Foramen magnum meningioma – upfront radiosurgery

SKULL BASE REGION	Foramen magnum
HISTOPATHOLOGY	N/A
PRIOR SURGICAL RESECTION	No
PERTINENT LABORATORY FINDINGS	N/A

Case description

A 55-year-old woman was found to have a right foramen magnum lesion, most likely a meningioma, after undergoing a magnetic resonance imaging (MRI) for new-onset vertigo, later attributed to benign paroxysmal positional vertigo. Serial MRIs studies demonstrated growth at a rate of 1 mm per year ( Figure 11.54.1 ). Because of the small size of the tumor and absence of any symptoms, both radiosurgery and surgical resection were discussed. After careful consideration, the patient opted for stereotactic radiosurgery (SRS) ( Figure 11.54.2 ).

Radiosurgery Machine	CyberKnife
Radiosurgery Dose (Gy)	15, at the 80% isodose line
Number of Fractions	1

Critical Structure	Dose Tolerance
Brainstem	15 Gy maximum point dose <1 cc >10 Gy
Spinal cord	10–12 Gy
Lower cranial nerves	Unknown, but significantly more tolerant than optic nerves
Vertebral artery	Very tolerant No evidence of stereotactic radiosurgery (SRS)-induced stenosis