Answer and Discussion of Quiz Set: K-001

4.    The nature of myelolipoma is most consistent with which of the following?

A.  A true neuoplasm with both the adipocytes and hematopoietic components coming from the same clonal origin.

B.  A hamartoma.

C.  Extrmedullary hematopoiesis in adipose tissue arising in adrenal gland.

D.  Dedifferentiated adrenal cortical cell is the origin of these tumors.

Answer and Discussion: The answer is (A). Recent demonstration of nonrandom x-chromosome inactivation in both the hematopoietic elements and adipocytes indicates that the adipocytes and hematopoietic component in myelipoma have the same clonal origin and porves that both components are neoplastic in nature and are related (Bishop E, Eble JN, Cheng L, et al., Am J Surg Pathol. 2006 Jul;30(7):838-43). Past theories of this tumor including hamartomatous origin, adrenal cortical cells dedifferentiate into adipocytes and hematopoiecit stem cells under the local influence of a hormone, hematopoietic cells differentiating from endothelium of the rich capillary bed of the adrenal glands, and that myelolipoma is a lipomatous site of extramedullary hematopoiesis.