A Rare Case of Subarachnoid Hemorrhage caused by Ruptured Venous Varix Due to Dural Arteriovenous Fistula at the Foramen Magnum Fed Solely by the Ascending Pharyngeal Artery

Abstract

Dural arteriovenous fistula (D-AVF) at the foramen magnum is an extremely rare disease entity. 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. The diagnosis of D-AVF at the foramen magnum as a cause of SAH may be difficult due to its low incidence. Furthermore, 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. Herein, we report on a rare case of SAH caused by ruptured venous varix due to D-AVF at the foramen magnum fed solely by the APA. A review of relevant literatures is provided, and the treatment modalities and outcomes are also discussed.

Keywords: Ascending pharyngeal artery; Dural arteriovenous fistula; Embolization; Foramen magnum; Subarachnoid hemorrhage.

Fig. 1. Initial brain computerized tomography shows subarachnoid hemorrhage at the cistern magna (A). Focal hematoma (white arrow) is observed on the left side of the foramen magnum which is suspected to be the point of rupture (B).

Fig. 2. Three-dimensional reconstruction (A), arterial phase (B), and venous phase (C) of left external carotid angiogram show a dural arteriovenous fistula at the foramen magnum fed by the hypoglossal branch (white arrowheads) of the neuromeningeal trunk (black arrows) of left ascending pharyngeal artery and drained into the suboccipital venous plexus and sigmoid sinus (long white arrows). The pharyngeal trunk (white arrows) and the odontoid arcade (black arrowheads) are also identified. Note the venous varix adjacent to the fistula.

Fig. 3. Three-dimensional reconstruction (A), arterial phase (B) of the left external carotid angiogram at a working angle demonstrate a venous varix distal to the fistula. The hypoglossal branch (white arrowheads) of the neuromeningeal trunk (black arrows) is the only route that leads to the fistulous point. The pharyngeal trunk (white arrows) is overlapped on it. The odontoid arcade (black arrowheads) is also visible.

Fig. 4. A superselectvie angiogram clearly shows the configuration of the target (A). Note that the microcatheter should be located as close to the fistulous point as possible. After injecting 0.4 mL of Onyx (B), the fistulous point and the ruptured venous varix are occluded (C).