The arrow-tipped loop is a marker of radiculomedullary vein thrombosis linked to the anti-reflux mechanism—angiographic anatomy and clinical implications

Introduction: This article proposes that the “arrow-tipped” loop or anastomosis classically described as an anatomic variant represents in fact a pathological phenomenon resulting from the partial thrombosis of a radiculomedullary vein (RMV) with a duplicated origin (double-rooted RMVs).

Methods: The arrow-tip loop concept proposed in this report is illustrated with angiographic observations of patients with underlying pathologies of the spinal venous system, three cases of spinal arteriovenous fistulas, and one case of spinal venous insufficiency.

Conclusion: While a thrombosed single-rooted RMV typically becomes anatomically and angiographically undetectable, double-rooted MRVs keep a flowing proximal segment made of their two rootlets of origin. This residual proximal segment takes the appearance of an arrow-tip loop, which therefore be seen as an indicator of spinal venous thrombosis.

Results: In each clinical case, the presence of arrow-tip loops was associated with diffuse alteration of the perimedullary venous system, including the lack of detectable RMVs. The angiographic appearance of the arrow-tip loops suggested partially thrombosed double-rooted RMVs, with rootlets originating either from the anterior or posterior spinal veins, or from both.