Frontotemporal Craniotomy

Frontotemporal Craniotomy

Indications

• Frontotemporal craniotomy with orbitozygomatic osteotomy is an adjunct to pterional craniotomy that allows greater rostral trajectory to midline structures. By removing the superior and lateral bony orbit, one gains a more anterior and inferior starting point for the approach than would be possible with a conventional pterional craniotomy.

• Removal of the zygomatic arch enables inferior displacement of the temporalis muscle, allowing for a lower starting point for subtemporal visualization.

Contraindications

• If a midline view of the suprasellar region is needed, a bifrontal craniotomy may be a better approach.

• Access to the petrous apex and retrosellar space is limited and requires a long reach.

Planning and positioning

• The exact positioning needs vary by case. The patient generally is placed supine on the operating table.

• The head is placed in a Mayfield head holder with two pins placed in the occiput just off the midline. The single pin is placed in the contralateral forehead, in the mid-pupillary line ideally behind the hairline.

• After pinning, the head is usually positioned such that the lateral orbital ridge and keyhole region is the highest point on the patient’s head. This position is achieved by about 5-1 degrees of contralateral head rotation and a slight degree of neck extension and head elevation.

Frontotemporal Craniotomy 15-1

Frontotemporal Craniotomy 15-1: Positioning the patient and head. The patient is placed supine on the operating table with the ipsilateral shoulder elevated as needed to facilitate head rotation toward the contralateral side. The skull clamp is fixated with the paired posterior pins at the equator in the occipital bone and the single anterior pin at the equator in the contralateral frontal bone superior to the orbit. The head is positioned by first elevating the head above the heart in the “sniffing position.” Second, the head is rotated up to 30 degrees to the contralate1ral side depending on the intended operation. Third, the neck is extended so that the vertex is angled down 10 to 30 degrees, allowing for self-retraction of the frontal lobe off the anterior cranial fossa floor. When the head is ideally positioned, the malar eminence of the zygomatic bone should be the highest point in the operative field.

Procedure

Frontotemporal Craniotomy 15-2

Frontotemporal Craniotomy 15-2: Skin incision. Various skin incisions can be used depending on the needs of the particular case. For most cases, particularly cases focused at the parasellar skull base and circle of Willis, a simple C-shaped incision beginning at the widow’s peak and extending posterolaterally back to the root of the zygomatic arch suffices.

Frontotemporal Craniotomy 15-3

Frontotemporal Craniotomy 15-3: Soft tissue elevation and identification of landmarks (petrous apex approach). The frontalis branch of the facial nerve runs in a posteroinferior to anterosuperior direction in a large subcutaneous fat pad that sits on the outside of the temporalis fascia and connects the skin to the temporalis fascia just behind the lateral orbital rim. To expose the lateral orbit and maxillary buttress safely and adequately, the scalp and fat pad must be separated from the temporalis muscle. The scalp and fat pad must be reflected anteriorly over the bone; this can be achieved by either a suprafascial or a subfascial approach.

• In the suprafascial approach, sharp dissection is used to create a plane beneath the fat pad and above the temporalis fascia. Blunt dissection is used to reflect the fat pad and scalp over the lateral orbit and maxilla until adequate exposure is obtained.

• In the subfascial approach, as soon as the fat pad is visualized, the temporalis fascia is elevated off the superficial surface of the muscle with scissors and is separated from the bone of the lateral orbit, maxillary buttress, and zygomatic arch with a small periosteal dissector. The scalp and fat pad are reflected anteriorly with the temporalis fascia to enter the lateral orbit.

Frontotemporal Craniotomy 15-4: Temporalis elevation. Regardless of how the frontalis nerve is removed from the muscle, two cuts are made in the temporalis muscle to elevate the muscle and leave a fascial cuff to reattach the muscle during the closure. One cut runs parallel and inferior to the superior temporal line, from the posterior surface of the lateral orbital rim at the McCarty keyhole, back about 1 cm in front of the posterior edge of the incision.

Frontotemporal Craniotomy 15-4

The second cut is made perpendicular to the first and is continued down to the root of the zygoma. Monopolar electrocautery is used to1 dissect the temporalis off the bone of the posterior face of the lateral orbital rim and off the squamous temporal bone down to the zygomatic arch. The dissection should be carried down until the inferior orbital fissure can be palpated with a No. 4 Penfield dissector anteroinferiorly.

Frontotemporal Craniotomy 15-5

Frontotemporal Craniotomy 15-5: Periorbital dissection and bony exposure. A small dissector is used to elevate the scalp off of the orbital rim from just medial to the supraorbital rim, down over the frontozygomatic suture, onto the maxilla and zygomatic arch. Dissection continues anteriorly until the zygomaticofacial branch of the maxillary nerve is encountered exiting the anterior surface of the maxilla. Soft tissue is also elevated off the zygomatic arch on all surfaces; this typically requires sharp dissection at points of dense attachment of the temporalis fascia. After releasing the supraorbital nerve, the periorbita is gently dissected away from the inner bony surface of the superior and lateral orbit. Dissection continues in the orbit in a lateral and inferior direction until the inferior orbital fissure is able to be palpated with a No. 4 Penfield. Although the inferior orbital fissure is identified by blind feel, ideally the probe should be visualized exiting the fissure in the subtemporalis space.

Frontotemporal Craniotomy 15-6

Frontotemporal Craniotomy 15-6: Frontotemporal craniotomy. The burr hole placed at the McCarty keyhole should be placed slightly more anterior than is typical. Ideally, the burr hole should expose the lateral orbit because two cuts involved in the orbitozygomatic osteotomy terminate in this burr hole. Also, it is important that the craniotomy cuts on the forehead come as anterior as possible. The footplate ideally should catch on the floor of the anterior fossa before turning laterally to the keyhole; this greatly simplifies the orbital cuts during the osteotomy.

Frontotemporal Craniotomy 15-7

Frontotemporal Craniotomy 15-7: Orbitozygomatic osteotomy. The exact location of the cuts from this osteotomy can be a source of confusion, but this can be greatly simplified if the six cuts are thought of as achieving two primary goals: two cuts to remove the superior orbit and four cuts to disconnect the maxillary buttress at its points of attachment.

Additional craniotomy. To take advantage of the visualization provided by the orbitozygomatic osteotomy, it is wise to perform an additional craniectomy to eliminate bony obstruction to viewing angles. The superior orbit should be removed with a rongeur to as close to the orbital apex and sphenoid wing as possible. Additionally, after using the additional temporalis retraction made possible by the zygomatic arch removal, the squamous temporal bone should be removed down to the floor of the middle fossa. If necessary, the lesser sphenoid wing should be drilled until no bony elevation exists between the globe and the anterior clinoid process.

Removal of Superior Orbit

• Two cuts are made at right angles to each other through the roof of the orbit and superior orbital rim.

• The first is an anteroposteriorly directed cut through the superior orbital rim just lateral to the supraorbital notch. This cut is carried as far posteriorly as possible.

• A second cut is made perpendicular to this cut, proceeding laterally and exiting the orbit at the keyhole burr hole.

Disconnection of Maxillary Buttress

• The maxillary buttress is a complex structure but is essentially attached to the skull in four places: deep, anterior, posterior, and superior. Each of the remaining four cuts of the osteotomy is directed at one of these attachments.

• Deep cut: The saw is placed into the lateral orbit and introduced into the inferior orbital fissure. The cut proceeds laterally until the lateral orbital rim is encountered.

• Anterior cut: This cut enters the inferolateral orbital rim and maxilla from the lateral edge of the deep cut and proceeds inferolaterally across the maxilla just posterior to the zygomaticofacial nerve. It continues across the entire maxillary buttress until the buttress is disconnected from the facial skeleton anteriorly.

• Posterior cut: This cut disconnects the zygomatic arch just anterior to its root. Repair is made easier by angling this cut and plating before disconnecting the osteotomy.

• Superior cut: This is the disconnecting cut that enters the inferior orbital fissure from the temporalis side. This cut runs superiorly through the lateral orbit until joining with the keyhole burr hole. By uniting with the orbital cuts, this cut disconnects the superior attachment of the maxillary buttress and removes the superolateral orbital rim through a C-shaped orbitotomy.

Frontotemporal Craniotomy 15-8

Frontotemporal Craniotomy 15-8: The dura is opened in a C-shaped fashion across the sylvian fissure, with the ends of the “C” roughly bifurcating the exposed portion of the frontal and temporal lobes, and carried as anteriorly as possible. The dura is flapped anteriorly to retract the periorbita and eye out of the field and is sutured to the scalp, with the stitches into the dura placed as low as possible to retract the dura as flat and out of the working view as possible.

Tips from the masters

• Placing the incision as close to the tragus as possible can complicate closure but is probably cosmetically superior.

• It is wise to attempt to spare the superficial temporal artery (STA) for several reasons. First, delayed bleeding from the STA is a frequent source of postoperative epidural hematomas requiring evacuation, and dealing with STA bleeding can often consume more time than it takes to spare the artery. Additionally, the STA is the principal blood supply to the scalp flap, and maintaining good scalp blood flow likely improves wound healing. Finally, the anterior branch of the STA runs roughly parallel and posterior to the frontalis branch of the facial nerve in the scalp and is a good indicator of how far the scalp can be separated from the temporalis fascia before the frontalis nerve needs to be separated from the temporalis muscle and protected.

• The STA typically lies in the subgaleal space above the temporalis fascia just anterior to the tragus. Metzenbaum scissors are used to dissect the galea away from the temporalis fascia to identify the STA before cutting it with the scissors.

• Care should be taken to preserve the periorbita because violation of this protective covering not only risks injury to the intraorbital contents, but also makes visualization of the reciprocating saw during the orbital osteotomy much more difficult.

Pitfalls

Care should be taken not to extend the inferior limb of the incision below the zygoma to avoid injuring the facial nerve branches that lie in the subcutaneous tissue of the subzygomatic face.

Dissection of the periorbita medial to the supraorbital nerve is unnecessary and risks injury to the trochlear attachment of the superior oblique muscle with resultant diplopia.

The lateral orbital wall should be preserved as much as possible to prevent the development of pulsatile enophthalmos postoperatively.