Foramen Magnum Dural Arteriovenous Fistula

Dural arteriovenous fistula (D-AVF) at the foramen magnum is an extremely rare disease entity.

Till 2001 only 16 cases have been reported of dural arteriovenous fistula (DAVF) at the foramen magnum.

It produces venous hypertension, and can lead to progressive cervical myelopathy thereafter. On the other hand, the venous hypertension may lead to formation of a venous varix, and it can rarely result in an abrupt onset of subarachnoid hemorrhage (SAH) when the venous varix is ruptured.

A dural arteriovenous shunt, which may be located in the region of the foramen magnum, should be suspected in those cases of subarachnoid hemorrhage in the posterior fossa or progressive myelopathy mimicking spinal DAVF ¹⁾.

When the D-AVF is fed solely by the ascending pharyngeal artery (APA), it may be missed if the external carotid angiography is not performed. The outcome could be fatal if the fistula is unrecognized.

Kim et al. reported on a rare case of SAH caused by ruptured venous varix due to D-AVF at the foramen magnum fed solely by the APA ²⁾.

DAVF at the foramen magnum can be treated very effectively and with minimal surgical trauma by direct microsurgical disconnection of the shunt. This surgical procedure is indicated if embolization with glue is not possible or is unsuccessful ³⁾.

Reinges et al. present three surgically treated patients with DAVF at the foramen magnum. In none of the three patients could the site of the arteriovenous fistula be suspected from the clinical presentation. The clinical course varied from acutely developing signs and symptoms to a 10-year history of very slowly progressing symptoms. After neuroradiological diagnosis the patients were operated on direct microsurgical disconnection of the arteriovenous shunt via an enlargement of the foramen magnum and a hemilaminectomy of C1. DAVF at the foramen magnum may thus present with slowly to acutely progressing clinical symptoms and signs. Spinal angiographic examination should include the level of the foramen magnum if standard spinal angiography of thoracic, lumbar, and sacral segments is negative in suspected spinal DAVF since the nidus of the shunt can be situated remote from the level of neurological disorder. DAVF at the foramen magnum can be treated very effectively and with minimal surgical trauma by direct microsurgical disconnection of the shunt. This surgical procedure is indicated if embolization with glue is not possible or is unsuccessful ⁴⁾.

Motebejane et al. reviewed clinical charts, radiological images, and operative notes of 12 patients who were diagnosed of foramen magnum dural arteriovenous fistula (DAVF) from December 1993 until April 2017. The angiographic studies were analyzed for feeding arteries, the location of the shunt, the venous drainage patterns, and the presence of venous side aneurysms.

Twelve patients were angiographically confirmed with foramen magnum DAVFs. They included 11 males and 1 female (M:F = 11:1). Mean age of 55.6 yr ranging between 42 yr and 71 yr of age. Eight patients presented with progressive myelopathy, 3 patients with posterior fossa intracranial hemorrhage, and 1 patient presented with lower cranial nerve IX and XII palsies due to mass effect.

A dural arteriovenous shunt, which may be located in the region of the foramen magnum, should be suspected in those cases of subarachnoid hemorrhage in the posterior fossa or progressive myelopathy mimicking spinal DAVF ⁵⁾.

A 35-year-old man was admitted with a right trigeminal neuralgia. Magnetic resonance imaging showed an abnormal flow void in the posterior fossa and a vascular structure next to the root entry zone of the right trigeminal nerve. Digital subtraction angiography showed a Cognard type IV DAVF located at the foramen magnum. The fistula was disconnected surgically. The patient was rendered completely pain-free, and the fistula did not recur during 4-year follow-up.

DAVF is a rare cause of TN. Surgical disconnection is an effective treatment method for TN caused by a foramen magnum DAVF ⁶⁾