Autopsy diagnosis of diffuse intrahepatic cholangiocarcinoma.

Intrahepatic cholangiocarcinoma (ICC), a severe liver cancer, makes up to 20% of all hepatic malignancies and is difficult to diagnose early due to its often asymptomatic nature. This case report documents a rare presentation of ICC with multiple diffuse nodules not previously recorded in medical literature. A 65-year-old man with no significant medical history presented with back pain, anorexia, and significant weight loss. Elevated tumor markers and enlarged lymph nodes were observed, though imaging did not reveal a primary liver mass. Diagnostic efforts, including computed tomography and positron emission tomography scans and biopsies of lymph nodes and bone marrow, suggested adenocarcinoma of unknown primary origin. A definitive diagnosis was only made post-mortem, revealing multiple diffuse nodules in the liver identified as ICC, marking a rare presentation without a primary mass. This case highlights the diagnostic challenges posed by atypical ICC manifestations, where typical imaging does not indicate a primary mass, delaying diagnosis and treatment. The findings emphasize the importance of considering ICC in differential diagnoses in cases of unknown primary adenocarcinoma with liver involvement. The discovery of ICC with diffusely infiltrative nodules underscores the necessity for comprehensive diagnostic evaluations in patients presenting with nonspecific systemic symptoms and abnormal liver findings.