Thrombotic risk and features of patients with inferior vena cava agenesis: a multicentre, retrospective, observational study

Inferior vena cava agenesis (IVCA) is a rare anomaly predisposing affected people to lower-limb venous thrombosis with low frequency of pulmonary embolism. Antenatal thrombosis and inherited thrombophilia have been suggested as causes of IVCA. However, there is little evidence on the clinical course and management of this condition. We designed a patient registry to assess the thrombotic risk and features of IVCA. In this this multicentre, retrospective, observational study, we included patients with IVCA diagnosed by routine imaging from 20 hospitals in Spain (n=18), Portugal (n=1), and Italy (n=1). Patients were identified from a systematic search in radiology databases using data extraction software (cohort A) and alternative searches in medical records for confirmed IVCA (cohort B; option allowed when systematic approaches were unapplicable). Primary outcomes were clinical and imaging features, thrombotic risk, phenotype of IVCA-associated thrombosis, anticoagulant treatment, and the results of thrombophilia testing. We included patients with IVCA diagnosed by routine imaging studies done between Jan 1, 2010, and Dec 31, 2022. In the systematic search, 4 341 333 imaging exams were screened from the radiology databases of eight centres. 122 eligible patients were enrolled in cohort A. A further 95 patients were identified by screening medical records at 12 centres, of whom 88 were eligible and included in cohort B, making a combined cohort of 210 patients. 96 (46%) of 210 patients were female and 200 (95%) were European or Hispanic. 60 (29%) of 210 patients had hepatic IVC interruption, whereas 150 (71%) had extrahepatic IVCA. In cohort A, 65 (53%) of 122 patients had venous thrombosis, with an estimated annual risk of 1·15% (95% CI 0·89–1·46). Extrahepatic IVCA was associated with a greater risk of venous thrombosis than hepatic IVCA (56 [67%] of 84 patients vs nine [24%] of 38 patients, odds ratio 5·31, 95% CI 2·27–12·43; p