2. INTRODUCTION
• The middle ear is recognized to be a very small space, almost inaccessible by microscope in
some regions.
• Despite the illumination and magnification offered by the operating microscope, it has proved
to have distinct limitations. The straight-line view offered by the microscope produces blind
spots during middle ear surgery.
• These limitations can be overcome with the complementary help of an endoscope, which
allows “looking around corners.”
• Other than a wider and clearer view of middle ear anatomy, endoscopy allows better
understanding of middle ear physiology and ventilation pathways that might cause pathology if
impaired.
3. • The middle ear can be conceptually
divided into subspaces on the basis of
their relationships with the
mesotympanum:
• The mesotympanum is the portion that
an observer can visualize through the
external ear canal by the use of an
otoscope or a microscope.
• Posteriorly to it lies the retrotympanum,
superiorly the epitympanum, anteriorly
the protympanum, and inferiorly the
hypotympanum (▶ Fig.)
Right ear. Drawing showing the hidden recess
of the middle ear. ct, chorda; ma, malleus; in,
incus; s, stapes; pr, promontory.
4. RETROTYMPANUM
• The retrotympanum is a
complex structure
consisting of different
spaces lying in the
posterior aspect of the
tympanic cavity (▶
Fig.).
Left ear. The position of the retrotympanic complex with
respect to the tympanic cavity (the red arrow shows where
the retrotympanum is located). ma, malleus; pr, promontory;
s, stapes; rw, round window; et, eustachian tube; ct, chorda;
in, incus; plm, posterior ligament of the malleus; pos,
posterior spine; dr, eardrum; sr, supratubal recess.
5. • The retrotympanum is
divided into the superior
retrotympanum and
the inferior
retrotympanum (▶ Fig.) by a
bony crest termed
the subiculum
Right ear. The subdivisions of the medial compartments of the retrotympanum. Two different portions
can be distinguished: an inferior retrotympanal space composed of the sinus subtympanicus lying
between the finiculus inferiorly and the subiculum superiorly; and a superior retrotympanal space
composed of the sinus tympani between the subiculum inferiorly and the ponticulus superiorly, with
the posterior sinus separated from the sinus tympani by the ponticulus. pr, promontory; s, stapes; et,
eustachian tube; f, finiculus; ap, anterior pillar; pp, posterior pillar; jb, jugular bulb; ss, sinus
subtympanicus; sty, styloid complex; su, subiculum; p, ponticulus; st, sinus tympani; ps, posterior
sinus; pe, pyramidal eminence; fn, facial nerve; cp, cochleariform process.
6. • We can identify four spaces in the
superior retrotympanum: two spaces
lying medial and anterior, and two
spaces lying lateral and posterior to
the third portion of the facial nerve
and the pyramidal eminence (▶ Fig)
• The pyramidal eminence is the
fulcrum of the retrotympanum. From
this structure arise two bony
structures: the chordal ridge
extending outward and transversally
toward the chordal eminence, and
separating the facial recess
superiorly and the lateral tympanic
sinus inferiorly; and the ponticulus
extending inward and transversally
to the promontory region dividing the
sinus tympani inferiorly and the
posterior tympanic sinus superiorly.
Right ear. Drawing representing the medial and lateral
spaces of the retrotympanum. pr, promontory; s, stapes;
su, subiculum; p, ponticulus; st, sinus tympani; ps,
posterior sinus; pe, pyramidal eminence; fn, facial nerve;
fs, facial sinus; ls, lateral tympanic sinus; rw, round
window; in, incus; ma, malleus; ct, chorda.
7. SINUS TYMPANI
• The sinus tympani lies medial to the pyramidal eminence, the stapedius muscle, and
the facial nerve and lies lateral to the posterior semicircular canal and vestibule.
• The superior limit of this space is represented by the ponticulus; the inferior
anatomical limit is represented by a prominent ridge extending from the styloid
eminence to the posterior rim of the cochlear window niche: the subiculum
• The sinus has great variability in size and shape.
8. Left ear. Transcanal endoscopic view of the medial spaces of the retrotympanum by
0° endoscope. The subiculum is a ridge of bone arising from the styloid complex to
the posterior pillar of the round window niche dividing the sinus tympani from the
sinus subtympanicus. pr, promontory; s, stapes; f, finiculus; jb, jugular bulb; ss, sinus
subtympanicus; sty, styloid complex; su, subiculum; p, ponticulus; st, sinus tympani;
ps, posterior sinus; pe, pyramidal eminence; fn, facial nerve; rw, round window; in,
9. Left ear. Transcanal endoscopic view of the retrotympanum and pyramidal eminence with
a 0° endoscope. The ponticulus is a ridge of bone arising from the pyramidal eminence to
the promontory region dividing the sinus tympani from the posterior sinus. pr, promontory;
s, stapes; su, subiculum; p, ponticulus; st, sinus tympani; ps, posterior sinus; pe,
pyramidal eminence; fn, facial nerve; rw, round window; in, incus; ma, malleus; cp,
cochleariform process.
10. Left ear. Endoscopic magnification of the medial boundary of the sinus tympani with a 45°
endoscope. Classical shape: the sinus is located between the ponticulus and subiculum
lying medial to the facial nerve and to the pyramidal process. pr, promontory; su, subiculum;
p, ponticulus; st, sinus tympani; ps, posterior sinus; pe, pyramidal eminence; fn, facial nerve;
ss, sinus subtympanicus; sty, styloid complex; pp, posterior pillar.
11. • The morphology of the sinus tympani was classified on the basis of intraoperative
findings and the anatomical variations of the ponticulus.
The sinus tympani is classified into different types on the basis of shape as follows-
• Classical shape: the
sinus is located between
the ponticulus and
subiculum lying medial to
the facial nerve and to
the pyramidal process
.
12. • Confluent shape: an
incomplete ponticulus is present
and the sinus tympani is
confluent to the posterior sinus
13. • Partitioned shape: a ridge
of bone extending from the third
portion of the facial nerve to the
promontory area is present,
separating the sinus tympani
into two portions (superior and
inferior)
.
14. • Restricted shape: a high
jugular bulb is present,
reducing the inferior extension
of the sinus tympani
15. • Several anatomical studies have focused on the depth of the sinus tympani.
• This is a very important detail because the deeper the sinus tympani the more difficult
it is to achieve radical removal of cholesteatoma. For this reason it will be useful for
the surgeon to study the extension of the sinus tympani before surgery.
• We have classified the depth of the sinus tympani into three types as follows-
Type A: small sinus tympani. The medial limit of the third portion of the facial
nerve corresponds to the depth of the sinus. In these cases, the sinus tympani is
small and does not exhibit medial and posterior extension to the facial nerve.
Type B: deep sinus tympani. The medial boundary of the sinus tympani lies
medially with respect to the third portion of the facial nerve and does not exhibit
posterior extension to the facial nerve.
Type C: deep sinus tympani with posterior extension. The medial boundary of the
sinus tympani lies medial and posterior to the third portion of the facial nerve. In
these cases, the sinus tympani is very large and deep and all these patients have
a well-developed mastoid.
16. Right ear. The depth
classification of the
sinus tympani. fn,
facial nerve; rw, round
window; pr,
promontory; st, sinus
tympani.
17. PONTICULUS
• The ponticulus is a bony ridge extending from the pyramidal process to the promontory region, which
separates the sinus tympani from the posterior tympanic sinus.
• The endoscopic approach allowed us to find three different variants of the ponticulus (Fig. 3).
• Classical morphology: in these patients the ponticulus is completely formed and it is like a ridge of
bone extending from the pyramidal process to the promontory area; this structure represent the
superior limit of ST dividing it from posterior sinus (Fig. 3a).
• Incomplete ponticulus: in these cases, ST and posterior sinus are confluent (Fig. 3b).
• Communicating ponticulus: in these subjects, the ponticulus is like a small bridge of bone and
there’s a communication between ST and posterior sinus under it (Fig. 3c).
18. Different morphologies of ponticulus. a classical morphology, b incomplete
ponticulus, c communicating ponticulus. st Sinus tympani, p ponticulus, rw round
window, pr promontory, ps posterior sinus, s stapes, pe pyramidal eminence, fn facial
nerve
19. Left ear. Ponticulus with bridge morphology, endoscopic view with 45° endoscope.
White arrow shows the communicating space between the sinus tympani and the
posterior sinus. pr, promontory; su, subiculum; st, sinus tympani; ps, posterior sinus; pe,
pyramidal eminence; p, ponticulus; fn, facial nerve; s, stapes.
20. SUBICULUM
• The subiculum is a bony ridge extending from the posterior lip of the round window niche
outward to the styloid eminence region, which separates the sinus tympani from the sinus
subtympanicus.
• The subiculum may be present—in which case the sinus tympani is separated by the inferior
retrotympanum—or may be absent, and in this case the sinus tympani is confluent with the
inferior retrotympanum . The bridge subiculum is a rare conformation; when present, under this
bridge of bone there is a communication between the inferior retrotympanum and the sinus
tympani
21. The subiculum is a ridge of bone
arising from the styloid complex to
the posterior pillar to the round
window niche, dividing the sinus
tympani from inferior
retrotympanum.
Right ear. In this case the sinus
tympani is confluent with the inferior
retrotympanum (sinus
subtympanicus) and the subiculum is
absent.
Left ear. Endoscopic views of the
retrotympanum in patients with
bridge subiculum (0° endoscope).
22. PYRAMIDAL EMINENCE AND SUBPYRAMIDAL SPACES
• In our experience performing endoscopic middle-ear surgery, close and variable relationships have
been noted between ST, posterior tympanic sinus (PTS) and the pyramidal eminence (PE).
• Pneumatization of the retrotympanum may extend to a variable degree into a recess under the PE. We
described this space in an unpublished work and we called this anatomical finding the ‘subpyramidal
space’ (SS).
• This space is limited laterally by the medial aspect of the pyramidal process, medially by the lateral
wall of the tympanum, inferiorly by the ponticulus, and posteriorly and superiorly by the Fallopian
canal, and it could be in direct anatomical continuity with the ST or with the PTS, depending on the
position of the ponticulus.
• Features of this space (particularly its depth) vary significantly and we found that it could range from
a total absence due to a complete development of the medial aspect of the pyramidal process, up to a
clear representation of the SS with a significant depth.
• The more SS is deep, the more a surgical approach is at high risk of leaving residual cholesteatoma. A
good knowledge of these anatomical spaces may help in reducing the risk of residual cholesteatoma
during middle ear surgery.
23. The subpyramidal space. a–
b retrotympanic space with
endoscope 45° angle view in a
subject with a confluent shape
of the ST; c magnification of
posterior sinus and
subpyramidal space
(arrow); d exploration of
subpyramidal space laying
under the pyramidal
eminence. st Sinus
tympani, pr promontory, ps post
erior
sinus, s stapes, pe pyramidal
eminence, fn facial
nerve, lc lateral semicircular
canal, an antrum, ss subpyramid
al space, PES posterior
epitympanic
space, cp cochleariform
process, ma malleus
24. INFERIOR RETROTYMPANUM
• Some authors have studied the anatomy of the inferior retrotympanum, but the region has been
largely neglected in the literature. This is probably because of the poor accessibility of that
space during conventional microscopic procedures.
• In fact, Proctor in his studies had already identified almost all of the structures in that region,
based on several temporal bone dissections. He identified a fairly constant structure, a ridge of
bone connecting the basal helix of the cochlea to the jugular wall of the tympanum, in relation
to the anterior pillar of the round window niche: the sustentaculum promontorii. He called it the
sustentaculum (from the Latin sustentaculum, support) because he thought that it sustained the
inferior tympanic artery, enveloping it during the development of the middle ear.
• The present authors have confirmed the presence of that structure in relation to the anterior
pillar of the round niche, identifying two variants: a ridge shape and a bridge shape. Thus
rename the sustentaculum promontorii the finiculus .
25. • In a more cranial position lies the superior lateral attic whose inferior limit is represented by
the incudo-malleolar fold.
• This anatomical area together with the medial attic is the so-called superior attic or upper
unit.
• Superior attic is in communication with the mesotympanum through the underlying
tympanic isthmus and posteriorly it is opened to the aditus ad antrum.
• Its upper limit is tegmen tympani, while the lower one is given by the second portion
(intratympanic) of the facial nerve and laterally it is bounded by the lateral bony wall of the
Atticus. The whole superior attic is ventilated through the isthmus.
• Epitympanic compartments receive their aeration via the large tympanic isthmus between
the medial part of the posterior incudal ligament and the tensor tendon.
26. Left ear. Transcanal endoscopic view of the inferior retrotympanum and
hypotympanum. pr, promontory; s, stapes; in, incus; ma, malleus; te, tegmen of
round window niche; su, subiculum; fu, fustis; co, sinus concameratus; sp,
sustentaculum promontorii; et, eustachian tube; ct, chorda.
27. Left ear. Endoscopic magnification of the inferior retrotympanum (0° endoscope) and
round window niche. pr, promontory; te, tegmen of round window niche; su, subiculum;
fu, fustis; co, sinus concameratus; sp, sustentaculum promontorii; ma, malleus; ap,
anterior pillar; pp, posterior pillar; rw, round window.
28. Tympanic isthmus. a magnification of the isthmus with a 0° endoscope; b magnification of the
isthmus with a 45° angle endoscope; c scheme of the
isthmus. ma Malleus, in incus, s stapes, cp cochleariform process, tt tensor tendon of the
malleus, PES posterior epitympanic space, ct corda tympani, tf tensor fold, fn facial
nerve, pe pyramidal eminence, lc lateral semicircular canal
29. EPITYMPANUM
• The epitympanic space is a pneumatized portion of the temporal bone superior to the
mesotympanum.
• Epitympanic diaphragm” consists of three malleal ligamental folds (anterior, lateral, and
posterior), the posterior incudal ligamental fold and two purely membranous folds (the tensor
fold and the lateral incudomalleal fold) together with the malleus and incus.
• From this anatomical point of view it is possible to classify the epitympanum in two different
compartments: a larger and posterior one (posterior epitympanic space—PES) and a smaller and
anterior compartment (anterior epitympanic space—AES)
• The lateral portion of posterior epitympanum is narrower and it is divided in two further
portions by the lateral incudo-malleal fold. They are separated and arranged one above the other:
the superior and inferior lateral attic (Fig. 6a–c). Inferior lateral attic is bounded superiorly by
the lateral incudo-malleal fold and it is located between the more declive portion of short process
and body of the incus medially and the medial aspect of the scutum laterally.
• Mesotympanic region guarantees ventilation of the inferior lateral attic.
30. Epitympanic spaces and their ventilation routes. a posterior view; b medial to laterally
view; c: lateral view. Long curved arrow ventilation route of the epitympanic-mastoid
compartments, short arrow ventilation route of the Prussack
space, ma Malleus, in incus, s stapes, cp cochleariform process, AES anterior epitympanic
space, PES posterior epitympanic space, pos posterior spine, et Eustachian tube, imlf lateral
incudomalleal fold, mlf lateral malleal fold, tf tensor fold, plm posterior malleal ligamental
folds, alm anterior malleal ligamental folds
31. PROTYMPANUM
• The protympanic space is a pneumatic portion of the middle ear that lies anteriorly to the
mesotympanum and inferiorly to the AES (Anterior Epitympanic Space). The
cochleariform process and the tensor fold with the tensor tympani canal represent the
upper limit of protympanic space, while posteriorly its limit is generally considered the
promontorium.
• Tympanic portion of Eustachian tube starts from the protympanum. Above and medially
to the Eustachian tube opening runs the internal carotid artery. Bone over this structure
could be thick or pneumatized with some cells in there (protympanic cells).
• Another important reason to explore this recess is that when we find protympanic cells in
a patient with cholesteatoma disease involving the protympanic space, we have to pay
more attention because these cells might hide the presence of cholesteatoma persistence.
32. Supratubal recess view with a 45° endoscope in the protympanic space. a right ear with
wide perforation of the drum; b magnification of the protympanum with a good view of the
anatomic relationship between Eustachian tube and the supratubal
recess. ma Malleus, in incus, s stapes, et Eustachian tube, sr supratubal recess, ct corda
tympani, pos posterior spine, rw round window, pr promontory, plm posterior malleal
ligamental folds
33. CONCLUSION
• With endoscopic middle ear surgery we think that “in vivo” endoscopy of middle ear is
the best way to explore the tympanic cavity and to understand the importance of
ventilation routes, which we believe are the most important pathogenetic causes in
chronic middle ear disease.
• Endoscopy allowed us to understand that ventilation in middle ear doesn’t mean just
Eustachian tube function, but also isthmus blockage, complete or incomplete tensor fold
and mastoid pneumatization.
• The goal of surgery in the chronic pathology of the middle ear should be restoration of
normal ventilation of the attical-mastoid area.
• These were the main reasons why we did a review of middle ear anatomy, especially
focused on how it appears to the surgeon while performing an endoscopic procedure.
