Fine-needle aspiration cytology of retroperitoneal extramedullary hematopoiesis: a case report

We report a 69 year-old man with left renal hilar tumor, which was incidentally detected and clinically suspected to be malignant. Interpretations of fine-needle aspiration (FNA) and frozen section of this tumor were not conclusive, and originally malignancy could not be ruled out. Later, correlation with the patient's history and bone marrow biopsy with cytological and histological pictures resulted in the diagnosis of a tumor of extramedullary hematopoiesis (EMH). This case shows that FNA cytology may be a useful method for diagnosing EMH. However, we also demonstrate the potential pitfall of misdiagnosing atypical megakaryocytes as malignant cells on FNA smears, or even in frozen sections, when clinical history and clinical data are not available. EMH should be considered in the differential diagnosis of patients with bone marrow disorders and mass lesions in extramedullary sites.