FINAL DIAGNOSIS: Adrenal gland (adrenalectomy): myelolipoma with extensive recent hemorrhage and necrosis
Myelolipomas are benign biochemically nonfunctioning tumors composed of an admixture of mature adipose tissue and normal hematopoietic cells. The vast majority occur within the adrenal glands, but several extra-adrenal myelolipomas (EAMLs) have been reported. Myelolipomas may be found within cortical adenomas and be associated with clinical evidence of hyperfunction. Several theories regarding the etiology of adrenal myelolipomas have been presented. The most widely accepted theory is that myelolipomas are due to a metaplastic change in the reticuloendothelial cells of blood capillaries in response to stimuli, including necrosis, infection or stress. The term myelolipoma was coined by Oberling in 1929.
Adrenal myelolipomas are rare benign tumors which are composed of hematopoietic elements and varying amounts of mature fat. In addition, these lesions may often contain calcifications. Most patients with adrenal myelolipoma are asymptomatic and the condition is discovered incidentally at autopsy, the incidence ranging from 0.08 to 0.2 percent. The lesions range in size from microscopic collections of fat and hematopoietic elements (myelolipomatous foci) to true "tumors" of up to 26.0 cm in maximum dimension. The typical extra-adrenal myelolipoma (EAML) is a solitary, well-defined mass within the abdomen, most commonly in the retroperitoneal presacral area. EAMLs may produce symptoms related to their mass effect, but they are occasionally incidental findings. Most commonly, patients are older than 40 years and have no hematologic abnormalities. It is important to distinguish EAMLs from other soft tissue tumors, in particular liposarcomas, myxoid malignant fibrous histiocytomas, extramedullary hematopoietic tumors, renal angiomyolipoma, and teratoma.
The key to CT diagnosis is a demonstration of a mass with fatty attenuation (decreased attenuation). The demonstration of fat density within an adrenal mass by CT is virtually diagnostic of adrenal myelolipoma. The sonographic findings are variable but frequently demonstrate mixed regions of hyperechogenicity as well as hypoechogenicity. In addition, calcifications may be demonstrated on sonography. The MR signal characteristics demonstrate high signal on T1 weighted images consistent with the mature fat that is often found in these lesions. Although imaging findings can be diagnostic, the importance of this lesion lies in its recognition as a benign entity. In cases where the imaging findings are inconclusive, a percutaneous biopsy would likely be diagnostic demonstrating tissue consisting of mature fat interspersed with hematopoietic elements resembling bone marrow.
Adrenal myelolipomas usually remain clinically quiescent. Previously, most reported cases were found incidentally at autopsy. Currently, most cases are detected during imaging procedures obtained for other reasons. Occasionally, clinical symptoms, most commonly abdominal pain, develop when the tumors become large. Spontaneous retroperitoneal hemorrhage is a possible complication of all large adrenal tumors. A review of the literature revealed 70 surgically documented cases of adrenal myelolipoma and 36 of these patients had clinical symptoms of abdominal pain or a palpable tumor. Associated medical problems in 53 of the 68 patients with surgically proved myelolipomas were obesity in 17, hypertension in 18 and a variety of chronic diseases in 18.
Management of adrenal myelolipomas should be individualized. Small asymptomatic myelolipomas diagnosed definitively on imaging studies are best followed expectantly. Symptomatic tumors can be treated with surgical excision and/or adrenalectomy.
Contributed by Hunter T Hardy, MD