Obturator Hook Sign as a Marker of Chronic Iliofemoral Venous Outflow Obstruction in Computed Tomography Venography – Multicentric Evaluation of Incidence and Clinical Significance

Abstract

Introduction: Chronic iliac venous outflow obstruction is a common condition that has been increasingly recognized as a causal factor in patients with both post-thrombotic syndrome (PTS) and nonthrombotic iliac vein lesions (NIVL). Diagnosis is challenging, and there is no gold standard diagnostic method. The aim of this paper is to describe the “Obturator Hook Sign” (OHS), a distinctive dilated angled vein, similar to a hook. It is identified mainly in Direct Computed Tomography Venography (DCTV), evidencing obturator vein engorgement as a marker of hemodynamically significant collateralization and representing an indirect sign for chronic iliac vein outflow obstruction. Methods: All CTVs of lower limbs performed from January 2014-August 2018 in Galway University Hospitals and the Galway Clinic were retrospectively reviewed. Data was analysed using SPSSv25.0. Results: In total, 531 CTV's were reviewed, of which 122 (23%) were performed for acute DVT, 183 (34.5%) for post-iliac stenting follow-up and 109 (20.5%) for etiologic study of CVD. OHS was identified in 73 CTV's: 29 Direct CTV's (40.3%) and 44 Indirect CTV's (10.6%). Two groups were defined depending on whether OHS was present, and significant predictors were identified: female sex (p=0.003), younger age (p=0.0004), DCTV (p< 0.0001), NIVL (p< 0.001), past history of iliofemoral DVT (p=0.002) and dilated pelvic veins (p< 0.0001). Obturator hook sign was significantly more common in chronic occlusions, when compared to chronic stenosis or acute occlusion (p< 0.0001). Findings from CTV were compared with results from ascending venography used as gold standard, and the sign proved to have high specificity (99.58% 95%c.i. 97.69-99.99%) and high positive predictive value (98.63% 95%c.i. 90.97-99.81%), while sensitivity and negative predictive value were relatively low (24.66% 95%c.i. 19.82-30.02% and 51.97% 95%c.i. 50.31-53.61%). Conclusion: The identification of haemodynamically 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 which is straightforward to identify, particularly in DCTV, immediately pointing us towards hemodynamically significant chronic iliac venous outflow obstruction diagnosis. It presents an exceedingly high specificity and positive predictive value, and although it is too early to call it pathognomonic, perhaps comparative analysis involving data from additional centres could lead to this conclusion. Disclosure: Nothing to disclose