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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_4453_Библиотеки_им_академика_М_И_Перельмана
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A.
B. Opened superior semicircular
C. Opened posterior semicircular
D.
E. Subarcuate artery
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A. Blue line of the lateral
semicircular canal
B. Blue line of the superior
semicircular canal
C. Blue line of the posterior
semicircular canal
D. Vertical segment of the
facial nerve
E. Incus buttress
109
Fig. 4.37 Expose the blue lines of the semicircular canals (right)
After the shapes of the three canals have been clearly exposed, remove
more bone from their lateral walls until the blue lines appear. Be careful
to protect the membranous labyrinth
Opened lateral semicircular
canal
canal
canal
Mastoid segment of the facial
nerve
Instruments: medium-sized diamond burs
Fig. 4.38 Open semicircular canals (right)
Use a hook to remove the outer thinned bone of the three semicircular
canals, then clearly identify their shapes. The superior and posterior
semicircular canals are situated almost perpendicular to the lateral
canal. The posterior end of the lateral canal sits just in front of the posterior canal level with its mid-point. The long axis of the posterior semi-
circular canal lies almost parallel with the plane of the posterior fossa
dura behind it and its ampulla sits at its inferior end close to or medial
to the vertical segment of the facial nerve. The superior end of the posterior semicircular canal joins the posterior end of the superior canal to
form the common crus
Instruments: hooks
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Y. Su et al.
A. Ampulla of the lateral
semicircular canal
B. Ampulla of the superior
semicircular canal
C. Posterior semicircular canal
D. Common crus
E. Single end of the lateral
semicircular canal
Fig. 4.39 Remove part of the lateral semicircular canal (right)
The three canals all connect with the vestibule. After drilling off more
bone from the lateral semicircular canal, the vestibule can be clearly
identied. The non-ampullated ends of the posterior and superior semi-
circular canals combine to form the common crus. The tympanic segment of the facial nerve is always close to the lateral semicircular canal
Instruments: medium-sized diamond burs
A. Vestibule
B. Remnant of the superior
semicircular canal
C. Common crus
D. Geniculate ganglion
E. Subarcuate artery
Fig. 4.40 Open vestibule (right)
With the outer bony wall of the vestibule drilled away, its cavity is
exposed. It lies between the IAC fundus medially and the oval window
laterally. It is anterior to the semicircular canals whose ve openings
open into its posterior wall. The cochlea lies anterior to the vestibule
with the ductus reuniens connecting the vestibule to the scala vestibuli
of the cochlea
Instruments: medium-sized diamond burs
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A. Opened vestibule
B. Geniculate ganglion
C. Mastoid segment of the
facial nerve
D. Endolymphatic duct
111
Fig. 4.41 Exposure of endolymphatic duct (right)
After drilling away the bone containing the common crus, the endolymphatic duct can be clearly identied. The endolymphatic duct connects
the utricle and the saccule to the endolymphatic sac
Instruments: small-sized diamond burs
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Anatomy ofSigmoid Sinus andJugular Bulb
YiSun
The sigmoid sinus is located within a bony sulcus lying at the
posterior edge of the mastoid segment of the temporal bone,
starting at the end of the transverse sinus and ending at the
jugular bulb. The sigmoid sinus is a space between the inner
and outer layers of the dura, separated from the mastoid air
cells by a thin layer of bone. The imaginary line connecting
the parietal notch with the mastoid tip can be taken as the
surface landmark of the sigmoid sinus. The average distance
between the posterior wall of the EAC and the anterior wall
of the sigmoid sinus is about 1.4cm. The average distance
between the cortex of the mastoid bone and the lateral wall
of the sigmoid sinus is about 1cm.
The position of the sigmoid sinus depends on the pneumatization of the mastoid. A posteriorly located sigmoid
sinus is found in well-pneumatized mastoids, whereas an
anteriorly located sigmoid sinus is found in poorly pneumatized mastoids. An anterior location is the most common
anatomic variation of the sigmoid sinus. If the distance
between the posterior wall of the EAC and the anterior wall
of the sigmoid sinus is less than 1cm, the sinus is said to be
anterior. This distance can be accurately measured in axial
sections of high-resolution computed tomography (HRCT).
CT scanning is currently a very reliable tool in determining
such anatomic variations.
The sigmoid sinus ends at the posterior margin of the jugular fossa, where it expands and arches upward to form the
jugular bulb. The jugular bulb is located within the posterior
compartment of the jugular fossa lying beneath the petrous
bone and joins inferiorly with the internal jugular vein. Its
width is about 15 mm and its height is about 14 mm. The
position and size of the jugular bulb are variable. Pulsatile
tinnitus is a common symptom in ENT practice and may be
due to a dilated mastoid emissary vein or sigmoid sinus diverticulum. Their presence is suspected if the tinnitus is in time
with the heart rate and can be relieved by soft compression of
the lateral side of the internal jugular vein in the neck.
Anatomic variations in the jugular bulb include a high
jugular bulb, jugular bulb diverticulum, and medially or laterally located jugular bulb. A high jugular bulb and jugular
bulb diverticulum are the most common. A high jugular bulb
is most commonly seen on the right side, which usually has
the dominant sigmoid sinus-internal jugular vein complex,
and is larger than the left. Anatomic variations in the jugular
bulb can usually be identied using HRCT.The incidence of
a high jugular bulb has been variously reported in different
studies because of different diagnostic criteria. A high jugular bulb incidence is reported when the jugular bulb extends
above the inferior aspect of the bony annulus—6%, the basal
turn of the cochlea—20.3%, the level of the round window—24%, and the bottom portion of the IAC—9%,
respectively.
A high jugular bulb is diagnosed if the jugular bulb dome
reaches or extends over the level of the round window or the
basal turn of the cochlea. Jugular bulb diverticulum is an
irregular outpouching that may extend to the anterior, medial,
or superior surface of the petrous bone, or to the IAC, and
results in relative rarefaction of bone between the posterior
fossa dura and the posterior semicircular canal. The incidence of a jugular bulb diverticulum is lower than that of a
high jugular bulb, at less than 1%.
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A. Posterior wall of the EAC
B. Tegmen mastoideum
C. Sigmoid sinus
D. Digastric ridge
E. Lateral semicircular canal
F. Superior semicircular canal
G. Posterior semicircular canal
H. Mastoid segment of the
facial nerve
113
Fig. 4.42 Skeletonization of the mastoid; exposure of the sigmoid
sinus (left)
Drill away the mastoid air cells, skeletonize the mastoid, and the dense
bone covering the sigmoid sinus can be seen. Gradually thin down the
bone until it is semitransparent, and then further skeletonize the three
semicircular canals, the mastoid segment of the facial nerve and the
digastric ridge. The spatial relationships and relative sizes of these anatomical landmarks can be observed, and this three-dimensional information should be fully considered throughout the dissection
Instruments: large-sized cutting burs, medium-
sized diamond burs
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A. Posterior wall of the EAC
B. Sigmoid sinus
C. Short process of the incus
D. Lateral semicircular canal
E. Superior semicircular canal
F. Posterior semicircular canal
G. Mastoid segment of the
facial nerve
H. Bony wall of the jugular bulb
Y. Su et al.
Fig. 4.43 Dissection of air cells inferior to the bony labyrinth and
retro-facial air cells (left)
The jugular bulb is located medial to the mastoid segment of the facial
nerve and digastric ridge, inferior to the posterior semicircular canal
ampullary end and the hypotympanum. The sizes and positions of jugular bulbs are variable. First, exploration of the jugular bulb is performed
gradually following the sigmoid sinus; next, to explore the position of
the jugular bulb, the mastoid segment of the facial nerve and posterior
semicircular canal are used as anatomical landmarks. The bone is gradually thinned down progressing inward
Instruments: medium-sized diamond burs
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A. Posterior wall of the EAC
B. Retro-facial air cells
C. Sigmoid sinus
D. Digastric ridge
E. Lateral semicircular canal
F. Superior semicircular canal
G. Posterior semicircular canal
H. Mastoid segment of the facial
nerve
Fig. 4.44 Exposure of the bone lateral to the jugular bulb (left)
The lower posterior bone over the jugular bulb is thinned down following the sigmoid sinus; the lateral bone over the jugular bulb is thinned
down following the mastoid segment of the facial nerve and digastric
ridge; the superior and lateral bone over the jugular bulb is then thinned
down, taking the posterior semicircular canal ampullary end as the
upper boundary. The position of the jugular bulb can then be identied.
If the sigmoid sinus is located anteriorly, the sigmoid sinus should be
skeletonized rst and then the bone over it should be dissected completely until it can be retracted to widen the operative eld. The vascular
wall of the jugular bulb is very thin; the bone over it should be gently
dissected and not drilled, in order to avoid injury to the jugular bulb
Instruments: medium-sized diamond burs
116
A. Posterior wall of the EA
B.
C. Superior semicircular canal
D. Posterior semicircular cana
E.
F.
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Y. Su et al.
A. Posterior wall of the EAC
B. Jugular bulb
C. Sigmoid sinus
D. Digastric ridge
E. Lateral semicircular canal
F. Superior semicircular canal
G. Posterior semicircular canal
H. Mastoid segment of the
facial nerve
Fig. 4.45 Exposure of the jugular bulb (left)
The lateral air cells over the jugular bulb are removed completely and
the bone over it is thinned down to expose the bulb. The full length of
the sigmoid sinus can be seen. The bottom end of the sigmoid sinus
turns forward and upward, then expands and arches upward to form the
C
Lateral semicircular canal
l
Eggshell bone over the
sigmoid sinus
Sigmoid sinus
jugular bulb. The intimate relationship between the jugular bulb and the
mastoid segment of the facial nerve, hypotympanum, posterior semicircular canal, sigmoid sinus, posterior fossa dura, and digastric ridge can
be observed
Instruments: medium-sized diamond burs
Fig. 4.46 Expose the sigmoid sinus
To train one’s abilities in accurate operative technique and use of the
bur, the bone over the sigmoid sinus should be thinned down gradually
using a large diamond bur until it is very thin and compressible. The
eggshell bone plate is dissected off the sigmoid sinus using a middle- ear
elevator, to expose the vessel wall completely
Instruments: large-sized diamond burs, middle ear elevator
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A. Lateral semicircular canal
B. Superior semicircular canal
C. Posterior semicircular canal
D. Mastoid segment of the
facial nerve
E. Endolymphatic sac
F. Retracted sigmoid sinus
G. Jugular bulb
117
Fig. 4.47 Dissection of sigmoid sinus, jugular bulb, and the posterior
fossa plate (left)
The bone over the sigmoid sinus, jugular bulb, and posterior fossa plate
is thinned down further, the last eggshell bone over the sigmoid sinus is
removed and the sigmoid sinus then retracts. Retraction of the sigmoid
sinus exposes the white endolymphatic sac, with the pink facial nerve
and yellow bony labyrinth lying deep in the mastoid cavity
Instruments: large- or medium-sized diamond burs, middle ear elevator
A. Digastric ridge
B. Mastoid segment of the
facial nerve
C. Second genu of the facial
nerve
D. Lateral semicircular canal
E. Posterior semicircular canal
F. Endolymphatic sac
G. Retracted sigmoid sinus
H. Jugular bulb
Fig. 4.48 Exposure of the whole jugular bulb (left)
The bone over the jugular bulb has been removed completely. The relationships between the jugular bulb and its landmarks are identied:
EAC medial end, hypotympanum oor, promontory (the oval window
and open scala tympani can be seen through the facial recess), posterior
semicircular canal ampullary end, IAC external end superiorly, mastoid
segment of the facial nerve anteriorly, digastric ridge inferolaterally,
sigmoid sinus, endolymphatic sac and posterior fossa dura posteriorly
Instruments: medium-sized diamond burs, middle ear elevator
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Y. Su et al.
A. Jugular bulb
B. Jugular bulb fossa
(bony wall)
C. Sigmoid sinus
D. Posterior fossa dura
Fig. 4.49 Jugular bulb (right)
In this picture, the full length of the right sigmoid sinus and jugular bulb
can be seen. The jugular bulb sits in the jugular fossa; the walls are thin
and semitransparent, and surgery should be performed carefully to
avoid injury to the thin bulb wall
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