Myelolipoma : Pathogenesis
Pathogenesis: Many myelolipomas arise in association with hormonally-active adrenal tumors, including adrenal cortical adenomas, adrenal cortical carcinomas, pheochromocytomas, and adrenal ganglioneuromas. Some arise in the setting of congenital adrenal hyperplasia (21-hydroxylase deficiency). It has been hypothesized that metaplasia of undifferentiated adrenal stromal cells under the influence of hormones leads to the formation of adrenal myelolipomas. For extraadrenal myelolipomas, the cell of origin is choristomatous hematopoietic stem cell rests. Some cases of myelolipoma with t(3;21)(q25;p11) have been documented. Most myelolipomas have non-random X-chromosome inactivation and both hematopoietic and adipose tissue are derived from the same clone (clonal). These studies suggest that myelolipoma should be considered to be a true neoplasm. The image shows normal trilineage hematopoiesis and a few fat cells in an adrenal myelolipoma.