INDICATIONS:

The tumors most commonly requiring combined anterior craniofacial surgery usually begin in the nose or sinuses. Many of these tumors to a greater or lesser degree are malignant . Inverting papilloma is an example of transitional type of tumor that is locally invasive, does not metastasize, but must be resected aggressively to avoid recurrence. Esthesioneuroblastoma varies from a very indolent to a highly aggressive tumors. Most tumors of nasal or para nasal sinus origin are squamous cell or adenocarcinomas of the maxillary or ethmoid sinuses.

Tumors with a primary intracranial origin such as meningioma, chordoma or chondrosarcoma require combined resection when they clearly violate the anterior fossa floor.

SURGICAL TECHNIQUE:

General anesthesia should be performed by a team experienced in neurosurgical procedures. A lumbar drain is routinely placed and patients are given prophylactic per operative antibiotic. The patient is then placed in a Mayfield head holder and positioned to optimize both the neurosurgical and facial approaches. The leg is propped to obtain a skin graft and fascia lata if needed.

The anterior craniofacial approach incorporates a combination of transfacial and transcranial procedures. The facial approach consists of a graduated greater exposure depending on the extent of disease. The basic is done through a lateral rhinotomy approach coupled with a low craniotomy. The lateral rhinotomy incision may be extended into a Web-Ferguson incision if a more extensive maxillary excision is required.

Craniotomy:

The craniotomy is tailored according to the extent of involvement of the anterior fossa floor, the sub cranial tumor location, and the degree of dural or frontal lobe invasion. A bicoronal scalp incision is made running 2 to 3 cms behind the hairline. The flap is elevated in the subgaleal plane down to the eyebrows , then to the lateral orbital walls laterally and just below the nasal globella medially. A large flap of pericranial tissue is created that will be used for later reconstruction. As the dissection proceeds the brows, the supratrochlear and supraorbital neurovascular bundles are exposed and preserved. 

The anterior cranial fossa is then exposed by removing a segment of bone which may be pedicled on the temporalis muscle or completely separated. The lower horizontal bone cut should be kept low to lessen the need for subsequent brain retraction. Withdrawing 25 to 50 ml of CSF from the lumbar subarachnoid catheter, lowering Pco2 through controlled hyperventilation, and occasionally administering mannitol or steroids further reduce the need for mechanical frontal lobe retraction.

The dura is then carefully dissected off the cristagalli and cribriform plate dividing the dural sleeves that extend along the olfactory nerves. The intracranial portion of the tumor extension is then assessed. If it involves the dura or in certain situations, frontal lobe this will have to be resected, together with the tumor, If the dura is intact, it is retracted back to the planum sphenoidale. 

Once the head and neck surgeon has completed the exposure and mobilization of the tumor transfacially a chisel or drill is used either from above or below to make the necessary bone cuts to encompass the tumor and deliver the specimen.

Facial Approach:

The facial approach depends on the extent of the tumor. Often utilizes modifications of a lateral rhinotomy incision which may or may not transect the upper lip. This depends on whether a total maxillectomy is done in conjunction with the resection. 

The periosteum is elevated from the nasal bone as well as from the medial and inferior surfaces of the orbit. 

The nasolacrimal duct is identified and transected distally. The anterior and posterior ethmoidal arteries are then identified and cauterized or clipped. 

In most cases it is necessary to perform a complete enbloc ethmoidectomy. For this purpose a contra lateral lynch incision is made to elevate the contra lateral periorbita, cauterize the anterior and posterior ethmoidal vessels, and make the appropriate osteotomies. 

If preoperative imaging studies confirm the presence of tumor in this, the soft tissues of the orbit, then orbital exenteration may be facilitated by extending the incision laterally to include a portion of the eyelids.

RECONSTRUCTION:

The secret of avoidance of post operative complications in anterior skull base surgery is the insurance of a water tight dural closure. If a portion of the dura has been excised, it is repaired with fascia lata. 

The pericranium is used for anterior cranial fossa reconstruction. It is usually pedicled on the supraorbital and supratrochlear arteries. The pericranial flap is placed across the defect in anterior cranial fossa. The distal end is clamped between the cranial floor bone and the overlying dura. It may be secured with sutures through the bone or anchored with fibrin glue. Unless a large amount of anterior cranial fossa bone has been resected and concern for brain herination exists, it is usually not necessary to place a bone graft across the bony defect. Also, it is usually not necessary to place a skin graft on the under surface of pericranium(facing the nasal cavity), since this tissue has been shown to "mucosalize" readily on its nasal cavity.

Once the pericranial flap is in place the spinal drain is clamped so that no further intraoperative CSF decompression will take place. This will allow gradual reexpansion of the brain to make contact with the pericranial flap, obliterating any residual dead space.

 Since the pericranial flap traverses the frontal sinus, it is necessary to obliterate the frontal sinus with fat or free muscle after removing all the mucosa in the sinus. If the sinus is quite large, it may be advisable to remove the posterior wall of the sinus completely and allow the brain and dura to expand and fill the space ( Cranialization of the frontal sinus) 

The bifrontal craniotomy bone flap is then replaced and secured according to the surgeon's preference. This may be done with wires, plates or sutures.

 In all cases, an exclusive nasal pack is placed for at least 5 days post operatively and a lumbar drain kept for the same duration. In significantly larger defects, particularly if orbital exenteration and facial skin is excised, a bulky free flap is considered.

Basal Sub frontal approach:

It is in many ways similar to the anterior craniofacial resection operation except that the Transfacial exposure is less extensive. Because the target area for this approach is more posterior (Sphenoid and clivus) than in the anterior cranio facial resection (ethmoid and cribriform), the craniotomy bone flap is larger, and the orbital bone cuts are broader. This approach also begins with a bicoronal incision.

After exposing the orbital rims, periorbita is elevated from beneath the orbital roofs and medial walls in preparation for osteotomy. Bifrontal craniotomy is then performed, and dura is elevated from above the orbital roofs and cribriform areas. Using malleable retractors to protect the brain and orbital contents, the reciprocating saw is used to create osteotomies that result in temporary removal of both orbital roofs and the supra orbital contents, the reciprocating saw is used to create osteotomies that result in temporary removal of both orbital roofs and the supra orbital bar.

The coronal osteotomies along the posterior orbital roof should be made as far posteriorly as possible to simplify reconstruction, by conserving orbital contour, and to prevent postoperative pulsatile exophthalmoses. 

The neurosurgeon completes the approach by drilling a small amount of bone remaining posteriorly to unroof the optic nerves, superior orbital fissures and sphenoid sinus. Extirpation then proceeds as required by the tumor, followed by reconstruction which is similar to that done for anterior craniofacial resection.