Behçet's Disease Revealed by a Thrombosed Aneurysm of the Superior Mesenteric Vein: A Case Report

Behçet's disease is a rare multisystemic vasculitis that can involve arteries and veins of all sizes. Vascular involvement is among its most severe manifestations and usually presents as venous thrombosis, whereas venous aneurysms are exceptionally uncommon. We report the case of a 33-year-old woman admitted for abdominal pain, in whom imaging revealed a saccular thrombosed aneurysm of the superior mesenteric vein extending to the portal confluence. The patient had recurrent oral aphthosis, cutaneous lesions compatible with erythema nodosum, arthralgia, a positive pathergy test, and positive HLA-B51 testing. The thrombophilia work-up was negative, and ophthalmological examination was normal. The diagnosis of Angio-Behçet's disease was established according to the International Criteria for Behçet's Disease. She was treated with high-dose corticosteroid pulses followed by intravenous cyclophosphamide and oral prednisone. Anticoagulation was initiated with low-molecular-weight heparin, then switched to vitamin K antagonists and subsequently to apixaban because of INR instability. Serial Doppler ultrasound showed progressive regression of the aneurysm and thrombosis, with partial portal vein recanalization. Given persistent fibrotic retraction of the portal vein and concern for progression toward portal hypertension, infliximab therapy was planned. This case highlights an unusual presentation of Behçet's disease revealed by a thrombosed superior mesenteric vein aneurysm and emphasizes the importance of early recognition, aggressive immunosuppressive treatment, multidisciplinary management, and close radiological follow-up.