A Transverse–Sigmoid Sinus Dural Arteriovenous Fistula with Multi-Compartmental Sigmoid Sinus Architecture Involving Both Normal Venous Drainage and Shunt Outflow

Objective: To report a rare transverse-sigmoid sinus (TSS) dural arteriovenous fistula (dAVF) with complete internal septation of the sigmoid sinus, enabling anatomical separation of shunt flow, normal cortical venous drainage, and successful transvenous Onyx embolization while preserving normal venous return. Case Presentation: A 69-year-old man presented with left-sided pulsatile tinnitus. DSA revealed a TSS dAVF fed by the branches of the ascending pharyngeal, occipital, and middle meningeal arteries. The sigmoid sinus exhibited complete internal compartmentalization; the inner compartment carried a retrograde shunt flow, and the outer compartment maintained antegrade cortical drainage via the lateral tentorial sinus. 3D rotational angiography and fusion imaging clearly delineated the compartments. A 5-Fr SOFIA Select (Terumo Neuro, Tustin, CA, USA) and a GREACH microcatheter (Tokai Medical Products, Aichi, Japan) were used to access the shunt compartment transvenously. After confirming the absence of internal jugular vein opacification, Onyx 18 (Medtronic, Irvine, CA, USA) was injected to completely obliterate the shunt without reflux. Postprocedural angiography revealed complete fistula occlusion and preserved cortical venous drainage. The patient's tinnitus partially resolved, and he was discharged with a modified Rankin Scale score of 1. Conclusion: This case highlights the importance of identifying dural sinus compartmentalization in dAVFs. Preoperative imaging enables compartment-specific embolization while preserving physiological venous drainage. Thrombosis-induced septation may underlie this anatomy, emphasizing the need for tailored endovascular strategies.