Leukaemic Effusion or Extramedullary Haematopoiesis?

We describe a case of leukaemic pleural effusion in a patient with acute myeloid leukaemia and marked marrow fibrosis. Cytologic evaluation of the pleural fluid revealed numerous large atypical cells, morphologically consistent with dysplastic megakaryocytes. This case underscores an important diagnostic pitfall, as such findings may be misinterpreted if the possibility of leukaemic infiltration is not considered. It highlights the critical importance of recognising key cytomorphologic features and integrating immunophenotyping, clinical history and radiologic findings to arrive at an accurate diagnosis. Awareness of this potential presentation is essential to avoid misclassification and ensure appropriate clinical management.