Positioning for Cranial Surgery

Published on 13/03/2015 by admin

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CHAPTER 26 Positioning for Cranial Surgery

Although it is not always adequately emphasized, positioning of the patient for intracranial procedures remains a critical step in a successful surgery. Optimal positioning allows the surgical team to complete their objective in the most effective fashion in many ways; for example, ideal positioning may reduce or eliminate the need for brain retraction, help provide a clear and bloodless field, reduce intracranial pressure and avoid venous obstruction, present the anatomy and pathology in the ideal perspective for the surgeon, and minimize the chance of avoidable complications such as brachial plexus stretch injuries and pressure neuropathies. This chapter reviews fundamental principles of positioning for the most common approaches to cranial disease.

Pterional (Frontotemporal) Craniotomy

The pterional craniotomy, otherwise known as the frontotemporal craniotomy, is considered to be the craniotomy most commonly performed by the neurosurgeon. Its versatility has made it a fundamental component of the neurosurgeon’s repertoire, and it (or its derivatives, such as the cranio-orbito-zygomatic approach) has become the craniotomy of choice for a large number of procedures. These procedures include but are not limited to the vast majority of supratentorial intracerebral aneurysms and pathologic processes of the anterior and middle cranial fossae, the central skull base, and in select instances, the posterior cranial fossa.

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).

Alternatively, the temporal or subtemporal approach can be accomplished with the patient in the supine position as long as the patient’s neck is supple and 90 degrees of rotation can be accomplished easily. A large roll under the ipsilateral shoulder can facilitate head rotation, and the other principles of positioning outlined for the pterional approach can then be applied.

Anterior Parasagittal and Subfrontal Approaches

The positioning is similar for the anterior parasagittal and subfrontal approaches, with only slight variations on the flexion angle of the head. The anterior parasagittal approach is typically used for interhemispheric approaches, such as for lesions of the anterior interhemispheric fissure, for distal anterior cerebral artery aneurysms, or for access to the third or lateral ventricles for colloid cysts or other intraventricular disease. The subfrontal approach is used for lesions of the anterior cranial fossa, such as meningiomas from the olfactory groove to the tuberculum sellae.

Perhaps more than for any other cranial procedure, the positioning for these approaches must take into account both the planned craniotomy site and the planned surgical incision. For the subfrontal craniotomy specifically, the bicoronal incision is typically several centimeters from the posterior edge of the craniotomy, and therefore it is important to position the patient so that both the incision and the craniotomy site are comfortably within the neurosurgeon’s operative reach.

Once the patient is ready for positioning, he or she is placed supine on the operative table before being pinned. As the incision is typically a bicoronal one, the patient must be placed in the head fixation apparatus such that sufficient room is given for the incision while not placing tension on the skin that could complicate the closure. The dual pins are placed behind the ear in the coronal plane; the single pin is placed at approximately the same point on the contralateral side. It is absolutely imperative to have confidence that the pins are securely fastened, something that may take up to 80 pounds of pressure with the Mayfield head holder tensioner.

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