Cranial Base

The goal in reconstructing the cranial base is reliable separation of saliva from the meninges and neurovascular structures. Because of the aggressive nature of many tumors of the cranial base, arguments have been made to delay reconstruction until permanent sections have confirmed tumor clearance and to cover the defects temporarily with a skin graft, to facilitate detection of recurrence.34 Although these are real concerns, in most instances, exposed vessels or tenuous dural closures mandate immediate flap coverage. Multiple frozen sections are used in our department in order to secure microscopically clear margins. Magnetic resonance imaging scans are used to detect recurrence under the flap. Local flap options (e.g., temporalis flap, galeal, and pericranial flaps) and regional flaps (e.g., pectoralis major, sternocleido-mastoid muscle, or latissimus dorsi flaps) are usually sufficient for most small to moderate cranial base defects. In extensive resections, however, the pericranial and temporalis flaps may be devas-cularized, and a regional flap may be limited by its arc of rotation. The temporalis muscle flap is also less reliable in its ability to cover medial and posterior cranial base defects.1

The rectus abdominis flap has been the free flap used most frequently in our department for cranial base defects. The flap can be harvested simultaneously with the resection, saving operative time. It has a long and large-diameter vascular pedicle and a large muscle volume that can be transferred with or without varying amounts of skin and vascularized fat to accommodate most defects.29 The latissimus dorsi can be used as a free flap in this area, but the patient must be repositioned so that the flap can be harvested simultaneously with the resection. The serra-tus anterior flap can also be used, but it is a smaller muscle flap than the latissimus dorsi, with all its disadvantages. Other flaps include the omentum which is soft and pliable with a long vascular pedicle; and there is no functional defect secondary to flap harvest.34 Although we have no personal experience with omen-tum, the main disadvantages are said to include the need for intra-abdominal surgery, the possibility for peritoneal bleeding, and respiratory compromise secondary to abdominal pain.34

Whether to reconstruct the bony cranial base remains a controversial issue. Proponents argue that reconstruction with bone is especially important in the anterior cranial base, in order to prevent herniation of cranial contents. Opponents state that the absence of bony reconstruction causes minimal if any her-niation of the brain, reduces the risks of infection of the bone fragments, and gives a better chance for skin grafts to take.35 In one study of 16 cranial base resections without reconstruction of the bone, only one herniation occurred through an absent orbital roof in a patient who had five previous surgeries and previous radiation therapy.36 The authors concluded that, in their experience, the presence of a defects in the bony cranial base did not predispose to an increased risk of complications. Our own experience supports these findings, as we have not seen any increased complications or herniations in those patients in whom the bony cranial base has not been reestablished. As long as adequate separation of the intradural and extradural spaces can be accomplished by local, regional, or free flaps, we do not recommend additional bony reconstruction for the cranial base.

0 0

Post a comment