Supine: Anterior Petrosal Approach 39

Petrosal Approaches
Anterior Petrosal Approach

1.65 The anterior petrosal
approach consists of a subtemporal crani-
otomy and an anterior petrosectomy. It is
also an option that can be combined with
the posterior petrosal approach. In this ex-
ample, the procedure is used with a sub-
temporal craniotomy. In the anterior
petrosectomy approach, the surgeon re-
moves the bone of Kawase's triangle in the
medial petrous apex, medial to Glasscock's
triangle. This maneuver provides a corridor
for approaching the petroclival region of
the upper posterior fossa from the middle
fossa. This approach improves exposure
for infraclinoidal basilar tip and upper mid-
basilar tip aneurysms as well as for pet-
roclival tumors that are located superior to
and anterior to the internal auditory
meatus. The anterior petrosectomy can be
performed with hearing preservation.

Kawase's
triangle

1.65

40 Surgical Positioning and Exposures

Epitympanum

(malleus)

Greater

superficial Seventh-eighth
petrosal cranial nerve
nerve complex

Lesser

superficial

petrosal

nerve

Kawase's

triangle

1.65

40

Surgical Positioning and Exposures

Epitympanum
(malleus)

Greater

superficial

petrosai

nerve

Lesser

superficial

petrosai

nerve

Seventh-eighth
cranial nerve
complex

1.66

1.66 A standard subtemporal
craniotomy is performed (see previous sec-
tion). The dura is elevated from the middle
fossa floor and petrous bone. The middle
meningeal artery is sacrificed at the fora-
men spinosum. Several structures are visi-
ble on the middle fossa floor, including the
mandibular division of the trigeminal nerve
at the foramen ovale; the lesser and greater
superficial petrosai nerves; occasionally
the internal carotid artery through a small
dehiscence in the bony floor; and the arcu-
ate eminence, which overlies the superior
semicircular canal. Critical structures usu-
ally obscured by bone include the petrous
carotid artery and its posterior loop, head
of the malleus in the epitympanum, genicu-
late ganglion, facial nerve, superior ves-
tibular nerve, cochlear nerve and cochlea,
and semicircular canals.

1.67 The greater superficial
petrosai nerve is sectioned near the facial
hiatus to prevent traction injury to the ge-
niculate ganglion while drilling is done in
this area. The horizontal section of the pet-
rous carotid artery is exposed using a high-
speed drill with a diamond burr. Removal
of the bone should not proceed to the poste-
rior loop in order to prevent injury to the
geniculate ganglion and cochlea.

1.68 Using a diamond burr,
the surgeon proceeds with dissection along
the greater superficial nerve to expose the
geniculate ganglion. The labyrinthine seg-
ment of the facial nerve marks the begin-
ning of the internal auditory canal. The
cortical bone of the superior semicircular
canal forms a 50-degree angle with the in-
ternal auditory canal. Drilling anterior to
the superior semicircular canal, the surgeon
exposes the dural sleeve of the internal au-
ditory canal.

r

Supine: Anterior Petrosal Approach 41

Superior

semicircular

canal

Geniculate ganglion

1.68

42 Surgical Positioning and Exposures

Geniculate ganglion

Bills' bar

Labyrinthine
segment of
facial nerve

1.69

1.69, 1.70 The cortical bone over-
lying the cochlea is removed until the coch-
lea appears as a blue line in the junction
between the carotid artery and the facial
nerve. A line drawn from the tip of Bill's
bar to the intersection of the carotid artery
with the trigeminal nerve (Miller's line) ap-
proximates the basal turn of the cochlea.

Miller's
line

Cochlea
(blue-lined)

1.70

43

Supine: Anterior Petrosal Approach

Anterior inferior

cerebellar Superior

artery petrosal sinus

Trigeminal
nerve

1.71

1.71 The remaining bone of
Kawase's triangle is removed. The dura is
opened along the inferior temporal lobe and
reflected inferiorly. The dural flap is then
split in midsection to the level of the supe-
rior petrosal sinus. Clips are placed on the
superior petrosal sinus. The sinus and ten-
torial dura are then incised toward a point
posterior to the insertion of the trochlear
nerve. The dura is then further split down
the line of Kawase's triangle, exposing the
contents of the upper posterior fossa.

44 Surgical Positioning and Exposures

1.72

1.73

Posterior Petrosal Approach

The posterior petrosal approach con-
sists of temporal craniotomy, suboccipital
craniotomy, and posterior petrosectomy.
In this approach, removal of the petrous
apex facilitates exposure of the middle and
upper posterior fossae. The petrosectomy
allows either a presigmoid or a retrosigmoid
approach in combination with subtemporal
exposure. The presigmoid approach pre-
serves all major venous structures except
the superior petrosal sinus. Section of the
superior petrosal sinus mobilizes the junc-
tion of transverse sinus and sigmoid sinus
and the entry site of the vein of Labbe.
Thus, the vein of Labbe is protected when
the temporal lobe is retracted. Addition of
the retrosigmoid approach more generously
exposes the posterior fossa and foramen
magnum. A subtemporal approach com-
bined with a retrosigmoid approach, in the
absence of presigmoid dissection, places
the vein of Labbe and the posterior tempo-
ral lobe in greater peril.

1.72 An armored endotra-
cheal tube is inserted to avoid obstruct-
ing the airway when the patient's head is
turned. Prior to positioning the patient, a
catheter is inserted into the lumbar spinal
canal for subsequent drainage of cere-
brospinal fluid. The patient is placed in the
supine position (as in the subtemporal ap-
proach). The right shoulder is elevated with
a gelatin pad to reduce torsion of the neck
and to promote venous return.

Supine: Posterior Petrosal Approach 45

1.74

1.73 The neck is extended to
bring the zygoma to the apex of the surgical
field. The head is rotated until the sagittal
suture is oriented parallel to the floor.

1.74, 1.75 The lateral oblique posi-
tion is an option when extensive exposure
of posterior fossa structures is required or if
the patient poorly tolerates neck rotation.

1.75

46 Surgical Positioning and Exposures

Sphenosquamosal
suture

Sphenoparietal
suture

Transverse
sinus

Coronal
suture

Squamosal
suture

1.76

1.76 Critical to the petrosal
approach is the surgeon's ability to project
the location of the petrous bone and deep
venous structures onto the surface
anatomy.

1.77 The temporal skin flap
is reflected inferiorly. The frontal skin flap
is reflected anteriorly. Hemostatic clips are
placed on the skin edges.

Temporal

skin

flap

Frontal
skin flap

1.77

Supine: Posterior Petrosal Approach 47

Asterion

Superior
| nuchal
* line

Transverse

sigmoid

junction

1.78

X

1.79

1.78 The temporalis muscle
is reflected anteroinferiorly, leaving a supe-
rior fascial cuff. Entry burr holes are posi-
tioned at the most anterior mastoid point
and below the asterion, which are above
and below the transverse sigmoid junction,
respectively. A second set of burr holes are
placed above and below the superior nuchal
line, isolating the transverse sinus. A pneu-
matic craniotome is used to partially dissect
a bone flap that overlies both the posterior
and the middle cranial fossae.

1.79 The sinus is dissected
free of the overlying bone plate. Using a
pneumatic craniotome, the surgeon con-
nects the burr holes. The bone flap is
elevated.

48 Surgical Positioning and Exposures

Transverse
/ sinus

1.80

Spine of Henle

Antrum

1.80 Bone overlying the sig-
rnoid and transverse sinuses is dissected
with a high-speed pneumatic drill.

1.81 The spine of Henle is a
landmark to the antrum. The antrum floor
is the cortical bone of the lateral semicircu-
lar canal, which serves as a guide to deeper
structures. The mastoid air cells are re-
moved, and the middle fossa and meatal
bone plates are dissected until the antrum is
identified.

Lateral

semicircular

canal

1.81

49

Supine: Posterior Petrosal Approach

Posterior semicircular
canal

Sinodural
angle

1.82

1.82 As the bone of the sino-
dural angle is removed with a diamond drill,
the sigmoid sinus and posterior semicircu-
lar canal are exposed. The posterior semi-
circular canal is identified by following the
lateral semicircular canal until it bisects the
posterior semicircular canal. Next, the mas-
toid air cells of the mastoid tip are removed
to expose the digastric ridge, which serves
as a landmark to the stylomastoid foramen
and the beginning of the fallopian canal.

1.83 Removal of the sigmoid
plate exposes the superior petrosal sinus.
The superior semicircular canal can be ex-
posed by following the posterior semicircu-
lar canal superiorly. Further removal of
mastoid air cells exposes the fallopian ca-
nal, which runs from the digastric ridge to
the antrum at approximately the same
depth as the posterior semicircular canal.

Superior

semicircular

canal

Superior
petrosal
sinus

50 Surgical Positioning and Exposures

Malleus

Incus

Stapes Facial
nerve

Geniculate

ganglion

Lateral

Superior
Posterior

Semicircular —
canal

Jugular
bulb

Superior
petrosal

sinus

1.84

1.85

1.84 Exposure of critical
structures embedded in petrous bone re-
quires the step-by-step approach described
in Figures 1.81-1.83.

1.85 The dura between the
sigmoid sinus and the petrous apex is ex-
posed. A dural incision is made in the pos-
terior fossa dura (inferior to the petrosal
sinus) and in the middle fossa dura (supe-
rior to the sinus).

Supine: Posterior Petrosal Approach 51

1.86

1.86 Clips are applied to the
superior petrosal sinus.

1.87 The superior petrosal si-
nus and tentorium are incised ventrally to-
ward the incisura in a course directed
posterior to the trochlear nerve.

1.87

Trochlear nerve

52

Surgical Positioning and Exposures

Abducens nerve
Basilar artery

Rons

Trigeminal
nerve

1.88

1.88 The surgeon gently ap-
plies 10-mm self-retaining retractors to the
posterior temporal lobe and lateral cerebel-
lar hemisphere to expose the medial tempo-
ral lobe, lateral pons, basilar artery, and
cranial nerves V through VIII.

1.89

Closure 1.89 The dura is closed with
a continuous absorbable suture. A dural re-
tention suture is placed in the center of the
bone flap. Stainless steel wires are placed
through the drill holes to secure the bone
flap. The ends of the stainless steel wires
are tucked into the drill holes.

Supine: Posterior Petrosal Approach 53

Fat graft

1.90

1.90 A free fat graft from the
abdominal wall closes the middle ear cavity
and fills the defect in the mastoid bone. The
temporalis muscle is split to cover the mas-
toid defect and then firmly reattached to the
superior fascial cuff.

1.91 A subgaleal drain is in-
serted and connected to continuous aspira-
tion. The galea is closed with absorbable
sutures and the skin is closed with metal
clips. A compression dressing and turban
are applied. The lumbar catheter is con-
nected to a closed drainage system for 72
hours; the level is set 5 cm above the exter-
nal meatus.

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