Direct arteriovenous fistula due to a blister-like aneurysm of the supraclinoid internal carotid artery hijacking its adjacent vein.

[BACKGROUND] This is the first report of a direct acquired arteriovenous fistula (AVF) between an intracranial aneurysm and its adjacent pial vein.

[CASE DESCRIPTION] A 33-year-old male suffered subarachnoid hemorrhage. Computed tomography angiography revealed an aneurysm of the supraclinoid internal carotid artery (ICA). Digital subtraction angiography (DSA) showed that the aneurysm of the supraclinoid ICA was blister-like and that one large vessel crossing the aneurysm provided two draining paths into the bilateral cavernous sinuses and superior sagittal sinus. Microsurgery confirmed the presence of a blister-like aneurysm and proved the vessel crossing and connected to the aneurysm to be a pial vein, resulting in a direct AVF between the aneurysm and its adjacent vein. The blister-like aneurysm together with some of the ICA wall was clipped to reconstruct the ICA and preserve the anterior choroidal artery (AchA). Postoperative DSA showed the following: the blister-like aneurysm had been completely clipped; the ICA was narrow, but the blood flow was sufficient; and the AchA was intact. After discharge, the patient recovered uneventfully without neurological deficits.

[CONCLUSIONS] Exceptionally, an intracranial ruptured aneurysm can hijack its adjacent pial vein as its draining path, forming a direct AVF. Microsurgery can be used to confirm the angioarchitecture of the AVF, and clipping is a good treatment choice.