The Neurotologist as Gamma Knife Radiosurgeon

The other related controversy is whether the facial nerve dissection and subsequent preservation are more difficult during microsurgical resection after radiosurgery. On one end of the spectrum, descriptions of no increased difficulty have been reported, and on the other end of the spectrum, markedly increased difficulty in separating the tumor from the facial nerve and poorer facial nerve function outcome has been reported. The report of Watanabe et al.4 included a histopathologic analysis of the resected facial nerve. They found microvasculitis of the facial nerve, axonal degeneration/loss of axons, and proliferation of Schwann cells. In light of the mechanism of delayed effects following radiosurgery, these findings are not surprising and based on my experience, the facial nerve is compromised and consequentially the neurotologist must be certain that the treatment plan avoids high radiation doses adjacent to the facial nerve. For this reason, if the neurotologist/neurosurgeon team and the patient have made a decision to resect a tumor previously treated with radiosurgery, it is important to review the treatment plan to determine the amount of radiation delivered to the facial nerve in order to appropriately counsel the patient preoperatively.

What Trends Should We Be Worried About for Our Patients?

A concerning early trend in stereotactic radiosurgery is the concept of debulking the tumor and subsequently radiating the tumor for the purpose of hearing preservation and facial nerve preservation. The single biggest variable during this process is how much tumor is resected prior to radiation. In the absence of applying intraoperative MRI to visualize the remaining tumor volume, it is difficult to be certain when or if the preoperative goal for debulking has been achieved. This approach is not being used in high-volume acoustic neuroma programs nationally, and the traditional neurotologist/neurosurgeon team is not involved with innovative surgical approach. I have seen and cared for several patients who had a neurosurgeon complete a debulking procedure that, based on MRI scans that I have reviewed, represents merely a biopsy rather than a debulking procedure. Aside from the unnecessary expensive of completing both the craniotomy and Gamma Knife radiosurgery, the ethical and moral questions presented by this practice are troubling.

In light of the current outcomes in microsurgery or stereotactic radiosurgery, there is no justification for this type of management algorithm. In contrast, Iwai and colleagues5 applied this concept in a more appropriate way. They reported a series of 14 patients managed over a six-year interval with acoustic neuromas too large (range 3.0 to 5.8 cm) to treat primarily with radiosurgery. Subtotal resection was achieved in 13 and partial resection due to hypervascularity was performed in one patient. After recovery, radiosurgery was performed to treat the remaining tumor. This latter management algorithm would be appropriate in selected patients.