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.

FIGURE 26-1 Positioning for pterional craniotomy. The ipsilateral shoulder is elevated with a shoulder roll, and the head is flexed slightly and rotated approximately 45 degrees toward the contralateral shoulder. The degree of rotation is adjusted on the basis of the surgical target. Ideal positioning should place the malar eminence at the highest point of the surgical field.

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).

FIGURE 26-2 Lateral decubitus positioning for subtemporal or temporal approach. Once the head is positioned so that the sagittal plane is parallel to the ground, the head is tilted slightly toward the floor, a maneuver that allows the temporal lobe to fall away from the middle cranial fossa. This position can also be used for the lateral suboccipital craniotomy by rotating the face toward the floor, again allowing the operative site to be the highest point on the surgical field.

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.

Once in pins, the patient is strapped in with a waist belt, and the head of the bed is raised until the vertex of the patient’s head is within the focal length of the neurosurgeon. The bed may be flexed slightly with concomitant lowering of the legs so that the thighs are elevated while the knees are flexed. Once the bed is in an appropriate position, the head is adjusted to the desired point. For the anterior parasagittal craniotomy, the head is flexed until the point of the planned craniotomy and the planned target are along a comfortable trajectory for the neurosurgeon. For the subfrontal approach, it is often necessary to actually extend the head slightly until the brow is the most superior point on the operative field. This will allow the frontal lobe to fall away from the anterior cranial fossa, minimizing retraction. During this extension, it is important to be mindful of the planned incision so as not to position it out of comfortable range of the surgeon. Despite the degree of flexion or extension, the head is kept in a neutral midline position along the long axis of the patient. Once it is in the desired position, the head is secured. The patient is then secured to the table with pressure points padded as outlined before (Fig. 26-3).

FIGURE 26-3 Positioning for anterior parasagittal or subfrontal approach. This is achieved through a standard supine position. The degree of flexion or extension of the head depends on the surgical target. For the subfrontal approach, the neck is extended past a perpendicular plane with the floor, allowing the frontal lobe to fall away from the anterior cranial fossa. For the anterior parasagittal approach, the head is flexed until the desired surgical site is comfortably within the surgeon’s operative field. This positioning may occasionally be modified to accommodate a posterior parasagittal approach. This entails shifting the pins in front of the external auditory meatus. This also requires a higher degree of flexion than in the anterior parasagittal approach. If too much flexion is needed, it may be necessary to perform the procedure from a prone position.

An alternative positioning strategy for the anterior parasagittal approach is to have the patient in a lateral position, with the side down depending on the pathologic process and the angle of attack. The head is then tilted upward until the surgical target is in the appropriate location, placing the pathologic process in the horizontal plane. This can be used, for example, with parasagittal meningiomas, whereby the ipsilateral frontal lobe may be placed dependent, facilitating brain retraction with the assistance of gravity. This position may also be used for approaches to the contralateral hemisphere through a transcallosal approach.³

Posterior Parasagittal Craniotomy

Despite its many similarities to both the anterior parasagittal and midline suboccipital craniotomies, the posterior parasagittal craniotomy does present several specific considerations. There are two distinct possibilities in positioning for a posterior parasagittal craniotomy, a decision that often depends on the posterior extent of the desired craniotomy. For cases in which the planned craniotomy is within several centimeters posterior to the cranial vertex, or if an awake craniotomy is desired, it is preferable to position the patient supine on the operative table. If it is farther posterior, the preferred position is often prone.

If the decision is made to approach the patient from the supine position, he or she is placed in the Mayfield-Kees head clamp with the pins oriented in the axial plane, with the posterior of the dual pins approximately 2 to 3 cm above the external auditory meatus and the single pin slightly anterior to this point on the opposite side. However, unlike the prone position, the clamp is placed underneath the patient’s neck when the pins are applied. Once the patient is in pins, the bed is flexed slightly until the site of the craniotomy is in the desired position. The neck can be flexed to augment this, a maneuver that may aid in decreasing complications such as air emboli that are associated with elevation of the back of the bed being too high. If an awake craniotomy is planned, the neck should remain in neutral position, with the thighs typically elevated to increase the patient’s comfort. Once in position, the headrest is locked into place. This can also be accomplished in a seated position, the details of which are outlined in “Midline Suboccipital Craniotomy.”

When the posterior parasagittal craniotomy is approached from the prone position, the pins are placed before the patient is flipped. These are placed as described earlier for the supine positioning. Once in pins, the patient is placed prone on the operative table; the arms are placed in the neutral position and are padded and tucked to the patient’s side. The patient’s chest lies on soft gel rolls placed parallel to the long axis of the body. It is important to avoid leaving electrocardiogram leads or wires on or across the anterior chest wall because this can produce pressure sores or abrasions. As is the case with all positions, the waist strap is placed before adjustments are made to the bed. Once the patient is strapped in, the bed is flexed into the Concorde position, with care taken to adjust the head positioning to avoid neck strain during flexion of the table. This is accomplished by flexing the legs and raising the head of the bed slightly. After an appropriate bed position has been achieved, the final manipulation entails extension or flexion of the neck. The degree of flexion depends on the exact location of the planned craniotomy, and this maneuver should be performed with the goal of placing the craniotomy site at the highest point of the operative field.

Midline Suboccipital Craniotomy

The suboccipital craniotomy is the preferred approach for the majority of fourth ventricular lesions, and it can provide access to midline cerebellar lesions and pineal lesions. For this approach, the patient is placed in the Mayfield-Kees head fixation apparatus with the pins just below the superior temporal line on both sides. The dual pin side is typically placed so that the posterior pin is 2 to 3 cm above the external auditory meatus; the single pin is placed slightly anterior at the same level on the contralateral side. The patient is placed prone on the operative table onto two large chest rolls, and the arms are tucked into neutral position along the length of the patient. The patient is strapped to the bed with a waist belt and is then moved into the Concorde position, with flexion of the legs and extension of the back (elevation of the head). The patient can be placed in additional reverse Trendelenburg to ensure that the head is above the level of the heart, with an accompanying decrease in venous congestion.

Once the bed is positioned correctly, the head is flexed until the chin is at least two fingerbreadths from the sternal notch. Although the patient’s neck may permit further flexion, it is important to leave at least two fingerbreadths to prevent complications with the endotracheal tube. Once flexed, the head is lifted upward while maintaining the same degree of flexion, effectively distracting the neck while keeping the head in fixed position. This last maneuver ensures that the intended craniotomy site is the most superior point of the patient before final clamping into place. The patient is secured to the table and padded (Fig. 26-4A).

FIGURE 26-4 A, Prone positioning for midline suboccipital approach. This is typically performed from the Concorde position. The head is flexed and elevated, making sure to keep two fingerbreadths between the chin and the chest. B, Seated positioning for midline suboccipital approach.

For the supracerebellar infratentorial position, the midline suboccipital approach is often best accomplished in the seated position. Although we think that this position can be awkward for the surgeon, it is perhaps ideally suited for this approach. The cerebellum falls away from the tentorium after arachnoidal adhesions are divided, and it provides a bloodless field. For the seated position, the patient is placed in pins with a configuration similar to that described earlier. Once in pins, the patient is strapped in with a waist belt, and the back is elevated until the patient is in the seated position. The bed is then flexed, with an elevation of the thighs and flexion of the knees until an adequate seated position is obtained. The head is then flexed slightly before the Mayfield-Kees head clamp is secured (Fig. 26-4B). This is done with a specific bed adapter that allows the Mayfield to be secured easily. The arms are then placed across the patient’s abdomen and secured. The lower extremities are often wrapped in compression stockings or wrap to facilitate venous return. Appropriate anesthesia precautions against air embolism, such as a central line and precordial Doppler probe, are placed, but that discussion is beyond the scope of this chapter.

Lateral Suboccipital Approach

The lateral suboccipital craniotomy or craniectomy is the most frequently used approach for access to the cerebellopontine angle and lateral cerebellum. In addition to tumors of the cerebellopontine angle and lateral cerebellum, the lateral suboccipital approach can be used in the treatment of a variety of posterior circulation aneurysms, including aneurysms of the anterior inferior cerebellar artery, as well as in the microvascular decompression of the trigeminal nerve. Variations of the approach, such as the far lateral transcondylar approach, may be used to access lesions of the anterior foramen magnum and aneurysms of the posterior inferior cerebellar artery.

This approach can be performed from a number of positions, a decision that is similar to many of those made in neurosurgery in that it is a matter of the physician’s preference. The lateral suboccipital approach can be done from a modified Concorde position, from a lateral park bench position, supine position, or even in the seated position, all of which have their advantages and disadvantages.

Our preference for many lateral suboccipital procedures is the modified Concorde position. For this, the patient is positioned exactly as with the midline suboccipital approach, with a slight modification to bring the site of the craniotomy or craniectomy into a more prominent location. By rotation of the patient’s head approximately 45 degrees to the shoulder ipsilateral to the lesion before the head is fixed in the Mayfield clamp, the planned surgical field is adequately exposed. The patient should be well secured to the table to facilitate additional bed rotation to achieve a far lateral trajectory (Fig. 26-5).

FIGURE 26-5 Positioning for lateral suboccipital approach. This position is similar to that for the midline suboccipital approach; however, the head is rotated so that the ipsilateral mastoid process is brought into the operative field. This head positioning may be achieved from the lateral position as well.

The park bench position is another potential option for the lateral suboccipital craniotomy and may be better, particularly for far lateral transcondylar approaches. The patient is positioned as described for the subtemporal craniotomy. After the body is in its final position, a small variation is performed by rotating the face slightly toward the floor. If the pins are placed properly, this slight rotation will align the Mayfield-Kees head clamp so that it is parallel to the floor and presents the craniotomy site as the most prominent part of the operative field. It is important to pad pressure points and to add an axillary roll as described for the temporal or subtemporal approach. An additional maneuver is to tape the ipsilateral shoulder inferiorly to provide more room for the surgeon to work. A supine position with a shoulder roll also may work for suitable patients.

For the sitting position, the patient is placed in pins with a configuration similar to that of the midline suboccipital position; the dual pins are placed 2 to 3 cm above the external auditory meatus on the side contralateral to the surgical site, and the single pin is placed 2 to 3 cm superior and anterior to the external auditory meatus. Once in pins, the patient is strapped in with a waist belt, and the back is elevated until the patient is in the seated position. The bed is then flexed, with an elevation of the thighs and flexion of the knees until an appropriate seated position is obtained. The head is then flexed slightly and rotated, depending on the pathologic process at hand, before the Mayfield-Kees head clamp is secured. The arms are then placed across the patient’s abdomen and secured.

Each of these positions for the lateral suboccipital approach has advantages and disadvantages. The modified Concorde position may be more comfortable for the surgeon, and for cerebellopontine angle disease, it takes advantage of gravity to aid in retraction of the cerebellum. There is a risk of air embolus, although it is decreased compared with the seated position. It also carries the risk of pressure sores and blindness from elevated intraocular pressures that are not typically seen with the park bench or seated position; however, these risks can be minimized with proper padding of pressure points and by ensuring that the head is above the level of the heart. The park bench position is more likely to have brachial plexus injuries or other stretch injuries; however, it facilitates cerebellar retraction and is also considered a comfortable position for the operating surgeon as long as the ipsilateral shoulder does not encroach. It also provides a lateral perspective anterior to the brainstem for the far lateral approach. The sitting position aids in lowering intracranial pressure as well as venous congestion and gives the anesthesiologist superior access to the face. It also provides a clear, bloodless field. However, it carries a higher risk of venous air embolism, tension pneumocephalus, and subdural hematomas.⁴ It is usually avoided in instances of patent foramen ovale (although not universally so), and it can create fatigue for the surgeon operating for extended periods with outstretched arms. The decision to select one position over another depends largely on the surgeon’s preference but also on the pathologic process at hand and the patient’s morphologic features.

Transsphenoidal Approach

As with the positioning for any cranial procedure, the positioning for transsphenoidal surgery is done to expose the intended target while maximizing the comfort of the surgeon. However, unlike in many other cranial procedures, incorrect positioning of patients for the transsphenoidal approach can make the surgery significantly more difficult or dangerous. With just a minimal alteration of the planned trajectory, a sellar approach can be missed altogether and result in the opening of the anterior cranial fossa. For this reason, it is imperative that the patient be positioned correctly, ensuring that the correct trajectory is taken.

At our institution, we use two different positions, depending on whether the patient is undergoing an endoscopic endonasal approach or the more traditional sublabial microscopic approach (Fig. 26-6). Ultimately, however, the position chosen and the approach taken come down to the physician’s preference.

FIGURE 26-6 A and B, Positioning for endonasal transsphenoidal approach. The head is placed on the headrest and positioned so that the bridge of the nose is parallel to the ground. The foot of the bed is rotated away from the surgeon to ensure minimal obstruction. C, Positioning for sublabial transsphenoidal approach. The head is placed in pins and rotated so that the surgeon’s trajectory is directed along a line from the base of the nose to the tragus.

Positioning for the endoscopic endonasal approach begins with placement of the patient supine on the operative table. The head is placed on a horseshoe headrest, and the right arm is tucked with the hand positioned underneath the right thigh. The patient is then strapped in by a belt across the thighs. The bed is turned so that the feet are approximately 30 degrees to the patient’s left in relation to the head. This allows the surgeon to stand as close to the head as possible without being obstructed by the body. Next, the bed is flexed into a beach chair position, and additional reverse Trendelenburg positioning is performed. This ensures that the head is sufficiently above the level of the heart, a maneuver that decreases venous congestion and subsequently decreases the bleeding encountered throughout the procedure. The bed is then tilted slightly to the right. Once the bed is in position, the head is turned to the patient’s right with the bridge of the nose parallel to the floor. The head is rotated as much as the neck will comfortably allow until the nostrils and nasal cavities are easily accessible from the surgeon’s standpoint.

The positioning for the sublabial microscopic approach must incorporate the microscope, and therefore proper positioning must take into account both the trajectory of the microscopic sight and the comfort of the operating physician while under the microscope. Similar to the previously described approach, the patient is placed supine on the operative table. The arms are tucked, and the patient is again belted in with a strap across the thighs. Unlike the positioning for the endoscopic approach, however, the patient is placed in the Mayfield-Kees pins. This will eventually allow the stabilization of the head in proper position and should allow the head to remain in this fixed position throughout the procedure. The pins are placed behind the ears to reduce potential obstruction of fluoroscopic images that are later obtained. Before the head is secured, the head of the bed is elevated slightly. The head is then flexed until the bridge of the nose is approximately 45 degrees from the horizontal axis. This degree of flexion is used to ensure that a line from the base of the nose to the tragus is along the same line as the surgeon’s line of sight during the procedure. As is done with the endoscopic approach, the head is rotated to the patient’s right until the patient is face-to-face with the surgeon before the Mayfield is finally locked in. This final position should allow the surgeon to comfortably operate under the microscope while giving sufficient room for the C-arm if needed.

Conclusion

An absolutely critical part of any neurosurgeon’s practice is to become familiar with the various positions and their associated procedures and to be able to use them effectively. Knowing how to correctly position a patient is perhaps as critical as knowing which procedure one should perform, for even the most well thought out surgical plan can be undone by positioning the patient improperly. By obtaining a firm grasp on potential options, the operating neurosurgeon is able to choose the procedure that best suits each particular patient, rather than operating on a variety of intracranial pathologic processes through a limited number of approaches.