Case of the Week

Background:

Dural arteriovenous fistulas (DAVFs) are pathologic shunts between dural arteries and dural venous sinuses. They account for 10–15% of cerebral vascular malformations and usually present in adulthood. They most commonly drain into the sigmoid, transverse, or cavernous sinuses. Most DAVFs are idiopathic, but they can occur following trauma or venous sinus thrombosis. The presence of cortical venous drainage is considered an aggressive feature in both the Borden and Cognard classification systems.

Clinical Presentation:

On examination, the patient displayed a broad-based gait and intention tremor. There were no sensory deficits suggesting a sensory ataxia. The Romberg sign was positive. In general, DAVF presentation relates to the pattern of venous drainage. Pulsatile tinnitus is one of the more common symptoms relating to lesions draining into the transverse or sigmoid sinuses. Additional posterior fossa AVF presentations include cerebellar symptoms, cranial nerve abnormalities, and intracranial hemorrhage.

Key Diagnostic Features:

• CT findings: CTA may show tortuous feeding arteries and stenosis or thrombosis of the dural venous sinus. Dilated vascular channels from transcalvarial perforating branches may be apparent.
• MRI findings:
  • T2: Serpiginous flow voids, edema relating to venous stasis, isointense sinus due to thrombosis
  • GRE: Potential blooming from thrombosed sinus
  • Contrast-enhanced MRA: shows angioarchitecture; time-resolved MRA may confirm the presence of an arteriovenous shunt
• DSA findings: may show feeders including dural or transosseous ECA branches, thrombosis/stenosis of involved sinus, flow reversal in dural sinus/cortical veins correlating with higher risk of hemorrhage, pseudophlebitic pattern of tortuous pial veins also correlating with higher risk of hemorrhage.

Differential Diagnoses:

• Neurodegenerative processes such as multiple system atrophy type C: would lack flow voids and present with a flattened and atrophied pons and medulla with the classic pontine hot cross bun sign.
• Paraneoplastic cerebellar degeneration: would likely display atrophy on MRI given progressive course.
• Genetic causes such as fragile X-associated tremor/ataxia syndrome: would likely present with cerebellar atrophy,

Treatment:

• Endovascular embolization (both transarterial and/or transvenous approaches): treatment decisions are made based on the angioarchitecture of dAVF, brain parenchymal region involved, and the direction of venous flow. If interventional management is difficult, surgery and, to a lesser extent, stereotactic radiosurgery can be offered.