This document describes the surgical technique for middle fossa surgery. It discusses the important anatomical landmarks in the middle fossa approach including the greater superficial petrosal nerve and arcuate eminence. It provides details on patient positioning, incision, craniotomy, exposure of the middle fossa floor, and finding the internal auditory canal medially and laterally. Applications of the middle fossa approach are summarized, including vestibular schwannoma surgery, vestibular neurectomy, facial nerve surgery, repair of tegmen defects, and petrous apicectomy. The middle fossa approach provides superior access while preserving inner ear function and the proximal intratemporal facial nerve.

1. MIDDLE FOSSA SURGERY
Dr surbhi
Patna medical college

2. Introduction
• MF floor
• the internal auditory canal (IAC),
• the posterior fossa
• petrous apex.

3. Surgical anatomy
The most important
landmarks in this
approach are:
• the middle meningeal
artery
• tegmen plate
• greater superficial
petrosal nerve (GSPN)
• facial hiatus
• arcuate eminence
• superior petrosal sinus
• meatal plane.

4. Of these by far the most useful for the surgeon is
the GSPN
• depth of dissection
• position of the facial nerve

5. recommended opening up the tegmen tympani
early in the dissection to expose two additional
landmarks of importance –
 the cochleariform process
 tympanic portion of the facial nerve
could effectively guide the surgeon onto the
labyrinthine segment of the facial nerve more
directly.

6. • The arcuate eminence has a variable
relationship to the superior semi-circular canal
It is advisable to use landmarks in addition to
the arcuate eminence in order to reach the IAC
safely

7. Patient position
• The surgeon sits at the head
• The patient lies supine with the head rotated
• the intermeatal line perpendicular to the floor.
• surgeons give mannitol

8. Incision
• This is either an inferiorly based U-shaped flap
or a vertical line. It begins 0.5 cm anterior to
the base of the helix, at the level of the
zygomatic arch, and extends approximately 7
cm superiorly.

9. • Branches of the superficial temporal artery
• The temporalis fascia plane
• An incision is placed in the temporalis muscle
• the squamous part of the temporal bone.
• The root of the zygoma indicates the level of
the MF floor and it is crucial that the initial
exposure adequately identifies this both
anteriorly and inferiorly.

10. Craniotomy
• This is sited two-thirds anterior
and one-third posterior to the
external auditory canal (EAC).
• An opening of 5 cm × 5cm
• It is bevelled posteriorly
• The craniotomy otologic burr or a
craniotome
• Utmost care should be taken not
to injure the underlying dura
during drilling.
• The opening then needs to be
lowered to the level of the MF
floor anteriorly and above the root
of the zygoma.
• Any air cells entered should be
sealed with bone wax.

11. Exposure of the middle fossa floor
• dural elevation is commenced
posteriorly.
• The superior petrosal sinus and
the sulcus at the transverse–
sigmoid junction are identified.
• A self-retaining retractor such as
the Fisch, Yasergill’s or House-
Urban retractor is applied when
the dura is sufficiently elevated.
• Care must be taken not to injure
the geniculate
• The arcuate eminence and the
GSPN are then identified.

12. • sharp dissection from the GSPN as it can be
densely adherent to it.
• the middle meningeal artery is anterolateral to
the GSPN
• If the vessel is divided, the foramen spinosum
will need to be sealed with bone wax.

13. • The bone anteromedial to
the arcuate eminence and
posterolateral to the
GSPN is termed the
‘meatal plane’ and lies
above the IAC
• It is often marked by a
shallow depression. The
angle between the GSPN
and the arcuate eminence
is bisected to identify the
axis of the IAC,

14. Finding the internal auditory canal at its
medial end (Porus Acousticus)
• In medial approaches to the IAC, the dura is elevated over
the meatal plane and the retractor is then inserted into the
petrous ridge with its tip lodged into the bony groove of the
superior petrosal sinus
• If the ridge is not clearly identified, the placement of the
retractor can be too far lateral and there is a risk of entering
the inner ear when undertaking the initial bony removal.
• The EAC and IAC are roughly in line, which helps with
orientation.
• Gentle and careful bone removal is undertaken with a
diamond burr over the meatal plane, slowly reducing it over
a broad area from the arcuate posteriorly to the limit of the
dural elevation anteriorly.

15. • The temporal bone is usually pneumatized or filled with
bone marrow anterior to the IAC.
• As the meatal plane is lowered, the IAC becomes visible. Its
medial end is then defined and troughs are drilled both
anteriorly and posteriorly to give more extensive exposure
and sufficient space for safe tumour removal.
• At this stage, a thin layer of overlying bone is left to protect
the dura of the IAC. The IAC is then followed laterally.
• Great care has to be exercised at this stage to ensure that no
inadvertent entry into the cochlea or the SSC happens

16. Finding the internal auditory canal at its
lateral end (Fundus Acousticus)
• The margin of error at the
lateral end of the IAC is
of the order of 1 mm
• House or Fisch.
• House,the GSPN is
delineated and followed
proximally through its
hiatus to the geniculate
ganglion. Then, by tracing
the labyrinthine segment
of the facial nerve, the
IAC is identified

17. • The Fisch technique was
developed to limit the
degree of dural retraction
and the risk of damage to
the labyrinthine segment of
the facial nerve.
• the tegmen is removed and
the SSC ‘blue lined’.
• Having identified this, the
IAC is then located within
an angle of between 45
degrees and 60 degrees
subtended from the ampulla
of the SSC.

18. Completion of internal auditory
canal exposure
• Bone removal in the meatal plane needs to be
more extensive in vestibular schwannoma
surgery than for vestibular neurectomy.
• More radical removal of bone is carried out for
access to larger vestibular schwannomas and is
sometimes referred to as the enlarged MF
approach.
• Access can be improved further by division of
the superior petrosal sinus.

19. • Approximately three-quarters of the circumference of the IAC at the
porous acousticus is exposed.
• This degree of exposure is not possible at the lateral end of the IAC
because of the proximity of the ampulla of the SSC and the cochlea.
• Bill’s bar, the vertical crest of bone separating the facial nerve from
the superior vestibular nerve, is identified at the lateral end.
• The fine eggshell of bone covering the dura is now carefully
removed and the dura incised along the posterior aspect of the IAC,
thereby avoiding inadvertent damage to the facial nerve.
• A dural flap is fashioned and the contents of the IAC identified.

20. Closure
• Any exposed air cell tracts must be waxed and a
muscle plug is placed in the IAC.
• If the tegmen has been removed, it should be
repaired with a bone graft or a bone pate slab to
prevent dural herniation.
• The dura can be hitched to the skull by dural
sutures to minimize the size of any extradural
collection.
• The temporal bone flap is then fixed back into
position.

21. • Internal auditory canal/cerebellopontine angle
surgery

22. VESTIBULAR SCHWANNOMA
SURGERY
• Both the MF and retrosigmoid (RS) approaches
have been used for attempted hearing preservation
in VS surgery.
• It is proposed as the hearing preservation
approach of choice in tumours extending far into
the lateral third of the IAC.
• The main disadvantage is relatively poor access
to the CPA and many surgeons would be hesitant
in utilizing this approach for tumours with an
angle component greater than 15 mm

23. • This has the advantage of ease of facial nerve
identification but the disadvantage in that
greater manipulation of the nerve may be
required to remove the tumour.
• Additionally, control of bleeding in the CPA
can be more difficult with the MF approach

24. VESTIBULAR NEURECTOMY
• The main indication for this is in patients with
Ménière’s disease
• The main advantage of the MF approach is
that it offers access at a more distal location
where the VIII nerve is naturally divided into
its vestibular and cochlear branches.

25. • Middle fossa floor

26. FACIAL NERVE SURGERY
• Indications for the MF approach have expanded to
address facial nerve pathology in its intracranial,
intracanalicular, labyrinthine, geniculate and
tympanic segments
• Decompression surgery is particularly appealing
in cases of Melkersson–Rosenthal syndrome
(MRS) and recurrent facial paralysis of unknown
origin. MRS is a triad of recurrent alternating
facial paralysis, recurrent facial and labial oedema
(cheilitis granulomatosa) and fissured tongue
(lingua plicata)

27. REPAIR OF TEGMEN DEFECTS,
CEREBROSPINAL FLUID LEAKS AND
MENINGOENCEPHALOCOELES
• Good outcomes are achieved with defects sealed
via the MF approach to the tegmen plate when
this is the site of the problem
• The procedure can be carried out through a ‘mini’
temporal craniotomy with a window of less than 4
cm. While drilling, bone dust is collected using a
bone-pate collector attached to the suction
apparatus.
• After elevation of the dura, all the defects in the
tegmen are exposed and sealed with bone pate
mixed with blood and fibrin glue

28. SUPERIOR SEMI-CIRCULAR CANAL
DEHISCENCE SYNDROME
• Plugging of the canal was performed using
fascia strips, bone dust and bone chips, which
are gently but securely placed inside the
dehiscent canal to obliterate the canal lumen
for 2–3 mm beyond either end of the
dehiscence.

29. Petrous apicectomy
• The MF craniotomy provides the shortest and
most direct route to the petrous apex.
• By elevation of the dura medial and anterior to
the IAC, the anterior apex can be exposed as
far as Meckel’s cave and the ipsilateral
cavernous sinus.

30. CONCLUSION
Middle fossa approaches:
• provide access superior and medial to the otic
capsule preserving inner ear function
• provide excellent access to the proximal
intratemporal facial nerve
• allow for the repair of tegmen defects with
preservation of middle ear function
• small- and medium-sized VS can be removed
with preservation of hearing.

31. • THANK YOU