Inferior vena cava agenesis (IVCA) is a rare and underdiagnosed congenital anomaly that predisposes to deep vein thrombosis (DVT). Optimal duration of anticoagulant treatment in these patients is not well established.
Observational retrospective study that included all consecutive patients older than 18 diagnosed with IVCA and DVT. Data including demographics, initial clinical presentation, modality of diagnosis, treatment and outcomes were obtained.
In patients with IVCA and DVT (n = 9), mean age was 42 and 66% were males. Five (55,5%) patients had bilateral DVT and the most frequent location was ilio-femoral. Only one patient had concomitant pulmonary embolism (PE). During follow-up (mean of 77.8 months), anticoagulation was withdrawn in 2 patients and both developed recurrence of DVT (22.2%, CI 95% 2.8-60.0). One minor bleeding (11.1%, CI 95% 0.3-48.3), five post-thrombotic syndrome (55.6%, CI 95% 21.2-86.3) and no deaths were registered.
In patients with DVT and IVCA, post-thrombotic syndrome was developed in approximately half of the patients. No major bleeding events were recorded during long-term anticoagulant therapy and recurrences occurred only in patients who had anticoagulation withdrawn. These data suggest that extended anticoagulant therapy might be considered in these patients.

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