Bifrontal Craniotomy – Part 2

Bifrontal Craniotomy 16-4: Identification of landmarks. If orbital osteotomy is planned, it is important to dissect the periorbita away from the orbital bone using gentle dissection because tears in the periorbita, besides increasing the risk of orbital complications, cause the orbital fat to extrude outward, making the osteotomy much more difficult. For unilateral orbital osteotomies, the dissection should begin underneath the superior orbital rim slightly medial to the supraorbital foramen and notch and extend laterally underneath the lateral orbital rim down to the level of the frontozygomatic suture.

Bifrontal Craniotomy

Bifrontal Craniotomy 16-4

The dissection should continue as far posteriorly into the orbit as is possible. If the supraorbital nerve is restrained by a bony foramen, this can be freed using an oblique cut with an osteotome to convert the foramen to a notch. The scalp dissection should continue down until the nasofrontal suture is visualized because the detaching cut of a bifrontal orbital osteotomy would run slightly superior to this suture.

Bifrontal Craniotomy

Bifrontal Craniotomy 16-5

Bifrontal Craniotomy 16-5: Unilateral or bifrontal craniotomy. Ideally, two burr holes—one placed at the McCarty keyhole and one placed directly posterior to this under the temporalis—should be enough to turn a frontal bone flap on one side. The bone flaps should extend laterally a few centimeters below the temporalis muscle cuff and as far anteriorly as allowed by the footplate.

Bifrontal Craniotomy

Bifrontal Craniotomy 16-6

Bifrontal Craniotomy 16-6: Orbital osteotomy (if needed). The cuts needed to remove the orbit in these approaches are more straightforward than the cuts needed for the orbitozygomatic approach. After dissecting the dura away from the orbital roof with a No. 1 Penfield, the orbit is entered first laterally with a reciprocating saw, and the lateral orbital rim is cut just above the frontozygomatic suture extending posteriorly into the burr hole at the keyhole. The roof is cut from lateral to medial in a plane just anterior to the crista galli. For the unilateral osteotomy, the cut is directed anteriorl1y slightly medial to the supraorbital foramen and proceeds anteriorly through the anterior face of the superior orbital rim, which detaches the orbital piece. In the bifrontal approach, the lateral orbital rim is cut bilaterally, and the orbital rim is cut from keyhole to keyhole running just anterior to the crista galli. Finally, the supraorbital bar is disconnected with a horizontal cut across the nasofrontal process just above the nasofrontal suture.

Bifrontal Craniotomy

Bifrontal Craniotomy 16-7

Bifrontal Craniotomy 16-7: Dural incision. After the bone work is done, the dura is opened with each side opened horizontally and as close to the frontal floor as possible (steps 1 and 2). The cut on each side should stop short of the superior sagittal sinus anteriorly. For a unilateral approach, this is all the dural opening required. Bifrontal approaches require that the sagittal sinus and falx be divided anteriorly. After a horizontal incision on both sides of the sinus, the frontal lobes are gently retracted away from the falx (steps 3 and 4) so that two 2-0 silk sutures can be passed through the falx below the sinus (steps 5 and 6). These sutures should ideally be placed as far anteriorly as possible. After tying these sutures over the top of the sinus, the sinus and falx are divided (step 7), and the basal dura is put under mild tension so that it lays as flat as possible and does not obstruct vision.

Closure

• Proper closure of these cases can be complex but is important for achieving good outcomes. First, the frontal sinus should be excluded from the intracranial space to prevent infection or mucoceles. The frontal sinus mucosa on the bone flap or orbital osteotomy piece should be completely stripped and lightly débrided from the inner table with a diamond drill bit. The remnant mucosa on the frontal sinus can also be stripped and drilled, or it can merely be folded inward on itself because sinus drainage remains adequate in most cases. The pericranial patch can be used to cover the sinus and should be placed below the osteotomy piece. In many cases, tumor resection leaves a defect in the anterior fossa that should be repaired by laying the vascularized pericranial patch under the frontal lobe and lightly tacking it in place with sutures laterally.
• The horizontal dural opening is closed by circumferentially sewing the dura to the pericranial patch that has replaced the basal dura.
• It is important to consider the final cosmetic result of the bony repair and to consider additional cranioplasty with hydroxyapatite or methyl methacrylate in this region because it is a prominent part of the patient’s face.

Tips from the masters

• It is usually wise to place a lumbar drain in these cases if an anterior fossa floor defect is anticipated.
• It is important that the eye is prepared into the field and that the drapes are placed below the globe so that the drape does not impede the forward folding of the scalp over the supraorbital rim, particularly if removal of the supraorbital bar is planned.
• If a combined rhinologic approach is planned for either closure or tumor resection purposes, the entire upper face and midface should be included in the field, with the lower drape being placed over the upper lip.
• For removal of tumors arising from the anterior midline skull base, such as olfactory groove meningiomas, it is helpful to dissect along the medial orbit until the anterior ethmoid arteries are visualized exiting the orbit through the lamina papyracea. By cauterizing and dividing these arteries, the dural blood supply to these lesions can be eliminated.
• The frontal bone flap should be created taking into account the highly cosmetic nature of the forehead region.
• In elderly patients, it is sometimes wise to put a paramedian burr hole on one side to prevent dural tears near bridging veins near the superior sagittal sinus; these burr holes should ideally be placed behind the hair line.
• Regardless of whether a unilateral or bilateral approach is being performed, we prefer to turn a unilateral bone flap stopping short of midline first and to dissect the sinus away from the bone under direct vision before performing the contralateral flap needed for the bifrontal approach. We believe this reduces the risk of sinus injury and prolonged hemorrhage that could occur while turning this extensive bone flap.
• In cases in which significant frontal retraction is anticipated, it is often wise to remove the orbital bar.

Pitfalls

The eyes are protected against the preparation solution by either suture tarsorrhaphy or Tegaderm dressings and ophthalmic ointment.

Care should be taken to avoid severing the supraorbital nerve anteriorly as it exits the orbit and to avoid going too laterally over the frontozygomatic process until the supratemporal fat pad has been dissected over the frontozygomatic process to protect the facial nerve.

It is important with unilateral orbital osteotomies that the periorbita not be stripped from the medial portions of the orbital roof because it is unnecessary and risks detaching the trochlear pulley of the superior 1oblique muscle, causing diplopia.

Bilateral approaches differ in that the periorbita should be stripped from the orbital roof medially and laterally. In our experience, patients do not notice diplopia from bilateral superior oblique trochlear detachment.

Removal of the orbital roof or lateral orbital wall is unnecessary (unless the orbital contents need to be exposed), in contrast to in the orbitozygomatic approach. The principal purpose of this osteotomy is to facilitate a low and flat trajectory toward the back of the anterior cranial fossa and less to remove visual obstructions around the sphenoid wing, as with lateral approaches. By avoiding excessive orbital bone removal, the risk of pulsatile enophthalmos is decreased.

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