Teaching Case

The patient arrived to the Emergency service with left hemiparesthesias. Non-contrast CT and CT-angiography were performed, followed by scheduled MRI and digital subtraction angiography. He was treated with endovascular therapy and the focal neurological symptoms disappeared.

Non-contrast CT and CT angiography demonstrated dilated vascular structures in the falx causing incipient hydrocephalus and enlarged vascular skull foramina. Postprocessing images revealed dilated extracranial arteries and collection of engorged veins in the region of Galen, suggesting dural arterio-venous fistula.

In addition to this, MRI supported the clustered vessels surrounding the straight sinus and Galen vein with arterial supply and vein drain. Moreover parenchymal oedema was seen in the right cerebral peduncle.

Finally, digital subtraction angiograms confirmed the presence of a falco-tentorial dural fistula with arterial supply from meningeal and occipital arteries and early venous drain to Galen vein and straight sinus. Furthermore, next to the choroidal plexus, there were dilated abnormal vessels that can correspond to venous congestion.

The neurovascular multidisciplinary team decided endovascular therapy due to a high-risk classification of the fistula. It was obliterated with Onyx by transarterial approach with superselective distal catheterization of arterial supplies.

Intracranial dural arteriovenous fistulas are abnormal connections between arteries and veins in dura-mater [1, 4] that occur mainly in women during the 5th - 6th decade [2, 4]. They account for about 10% of all intracranial vascular malformations and their localization is variable, the posterior fossa being the most frequent [1, 2, 4]. Symptomatology is determined by shunt localization [1, 2, 4] and vein drainage pattern [4]. The most serious clinical presentation is haemorrhage, seizures or neurological deficits [1, 4].

Pathophysiology remains uncertain, but the most accepted theory in an acquired vein disorder [1, 3, 4]. Currently, the most commonly used scales are Cognard and Borden classifications [2, 4].

CT is the initial imaging test [1, 3, 4]. It can depict dilated arteries, especially external carotid artery branches, accompanied by osseous resorption due to an enlargement of vascular foramina, and venous ectasia with surrounding oedema and hydrocephalus [1, 2, 3]. Complicated cases can start with subdural, subarachnoid or most commonly intraparenchymal haemorrhage [1, 2, 4]. However, CT sensibility and specificity are limited [1, 3]. CT-Angiography rises sensibility up to 93% [1] and is important for treatment planning [4] but it can't evaluate the venous drain precisely.

MRI is useful for screening and follow-up. T2 and SWI sequences show prominent and asymmetric vascular structures with hypointense signal inside the veins because of increased deoxyhemoglobin content while TOF images demonstrate arterial flow in venous vessels [1, 2, 3, 4]. Other imaging features are restricted diffusion and a better evaluation of parenchymal oedema [3, 4]. Furthermore, gadolinium-enhanced time-resolve dynamic-
MRI increases sensibility and specificity up to 100% [3, 4]

Digital-subtraction angiography is the gold standard diagnosis technique due to its higher temporal, spatial and contrast resolution and allows endovascular therapy. [1, 2, 4]. Six-vessel angiography is recommended because shunt locations can be multiple and remote [1].

Treatment and follow up depend on natural history and patient preferences. Endovascular therapy is the first-line treatment if vessel anatomy is favourable. Procedure approach can be transarterial, transvenous or direct puncture [1, 2, 4].
Endovascular embolic agents include ethylene-vinyl-alcohol copolymer (Onyx). It's a nonadhesive embolic agent suspended in DMSO with tantalum for radioopacity. DMSO diffuses from the mixture on contact with blood causing polymer precipitation without vessel wall adhesion. This permits a more controlled injection, multiple pedicules and treatment of the vein's origin, and angiographic control during the entire process. Therefore curative rates reach 80-100% [1, 4]

Open surgical treatment or radiosurgery are other treatments available [1, 2, 4].