Osseous metaplasia in adrenal myelolipoma; second documented case in human literature

Abstract

Adrenal myelolipomas are rare benign tumors composed of mature adipose and hematopoietic tissue.  The prevalence of adrenal myelolipoma on autopsy is 0.08-0.4%.  Osseous metaplasia within myelolipoma is an extremely rare pathology, with few cases reported in the literature. This study aims to report a case of adrenal myelolipoma with osseous metaplasia, a pathology only reported once in human studies, and to evaluate its clinical and pathological characteristics. A 75-year-old female with a history of hypertension, diabetes, and hyperlipidemia presented with left flank pain. An MRI of the abdomen revealed a left adrenal mass (7x6x5 cm). Preoperative hormonal evaluation, including serum cortisol and plasma metanephrines, were unremarkable and ruled out a functional adrenal tumor.  An uneventful robotic assisted adrenalectomy was performed. The resected specimen was an encapsulated adrenal and mass measuring 5.8x5.1x4.8 cm and weighed 78 g. There were areas of hemorrhagic and fatty tissue. Findings were consistent with a left adrenal myelolipoma with osseous metaplasia, calcification, and fibrosis. She had an uncomplicated postoperative course and was discharged on post operative day two. Adrenal myelolipomas are a rare pathology, accounting for only 2-4% of adrenal tumors. Though the etiology remains unclear, the most widely accepted theories are adrenocortical cell metaplasia of the reticuloendothelial blood capillaries or bone marrow cells embolism and hypertrophic reticulum cells.    While adrenal myelolipomas are most commonly found incidentally, CT scan is the most sensitive in detecting fat, and therefore detecting these tumors. Most patients are asymptomatic, but larger tumors have been shown to be associated with flank, abdominal and back pain. Most tumors are hormonally inactive, but 10% are hormonally active tumors. Metaplasia can occur due to many conditions including vitamin A deficiency, neoplasia, stress, and chronic inflammation. It was discovered in the adrenal cortex of the two-toed sloth that showed erythroid and myeloid elements. To the best of our knowledge there is only one reported similar case in the human study literature, which documented a patient with hypertension, diabetes, and Cushing syndrome with an adrenal mass. The resected specimen pathology was consistent with mature adipose tissue and areas of osseous metaplasia. Adrenal myelolipoma with osseous metaplasia is an extremely rare pathology, To the best of our knowledge and literature review there is only one case documented in humans. Further evaluation is needed to determine the prognostic factors and sociodemographic associations associated with adrenal myelolipomas exhibiting these specific pathologic characteristics.