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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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200 ■ ANATOMY OF THE TEMPORAL BONE WITH SURGICAL IMPLICATIONS
within or near the internal auditory canal. In his review of 100 human temporal bone specimens, this arterial loop was either the main trunk or a branch
of the anterior inferior cerebellar artery in 80%, the accessory anterior cerebellar artery in 17%, and a branch of the posterior inferior cerebellar artery in 3%.
In 40% the loop was located within the internal auditory canal, in 27% it was
at the meatus, and in 33% in the cerebellopontine angle (Figs. 7–11).
Figure 5
A higher magnification of Figure 4
shows the atrophic changes in the wall
of the internal carotid artery (female,
age 72yr).
Figure 6
An accessory meningeal artery may
occasionally be seen in horizontal temporal bone sections. It occupies a bony
canal lateral to the facial hiatus (female,
age 49yr).
CHAPTER 7: VASCULAR ANATOMY ■ 201
Figure 7
The anterior inferior cerebellar artery
(AICA) frequently loops deeply into
the internal auditory canal as shown
here (male, age 87yr).
Figure 8
The anterior inferior cerebellar artery is
seen in the internal auditory canal
(IAC) (female, age 96yr).
Blockage of the anterior inferior cerebellar artery causes necrosis of
labyrinthine and brain stem structures, but is rarely fatal. Disruption of the
anterior inferior cerebellar artery during surgical procedures in the internal
auditory canal or cerebellopontine angle may result in uncontrollable
bleeding.
202 ■ ANATOMY OF THE TEMPORAL BONE WITH SURGICAL IMPLICATIONS
Figure 9
Here is another example of the anterior
inferior cerebellar artery (AICA) looping deeply into the internal auditory
canal (IAC). An incidental feature is an
otosclerotic focus at the anterior margin of the oval window (female, age
75yr).
Figure 10
In this case the anterior inferior cerebellar artery lies in a groove on the posterior wall of the petrous bone and enters
the internal auditory canal (IAC) to
form a tortuous loop (male, age
unknown).
THE MAJOR VEINS
The venous sinuses of the dura mater are low-pressure, valveless venous
channels which drain the temporal bone, orbit, and brain. They are located
between the two layers of the dura mater and are lined with an endothelium
which is a continuation of that which lines the tributary veins. Of special
relevance to temporal bone anatomy are the lateral sinus, the superior
petrosal sinus, and the inferior petrosal sinus.
The lateral sinuses provide the major venous drainage from the head to
the neck and are appropriately the largest of the sinuses. They begin at the
CHAPTER 7: VASCULAR ANATOMY ■ 203
internal occipital protuberance as continuations of either the superior sagittal
sinus (usually on the right side) or of the straight sinus, and then course in the
attached margin of the tentorium cerebelli to the bases of the petrous bones.
Each lateral sinus heads medially and inferiorly in an S-shaped sulcus in the
mastoid bone (the sigmoid sulcus) to end in the internal jugular vein (Fig. 12).
The sigmoid part of the lateral venous sinus may bulge anteriorly into the
mastoid air cell system where it is vulnerable to surgical injury (Fig. 13). The
Figure 11
The anterior inferior cerebellar artery
extends deeply into the internal auditory canal (IAC) (male, age 83yr).
Figure 12
The relationship of the sigmoid part of
the lateral venous sinus to the mastoid
air cell system is shown. The posterior
canal produces a slight prominence on
the posterior wall of the petrous bone
(male, age 72 yr).
204 ■ ANATOMY OF THE TEMPORAL BONE WITH SURGICAL IMPLICATIONS
intimate relationship of the lateral venous sinus to the mastoid also makes it
susceptible to thrombosis in severe mastoid infections. The position of the
sigmoid sinus in relation to the labyrinth is variable (Figs. 14–18) and, according to Montgomery (267), anterior positioning of the sinus usually indicates
underdevelopment of the mastoid air cell system.
The superior petrosal sinus occupies the superior petrosal sulcus which
runs along the petrous ridge enveloped in the attached margin of the tentorium cerebelli. It links the cavernous sinus with the lateral sinus; among its
tributaries are veins from the tympanic cavity, cerebellar veins, and inferior
cerebral veins.
Figure 13
The sigmoid sinus is that portion of the
lateral venous sinus which occupies the
sigmoid sulcus. It may protrude deeply
into the posterior part of the mastoid
air cell system. The operculum overlies
the endolymphatic sac (female, age
75yr).
Figure 14
In this case the lateral venous sinus
heads toward the jugular bulb without
forming a sigmoid segment. It forms a
membranous party wall with the posterior canal (male, age 54 yr) (see Fig. 15 on
p. 205).
CHAPTER 7: VASCULAR ANATOMY ■ 205
The inferior petrosal sinus runs in the inferior petrosal sulcus at the
petro-occipital suture line and connects the cavernous sinus with the jugular
bulb. Its tributaries consist of the internal auditory veins and veins from the
pons, medulla, and inferior aspect of the cerebellum.
The petrosquamous sinus is variably present; it occupies the petrosquamous junction and drains into the lateral sinus.
Emissary veins connect the extracranial veins with the cranial sinuses.
The mastoid emissary vein traverses the mastoid foramen and carries blood
from the occipital or posterior auricular vein to the lateral sinus. It may be
large and can be transected, causing troublesome bleeding during mastoid
surgical procedures as when soft tissues are elevated to expose the cortical
bone of the mastoid.
Figure 15
High power view from Figure 14 showing the membranous party wall
between the lateral venous sinus and
the posterior canal (male, age 54yr).
Figure 16
In this case the lateral sinus passes
directly to the jugular bulb without
forming a sigmoid segment. The
endolymphatic sac lies in close proximity to the sinus (male, age 56yr).
206 ■ ANATOMY OF THE TEMPORAL BONE WITH SURGICAL IMPLICATIONS
Occasionally a large vein is seen within the fallopian canal, a condition
which may cause bleeding during explorative procedures on the facial nerve
(Fig. 19).
The internal jugular vein is a direct continuation of the lateral sinus. It
begins at the base of the skull in the jugular foramen where it is dilated and
is referred to as the jugular bulb; there is great variability in the dimensions
of the jugular bulb, but it averages 15mm in width and 20 mm in height
(268). The right jugular bulb is usually somewhat larger than the left. In
Figure 17
The jugular bulb may fail to reach the
level of the hypotympanum (female,
age 78yr).
Figure 18
In this ear the lateral venous sinus is
located in an anterior position near the
posterior canal and endolymphatic sac.
An unrelated finding is obliteration of
the round window niche by otosclerosis (female, age 82yr).
CHAPTER 7: VASCULAR ANATOMY ■ 207
keeping with the inconstancy of venous structures, it may appear high in the
middle ear, encroaching upon the tympanic annulus and round window
niche, in which case it may cause conductive hearing loss (269) (Figs. 20–22).
The bony shell may be variably dehiscent (Figs. 23–25), with reported
incidences of between 6% and 7% (268, 270).
Figure 19
The head of the malleus is in fibrous
contact with the tegmen tympani but is
not ankylosed to it. Alarge vein accompanies the facial nerve in the tympanic
segment of the fallopian canal (male,
age 70yr).
Figure 20
The jugular bulb lies in its normal position in the floor of the hypotympanum
with its bony wall intact (female, age
77yr).
208 ■ ANATOMY OF THE TEMPORAL BONE WITH SURGICAL IMPLICATIONS
Figure 21
In this ear the jugular bulb extends
superiorly into the mesotympanum. It
rests against the tympanic membrane
and obliterates the round window
niche. No tests of auditory function are
available; however, a conductive hearing loss would be expected (female,
age 68yr).
Figure 22
In this ear the lateral venous sinus
and the jugular bulb are located
anteriorly. The mastoid is narrow
(female, age 80yr).
A high jugular bulb is susceptible to injury during surgical procedures
in which the tympanic membrane is elevated from its sulcus. Ahigh jugular
bulb diminishes the depth of the hypotympanic space, which may increase
the difficulty of establishing an aerated hypotympanum in tympanoplasty
surgery. On otoscopic examination a high jugular bulb may be mistaken for
a glomus body tumor.
CHAPTER 7: VASCULAR ANATOMY ■ 209
Figure 23
This case shows small dehiscences in
the bony wall of the jugular bulb (male,
age 45yr).
Figure 24
This section depicts a superiorly located
jugular bulb impinging on the tympanic
annulus. A jugular bulb in this location
can be inadvertently opened during
surgical elevation of a tympanomeatal
flap (female, age 75yr) (see Fig. 25 on
p. 210).
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