Skull Base Tumors

supratrochlear vessels). A bi-frontal bone flap is then raised, either as a free flap or pedicled on temporalis. Care should be taken to keep the dura intact whilst opening the bone.

Exposure of the floor of the anterior fossa is best achieved by opening the dura on either side of the superior sagittal sinus as far anteriorly as possible. The sinus and underlying falx can then be divided between stay sutures. If a lumbar drain has been inserted, this can now be opened to allow CSF to drain. Diuretics may help provide good exposure without retraction of the frontal lobes.

Full exposure of the anterior cranial fossa floor invariably requires division of the olfactory tracts. Of course, if one or both can be protected, so much the better but, usually, patients with tumors requiring such an approach are anosmic.

The basal dura is reflected along the cribriform plate to the planum sphenoidale (if dura is involved, then it is mobilized more laterally and involved dura is resected with the tumor). Further cuts can then be made into the bone outside the tumor margins through the roof of the ethmoid/orbit laterally, through the planum sphenoidale into the sphenoid sinus posteriorly and through the floor of the frontal sinus into the anterior ethmoid anteriorly (these cuts are often made from both above and below). The tumor specimen is then only attached by the perpendicular plate of the ethmoid (which forms the postero-superior part of the nasal septum), and this is divided using heavy scissors. The specimen can then be "rocked out" through the transfacial exposure, dividing any mucosal attachments that might still remain.

The resultant defect has as its anterior margin the anterior wall of the frontal sinus/nasion, posteriorly the remaining portion of the sphenoid sinus and optic nerves, and the periorbita laterally. Inferiorly, the defect is open to the nasopharynx. Reconstruction of the defect in the anterior cranial fossa floor involves use of the pericranial flap - it is "posted" back into the anterior fossa over the supraorbital bar of bone (and beneath the frontal bone when it is replaced at the end of the procedure). This vascularized graft is then sutured to the basal dura (and if sutures are too difficult to place, tissue glue is used) to provide a carpet-like resurfacing of the anterior cranial fossa. A second layer of free pericranium, placed intradurally, can then be used, again, glued into position. We have not found it necessary to replace bone and have had no problems with brain herniation. However, great care must be taken with this repair to achieve a water (CSF)-tight closure. The use of the lumbar drain post-operatively helps.

Often, the nasolacrimal duct is transected during this approach, and can be stented at the end of the procedure. The nasal cavity is then packed to help avoid a post-operative cerebrospinal fluid leak.

Anterolateral Craniofacial Resection

Antero-lateral craniofacial resection also encompasses structures of the anterior mid-line and paramedian skull base but may also include the orbitomaxillary and infratemporal regions, as well as the floor of the middle cranial fossa.

Indications

• As for anterior CFR, but with orbital involvement.

• Extensive maxillary tumors with orbital/ ethmoidal involvement.

• Extensive transcranial middle fossa tumors, e.g. meningiomas.

Surgical Steps

This approach can be performed through a bicoronal scalp flap, especially if a dural graft is required to effect a repair. Alternatively, an extended pterional flap may be used.

The facial incisions are usually paranasal, with possible lip splitting and eyelid incisions. The precise shape of the craniotomy and the extent of any facial osteotomies depend on the size and site of the tumor. For a purely intraorbital tumor, a pterional approach with extra-dural removal of lateral and superior orbital walls provides good access to the posterior part of the orbital cavity. Clearly, this would be inadequate for an extensive maxillary or ethmoidal lesion with orbital involvement, when a bifrontal flap will allow far better access. As regards the facial osteotomies, in general, they are made within the orbit along the medial and lateral wall as well as across the zygoma.

For reconstruction, following dural repair, soft tissue may be brought into the area using either temporalis muscle or a free microvascular flap, depending upon the size of the defect.

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