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Neuroradiology Case of the Week

Case 298

Scott Rudzinski, Sudhir Kathuria, MD, and P-L Westesson, MD, PhD, DDS

Clinical Presentation: An 85-year-old man with previously diagnosed prostate cancer now presents with new onset of seizures also associated with progressive right extremity weakness.

Imaging Findings: The patient's first MR shows subtle leptomeningeal enhancement of the left frontoparietal region on T1WI (Fig. 1) and subcortical edema in the same region on T2WI (Fig. 2). One month later, a new MR shows increased edema and gyral enhancement of the left frontoparietal region (Fig. 3). Selective conventional angiogram of the left external artery demonstrates the site of fistula from frontoparietal branch of the middle meningeal artery (Fig. 4). CTA reconstruction shows prominent veins along the pial surface of the brain (Fig. 5).

Diagnosis: Dural arteriovenous fistula

Discussion: Intracranial dural arteriovenous fistulas (dAVFs) represent 10-15% of all cerebral vascular malformations with AV shunting. Although dAVFs can occur anywhere in the dura mater covering the brain, they occur most frequently in the cavernous and transverse-sigmoid sinus. Two distinctions of dAVFs exist, the more common adult-type, usually presenting in middle to old age, and the rare infantile-type. Adult dAVFs are usually acquired, and may be idiopathic or can occur in response to trauma, venous occlusion, or venous hypertension. The most probably etiology is neoangiogenesis due to poor venous drainage. There is no predilection of sex or ethnicity. Patients with benign dAVFs may be asymptomatic or may manifest with tinnitus or orbital venous congestion, and most have an excellent natural history. Aggressive dAVFs have retrograde leptomeningeal venous drainage (RLVD) and can present with CNS symptoms including focal neurological deficits, seizures, intracranial hypertension, and altered mental status.

     Cognard, et al. described a classification that correlates venous drainage pattern, which is listed as follows (hemorrhage rate described in parentheses):
              I    – Antegrade sinus drainage
              II   – Insufficient antegrade sinus drainage
              IIa – Retrograde sinus drainage only
              IIb – Retrograde cortical venous reflux (CVR) only (10-20% hemorrhage rate)
              III  – CVR only without venous ectasia (40% hemorrhage rate)
              IV – CVR only with venous ectasia (66% hemorrhage rate)
              V  – Spinal venous drainage

     The best imaging tool for dAVFs is digital subtraction angiography with superselective catheterization of dural, transosseous feeders. CT is most often normal, but may show tortuous dural feeders and an enlarged dural sinus. On MR images, dilated pial vessels (signal voids), diffuse white matter edema, and diffuse contrast material enhancement are signs of aggressive dAVFs. However, MR findings may be variable according to the degree of venous congestion and the regional venous anatomy (collaterals). T2WI can also show flow voids and may show focal hyperintensity in adjacent brain. Suspicious flow void clusters around the dural venous sinus should alert one to the possibility of dAVF, and lead to further workup. DWI is normal unless there is venous infarct or ischemia. dAVFs may be better appreciated on MRA by detecting venous flow-related enhancement. MRV may detect an occluded parent sinus or collateral flow.
     On angiography the most common site of dAVFs is the wall of the transverse or straight sinus (35-40% of all dAVFs). Multiple arterial feeders are typical with branches from the external carotid artery most commonly. The involved dural sinus may be thrombosed. Arterial inflow into a paralleled venous channel, or recipient pouch, is commonly seen. Flow reversal in dural sinus and cortical veins correlates with progressive symptoms and risk of hemorrhage.
     Clinical course depends on location and venous drainage pattern. The most aggressive dAVFs are those in the tentorium and those with RLVD. Ninety-eight percent of dAVFs without RLVD have a benign course, and can be observed depending upon clinical symptoms. Treatment options of aggressive dAVFs include endovascular intervention, surgical resection, and stereotaxic radiosurgery generally in combination.

References:

1. Harnsberger HR. Diagnostic Imaging: Head and Neck. Amirsys, UT. 2004.
2. Cognard C, Gobin YP, Pierot L, Bailly AL, Houdart E, Casasco A, Chiras J, Merland JJ. Cerebral dural arteriovenous fistulas: clinical and angiographic correlation with a revised classification of venous drainage. Radiology. 1995 Mar;194(3):671-80. [Medline]
3. Kiyosue H, Hori Y, Okahara M, Tanoue S, Sagara Y, Matsumoto S, Nagatomi H, Mori H. Treatment of intracranial dural arteriovenous fistulas: current strategies based on location and hemodynamics, and alternative techniques of transcatheter embolization. Radiographics. 2004 Nov-Dec;24(6):1637-53. [Medline]
4. Kwon BJ, Han MH, Kang HS, Chang KH. MR imaging findings of intracranial dural arteriovenous fistulas: relations with venous drainage patterns. AJNR Am J Neuroradiol. 2005 Nov-Dec;26(10):2500-7. [Medline]
5. Lee SK, Willinsky RA, Montanera W, terBrugge KG. MR imaging of dural arteriovenous fistulas draining into cerebellar cortical veins. AJNR Am J Neuroradiol. 2003 Sep;24(8):1602-6. [Medline]