Skull Base Surgery of the Posterior Fossa

30

clamp after the body is positioned and maintain
direct manual control of the head.
Starting from a supine position, the patient is
translated such that the shoulders are 2–4 cm
above the end of the bed. The patient is then
translated laterally such that the contralateral hip
lies past the midline of the bed, often with the
ipsilateral hip (temporarily) suspended by an
assistant off the edge of the bed. Simultaneous
with this translation, the torso is rotated to bring
the ipsilateral shoulder up and over midline into
the three-quarter prone position. Alternatively, if
a lumbar drain is to be placed, the rotation may
be paused at true lateral for insertion and then
continued to three-quarter prone. An axillary roll
is placed one handbreadth below the axilla, at the
mid-nipple line. The dependent arm may be left
extended and supported on a bed-rail arm board
or may be slung in the armature of the head
clamp, suspended hanging over the edge of the
bed [ 16 ]. The independent arm is supported on
pillows or an elevated arm board, with care to
minimize pressure in the brachial fossa (Fig. 2.4a,
b). The dependent leg is left extended, with care
to pad the fibular head to prevent a peroneal
nerve palsy. The independent leg is flexed at the
hip and knee, allowing the iliac crest to roll over,
and the pelvis is positioned with the same degree
of rotation as the shoulders and torso.
The whole bed is then placed into a 10–15°
reverse Trendelenburg position. This elevation

increases venous outflow from the head.

Combined with subarachnoid drainage, this

should provide a significant working corridor

without the need for hyperosmolar agents (e.g.,

saline or mannitol). If not already done, the head

is placed into three-point skull clamp pin fixa-

tion, with one pin on the contralateral forehead

(taking care not to pin the temporal branch of the

facial nerve) and two pins at the contralateral

asterion and inion. The head is then titled 5–10°

toward the contralateral shoulder, opening the

angle between the cardinal axis of the cranium

and the torso. The head is rotated 10–15° to the

contralateral shoulder, and the chin is flexed

toward the sternum, taking care not to compro-

mise the airway or contralateral jugular vein.

Prior to locking the pin clamp to the bed, anesthe-

sia should confirm the patency and position of the

airway. Rotation and flexion of the head may dis-

lodge a shallow intubation. If the head is over-

rotated or over-flexed, the contralateral internal

jugular vein may be compressed, leading to an

increase in intracranial pressure and intraopera-

tive cerebellar swelling.

The patient’s body is securely restrained so

that the operating table can be rotated liberally to

maximize the angle of approach for the micro-

scope. This usually involves a vacuum positioner

and reinforcement with nonperforated cloth tape

across the shoulder, torso, and hips. In larger

patients, the ipsilateral shoulder is taped down

Fig. 2.4 (a, b) Photographs showing two patients in a three-quarter prone position, with the pressure points padded and
the patients secured to the operating tables

C. Bowers et al.