Massive pleural effusion due to transdiaphragmatic extension of intrahepatic cholangiocarcinoma

A woman in her 60s presented with dyspnoea and was found to have a massive right pleural effusion. Although pleural fluid cytology was negative, contrast-enhanced CT revealed a large tumour in the right hepatic lobe extending across the diaphragm into the thoracic cavity. Liver biopsy demonstrated poorly differentiated squamous cell carcinoma; however, the primary site could not be definitively determined. Based on the pattern of tumour extension on imaging, the lesion was clinically diagnosed as intrahepatic cholangiocarcinoma (ICC) with transdiaphragmatic extension into the thoracic cavity. Systemic chemotherapy resulted in marked regression of both the intrathoracic lesion and pleural effusion, allowing the patient to be discharged. ICC presenting with massive pleural effusion is rare. This case highlights the importance of integrating imaging and pathological findings when establishing a diagnosis.