General Principles of Skull Base Surgery

It is clearly important that any patient with a skull base tumor should be told the long-term outlook of the tumor itself, i.e. the natural history of the pathology. They also need to be informed of all the management options available and these would usually include:

• Conservative management - monitoring the tumor with serial imaging.

• Conventional surgery - again, patients need information regarding outcomes, surgical morbidity and mortality. The figures one quotes need to relate to your own experience, as well as figures taken from the literature.

• Radiotherapy/stereotactic radiosurgery.

There will be occasions when combinations of the above are appropriate, e.g. where partial removal and post-operative radiotherapy may be the most suitable option.

The choice of management option will rely on such factors as the age of the patient and their general medical status, the natural history of the tumor, the location and size of the tumor, the potential risks of the surgery/radiotherapy/

radiosurgery and, importantly, the skill and experience of the skull base team.

As far as the operation is concerned, the surgeon should be guided by one overriding principle: removal of adequate amounts of bone from the cranial base should provide sufficient access without the necessity to retract dura/ brain. Remove bone before considering retracting brain, dura or the cranial nerves.

Even though many neoplasms involving the skull base are benign or locally confined malignant lesions, radical resection of extensive lesions remains difficult. The reasons for this include:

• The necessity to retract the brain to achieve tumor exposure (even when adequate bone removal has occurred), with the possibility of retraction-related cerebral injury.

• The involvement by tumor of basal blood vessels, injury to which may lead to stroke and/or death.

• The involvement of the cranial nerves, injury to which may result in significant functional deficits. In any surgical procedure which involves risk to the facial nerve, use of intraoperative electro-physiologic monitoring of the nerve is mandatory.

• The potential for CSF leakage through the skin, paranasal sinuses or nasopharynx, which may be followed by meningitis and death. In any case where the risk of post-operative CSF leak is high, use of a lumbar drain in the post-operative period should be considered.

In the past, the surgical treatment of skull base tumors has been associated with a high rate of local recurrence (related to the problems of gaining good surgical access and the involvement/close proximity of vital structures). Postoperative monitoring is therefore an extremely important part of their management and this will involve serial imaging. A 'base line' scan would usually be performed about 3 months following the surgery and then at regular intervals (often between 6 and 12 months). The choice of imaging may vary occasionally, although MRI will be the modality of choice in the majority of instances.

In some areas of the skull base, e.g. the nose/paranasal sinuses, imaging may be supplemented by endoscopic follow-up. Certainly, in extracranial skull base tumors in this area, endoscopic examination and biopsy will provide a more sensitive follow-up than any imaging modality currently available. The follow-up period varies according to the pathology, but often would be for a minimum of 5 years.

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