CyberKnife Radiosurgery for Lesions of the Foramen Magnum
The region of the foramen magnum (FM) presents an especially difficult area for therapeutic intervention. Indeed, this location is challenging to access surgically, particularly in the case of intramedullary and anterior lesions. Therefore, the potential for morbidity associated with therapy to the foramen magnum, most frequently in the form of lower cranial nerve deficits, has encouraged the search for methods that can effectively treat lesions of this region while sparing the important neighboring structures. We report our experience in the use of Cyberknife radiosurgery as a treatment option for these lesions. Thirty-five patients (17 men, 18 women; mean age, 51 yr; range, 18–83) with 35 lesions either spanning or approximating the foramen magnum were treated with the CyberKnife radiosurgical system. Histologies were determined either by prior surgery or radiographic criteria and included 25 benign tumors (nine meningiomas, five schwannomas, four neurofibromas, three hemangioblastomas, two ependymomas, one chordomas, and one pilocytic astrocytoma) along with 10 malignant growths (nine metastases and one chondrosarcoma). Twenty-seven (77%) patients presented with at least one sign and/or symptom, while eight (23%) patients were completely asymptomatic. The most common symptoms were headache, limb numbness, and limb/truncal ataxia, all of which were reported by ten (29%) patients. Among cranial neuropathies, CN XII dysfunction was evident in four (11%) patients. The specific fractionation schedule (mean of 1.8 sessions; range, 1–5) was based on the size of the treated lesion. The mean dose utilized was 19 Gy. Radiographic follow-up was obtained for twenty-three (66%) patients. Nine of the twenty-three (39%) were stable in size, ten lesions decreased in size (43%), and four lesions increased in size (17%). In terms of symptom relief, follow-up was collected for twenty-four (69%) patients. Eleven (46%) of these patients experienced no change in their signs or symptoms, while seven (29%) patients experienced improvement. Six (25%) patients witnessed deterioration in their signs and symptoms. Overall, eighteen (75%) patients had their signs and symptoms either stabilize or improve. There were eleven (31%) deaths in our series, eight of which were related to the disease (though not directly related to CyberKnife treatment) and three of which were from unrelated causes. Complications directly related to CyberKnife radiosurgery were noted in four (11%) of the thirty-five patients. These included one case of temporary emesis immediately following treatment, one case of cystic enlargement two months out, and two cases of radiation necrosis (occurring 1.5 yrs and 2.5 yrs out from treatment). Cyberknife radiosurgery can be an effective treatment for many foramen magnum lesions.