Perimedullary AVF¶

Definition¶

A perimedullary arteriovenous fistula (Type IV) is a direct arterial-venous connection on the pial surface of the spinal cord, without an intervening nidus. The anterior spinal artery or posterior spinal arteries directly shunt into a perimedullary vein. Three subtypes exist based on size and flow characteristics.

Subtypes¶

Type IVa — Small, single feeder, low flow. May be clinically silent or cause mild myelopathy.
Type IVb — Medium, multiple feeders, moderate flow. Progressive myelopathy.
Type IVc — Large, giant perimedullary vein, high flow. Can cause mass effect from the giant venous varix in addition to venous congestion.

Imaging Findings¶

MRI¶

Dilated perimedullary veins (flow voids on the cord surface)
Cord edema from venous congestion (similar to dural AVF)
Type IVc may show a large venous varix (round flow void) that can compress the cord
MRI appearance can overlap with dural AVF

Spinal Angiography¶

Direct connection from anterior or posterior spinal artery to perimedullary vein on the cord surface
No nidus (distinguishes from AVM)
The fistula is on the cord surface (distinguishes from dural AVF, which is at the nerve root sleeve)

Clinical Pearl

Perimedullary AVF can be difficult to distinguish from dural AVF on MRI alone — both show cord edema and perimedullary flow voids. Spinal angiography is required to distinguish them because the treatment approaches differ: dural AVFs are treated at the dural sleeve level, while perimedullary AVFs require treatment at the pial surface of the cord.

Key Points¶

Direct fistula on the pial surface of the cord — no nidus
Three subtypes by size and flow (IVa, IVb, IVc)
MRI overlaps with dural AVF — angiography distinguishes them
Type IVc can cause cord compression from giant venous varix
Treatment may include embolization and/or surgery

References¶

Barrow DL, Colohan AR, Dawson R. Intradural perimedullary arteriovenous fistulas (type IV spinal cord arteriovenous malformations). J Neurosurg. 1994;81(2):221-229. https://pubmed.ncbi.nlm.nih.gov/8027805/
Kona MP, Buch K, Singh J, Rohatgi S. Spinal Vascular Shunts: A Patterned Approach. AJNR Am J Neuroradiol. 2021;42(12):2110-2118. https://pmc.ncbi.nlm.nih.gov/articles/PMC8805746/
McCarty J, Chung C, Samant R, et al. Vascular Pathologic Conditions in and around the Spinal Cord. RadioGraphics. 2024;44(9):e240055. https://pubs.rsna.org/doi/full/10.1148/rg.240055
Ji T, Guo Y, Shi L, Yu J. Study and therapeutic progress on spinal cord perimedullary arteriovenous fistulas. Biomed Rep. 2017;7(3):214-220. https://pubmed.ncbi.nlm.nih.gov/28808569/
Phadke RV, Bhattacharyya A, Handique A, et al. Endovascular Treatment in Spinal Perimedullary Arteriovenous Fistula. Interv Neuroradiol. 2014;20(3):357-367. https://pmc.ncbi.nlm.nih.gov/articles/PMC4178764/
Spinal arteriovenous fistula. Radiopaedia.org. https://radiopaedia.org/articles/spinal-arteriovenous-fistula