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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_4501_Библиотеки_им_академика_М_И_Перельмана
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60 ■ ANATOMY OF THE TEMPORAL BONE WITH SURGICAL IMPLICATIONS
Figure 38
There is a fibrous attachment of the
head of the malleus to a bony spur arising from the lateral wall of the epitympanum causing no effect on hearing
(female, age 22yr).
Figure 39
A bony spur projects from the lateral
epitympanic wall to make a fibrous
attachment to the lateral aspect of the
head of the malleus. We propose that
these fibrous attachments may, in some
instances, lead to bony ankylosis and
fixation of the malleus (male, age 36 yr).
Figure 40
A vertical section illustrates that the
superior aspect of the head of
the malleus is in fibrous union with the
tegmen tympani. There was no documented hearing loss. There is an exceptionally large vein in the fallopian
canal, an anatomical variant probably
representing a persistent lateral capital
vein (female, age 87yr).
CHAPTER 3: THE MIDDLE EAR ■ 61
We have found ankylosis of the head of the malleus in 15 of 1200
temporal bones which had no other evidence of middle ear abnormality or
disease. Malleus ankylosis can be diagnosed clinically by pneumatic
otoscopy or by palpation and is thus differentiated from stapes fixation
which it mimics functionally (Figs. 41–43) (14–17).
The Incus
The incus, the largest of the auditory ossicles, consists of a body, short
process, long process, and lenticular process. The body of the incus rests in
the epitympanum in association with the head of the malleus. Movement of
the incus is closely geared to that of the malleus by virtue of their cog-type,
saddle articulation (see p. 70); this gearing is responsible for the “secondary
Figure 41
In this ear with chronic otitis media,
there is bony fixation of the malleus to
the anterolateral wall of the epitympanum. There was a mild conductive
hearing loss (female, age 64yr).
Figure 42
This horizontal section through the
epitympanum of the left ear of a
60-yr-old female with otosclerosis and
conductive hearing loss shows the head
of the malleus fixed by a trabeculum of
lamellar (not otosclerotic) bone which
reaches from the anterior epitympanic
wall to the anterior aspect of the head
of the malleus.
62 ■ ANATOMY OF THE TEMPORAL BONE WITH SURGICAL IMPLICATIONS
Figure 43
There is ankylosis of the head of the
malleus to the lateral epitympanic wall
by lamellar (not otosclerotic) bone.
Otosclerosis was also present and
stapedectomy 13yr before death had
resulted in excellent hearing improvement (female, age 82yr).
incus effect” (14, 15) in which malleal fixation also interferes with the transfer of sound energy through the incus.
The short process of the incus extends posteriorly, occupying the posterior incudal recess (fossa incudis) (Fig. 27); in some cases, the short process may
be long and slender (Fig. 44). The long process reaches inferiorly, paralleling the
manubrium, to end in the lenticular process; the convex surface of this process
articulates with the concave surface of the head of the stapes in the diarthrodial
incudostapedial articulation (Fig. 45). The horizontal, cross-sectional configuration of the long process of the incus is circular (Figs. 46 and 47), in contradistinction to the ovoid shape of the manubrium of the malleus. These differing
shapes are taken into consideration in the design of prostheses (Fig. 48).
Figure 44
This view is through the axis of rotation. The long and slender short
process of the incus as seen in this ear
makes the name seem somewhat incongruous (female, age 82yr).
CHAPTER 3: THE MIDDLE EAR ■ 63
Figure 45
The head of the stapes articulates with
the lenticular process of the incus and
also acts as a site of attachment for the
stapedius tendon. There is partial
resorption of the long process of the
incus presumably caused by osteoporosis (male, age 71yr).
Figure 46
The anatomic relationships of the long
process of the incus, the lenticular
process, and the head of the stapes are
shown (male, age 63yr).
64 ■ ANATOMY OF THE TEMPORAL BONE WITH SURGICAL IMPLICATIONS
Figure 47
The long process of the incus is roughly
circular in cross section. There are
numerous nutrient vessels within the
bone as well as in the surface mucosa
(female, age 54yr).
Figure 48
The round cross-sectional configuration of the long process of the incus
permits a simple, crimp-on prosthesis
as is schematically illustrated (78).
CHAPTER 3: THE MIDDLE EAR ■ 65
Three ligaments anchor the incus in place. The posterior incudal ligament secures the short process in the posterior incudal recess. Anteriorly, the
medial and lateral incudomalleal ligaments secure the body of the incus to
the head of the malleus (Figs. 27 and 49).
Calcification of the posterior incudal ligament has been noted on
histopathological examination of the temporal bone; however, its effect on
sound conduction is unknown. A superior incudal ligament has been mentioned (4); however, we have not been able to identify such a structure.
The long process of the incus is highly susceptible to osteitic resorption
caused by chronic otitis media (Fig. 45).
In newborn infants, both the malleus and incus have large marrow
spaces (Fig. 50) which may persist into adulthood.
Figure 49
The embryologic derivation and purpose of the consistently present notch in
the short process of the incus, first
described by Lempert and Wolff (79), is
not known. In this ear, the chorda tympani nerve lies in a groove on the
medial aspect of the base of the anterior
process of the malleus (female, age
53yr).
Figure 50
In infancy, the malleus and incus
normally contain a central core of bone
marrow (female, age 25 days).
66 ■ ANATOMY OF THE TEMPORAL BONE WITH SURGICAL IMPLICATIONS
Figure 51
There is a pneumatized pit in the long
process of the incus. These excavations
in the incus are seen in the course of
otologic surgery. Fluid with proteinaceous precipitate (arrows) occupies the
pneumatized spaces. Fluid collections
in the tympanomastoid compartment
sometimes occur as a terminal event in
patients in coma and/or circulatory
failure (male, age 77yr).
It is common for the long process to show slight pneumatization in the
form of a pit (Fig. 51). Highly pneumatized incudes are rare (Figs. 52 and 53),
but in such cases the long process would be vulnerable to fracture during
surgical manipulation.
The Stapes
The stapes is the smallest and the most medial link of the ossicular chain; it
consists of a head, footplate (the basis stapedis), and two crura or legs (4).
The anterior crus is straighter and more delicate than the posterior (Figs. 10
and 54). There is an irregular area near the superior aspect of the posterior
Figure 52
There is extensive pneumatization
of the bony long process and body
(see Fig. 53 on p. 67) of the incus. The
ostium (left view) is located on its
anteromedial aspect approximately
2mm from its inferior tip. As the pneumatized area extends superiorly (right
view), only a shell of bone remains
(female, age 44yr).
CHAPTER 3: THE MIDDLE EAR ■ 67
Figure 53
Same ear as Figure 52 showing the
pneumatization extending into the
body of the incus (female, age 44yr).
Figure 54
This cross-sectional view of the stapes
shows the crura and head; the
stapes has no neck. An expanding
otosclerotic focus at the anterior
margin of the footplate has caused jamming of the posterior edge of the footplate against the margins of the oval
window, resulting in mild conductive
hearing loss (female, age 86yr).
crus to which the stapedius tendon variably attaches. The area delimited by
the concave arches of the crura is the obturator foramen, sometimes bridged
by a veil of mucous membrane.
The footplate, in association with the annular ligament, seals the oval
window (Figs. 55 and 56). The shape, thickness, and curvature of the footplate are inconstant. On its lateral surface, it has a variably present longitudinal ridge known as the crista stapedis. The vestibular surface may be flat,
slightly convex, or slightly concave. The head articulates with the lenticular
process of the incus at its fovea (see the sections on articulations on p. 74), and
it may have a muscular process for the attachment of the stapedius tendon.
The relative thickness and curvature of the crura vary among individuals, as does the locale for attachment of the stapedius tendon. Both the
external configuration and the degree of internal excavation may vary in the
head and crura.
68 ■ ANATOMY OF THE TEMPORAL BONE WITH SURGICAL IMPLICATIONS
Figure 55
The normal stapes are seen in relation
to the adjacent anatomic structures. The
posterior crus is normally more curved
than the anterior one. Posterior tilting is
caused by the unopposed pull of the
stapedius muscle and is routinely
observed in postmortem specimens
(male, age 45yr). Abbreviations: IAC,
internal auditory canal; EAC, external
auditory canal.
Figure 56
An infrequent finding is that of a
sesamoid bone in the anterior aspect
of the stapediovestibular articulation
(male, age 78yr).
The depth of the fovea for the lenticular process of the incus and the
presence of a muscular process on the head are variable. The obturator foramen is embryologically related to the stapedial artery which at one time
passes through the blastema of the stapes (see chap. 9). Presumably, failure
of normal interaction between these two structures causes occasional columellar formation of the stapes (Fig. 57). In cretins, the stapes show a consistent anomaly (Fig. 58). The Mondini anomaly may be associated with defects
in the footplate, leading to cerebrospinal fluid otorrhea and meningitis (18).
The most dependable method for removing the stapes without fracturing it is to cut its tendon and rock it forward by gentle pressure on the
posterior surface of its head, keeping the stress in the plane of the crura.
CHAPTER 3: THE MIDDLE EAR ■ 69
Figure 57
The left ear of this 30-yr-old man with
conductive hearing loss demonstrates
congenitally malformed crura. The
capitulum is well developed, but the
crural arch is replaced by a single thick
columella making fibrous contact with
the promontory immediately inferior to
the oval window. The footplate was
also deformed and fixed.
Figure 58
This right ear of a 43-yr-old congenitally deaf female shows the classical
middle ear anomalies of cretinism. The
stapedius muscle and tendon are
absent, as are the pyramidal eminence
and facial recess. The head of the stapes
and the lenticular process of the incus
rest against the posterior wall of the
tympanic cavity. The facial nerve is
widely dehiscent.
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