Rapidly progressing lepidic pulmonary metastases from a treated poorly differentiated hepatocellular carcinoma demonstrating new pathologic features of cholangiocarcinoma: A potential diagnostic pitfall that may mimic pneumonia.

Although the lung is a common site for metastatic disease from extrathoracic malignancies, a pattern of lepidic growth of these metastases is considered rare. A 67-year-old man with a history of partial hepatectomy for hepatocellular carcinoma (HCC) presented to our hospital with dyspnea and a nonproductive cough. Chest radiographs and computed tomography imaging demonstrated consolidation in the right upper lobe and an ipsilateral pleural effusion. Findings were initially suspected to be secondary to infection, given the radiographic appearance and the rapid development from a normal computed tomography 3 months previously. However, the patient did not have convincing clinical evidence of pneumonia, and after little change after antibiotic therapy, a thoracentesis and pleural biopsy were performed that were positive for malignancy. Although immunostaining and morphology closely resembled the patient's primary HCC, new pathologic features of cholangiocarcinoma were found. We herein report the first case of rapidly progressing lepidic pulmonary metastases from an HCC that dedifferentiated into a hepatocholangiocarcinoma.