Extrahepatic Portal Vein Occlusion and Collateral Formation Following Anticoagulant-Induced Thrombosis Regression in a Portal Vein Aneurysm: Potential for Misdiagnosis As Primary Extrahepatic Portal Vein Occlusion.

Both extrahepatic portal obstruction (EHO) and primary extrahepatic portal vein aneurysm (PVA) are rare diseases of the hepatic vascular system with limited understanding of their natural histories. While there is no known relationship between the onset or formation of these two conditions, we encountered a case that may suggest a mutual association. A 40-year-old man was presented to the Department of Gastroenterology at our hospital with complaints of dull abdominal pain and fever. Three years prior, the patient had been incidentally diagnosed with a primary extrahepatic PVA. Due to an inflammatory reaction and elevated hepatic enzymes shown in laboratory data, along with a thrombosis complicating the PVA, anticoagulant therapy was initiated. Following the introduction of this treatment, his abdominal symptoms and inflammatory reaction improved. Subsequent follow-up abdominal imaging showed that both the PVA thrombosis and the aneurysm itself had diminished. The patient's portal vein system ultimately developed EHO with collateral vessels. This case is significant because it suggests a potential etiology for what is conventionally diagnosed as "idiopathic" EHO in adults. It highlights the importance of cautiously diagnosing EHO, considering the possibility that it may develop as a complication of portal vein obstruction caused by PVA thrombosis.