CHAPTER 26 Positioning for Cranial Surgery
Pterional (Frontotemporal) Craniotomy
Positioning for the pterional craniotomy begins with placement of the patient supine on the operative table. The patient is then placed in the Mayfield-Kees head fixation or similar cranial immobilization apparatus. When possible, we prefer to position the pins such that the single pin is placed in the frontal bone contralateral to the operative target, approximately 2 to 3 cm above the brow. The dual pins are then placed in the occipital bone on the ipsilateral side. It is usually preferable to place the pins along the axial plane; however, depending on the extent of the planned skin flap, it may be necessary to orient the pins along the sagittal plane. Others, however, advocate placing the single pin posteriorly, a decision that typically comes down to the surgeon’s preference.1 Regardless of this decision, careful attention should be paid to avoid the frontal sinus anteriorly and the mastoid air cells posteriorly. Once the patient is in pins, a shoulder roll is placed under the ipsilateral shoulder along the long axis of the patient. This allows adequate rotation without compromising venous return by obstructing the jugular veins in the neck. We also generally place the patient in some reverse Trendelenburg to promote brain relaxation and to allow the head to be fixed higher than the level of the heart.
Once the patient’s body has been positioned correctly, the head can be adjusted. Appropriate positioning of the head requires a combination of head flexion, rotation, and neck extension that is designed to provide the ideal surgical trajectory while minimizing brain retraction. The head is first rotated toward the contralateral shoulder. The degree of rotation can vary greatly and is largely dependent on the desired surgical target. For example, internal carotid artery disease is often approached from 5 to 20 degrees of contralateral rotation; anterior communicating artery aneurysms may require up to 60 degrees of rotation to allow optimal visualization of the anterior communicating artery complex. In general, for approaches requiring wide opening of the sylvian fissure, avoidance of excessive rotation is preferred because the greater the contralateral rotation, the more the temporal lobe and its operculum obstruct the trajectory into the sylvian fissure. Once the desired degree of rotation is obtained, the head is laterally flexed slightly, followed by an extension of the neck. This last maneuver should present the malar eminence as the highest point on the patient and aids in retraction by allowing gravity to pull the frontal lobe from the skull base. Once it is in position, the head fixation device is secured to the table (Fig. 26-1). The patient’s arm that is adjacent to the scrub nurse or technician is padded and tucked close to the body; the other arm is supported on an arm board to provide unfettered access for the anesthesiologists. Pillows and padding are placed under the patient’s knees and feet, and the patient is secured to the table with a padded safety belt or padding and tape. In cases in which significant bed rotation is anticipated during the surgery, additional tape or belts are applied to secure the patient to the table.
Temporal and Subtemporal Approach
The temporal or subtemporal craniotomy (or derivatives such as a middle fossa, extended middle fossa approach) may be performed alone (such as for petrous apex disease, other disease of the middle fossa, or basilar apex aneurysms). It may also be performed in conjunction with another approach, such as the pterional or lateral suboccipital craniotomy.2
In preparation for the subtemporal craniotomy, the pins are placed for a lateral park bench position. This is accomplished by placing the single pin of the Mayfield-Kees head clamp into the frontal bone 2 to 3 cm above the ipsilateral brow and the dual pins in the occipital bone along the axial plane at midline and contralateral to the surgical site. Once in pins, the patient is placed on the side opposite the operative site on top of a vacuum-ready beanbag, with the inferior arm extended perpendicular to the patient’s body on an arm board. In this position, it is critical to place a small axillary roll under the inferior axilla to avoid compression or other injury to the axillary artery or brachial plexus. Once the dependent arm is properly positioned and the beanbag is hardened, padding is placed between the superior arm and the patient’s body. The arm is then placed in neutral position along the long axis of the torso, with slight flexion at the elbow before it is secured. For the subtemporal approach or middle fossa approach, correct head positioning is critical. The patient is placed in reverse Trendelenburg position to place the head above the level of the heart. In addition, the neck is laterally flexed, with the dependent ear being brought toward the ipsilateral shoulder. This also uses gravity to facilitate gentle retraction of the temporal lobe. The head fixation apparatus is then secured to the table, and the patient’s body is supported with safety belts and tape (Fig. 26-2).
