Mediastinal myelolipoma/extramedullary hematopoiesis presenting as a mass: rare differential diagnosis among mediastinal tumors.

objectivesMediastinal myelolipoma/extramedullary hematopoiesis presenting as a mass is infrequent and can lead to misdiagnosis. Here we describe a large series aiming to illustrate the clinicopathologic features.

methodsWe retrospectively searched mediastinal tumors and myelolipoma diagnosed at the Department of Pathology, West China Hospital from 2010 to 2015 and collected 14 mediastinal myelolipoma/extramedullary hematopoiesis cases presenting as an encapsulated mass among 1324 mediastinal mass diseases and 252 myelolipomas.

resultsThere were 8 females and 6 males aged from 35 to 67 years old, most of whom were diagnosed incidentally. Cross-sectional imaging revealed encapsulated masses located in the posterior mediastinum with fat and soft tissue density showing heterogeneous enhancement. Radiologic diagnosis was neurogenic tumor for most cases. All but one patient underwent surgery and postoperative pathologic findings showed fat and hematologic elements. Considering the accompanying hematologic disorders, 5 patients were diagnosed as extramedullary hematopoiesis and the remaining 9 as myelolipoma. The average hematopoietic tissue percentage in extramedullary hematopoiesis was 70%, significantly higher than it was in myelolipoma. Patients showed no sign of recurrence or metastasis apart from the patient with hepatocellular carcinoma.

conclusionsMediastinal myelolipoma/extramedullary hematopoiesis is a rare entity of solid tumors in the posterior mediastinum, affecting patients from their third decades, with no sex predilection and lacking unique clinical symptoms, and may be misdiagnosed as a malignant tumor on cross-sectional imaging. The final diagnosis relies on pathologic findings, and the precise classification of myelolipoma or extramedullary hematopoiesis relies on percentage of hematopoietic tissue and accompanying clinical symptoms. Surgery is the recommended treatment.