Case Report: Adult-onset diffuse hepatic hemangiomatosis with rapid progression: an autopsy case with diagnostic difficulty.

Diffuse hepatic hemangiomatosis (DHH) in adults is a rare benign vascular tumor of the liver that histologically resembles a hepatic hemangioma but is characterized by an infiltrative growth pattern despite the absence of cytologic atypia typical of hepatic angiosarcoma. Although generally indolent, its clinical course is variable, and rapidly progressive or fatal cases have been reported. Due to its rarity and overlapping radiological and histopathological features with those of other vascular lesions, its diagnosis can be challenging. We present the case of a 51-year-old female with multiple hepatic lesions, initially suspected to be hepatic hemangiomas. Six months later, the lesions had progressed rapidly. A percutaneous liver biopsy revealed dilated sinusoids lined with endothelial cells without marked atypia, thus suggesting a benign vascular lesion. However, the rapid clinical course raised concerns regarding hepatic angiosarcoma, and the patient received weekly paclitaxel followed by durvalumab. No therapeutic response was observed, and the patient died of tumor rupture. Autopsy revealed diffuse replacement of the hepatic parenchyma with multiloculated cystic vascular spaces lined with pleomorphic endothelial cells. No histological heterogeneity or extrahepatic lesions are observed. These findings supported the diagnosis of DHH. This case report contributes to the current knowledge of the clinical and pathological features of this rare entity. In addition, pleomorphic endothelial cells observed during autopsy may be attributable to treatment-related artifacts.