Chylous pleural effusions simulating leukemic infiltrate associated with thoracoabdominal disease and surgery in infants.

Surgical procedures and diseases in childhood involving damage to or obstruction of the thoracic duct and related lymphatic channels can cause pleural effusions that are often chylous and can be massive. The morphology of fluid cytology in these cases can prompt a mistaken diagnosis of a hematolymphoid malignancy. We describe 6 infants, aged 3 days to 5 months, in whom thoracoabdominal disease and/or surgical procedures interfered with lymphatic drainage of the thorax and pleural space. In 5 cases, the clinically significant chylous pleural effusion was postoperative; in 1 case, it was related to congenital abnormalities. After chest tube drainage, the effusion resolved in all cases. Fluid cytology revealed a predominant population of small to medium immature-appearing cells with moderate amounts of basophilic cytoplasm without granules. The nuclei were often irregular or slightly lobulated, with evenly dispersed chromatin and occasionally prominent nucleoli. Flow cytometry performed on these cases revealed a heterogeneous population of lymphoid cells, most of which showed phenotypic markers typical for mature T cells. A complete patient history and ancillary studies in such cases can correctly characterize the cells to reach an accurate diagnosis.