An extramedullary foramen magnum cavernous malformation presenting with acute subarachnoid hemorrhage: Case report and literature review

OBJECTIVE AND IMPORTANCE: This case summarizes our experience with the first described intradural extramedullary cavernous malformation at the foramen magnum and reminds the neurosurgical community to consider cavernous malformations in the differential diagnosis for subarachnoid hemorrhage. CLINICAL PRESENTATION: A 21-year-old man presented with an occipital headache, photophobia, nausea, neck stiffness, and fever of 10 days' duration. A lumbar puncture yielded a clear pink fluid with 300 leukocytes/mm³ (30% neutrophils and 65% lymphocytes) and 42,200 erythrocytes/mm³, a protein count of 243 mg/dl, and a glucose count of 56 mg/dl. Computed tomography revealed a 1.5-cm right-sided dural-based mass of high attenuation that spanned the foramen magnum and a segment of the upper spinal canal. Magnetic resonance imaging showed a loculated, heterogeneously enhancing mass with a cystic component that slightly displaced the medulla to the left. An angiogram was negative for aneurysms and vascular malformations but did show an area of early filling and slow washout of the epidural venous plexus at the posterior canal margin of C1 and C2. INTERVENTION: A suboccipital craniectomy and C1 laminectorny were performed. Upon opening of the dura, an encapsulated mass was visualized. The lesion was located on the right lateral surface of the cervicomedullary junction and was entirely extraparenchymal. The mass was microsurgically dissected, and its associated venous malformation was left intact. The patient's postoperative course was uneventful, with a return to baseline function. Pathological examination confirmed the diagnosis of cavernous malformation. CONCLUSION: : Our report not only presents a unique combination of pathological lesion, location, and presentation but also demonstrates that such lesions may be treated surgically with excellent results.