Sub-Torcular Cranial Venous Outflow in Intracranial Venous Hypertension: Anatomic and Hemodynamic Insights Following Venous Sinus Stenting

BACKGROUND AND PURPOSE: Venous sinus stenosis is a recognized cause of venopathic intracranial hypertension (VIH) and a therapeutic target in idiopathic intracranial hypertension (IIH). Previously observed sub-torcular venous collateral flow is poorly classified, and their dynamics following venous sinus stenting (VSS) remain poorly understood. This study aimed to better describe these venous collaterals in patients undergoing VSS. MATERIALS AND METHODS: We retrospectively reviewed consecutive adults who underwent VSS for venous sinus stenosis with high-resolution 2D venography between January 2024 and June 2025. Three neurointerventional reviewers independently classified collaterals by anatomical origin: Type 1 (torcula/transverse origin), Type 2 (sigmoid sinus origin), or Type 3 (jugular bulb origin). Pre- and immediate post-stent venograms were qualitatively assessed for collateral flow resolution and quantitatively analyzed to calculate percent change in collateral areas and Jaccard similarity indices following spatial alignment. RESULTS: The cohort comprised 41 unique patients who underwent 48 VSS procedures (92% female; mean age 38.5 ± 12.2 years). Among the 48 procedures, sub-torcular collaterals were present in 46 (96%): Type 1 in 21 (44%), Type 2 in 14 (29%), and Type 3 in 30 (63%); 17 procedures (35%) had multiple types. Expert interobserver agreement was almost perfect for Type 1 and substantial for Types 2 and 3 (Fleiss κ=0.856, 0.745, and 0.687, respectively). Qualitative post-stenting collateral status differed between Types 1 and 3 (p=0.02). Type 3 channels remained angiographically opacified in 16/30 procedures, whereas Type 1 flow more often decreased (11/21) or was no longer opacified (7/21). Quantitatively (n=29), neither median percent change in area (Type 1: 13.22% vs Type 3: 16.32%, p=0.76) nor Jaccard index (Type 1: 57.56 vs Type 3: 63.67, p=0.24) differed significantly. CONCLUSIONS: Sub-torcular venous collaterals are common in patients with VIH undergoing VSS and can be classified by anatomical origin. Jugular bulb-origin collateral flow decreased less often post-stenting than torcular-origin collaterals, a difference more apparent on qualitative assessment than on current quantitative metrics. These findings suggest that subtorcular venous collateral assessment can be standardized despite clinical variability and that such pathways represent a component of cerebral venous adaptation in the setting of venous sinus stenosis.