastoid tip.
All bone lateral to the facial nerve between the tegmen and the floor of the
external auditory canal is removed to eliminate the posterior bony canal
wall. The remainder of the mastoid bowl should be well saucerized,which
in actual surgery allows soft tissue to better obliterate and shrink the
remaining open cavity.
The flnal step to insure access to the open cavity is adequate soft tissue
'meatoplasty. This manual does not describe this technique but
emphasizes its importance and encourages you to review relevant
referencesand videotapes.
Posterior buttress Annulus flbrosis
Malleus
Incus
Landmarks:
Incus
Facial nerve
canal
Buttresses (anterior and
posterior)
lrl
-.1rl
L
t
I
3
-t
j
/-J
a
,.J
-,.1
a
,4
-;4
l1
Fa
/a
-
ra
-
tl
/f
tt
-Jt]
-all
/J
f
-
a
I
-J
l}
/
t
FJ
t
-
3
tst
C
,-a
t
(
C
(
€
r
V
F
I
F
-l I
;J,
J
;J
J
etJ
tr
Figure 59

Removingthe Posterior GanalWall
Articular surface
Stapes
lJ
E
E14
E
)4
)1
)A
)i
w)*
)4
Figure 6O
Tegmen
Cochleariform processPyramidal process
Anterior buttress
Eustachian tube
89
Figure 61

A
Ut
-a!l
/
]. 1
-ttlDl
1
tL,
},J
rl'
-Jt.
rL
,1
!
4
!.
4
!.
€
€
€
(
€
4
r1
4rD
t
'+J
3
-
I
-1
3
-1
rt}
,1
t}
t-J
f
€
€
C
d
€
€
€
qy
-i
J:t
v
g
-lLa
iI
J
rJ
^l
Notes

lndex
A
ampulla
of horizontal semicircular canal, Fig. 38
ofposterior semicircular canal, Fig. 38
of superior semicircular canal, 58-6O, 62,
64, 7O: Fig. 38-42
annular ligament, 41
annulus, 21, 42, 76, 78, 80
annulus fibrosis,42,44; Fig. 30-31,50-51,59
anterior buttress, 60, 86, 88; Fig. 58, 60
anterior canal bulge, 7a-79: Fig. 5l
anterior canal wall, 80
anterior crus, Fig. 52
anterior stapedial crus, Fig. 15
antrum, 9, f f , 14, 16,20, 4a
arachnoid, 4O
arcuate eminence, 68; Fig. 45A
articular process, Fig. f5
articular surface, Fig. 60
attic, 25
auditory canal (external), see external auditory
canal
auditory nerve, 62, 64
auricle, 48
B
barber pole, 3l
Beaverknife [#59], 34
Bill's bar, 58, 64, 7O, 72: Fig. 43-44, 46C
body ofthe incus, 26; Fig. f8
bone wedge, 59; Fig. 4O
bony-cartiliganous junction, 76; Fig. 5O
bony fallopian canal, 38
bony operculum, 52
buttress, 23-24, 86: Fig. f 3-f 4, L9-21,23,3L
anterior, 60, 86, 88; Fig. 58,6O
posterior, 88; Fig. 59
of iricus, 4f ; Fig. 28-3O
posterior, 88; Fig. 59
c
canal oftensor tympani, F.ig.16,33
canal skin. 74. 76
canal wall (posterior), seeposterior canal wall
canaloplasty, 76
capitulum of the stapes, 23; Fig. 52
carotid artery, 41, 44, 72; Fig. 31-32
carotid siphon, 72: F:ig.47
cerebrospinal fluid, 60
cholesteatoma,20, 24-26, 4l-42
chorda tympani, 16, 20-22, 29, 31, 4l-42; Fig.
10, 12-13, L5, L6-20,22, 24, 2a-29, 52-53
chronic otitis media. 25. 3O
cochlea, 41, 72: Fig. 45A, 46C,47
cochlear aqueduct, 60; Fig. 4l
cochlear nerve, Fig. 44,45A
cochleariformprocess,23, 29-31, 70; Fig. 15, 16,
19, 33,46C, 61
cog,26i Fig. fG
common crus, 52, 54; Fig. 36, 38
cranial nerves, 6O
craniotomy window, 68
crimper, Fig. 53
crista, see transverse crest
crotch.4l.44
D
digastric muscle, 14, 29: Fig. f 2, LA,20,22,24
digastric ridge, 14; Fig. 8, I
Donaldson's line, 38; Fig. 25
dural plate
middle fossa,l1-12, 25, 39,48, 50, 52, 60,
88
posterior fossa, 12, 41, 58
E
eleventh cranial nerve. 6O
elliptical recess of utricle, 54; Fig. 37
endolymphatic duct, 39, 52,54; Fig. 36, 38
endolymphatic sac, 14, 38-4O, 52; Frg. 25-27,36
epitympanic tegmen, middle ear, 88
epitympanum, ll, 14,24,26,68,70: Fig. f4, 16,
25,33
Eustachian tube, 44, 48, 68, 72iFig.16,33,
46C, 6r
exostoses, 76
extendedfacial recess,48; Fig. 31,33
external acoustic meatus, 8
external auditory canal, 8-9, 12, 29, 48,74,76,
88; Fig. 3,45A'
external genu lfacial nerve], 14, 20-21,29-31, 51,
58, 88; Fig. r1-13, L7-La,2L,23,39
F
facial canal, 21, 5a,60, 62, 64
facial hiatus, 68
facialnerve,16, 20, 24-25,2a,44,4a,54,62,
64, 68, 88; Fig. 10, 16, 25-3L,35-37,
40-44,45A,46A-46C, 58
"barberpoling".3l
descendingsegment.22,29,31, 38, 41,52,
58; Fig. 12,17-L9,23
externalgenu, 14, 2O-2I,29-3I,5f, 58, 88;
Fig. 11-13, t7-t9, 2L, 23, 39
horizontal segment, 20, 23, 3O-31,5l ; Fig.
14, 19
internal genu, 64, 70
labyrinthine, 34, 7O
mastoid segment,14,29, 31,34
mlddle ear segment, 31, 34
sheath, 16, 2l-22, 29, 32-35: Fig. 2L,24
ty.rnpanicsegment, Fig. f 5, L7, 19,23
facial recess, 16, 20-26, 28-31, 4l-43, a6; Fig.
t0-16. r8.28-30
(extended), see extended facial recess
facial ridge, 86, 88
falciform crest, see transverse crest
Fallopian canal, 38, 64, 88; Fig. 44i
medial porous, 34
foramen spinosum, 68; Fig. 45A-458
footplate, stapes, Fig. 55
fossaincudis, 14, 16, 20,28,30, 41, 88; Fig.
8-ro, 12, 20, 26-29, 3L, 57
G
geniculate ganglion, 30, 62,64, 68, 70, 72i Fig.
464-46C,47
glenoid fossa,24,78
glomus tumors, 41-42
graft technique (lateral), 76, 78
greater superficial petrosal nerve
seepetrosal nerve
4
v
9
9tr{
-rl
t/l
.J
f-' I
J
f-, i
J
tLr
tt/
tl-
ll
rL
1
!t-
4
t-
/t.-
..J
t-
t-
/
l-
/
-l/
lz1
J
tl-
/
t-
I
t
/
t-
-1
t-
.J
t-
,.2
t-
t-
/
a-
/tl-
/-'
t-
-.-t-
-
t-
I
t-.
11
-
,.J
U
|1
ar
)-r
J
a
3
f,
J
J
cl

t"i"
i'-r
El-
,>iJ r{
t-
?l naro €rngre,rr, r+
| _ head of malleus, 25-26, 70: Fig. f5
A Henle (spine o0, seespine of Henle
|
- horizontal semicircular canal see semicircular
A canal
I hypotympanum, 4l-42, 44, 48: Fig. f6, 30-31
nt-I
n|
- incudomallearjoint, 82: Fig. 14
n incudostapediatloi.rt, zS, dO; Fig. f3,52
|
- incus. 16. 23-25, 30,48, 80, 82; Fig. 11, 13-14,
n r9-2r,29,28-31, s4-36, 46A,46c,54,
| - 58-59
n bodyof,26: Fig. 18
I
- buttress. 3O,4l: Fig. fO-12,29-30
2 lenticular process. 23: Fig. 14, f9
I
-
long process,3O: Fig. 12, la,52
A
replacementprosthesis. Fig. 56
I
- short process,23
3
itrtr'""lFt,rditel?;anal, l l, 50, 58-64, 70, 72;
]2 "blue--lined".60. 70. 72: Fig. 4l
| - inferior border, 60. 62; Fig. 39-40
f"
posterior.superior. 6O
t - superior border, 62: Fig. 39-4O
l-f ciuia Fig..42
| - internal carotid artery, see carotid artery
l-f internal genu offacial nerve. 64
I
r.J
rc| - Jacobson'snerve. 8O: Fig. 15,33
P
j"e5f;3,"1?:
;3''n'
38,4t'42,44,48'60;Fig.
P iff$::i::li$!ii,1t1;t?t,tl"'
f"K
F Koerner'sseptum,Io. 14;Fig.5
?i, .lL
3 labyrinth. 5o-51. 62: Fig. s4,37
n
labyrinthectomy, 5O-55, 68, 74,86; Fig. 34-38
I
-- transcanal. 82
14 labyrtinthine bone, 14, 39, 50, 52,59-60,70
I - lateral graft technique.
3 "".iii,l'"",'11?"5:1!'i::n"H:,a lenticular processo[ incus. see incus
I - ligament of short process.Fig. 14
3 lH,rJ:#33Jiii;1,1=l?..,""""
rc
longprocessof malleus,seemalleus
At
malleus,4a,70,78, 80,82; Fig. 464, 46C, 51,
54. 58-59
handle (mucoperichondrium), see malleus,
manubrium
head,24; Fig.14-15
long process, 26
short process, Fig. 49
manubrium, Fig. f6, 52-53,55
mastoid, 8, 70, 88
antrum. see antrum
caily, 12,2I, 4l
cortex9-lO, 14; Fig. 5,34
process,8; Fig. 3
tip, 9-r2, 14, 16, 39, 44,88; Fig. 4-7,l0-ll,
La, 24-25, 34, 45A, 4a, 57
meatoplasty, 86, 88
middle ear
cavrly,20,72
dissection. 74-83: 48-56
middle fossa. 12. 34
approach, 6a-72i Fig. 45-47
dural plate (tegmen tlnnpani), ll-12, 14,25,
48, 50, 52,60,88; Fig. 6
middle meningeal artery, 68, 70, 72; Fig. 46.{
myringoplasty knife, Fig. 55
N
nasopharynx, 72
ninth cranial nerve, 6O
o
occiput, 12
operculum (bony), 52
ossicles,25,82: Fig. 17
ossicular chain, 3O, 7O, 8O
otic capsule, 14
oval window, 82; Fig. 56
overlay graft technique, 76
P
peritubular cells, Fig, 16
petrosal nerve (superficial, greater), 68, 7O; Fig.
45A-458,46A,46C,47
petrosal sinus
inferior, 44
superior, f2,59-60,68
groove, Fig. 45A
petrosquamous suture line, 14
petrous apex, 14, 26, 60, 72: Fig. 45A,47
petrous bone, 58
porus acusticus, 58, 6O, 64; Fig, 4l-43,47
posterior approach, 88
posteriorcanalwall, 9-12, 14, 21, 25,28, 38-39,
4r, 48,50, 88; Fig. 5-13, 14, L7-2L,
24-2a, 3r,34-35, 38, 57-61
posterior crus, Fig. 52
posterior fossa, 12, 68, 72
dural plate, 12, 14,38, 4r, 52, 58-60; Fig.
40,42
promontory, 23, 80; Fig. f3, 15-16,33,53
pyramidal process,23; Fig. 13, 15-16, 29,32,61
R
retrofacial area, 38, 4l
retrofacial cells, 39, 44. Fig. 25-27,31-32
retrofacial recess, 38, 4l
Rosen needle, 32: Fig. 2l-22
round window, 20, 23, 82; Fig. 13, L5, 32
s
saccule, spherical recess, 54; Fig. 37
scutum, 24, 8OtFig. 53-54, 58
t-
|4 H::ffiT'Jlffifl';i;3;"Tfi.1;1

semicircular canal
amPulla, 59-60, 64' 7O: FiE 4Q-42
horizontal,14,16,25,28,31' 38' 51' 88;
Fig. 8-13, 15-16, 18, 2O-2L,23' 25-3r'
35-36. 57-58, 61
posterior, 16, 38, 5l-52,64: Fig. 9' 12' 18'
20-2L, 25-27, 32, 34-35, 3a
superior 24,50-52,68,72: Fig. 35-36' 38'
454.47
shunt tube, 4OtFig.27
sigmoid sinus, lO, 12, 14, 38-39, 44' 59-6O' 88;
Fig. 7, 8, 10-12, 18, 24-27, 32, 34, 39' 41'
57-5A
plate, 12, 14
singular nerve, 64; Fig. 42,44
sinodural angle, 9-12, 14, 50, 58-6O;Fig. 6-8' fO'
24-27,34,39, 4L,57
skull base, 44
snake eyes, 52
spherical recess of saccule, 54; Fig. 37
spine of Henle, 8-9, 12, f 4; Fig. 3-4,44
spine (suprameatal), see spine of Henle
squamosa, 68
stapedial tendon, 23, 80; Fig' 13' 15' 31
stapes, 23-24, 30, 4I, 48, 82; Fig. L2-13, L4,
18-19, 21, 28-29,3r,46^A, 54, 60
capitulum, 23; Fig. 52
footplate, 54, 80
superstructure, 80
wire, Fig. 53
sternocleidomastoid muscle, 8
st5rloidprocess, Fig. 45A
stylomastoid. foramen, 14, 29, 3 f ; Fig. 17-L8' 20,
22.24
subarcuate artery, 52; Fig' 36, 38-40
subarachnoid space, 40
subperiosteal abcess, 8
sulcus (anterior), 78
superior ligament, Fig. 14-15
suprameatal sptne (of Henle), see spine of Henle
T
tegmen tympani, lO-tL,24,30, 48, 6O, 88; Fig.
5-6, 8-10, 12-16,19, 23, 25-27, 30,
32-36, 39, 4r-42, 45A, 57-58, 60
temporal line, 8-9; Fig. 3-4
temporalis muscle, 8
temporomandibular joint, 48,78; Fig. 33
temporoparietal suture, Fig. 45A'
tensor tympani, canal, Fig. 16, 33
tenth cranial nerve, 6O
tentorium, 68
transcochlear approach, 4l
translabyninthine approach, 41, 64
transverse crest, 64; Fig. 42-44
transverse sinus, 59
tympanic membrane, 20,22, 4l-42' 4a' 74' 76'
8O,82; Fig. 17,30
tympanic plexus, 8O
tympanic rinig,44,48; Fig' 33, 48
tympanic sleeve,Fig. 33
tympanomastoid suture, 14,76' 78; Fig' 5O
tympanomeatal flap, Fig. 52-54
tympanosquamous suture, 76, 78: Fig. 50
u
umbo, Fig. 30,49
utricle, see elliptical recess
94
v
vascular strip, 76; Fig. 49,5l
vertical crest, see Bill's bar
vestibular nerve, 6O, 62, 64
inferior, Fig. 42-44
superior, 62, 64, 72; Fig. 42-44, 46C, 47
vestibule, 50-54, 58, 82; Fig. 39-41' 464
z
zygoma,24
zygomatic arch, 8
zygomatic process, Fig. 454
zygomatic root, 10, 14, 16, 24, 48; Fig. 5, 9-f1,
L4-r6,2A,33-34, 48, 58
g
.U
:J
I
Isl
tI
"l
tl
-el
,.4,
''I
s'-,ol
€
-lF
*l
,1
.3
1
IJ}
tEa
]f
.J
I
1
s
/
3
ra
3
1
3
f--
3
/-A
.3
r-a
3
F
t3
,;J
]
C
t
r
€
€
€
€
i
q
e,
cJ
J
J
d
ed

Temporal bone dissection (house)

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Temporal bone dissection (house)

Similar to Temporal bone dissection (house) (20)

More from Prasanna Datta

More from Prasanna Datta (20)

Recently uploaded

Recently uploaded (20)

Temporal bone dissection (house)