Unilateral pleural effusion with capillary haemangioma

Here, we report a case of haemangioma on middle mediastinum accompanied by unilateral pleural effusion, which was initially suspected to be lung cancer and pleurisy. During annual check‐up, chest radiography of a 30‐year‐old female showed homogeneous opacity in the left lower pulmonary field. Excision was performed, and the mass was pathologically diagnosed as benign mediastinal vascular tumour with exudative pleural effusion. To our knowledge, this presentation occurs in <0.5% of tumours of the mediastinum, and furthermore, the presence of pleural fluid is extremely rare, and the underlying mechanism is unknown. Although mediastinal haemangioma is hard to diagnose without surgery, we should include it in the differential diagnosis of a tumour with unilateral pleural effusion.