Subarachnoid hemorrhage secondary to Chiari 1 malformation in a patient presenting with recurrent severe headache: A case report, imaging, and anatomic considerations.

BACKGROUND

Chiari 1 malformation (CM1) is a structural anomaly characterized by cerebellar tonsillar herniation through the foramen magnum. While typically associated with syringomyelia or hydrocephalus, its potential relationship with subarachnoid hemorrhage (SAH) remains poorly reported in the literature.

CASE DESCRIPTION: We present the case of a 77-year-old woman who experienced recurrent episodes of thunderclap headache, which eventually progressed to altered consciousness following admission. Neuroimaging revealed a SAH involving the fourth ventricle and basal cisterns, alongside cerebellar tonsillar herniation and obstructive hydrocephalus, with no arterial source identified on serial angiography. Magnetic resonance imaging confirmed CM1, with tonsillar descent to the C1 level. The patient underwent suboccipital decompression for refractory intracranial hypertension that prevented weaning from the external ventricular drain. Intraoperative exploration revealed an abnormal posterior spinal vein traversing the arachnoid membrane, which was suspected to be the source of the hemorrhage and was successfully coagulated.

CONCLUSION

To the best of our knowledge, this is the first documented case of CM1 presenting with recurrent SAH in the absence of aneurysmal or arteriovenous pathology. Our findings suggest a possible venous etiology related to anomalous posterior spinal venous drainage, which may have contributed to the hemorrhage and obstructive hydrocephalus. The patient's clinical improvement following Chiari decompression supports the role of surgical intervention in relieving cerebrospinal fluid outflow obstruction and elevated intracranial pressure in such cases. This case highlights the importance of considering venous anomalies in the differential diagnosis of non-aneurysmal SAH and underscores the need for heightened awareness of vascular variations in CM1 patients presenting with acute neurological symptoms.