Risk of recurrence of unusual site venous thromboembolism.

The term unusual site venous thrombosis defines uncommon clinical manifestations of venous thromboembolism occurring in sites different from the lower limbs or the lungs, with peculiar pathophysiological features and clinical history. Information on long-term outcomes of unusual site thrombosis is generally scant, because most studies are small and usually retrospective. Recurrence rate of cerebral vein thrombosis is about 2/100 patient-years; the only identified predisposing factors have been male gender and personal history of thrombosis. Retinal vein occlusion showed a recurrence in the same eye of 2.5% and in the fellow eye of 11.9% within four years. Hypercholesterolemia, hypertriglyceridaemia and hyperhomocysteinaemia were significantly associated with recurrent events. Recurrence rates of splanchnic vein thrombosis are difficult to estimate given the heterogeneity of patient populations; higher recurrence rates are reported in the cirrhotic population (from 27% to 38.5%). Hormone therapy, myeloproliferative neoplasm or other prothrombotic states, and absence of anticoagulant therapy emerged as independent prognostic factors. Future studies should aim at better assessing the risk of recurrence in different patients subgroups and at identifying more accurate prognostic markers.