Background <p>Primary splenic angiosarcoma is a rare aggressive vascular neoplasm. Although hepatic metastases are common, diffuse intrasinusoidal hepatic involvement is extremely rare and poses a significant diagnostic challenge.</p> Case report <p>A 60-year-old woman presented with bilateral lower extremity edema, hypoalbuminemia, and thrombocytopenia. Contrast-enhanced computed tomography revealed marked splenomegaly, but no distinct hepatic lesions. Gadoxetic acid-enhanced magnetic resonance imaging revealed reduced hepatic uptake without focal abnormalities. ¹⁸F-fluorodeoxyglucose positron emission tomography–computed tomography revealed diffuse radiotracer uptake in both the liver and spleen, raising the suspicion of an infiltrative malignant process, such as lymphoma. Liver biopsy revealed sinusoidal infiltration by atypical cells positive for cluster of differentiation 31 and <i>ETS</i>-related gene, but lacked architectural features diagnostic of angiosarcoma. Due to diagnostic uncertainty and concerns regarding splenic rupture, splenectomy was performed. Histopathological examination confirmed a primary splenic angiosarcoma with diffuse intrasinusoidal hepatic metastasis.</p> Conclusion <p>Primary splenic angiosarcoma rarely presents with non-nodular intrasinusoidal hepatic metastasis, mimicking infiltrative liver diseases. Liver biopsy may fail to yield a definitive diagnosis. Therefore, a splenectomy may be required to establish a definitive diagnosis and guiding appropriate management when liver biopsy is inconclusive. Recognizing this uncommon metastatic pattern is crucial to avoid misdiagnosis and ensure timely treatment.</p>