For small skull base defects, generally limited to the cribriform plate and the area between the orbits, local vascularized flaps are able to create an adequate seal between the intracranial and extracranial cavities, and suspend the frontal lobe over the defect.
The most common indications for central anterior craniofacial resection are:
Olfactory groove tumors
meningiomas around the orbit
The anterior-based pericranial flap is very versatile and can be used in sealing of the nasal cavity in frontal sinus reconstruction, for closure, or obliteration of skull base defects, etc.
The pericranial flap can also be extended to fill small volume defects. When more skull base coverage is needed than what can be provided by pericranial flap, the temporoparietal fascial flap can be used as an adjunct.
The pericranial flap is vascularized by the deep branches of the supraorbital and supratrochlear arteries and veins which course between the galea-frontalis muscle layer and the pericranium.
In order not to devascularize the flap during preparation, these layers must not be separated too far anteriorly and inferiorly.
Goals of reconstruction
Successful reconstruction of the skull base depends on several key principles to minimize the likelihood of perioperative complications and restoration of anatomical boundaries and barriers. Key elements are:
Obtain a watertight dural seal
Separate intracranial and extracranial cavities
Obliterate dead space and/or sinuses
Suspend or support neural structures
Restore or preserve function and form
Ideal Reconstructive Procedure
The most important element is to use tissues with robust blood supply. Although there are a variety of options, choices can be made based on the following principles:
Single stage procedure
Minimal donor site morbidity
Tissues must tolerate the burden of healing related to: o Radiation therapy o Previous chemotherapy o Poor vascularity o Local contamination
Because of the proximity to the skull base to the central nervous system, any complication arising from procedures in this area can be life threatening. Areas to pay specific attention are:
Calvarial bone or dural involvement
Inelasticity of scalp
Distance to neck vessels
Biological tumor behavior
2. Preparation of the pericranial flap / Galeal pericranial flap
The preparation of the pericranial flap is described in the coronal approach. Some surgeons prefer to include the galea together with the pericranium, to improve the flap vascularity (Galeal pericranial flap).
3. Access to the tumor
Some surgeons will elect to place a lumbar drain prior to initiating the procedure, to allow for relaxation of the brain during surgery.
Tumor access from the cranial side
The tumor is exposed on the cranial side through one of the three following approaches:
The choice should ensure adequate tumor exposure and minimize brain retraction.
Tumor access from the nasal side
On the nasal side, the tumor can be exposed via a lateral rhinotomy incision or endonasally with endoscopes.
4. Resection of the tumor
Incision of nasal septum
Using the electrocautery an incision is made through the nasal septum from the top of the nasal vault just down to the premaxillary crest, 1 cm anterior to the tumor margin.
A second incision is made along the premaxillary crest posteriorly to the sphenoid rostrum.
These cuts can also be made endoscopically without a Lateral Rhinotomy.
The tumor is approached from the cranial side.
The frontal lobes are retracted and a small round burr is used to incise the cranial base around the cribriform plate.
Depending on the extension of the tumor, one or both of the lamina papyracea could be preserved.
The orbital periosteum is elevated on both sides.
Scissors are used to cut the posterior bony septum.
The tumor is removed en block with the cribriform segment and submitted for permanent pathological examination.
Surgical margins are now checked with frozen sections to ensure the adequacy of the tumor resection.
The pericranial (or the Galea pericranial) flap is rotated into the skull base and secured to the dura and the planum sphenoidale. This repair can also be supported by the placement of tissue glue.
The frontal bone flap is now replaced. Care is taken to ensure that adequate space is left between the frontal bone flap and the supraorbital rim so as not to compress the pericranial flap.
To accomplish this, a small amount of the frontal bone flap is removed in its lower edge
6. Aftercare following skull base reconstruction
Keeping the patient’s head in a raised position both preoperatively and postoperatively may significantly improve edema and pain.
The patients neurological status should be evaluated as soon as it is feasible. Regular postoperative neurological checks should be performed.
Nose-blowing should be avoided for at least 3 weeks following frontal sinus and skull base repair.
The use of some of the following perioperative medication is controversial. There is little evidence to make strong recommendations for postoperative care.
Analgesia as necessary
Antibiotics (many surgeons use perioperative antibiotics. There is no clear advantage of any one antibiotic, and the recommended duration of treatment is debatable.) The spectrum should be according to the existing bacterial flora, especially in the combined intra and extra cranial procedures.
Nasal decongestant may be helpful for symptomatic improvement in some patients.
Corticosteroids, may help with postoperative edema.
If a free flap is utilized for the reconstruction 100 mg of aspirin/day is recommended.
Ophthalmic ointment should follow local and approved protocol. This is not generally required in case of periorbital edema. Some surgeons prefer it. Some ointments have been found to cause significant conjunctival irritation.
Postoperative examination by an ophthalmologist may be requested. The following signs and symptoms are usually evaluated:
Extraocular motion (motility)
If the patient complains of epiphora (tear overflow), the lacrimal duct must be checked
If the patient complains of eye pain, evaluate for corneal abrasion
Note: In case of postoperative diplopia, ophthalmological assessment is needed to identify the cause. Hess-chart testing should be performed if diplopia persists.
A head CT scan is obtained postoperatively to provide a patient baseline and evaluate for intracranial bleeding, dead space, and pneumocephalus.
Subsequent imaging can be based on the patients' postoperative course.
Remove sutures from skin after approximately 7 days if nonresorbable sutures have been used. If the patient has had previous radiation, the sutures should be left in for 10 days. Moisturizing lotion should be used on the skin wounds to minimize excessive scarring after sutures are removed. Avoid sun exposure and tanning to skin incisions for several months.
Patients are started on a liquid diet, and advanced to regular diet as tolerated.
Clinical follow-up depends on the complexity of the surgery, and the patient’s postoperative course. Other issues to consider are:
Mucocele formation (can occur years after injury)
Sensory nerve compromise
Cranial vault contour deformity
Travel in pressurized aircraft is permitted 4 – 6 weeks postoperatively. Mild pain on descent may be noticed. However, flying in non-pressurized aircraft should be avoided for a minimum of 12 weeks. No scuba diving should be permitted for at least 12 weeks. Additionally, the patient should be warned of long term potential risks.
Reconstruction with free flap
When a free flap is utilized, it should be regularly monitored to ensure vascular integrity. Physical examination, assessing the flap color, turgidity, and capillary refill should be routine for at least the first 48 hours postoperatively. Hand-held Doppler probes can be used to assess blood flow. In case of doubt of the vitality of the flap, pin-prick assessment with a 25 gauge needle to look for bright red bleeding. In cases of buried flaps, an implantable Doppler placed just distal to the venous anastomosis can be utilized.
Radial forearm free flap The radial forearm free flap donor site should be closed with a skin graft and a bolster placed over the area. The arm is then cast or placed in a volar splint for 7 days prior to removal to ensure graft take. If bone is taken and the radius plated, appropriate follow-up with an orthopedic or hand specialist should be arranged.
Rectus abdominous and iliac crest Rectus abdominous and iliac crest donor sites require that the patient not strain or lift heavy objects for at least 4 weeks to avoid hernia formation.
Anterolateral thigh Patients should avoid climbing stairs for 2-4 weeks after surgery. They should also be observed for seroma formation at the wound bed. Furthermore, patients often need physical therapy to rehabilitate the donor site.
Latissimus dorsi There are no special issues for this flap except the suction drains should be left in place for 5-7 days as there is a 40 % risk of seroma formation. If a seroma does occur it can be aspirated with a large gauge needle as necessary.