Monday 16 September 2013
(myelo-, from the ancient greek μυελός, marrow; lipo, meaning of, or pertaining to, fat; -oma, meaning tumor or mass); nodular extramedullary hematopoiesis
Definition: Myelolipoma is a benign tumor-like lesion composed of mature adipose (fat) tissue and haematopoietic (blood-forming) elements in various proportions. Myelolipomas can present in the adrenal gland, or outside of the gland.
Microscopy associates mature and immature hematopoietic tissue, lymphoid aggregates and mature adipocytes.
Myelolipomas arising in extra-adrenal sites are rare. Extra-adrenal myelolipomas may have a predominance of either the hematopoietic or fatty component, chiefly the latter, and generally have a more conspicuous lymphocyte population.
Although the components of these tumors are the same, we consider them separable clinically, pathogenetically and, in many cases, pathologically.
Extra-adrenal myelolipomas are single and usually occur within the abdomen. Extramedullary hematopoietic tumors have a predominance of the hematopoietic component, with erythroid hyperplasia of that component.
Myelolipomas are rare. They have been reported to be found unexpectedly at autopsy in 0.08% to 0.4% of cases (i.e.: somewhere between 8 per 10,000 and 4 per 1,000 autopsies). There is no gender predilection, males and females are affected equally. The peak age range at diagnosis is between 40 and 79 years of age.
adrenal gland (about 3% of all adrenal tumours) (adrenal myelolipoma)
mediastinum (mediastinal myelolipoma, pleural myelolipoma)
liver (hepatic myelolipoma)
gastrointestinal tract (digestive myelolipoma)
presacral myelolipoma (7051876)
- hemolytic anemia with pyruvate kinase deficiency (6708396)
Considered in the differential diagnosis are reactive extramedullary hematopoietic tumors that usually occur in patients with severe chronic anemias.
Patients with extramedullary hematopoietic tumors are characterized by anemia, frequent hepatosplenomegaly and abnormal peripheral blood smears, and may be any age.
The tumors are usually multiple and usually located in the mediastinum or epidural space.
In contrast, patients with extra-adrenal myelolipomas are usually older than 40 years, have normal blood studies, absent hepatosplenomegaly, and usually have chronic debilitating diseases or endocrinopathies.