Objective: Pure subarachnoid hemorrhage (SAH) secondary to spine cavernous malformation is rare. Method: Female, 41 year old, with a massive intraventricular and SAH secondary to a extramedullary intradural foramen magnum cavernous malformation. The patient developed a sudden headache and drowsiness without neurological deficits. A CT scan revealed a massive SAH without intraparenchymal blood. Angiogram was negative for aneurysm or vascular malformation. A MRI showed an extramedullary intradural mass in the foramen magnum. She underwent a neurosurgical resection of the mass. Results: No complications due to resection and the pathological test revealed a cavernous malformation. Conclusion: This is the second case of foramen magnum cavernous malformation reported in literature. It should be considered a differential diagnosis of SAH with negative angiogram and surgical treatment usually provides good outcomes.
