- BACKGROUND AND PURPOSE Intracranial hypertension develops in only some patients with lateral sinus thrombosis (LST), for reasons that are unclear. The purpose of this study was to evaluate a possible association between patency of the unaffected sinus and clinical presentation of unilateral LST. METHODS A computerized search identified patients with LST, hospitalized in Soroka Medical Center. Patients with signs of increased intracranial pressure (iICP) and those with normal intracranial pressure (nICP) were compared. CT venography or MR venography confirmed the diagnosis, located the thrombosis, and determined the dominant lateral sinus (LS). Diameters of the right and left LSs (the occluded and unaffected) were compared to the diameter of the distal superior sagittal sinus (SSS). RESULTS Of the 50 patients identified, 30 had iICP and 20 nICP. The dominant LS was the right one in 39 (78%) and the left one in 8 (16%); 3 (6%) had equal LS dominance. The dominant sinus was affected in 32 (70%) and the non-dominant in 15 (30%) patients. iICP was detected in 28/32 (81%) of patients with the dominant side affected, and 3/15 (20%) of those with non-dominant thrombotic sinus (P = .002). The unaffected sinus was narrower in iICP patients (size relative to SSS diameter = 43% in iICP vs. 86% in nICP [P = .0002]; size grading, according to Farb's method was 1.86 in the iICP vs. 3.57 in the nICP group [P = .0001]). CONCLUSIONS Thrombosis was more common in the dominant LS. Unaffected LS patency appears to be associated with the development of increased ICP.