Adrenal Myelolipoma: A Histomorphologic Reappraisal.
Melike Pekmezci, Guliz A Barkan, Girish Venkataraman, Gladell P Paner. Loyola University Medical Center, Maywood, IL; University of Chicago Hospital, IL
Background: Adrenal myelolipoma (AML) are believed to be clonal proliferation of both its adipose tissue and hematopoietic elements. Variations in these 2 components can occur, and features unique or comparable to elements in other related processes [e.g. intra-adrenal fats/lipomas, extramedullary hematopiesis (EMH)] and normal bone marrow (BM) that may enhance its morphologic diagnosis has not been fully studied.
Design: We performed a detailed morphologic review of histologic and/or hematologic features 16 AML (12 surgical, 4 autopsies), 6 intra-adrenal fats/lipomas, 2 EMH, and 16 age-matched NBM.
Results: All AML arose intra-adrenally and were non-encapsulated. However, large AML characteristically pushed and "acquired" the native adrenal capsule, and occasional thin to subtle strips of compressed adrenal cortical cells were seen at the pushed capsule. When within the adrenal parenchyma, AML mostly had pushing borders (14/16) with relatively regular boundary from surrounding adrenal tissue. In contrast, adrenal fats/lipomas mostly had foci of adrenal parenchyma intermingled with the fat. Old hemorrhage was present focally (12/16). Fat necrosis was seen in 2/16 AML presumed to be due to large tumor size (9.5 cm and 16.5 cm). AML size varied significantly (0.2 cm to 16.5 cm). In addition, there were 2 “early foci” AML characterized by microscopic intra-parenchymal adrenal fat admixed with very few hematopoietic cells, mainly erythroid precursors without obvious megakaryocytes. AML can be “fat predominant” (≤25% cellular) in 11/16 and hematopoietic elements were focal to rare (≤5% cellular) in 5/16. There was no “fat poor” (>75% cellular) AML, as opposed to EMH (1/2). Hematopoietic elements showed erythroid predominance (M:E ratio<1) in 10/16 AML unlike in the age-matched NBM. In contrast to NBM, all AML cases showed left shift in myeloid series, prominent in 14/16 and minimal in 2/16. Myeloid left shift was also prominent in 2 EMH. Megakaryocytes were identified in 13 AML ranging from 1/10HPF to 97/10HPF. All 3 AMLs without megakaryocytes were tumors less than 0.2 cm in size. Some AML contained naked megakaryocytes (5/12) and rare micromegakaryocytes (5/12).
Conclusions: Tissue components of AML possesses unique features distinct from adrenal fat/lipomas. Likewise, hematopoietic elements of AML show distinct features from NBM. Recognization of these unique morphologic features and its spectrum of histologies may help in the accurate diagnosis of AML.
Tuesday, March 1, 2011 1:00 PM
Poster Session IV # 162, Tuesday Afternoon