Primary leiomyosarcoma of the portal vein: A progressively enhancing fusiform mass without biliary dilatation as a rare differential for hilar tumors.

Primary leiomyosarcomas of the portal vein are exceedingly rare vascular neoplasms. Given the limited number of reports on their imaging features, achieving an accurate preoperative diagnosis is challenging yet essential for determining the optimal treatment strategy. Here, we report a case of an incidentally discovered primary portal vein leiomyosarcoma in an asymptomatic man in his forties. We emphasize the diagnostic significance of its fusiform intraportal morphology. Unenhanced computed tomography (CT) revealed a distinct 45-mm fusiform mass in the hepatic hilum, while dynamic contrast-enhanced CT showed heterogeneous progressive enhancement without biliary dilatation. Magnetic resonance imaging depicted the tumor as hypointense on T1-weighted images and heterogeneously hypointense on T2-weighted images, with notable diffusion restriction. A percutaneous CT-guided biopsy indicated sarcoma with smooth muscle differentiation, and subsequent surgical resection confirmed leiomyosarcoma originating from the tunica media/adventitia of the portal vein. Recognition of a fusiform, progressively enhancing intraportal mass without biliary dilatation can aid in an early and precise preoperative diagnosis.