54 Surgical Positioning and Exposures

Mayfield skull-
fixation device

1.92

Lateral Oblique Position 55

Superior
temporal
line

Lateral Oblique Position

The lateral oblique position is pre-
ferred for the suboccipital approach. Some
surgeons still prefer to have the patient in
the sitting position for lesions of the pineal
region and vascular malformations of the
cerebellar hemisphere and vermis. This
preference is based on the presumption that
the sitting position enhances drainage and
exposure of the operative field. However,
after more than 10 years experience using
the lateral oblique position, we have con-
cluded that this position provides equal ex-
posure, gives greater access to deep
structures, eliminates the problem of air
embolism, and improves the surgeon's
comfort (which is critical to the outcome of
any operation).

1.92 In procedures that use
the lateral oblique position, an armored en-
dotracheal tube is required to prevent air-
way obstruction when the patient's head is
rotated or flexed. A three-point skull-fixa-
tion device is attached to the skull while the
patient is supine. With the surgeon control-
ling the head, the patient is turned into the
lateral oblique position. After a gelatin roll
is placed beneath the dependent axilla, the
head (fixed in the Mayfield skull-fixation
device) is secured to the table.

1.93 The three-point skull-
fixation device is positioned so that two
points are located on the dependent side of
the skull. The pins are placed in the un-
shaved scalp at the midpoint of the cranium
(above the external auditory meatus) and at
the level of the superior temporal line. The
surgeon must ascertain that the clamp does
not contact any area of the face and is
firmly secured to avoid slippage. When the
pressure-sensitive gauge shows three ten-
sion rings (60 lb/in²), pressure is adequate
to secure the head in the clamp.

A radiolucent head-fixation device is
used if imaging or angiographic studies are
anticipated. Prior to positioning the patient,
an angiographic sheath is placed in the right
groin for subsequent angiography and is
maintained with a pressurized heparin
solution.

56 Surgical Positioning and Exposures

1.94

1.94 The patient's thorax is
elevated 15 degrees and the head is main-
tained in neutral flexion for most vascular
procedures. To avoid compressing the bra-
chial plexus and obstructing venous return
from the arm, a gelatin pad is placed in the
axilla. All pressure points are securely
padded. When the patient is firmly re-
strained on the table, liberal movements of
the operating table during the procedure are
permissible.

1.95 The patient's head is
maintained in 0 degrees rotation.

1.95

Lateral Oblique Position

57

1.96

1.96 A special operating
room setup is used for the right suboccipital
approach. The scrub nurse stands opposite
the surgeon; the anesthesiologist is at the
foot of the table; and the surgeon and
the assistant are positioned at the side of
the patient's dependent shoulder.

58 Surgical Positioning and Exposures

Ceiling-mounted
V" microscope track

1.97

1.97 Some variations in the
operating room setup are required for a left
occipital approach when the patient is in
the lateral oblique position.

59

Lateral Oblique: Suboccipital Approaches

Lateral

hemispheric

incision

Midline
incision

1.98

Suboccipital Approaches

Suboccipital approaches are preferred
for lesions of the cerebellum, pineal region,
fourth ventricle, dorsal and lateral brain-
stem, cerebellopontine angle, and foramen
magnum.

1.98 Three skin incisions
provide exposure to all infratentorial le-
sions. First, a midline skin incision (with
bilateral fascial extension) gives excellent
exposure of the vermis, fourth ventricle,
pineal region, and posterior craniovertebral
junction. Second, the lateral hemispheric
(hockey-stick) incision, extending from the
mastoid to midline, exposes large lesions of
the cerebellar hemisphere and extra-axial
spaces of the lower posterior fossa. Third,
the retromastoid straight incision is effec-
tive for exploring the lateral posterior
fossa.

1.99

1.99 Four exposures provide
access to most lesions of the posterior
fossa. Midline approaches, supracerebellar
(A) and transvermian (B), expose the fourth
ventricle, upper brainstem, and pineal re-
gion. Lateral suboccipital approaches (C)
give access to the cranial nerves, lateral
brainstem, vertebrobasilar artery, extra-

axial lesions, and some lateral brainstem
lesions. Upper lateral suboccipital and
combined suboccipital approaches (D) pro-
vide access to the tentorial area, incisura.
upper clivus, upper cranial nerves, and
petrous bone. A combination of these ap-
proaches may be used for complex lesions
of this region.

60

Surgical Positioning and Exposures

1.100

Upper Lateral Suboccipital Approach

The upper lateral suboccipital ap-
proach gives access to the cerebellopontine
angle and to the lateral brainstem.

1.100 For an upper lateral
suboccipital approach, the patient is placed
in the lateral oblique position. The thorax is
elevated 15 degrees and the head is in neu-
tral flexion. A straight or hockey-stick inci-
sion may be used.

1.101 The head is maintained
in 0 degrees rotation.

1.102 The straight incision is
made 1 cm medial to the mastoid notch and
extends 4 cm above and below the notch.
The bone flap is sited below the asterion
and medial to the mastoid. A single-entry
burr hole is made 1 cm medial and inferior
to the asterion.

1.101

61

Lateral Oblique: Upper Lateral Suboccipital Approach

1.102

1.103 The skin is incised and
hemostatic clips are applied to the skin
edges. A muscle-splitting incision, made
down to the periosteum, extends from the
level of the foramen magnum to above the
superior nuchal line. Care must be taken to
avoid damaging the condylar venous plexus
and vertebral artery. Muscle and perios-
teum are reflected with periosteal eleva-
tors. A single-entry burr hole is made 1 cm
below and medial to the asterion. The bone
flap (3 cm in diameter) is cut with a pneu-
matic craniotome.

I

Surgical Positioning and Exposures

Sigmoid sinus

1.104

1.104 The mastoid bone is re-
moved to expose the medial aspect of the
sigmoid sinus.

1.105 Open mastoid air cells
are filled with bone wax.

1.105

63

Lateral Oblique: Upper Lateral Suboccipital Approach

1.106

Flocculus

1.107

1.106 The dura is incised par-
allel to the sigmoid and transverse sinuses.

1.107 The venous sinuses and
adjacent dura are retracted with dural re-
tention sutures. A 10-mm self-retaining re-
tractor is placed on the lateral cerebellum
and flocculus to expose the upper regions
of the posterior fossa.

64 Surgical Positioning and Exposures

1.108

1.108 Gentle retraction of the
cerebellum and flocculus exposes the
arachnoid that overlies the cranial nerves
and posterior fossa vessels. The arachnoid
is sharply incised with an arachnoid knife.
Cerebrospinal fluid is aspirated while cere-
bellar retraction is increased. The abducens
nerve, lateral medulla, and basilar arteries
are exposed,

1.109 The dura is closed with
absorbable sutures. A fascial patch graft is
needed to achieve a watertight closure.

Fascial

graft

1.109

Lateral Oblique: Upper Lateral Suboccipital Approach 65

1.110

1.110 The bone flap is secured
with stainless steel wires through predrilled
holes. The ends of the wires are tucked into
the drill holes.

1.111 Large defects in the
mastoid are filled with a free muscle graft.
The cervical muscles and fascia are reap-
proximated with absorbable suture.

Muscle
graft

1.111

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