Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_4501_Библиотеки_им_академика_М_И_Перельмана
.pdf
80 ■ ANATOMY OF THE TEMPORAL BONE WITH SURGICAL IMPLICATIONS
THE MUSCLES
The Stapedius Muscle
The stapedius muscle, the smallest of the skeletal muscles, lies in a bony
sulcus adjacent to the facial canal in the posterior wall of the tympanic
cavity. This penniform muscle is a mixture of striated and nonstriated fibers
that converge into a tendon which emerges from the orifice of the pyramidal
eminence into the tympanic cavity. It variably attaches to the head and/or
posterior crus of the stapes (4) (Figs. 74–76). The stapedius muscle receives
its innervation from the facial nerve. Its contraction draws the anterior
border of the footplate laterally and the posterior border medially. This
tilting of the stapes stretches the annular ligament, thus fixing the footplate
and damping its response to acoustic stimulation.
Figure 73
The incudostapedial articulation shows fusion
of the articular surfaces (grade III changes).
Audiometric tests showed no conductive
hearing loss (female, age 96yr).
CHAPTER 3: THE MIDDLE EAR ■ 81
Figure 74
The stapedius tendon normally attaches
to the head of the stapes and to the
capsule of the incudostapedial articulation (female, age 5yr).
Figure 75
The stapedius tendon emerges from the
pyramidal eminence to attach to the
head of the stapes (male, age 44 yr).
82 ■ ANATOMY OF THE TEMPORAL BONE WITH SURGICAL IMPLICATIONS
The Tensor Tympani Muscle
The tensor tympani muscle, in concert with the stapedius muscle, acts to
modify the movements of the ossicular chain. The tensor tympani muscle
(Fig. 77) arises from the cartilage of the eustachian tube, the walls of its
enveloping semicanal, and the adjacent portion of the greater wing of the
sphenoid bone. A bony sheath, the semicanal, houses the muscle for the
majority of its 2cm length. The fibers converge to form a central fibrous core
which, proceeding posteriorly, forms the tendon of the muscle. The most
medial fibers of the tendon attach to the concave surface of the cochleariform
(spoon-shaped) process, at which point the main body of the tendon turns
laterally to attach to the medial and anterior surfaces of the neck and the
manubrium of the malleus. It should be observed that the cochleariform
process does not function mechanically in the same fashion as a pulley.
Lupin (22), on the basis of anatomic dissections, suggests that the
tensor tympani muscle represents a continuation of the muscle fibers of the
tensor veli palatini muscle (Fig. 78). Its innervation is from the trigeminal
nerve via the nerve to the medial pterygoid muscle. Histologically, striated
as well as nonstriated muscle fibers can be observed. The muscle bundles
and tendinous fibers are surrounded by varying amounts of adipose tissue
(Fig. 79). This tissue may facilitate their adaptation to the confines of the
bony semicanal upon contraction. The action of the tensor tympani muscle
is to draw the manubrium medially, thus tensing the tympanic membrane.
Spontaneous contractions of this muscle may cause a clicking or
fluttering tinnitus in the ear and/or vertigo. Cutting the tendon has been
advocated for the relief of these symptoms (23).
Figure 76
In this case, the stapedius tendon
attaches to the posterior crus of the
stapes (female, age 73yr).
CHAPTER 3: THE MIDDLE EAR ■ 83
Figure 77
The tensor tympani tendon makes a
nearly right-angled turn at the
cochleariform (spoon-shaped) process
on its way to the neck of the malleus
(male, age 45yr).
Figure 78
This illustration shows the probable
derivation of the tensor tympani muscle from the tensor palatini muscle.
Source: Courtesy of Lupin (22).
84 ■ ANATOMY OF THE TEMPORAL BONE WITH SURGICAL IMPLICATIONS
Figure 79
Normally, there is adipose tissue surrounding the bundles of the tensor
tympani muscle. Presumably, this
yielding tissue facilitates contraction of
the muscle within its bony semicanal.
The muscle consists predominantly of
striated fibers (inset) (male, age 66yr).
Figure 80
The black dots in this sketch show the
location of ectopic muscle bundles in
25 of 500 ears studied by Wright and
Etholm (24). Abbreviations: OW, oval
window; RW, round window.
Ectopic and Anomalous Muscles
Wright and Etholm (24) found a total of 28 ectopic or anomalous muscles in
a study of 500 temporal bone specimens (Fig. 80). In no case was the muscle
anomaly bilateral and in three ears there were two separate anomalies.
Ectopic muscle was most frequent along the course of the facial nerve, either
within or close to the fallopian canal. They attributed this anomaly to the
persistence of mesenchymal rests along the hyostapedial ligament
(interhyale—see chap. 9) which in the seven-week embryo connects the
primordial stapes to the laterohyale of Reichert’s cartilage origin.
In three temporal bones, they found the tensor tympani muscles split
into medial and lateral bundles. The lateral bundles followed the normal
path of the tensor tympani muscle to the cochleariform process. In two of
three cases, the medial bundles pursued aberrant courses within the fallop-
CHAPTER 3: THE MIDDLE EAR ■ 85
ian canals and terminated by joining with the stapedius muscles. In certain
mammals, the tensor tympani may show a double origin—one from the
semicanal and one from the medial wall of the middle ear (1).
Wright and Etholm (24) observed anomalies of the stapedius muscle in
six ears. In two cases, the stapedius tendons, muscles, and pyramidal eminences were rudimentary; in two, the stapedius tendons were absent; and in
two, there was duplication of the muscles. In one of the latter cases, the
duplicate muscle bundle was located superior to the normal muscle (Fig. 81)
and the associated tendon failed to gain access into the tympanic cavity. The
authors suggested that premature separation of the interhyale from the
stapes due to an aberration of development was responsible for these anomalies. They noted that anomalies of the stapes bone were frequently associated with muscle anomalies. Hoshino and Paparella (25) found absent
stapedius muscles, unassociated with any other congenital anomaly, in
approximately 1% of ears undergoing surgical procedures. The presence of
ectopic muscle in the middle ear appears to be of no clinical importance.
THE MIDDLE EAR SPACES
The tympanic cavity is a cleft in the sagittal plane measuring about 15mm in
the vertical and anteroposterior dimensions; in its transverse dimension, it
expands superiorly to 6mm and inferiorly to 4 mm from a central constriction of 2mm (Fig. 82). It is pneumatized via the eustachian tube which links
it with the nasopharynx; posteriorly, the mastoid antrum connects the tympanic cavity with the mastoid air cells. It is traversed by the ossicular system
and is lined by mucous membrane.
The floor of the tympanic cavity (jugular wall) is composed principally
of the jugular bulb, the surface of which may show irregularities due to
Figure 81
This photomicrograph shows ectopic
muscle in the tympanic segment of the
fallopian canal (male, age 30yr).
86 ■ ANATOMY OF THE TEMPORAL BONE WITH SURGICAL IMPLICATIONS
overlying pneumatized cells (Fig. 83). In the posterior part of the floor is the
root of the styloid process which gives rise to the styloid eminence.
The posterior wall (mastoid wall) of the tympanic cavity narrows
inferiorly and features numerous anatomic structures. At its inferior aspect,
tympanic air cells are surmounted by the pyramidal eminence from which the
tendon of the stapedius muscle emerges. The chordal eminence is lateral to the
pyramidal eminence and medial to the posterior rim of the tympanic membrane; there is a foramen in this eminence, known as the iter chordae
posterius (or the apertura tympanica canaliculi chordae tympani), through
which the chorda tympani nerve gains access to the middle ear. The facial
recess is interposed between the chordal eminence laterally and the pyramidal eminence medially. Acting as the superior limit of the facial recess is the
incudal fossa, in which the short process of the incus is held in place by the
posterior incudal ligament. More superiorly, the epitympanic recess opens
into the mastoid antrum. There are three ridges connecting the three
eminences of the posterior tympanic wall: the chordal ridge links the chordal
eminence to the pyramidal eminence, the styloid ridge connects the styloid
prominence to the chordal eminence, and the pyramidal ridge joins the styloid
prominence to the pyramidal eminence (26).
The anterior wall of the middle ear (carotid wall) narrows inferiorly
where it is formed by the thin bony shell of the carotid canal which is often
covered by pneumatized cells. Located more superiorly in the anterior wall
is the orifice of the eustachian tube and above it the tensor tympani muscle
lies in its semicanal.
The roof (tegmental wall, tegmen tympani) separates the tympanic
cavity from the cranial cavity. In an autopsy series, 6% of cases showed
dehiscences in this wall (27).
The lateral boundary (membranous wall) is composed of the tympanic
membrane, the bony tympanic ring, and a layer of bone from the squama—
the scutum or shield of Leidy (28). Erosion of the scutum is a classical radiologic sign of cholesteatoma of the epitympanum.
The medial wall (labyrinthine wall) of the tympanic cavity is marked by
three main depressions—the sinus tympani, the round window niche, and the
Figure 82
Schematic view of the middle ear cleft.
Source: After Deaver (80) and Brodel (81).
CHAPTER 3: THE MIDDLE EAR ■ 87
oval window niche (Fig. 84). The sinus tympani lies between the ponticulus
which bridges the gap between the pyramidal eminence and the promontory
superiorly, and the subiculum (subiculum promontorii), a ridge stretching inferiorly between the styloid eminence to the posterior lip of the round window
niche (29). The round window niche is located anteroinferior to the subiculum
and posteroinferior to the promontory; the latter structure is the bulge of the
bone overlying the basal turn of the cochlea. The oval window niche is anterosuperior to the ponticulus and the cochleariform process of the tensor tympani
muscle is even more anteriorly and superiorly located. Located posterosuperiorly is the prominence of the facial canal as it traverses the medial wall and then
descends along the mastoid wall of the tympanic cavity.
It is useful in descriptions of disease or surgery to divide the middle
ear space into four regions: (1) The mesotympanum (middle ear proper) is that
area located medial to the tympanic membrane and the bony tympanic
annulus. (2) The epitympanum is that area that lies superior to a horizontal
plane drawn through the most superior level of the tympanic membrane (4).
Figure 83
This vertical section depicts the relative positions of the oval and round windows. The facial
nerve runs in the medial wall of the middle ear
at the boundary of the mesotympanum and epitympanum. The hypotympanum is normally
studded with trabeculations. The infralabyrinthine cell tract can be the site of extension
for cholesteatomas and neoplasms (male, age
unknown).
88 ■ ANATOMY OF THE TEMPORAL BONE WITH SURGICAL IMPLICATIONS
It is approximately one-third the vertical dimension of the entire tympanic
cavity, and houses the head of the malleus as well as the body and short
process of the incus. (3) The protympanum lies anterior to a frontal plane
drawn through to the anterior margin of the tympanic annulus. It leads to
the tympanic orifice of the eustachian tube. (4) The hypotympanum is that part
of the middle ear located inferior to a horizontal plane through the most
inferior part of the tympanic annulus.
Otologic surgeons are aware of variability in the depth of the hypotympanum. This variability may be ascribed to its tripartite origin (30) from the
tympanic bone, the otic capsule, and the petrosa. Ashallow hypotympanum
is usually associated with a superiorly located jugular bulb and can be an
undesirable anatomic feature in tympanoplasty surgery where one of the
objectives is to preserve or attain a pneumatized hypotympanic space.
Otologic surgeons are required to have an intimate knowledge of the normal
and variant anatomy of the middle ear if removal of disease (granulations,
cholesteatoma, etc.) and preservation of function are to be realized.
The Anterior Epitympanic Recess
The anterior epitympanic recess is located anterior to the head of the
malleus. Its boundaries include the middle cranial fossa superiorly, the
petrous apex and middle cranial fossa anteriorly, the tympanic bone laterally
and inferiorly, and the facial nerve and geniculate ganglion medially.
Posteriorly, it communicates with the epitympanum (Figs. 85–87). Also
known as the “sinus epitympani” (31), this recess varies greatly in size; it
may be quite large, in which case it may be partly walled off from the
epitympanum by a perforate septum.
Figure 84
The tympanic sinus is one of the three
major depressions of the medial wall of
the tympanic cavity. The ponticulus
limits this space superiorly, while the
subiculum limits it inferiorly. Its extension posteriorly is variable and may
amount to several millimeters. Source:
After Donaldson et al. (82).
CHAPTER 3: THE MIDDLE EAR ■ 89
Figure 87
In this ear, the genu of the facial nerve
lies immediately beneath the dura of
the middle cranial fossa (male, age
50yr).
Figure 85
In this ear, the anterior epitympanic
recess bulges into the middle cranial
fossa. This configuration renders it susceptible to perforation during surgical
procedures in the middle cranial fossa
(male, age 46yr).
Figure 86
The anterior epitympanic recess may
be partly isolated from the epitympanum by a bony septum (female, age
75yr).
Соседние файлы в папке Библиотека им академика М.И. Перельмана