Evaluation of incidence and clinical significance of obturator hook sign as a marker of chronic iliofemoral venous outflow obstruction in computed tomography venography

Abstract

ObjectiveThe aim of this paper was to describe the obturator hook sign (OHS), a distinctive dilated angled vein similar to a hook, by computed tomography venography (CTV). It is identified mainly on direct CTV (DCTV) as opposed to indirect CTV (ICTV), evidencing obturator vein engorgement as a marker of hemodynamically significant collateralization and representing an indirect sign for chronic iliac vein outflow obstruction. MethodsAll CTV studies of lower limbs performed from January 2014 to August 2018 in Galway University Hospital and the Galway Clinic were retrospectively reviewed. Data were analyzed using SPSS software (version 25.0; IBM Corp, Armonk, NY). ResultsIn total, 531 CTV studies were reviewed, of which 122 (23%) were performed for acute deep venous thrombosis, 183 (35%) for follow-up after iliac stenting, and 109 (21%) for etiologic study of chronic venous disease. For the purpose of analysis for the presence of OHS, only first-time CTV studies were included in patients who were never submitted to venous intervention (n = 296), of which 40 were DCTV (14%) and 256 were ICTV (86%). Two groups were defined according to whether OHS was present, and significant predictors were identified: female sex (P = .038), younger age (P < .0001), DCTV (P < .0001), nonthrombotic iliac vein lesion (P < .001), past history of iliofemoral deep venous thrombosis (P < .0001), and dilated pelvic veins (P < .0001). OHS was significantly more common in chronic occlusions compared with chronic stenosis or acute occlusion (P < .0001). Findings from DCTV and ICTV were compared with results from ascending venography as the “gold standard,” and the sign proved to have high specificity and positive predictive value (100% for both tests), whereas sensitivity and negative predictive value were low for both DCTV (65% [95% confidence interval (CI), 43%-84%] and 11% [95% CI, 7%-18%], respectively) and ICTV (8% [95% CI, 4%-14%] and 6% [95% CI, 9%-20%], respectively). From analysis of the remaining CTVs, particularly follow-up after iliac stenting, an interesting fact was recognized: successful venous stenting was associated with OHS disappearance, and stent occlusion was also sometimes associated with OHS reappearance or appearance de novo. ConclusionsThe identification of hemodynamically significant lesions in patients with clinically significant chronic venous disease is the aim of any form of imaging. In this study, we have depicted a previously undescribed sign that is straightforward to identify, particularly in DCTV, immediately pointing us toward hemodynamically significant chronic iliac venous outflow obstruction diagnosis. It is too early to call it pathognomonic, but perhaps comparative analysis involving data from additional centers could lead to this conclusion.