Paul Donald
INTRODUCTION
The harvesting and placement of the pericranial flap has become the keystone technique in the reconstruction of the anterior skull base following resections of intracranial/extracranial tumors. During the coronal incision of the scalp for the anterior craniotomy, the pericranium is carefully preserved.
Usually, the floor of the anterior cranial fossa and often the cribriform plate, as well as adjacent dura, have been removed as part of the exenteration procedure (Fig. 40.1). The reconstruction dictates that the dura is closed, establishing a watertight seal, and that some form of lining of the subcranial exenteration cavity is placed. The interposition of some type of firm, resilient vascularized tissue is required to reinforce the dural repair as well as to serve as a nutrient bed for a split-thickness skin graft or free flap. The pericranial flap best serves these needs.
FIGURE 40.1 Exenteration defect following anterior skull base resection requiring a three-layer reconstruction.
HISTORY
In the taking of the history, it is important to note whether the patient has had prior craniotomy and if he or she has been treated with radiation in the past to the anterior cranial fossa. This is not an uncommon experience in patients with recurrent meningioma or a patient with a prior history of surgery and radiation for cancer of the ethmoid or maxillary sinus with intracranial penetration. The past history of a frontal craniotomy makes the harvest of a pericranial flap at this site extremely difficult and sometimes impossible.
A history of prior irradiation will jeopardize not only the survival of the flap but also the viability of the underlying cranial bone. The use of some form of free vascularized tissue to line the subcranial cavity is often mandated in these cases to establish a good blood supply to these compromised tissues.
PHYSICAL EXAMINATION
Examination of the defect will determine if the pericranial flap is the appropriate donor site. The blood supply to the flap should be evaluated to assure that it is intact and that the flap is well vascularized. There should be no evidence of prior surgery, trauma, or radiation to the donor site. The width of the flap should be wider than the expected cranial floor defect. Finally, before beginning the flap reconstruction, the dural reconstruction should be examined to assure that it is watertight to decrease the potential for CSF leakage.
INDICATIONS
The pericranial flap is indicated for central defects of the skull base.
CONTRAINDICATIONS
Contraindications to the pericranial flap include when the flap vascularity has been compromised by injury to the blood supply or in some previously radiated patients, the flap may not be hearty.
PREOPERATIVE PLANNING
Unless a prior craniotomy has been performed, there is little preoperative planning. If a prior craniotomy has been performed and the pericranial flap has been previously used for a reconstruction of the central skull base, I prepare for the possibility of a free flap for reconstruction. A free flap reconstruction is the only alternative because a temporalis flap will not reach the midline.
SURGICAL TECHNIQUE
Under general anesthesia, the patient usually has a tracheostomy done, to prevent postoperative tension pneumocephalus, and the head is place in a padded Mayfield headrest. The anterior aspect of the hair is usually shaved in order to prevent hairs from prolapsing into the wound at the time of closure at the end of the procedure. The scalp incision is outlined in methylene blue in a curvilinear fashion from the anterior–superior aspect of the auricle over the vertex of the skull running about 2 cm behind the hairline to the opposite side (Fig. 40.2). Injection of the scalp along the incision line is then done with a solution of ½% Xylocaine with 1 in 20,000 epinephrine.
FIGURE 40.2 Scalp incision outlined.
The coronal scalp incision is then made with a scalpel usually one side at a time, taking great care to avoid incising the pericranium. Periodic gentle blunt elevation in the depths of the incision with the back of the scalpel handle will allow easy identification of the area of the pericranium. Hemostasis is secured along the edges of the scalp incision by the placement of Raney clips and the use of the bipolar cautery. The elevation of the scalp flap proceeds toward the brows taking care not to make holes in the underlying pericranium. As the more posterior elevation of the flap proceeds over the temporalis muscle, care is taken to incise a semilunar portion of superficial temporal fascia keeping it attached to the scalp (Fig. 40.3). This will protect the temporal branch of the facial nerve as the flap elevation proceeds anteroinferiorly.
FIGURE 40.3 Semilunar flap of superficial and deep temporalis fascia kept adherent to the skin to protect the frontal branch of the facial nerve.
The flap elevation stops at the brows. Care is taken not to injure either the supraorbital or supratrochlear vessels as they emerge from their respective foramina in the region of the brows as they provide the vascular pedicle for the pericranial flap. Dissection is directed superiorly where a retrograde elevation under the scalp posterior to the coronal incision will provide additional length to the pericranial flap. Paired vertical incisions are made in the pericranium each at the lateral extremities of the flap and carried under the retrograde part of the elevated scalp. They are then connected over the vertex. The width of the flap will be predicated on the anticipated width of the defect. The pericranial incisions are carried down to the lateral brows. The pericranium is then carefully separated with a Langenbeck dissector from the underlying calvarium from under the superior extension of the scalp flap down to the brows (Fig. 40.4). A four-by-four gauze sponge soaked periodically in saline is placed over the pericranial flap as it lies against the raw undersurface of the coronal scalp flap while the resection part of the procedure is carried out.
FIGURE 40.4 Pericranial flap elevated.
An alternative to constructing the pericranial flap in this fashion, especially when the width of the defect in the cranial floor is hard to predict, is to keep the pericranium attached to the scalp flap to be separated from its undersurface at a width necessary to cover the defect after the resection; this is done by elevating the retrograde part of the pericranial flap first, and then, once the site of the scalp incision is reached, the vertical incisions in the pericranium are made on the calvarium as the elevation of the scalp flap proceeds inferiorly. The pericranium is elevated from the underlying skull over the width of this flap, and the more lateral elevation is between the galea and the pericranium.
POSTOPERATIVE MANAGEMENT
At the completion of the resection, there is an eventration in the anterior fossa floor. Bleeding is stopped from any brain tissue and dural resection is repaired usually with temporalis fascia or fascia lata. The pericranial flap is now turned 90 degrees on its vascular pedicle and placed over the defect in the cranial floor (Fig. 40.5). It is important to bridge the entire bony gap with tissue left over to tuck between the bone of the planum sphenoidale and the dura. It is important to extend the flap beyond the area of the repaired dural defect. Thus, the flap goes from its pedicle on the brow, over the inferior aspect of the craniotomy cut, across the intact portion of the anterior floor at the anterior limit of the resection, across the open resection site over the dural graft to finally be tucked between the bone remaining at the posterior limit of the dissection and the dura.
FIGURE 40.5 Pericranial flap tucked into position.
One of the biggest problems in the placement of the flap is to fix it to the posterior aspect of the anterior fossa floor in the area of the sphenoid sinus. The surest way is to place several drill holes in the bone and then parachute in the end of the flap. This is augmented by the use of tissue glue.
Nasal packing is placed for 5 days, and the patient is monitored for CSF leak. Antibiotics are administered while the nasal packing is in place.
COMPLICATIONS
Complications include CSF leak, meningitis, and pneumocephalus. I take care to make sure that positive pressure nasal ventilation is avoided at all cost to prevent pneumocephalus.
RESULTS
The results with this form of reconstruction are generally excellent. The flap and technique are reliable and reproducible.
There are some advocates of the pericranial flap that state that including the galea is essential to preserve a healthy blood supply. The problem with this technique is that the blood supply to the forehead skin may be compromised especially in someone who has had prior radiation. In using the pericranial flap without including the galea in well over 150 patients, I have had only one flap slough. This was in a man who insisted on smoking during the immediate postoperative period. First, the skin graft sloughed and then the pericranial flap died. This produced a brain fungus of the frontal lobe that required resection and the placement of a radial forearm free flap over the defect.
PEARLS
• To avoid the potential for compromise of the flap’s blood supply, a strip of bone at the inferior aspect of the craniotomy flap is removed (Fig. 40.6).
• On some occasions, the frontal bone is involved with tumor as is the orbit requiring orbital exenteration and resection of a portion of the frontal calvarium including the vascular supply on one side to the projected pericranial flap. Even a wide flap will survive on a single pedicle, from the opposing side as demonstrated in Figure 40.7. This patient had a large portion of frontal lobe dura removed as well as the frontal bone on the left side that included both the supraorbital and supratrochlear arteries as part of a craniofacial resection for a squamous cell carcinoma of the frontal and ethmoidal sinuses. The flap survived on a single contralateral vascular pedicle and the patient is alive and free of cancer 14 years postoperatively.
• If a prior craniotomy has been done and the pericranium is of poor quality, the donor site can be constructed from a temporalis fascial flap pedicled on the superficial temporal artery whose pericranial extension goes across the vertex posterior to the prior craniotomy.
• My preference for reconstruction of anterior skull base resections is dural grafting, pericranial flap, and a split-thickness skin graft to line the cavity. The rationale for this is that the bulk of the free flap, especially if an anterolateral thigh flap or latissimus dorsi flap is used, will obscure the appearance of a local recurrence. Neither MRI nor CAT scanning will reveal an early recurrence. Unfortunately, even PET scans are not entirely reliable in detecting early recurrent disease. The notion of the patient having had the “ultimate operation” and that any further intervention for early recurrence is hopeless is clearly nonsense. Early detection is the key to successful salvage.
FIGURE 40.6 Bar of bone is cut from the inferior aspect of the cranial bone flap to relieve any compression on the pedicle of the pericranial flap.
FIGURE 40.7 Large pericranial flap pedicled on only one supraorbital and supratrochlear artery from the side opposite the defect.
PITFALLS
• The pedicle of the flap may be pinched when the craniotomy bone flap is returned to its position and fixed in place if a small cutting tool such as the Midas Rex drill is used to do the craniotomy.
INSTRUMENTS TO HAVE AVAILABLE
• Standard head and neck surgical set
• Osteotome
• Periosteal Freer
SUGGESTED READING
Zanation AM, Snyderman CH, Carrau RL, et al. Minimally invasive endoscopic pericranial flap: a new method for endonasal skull base reconstruction. Laryngoscope 2009;119(1):13–18.
Patel MR, Shah RN, Snyderman CH, et al. Pericranial flap for endoscopic anterior skull-base reconstruction: clinical outcomes and radioanatomic analysis of preoperative planning. Neurosurgery 2010;66(3):506–512; discussion 512.
Zhang FG, Tang XF, Hua CG, et al. Anterior skull base reconstruction with galeal-frontalis-pericranial flap based on temporalis myofascial flap. J Craniofac Surg 2010;21(4):1247–1249.