Adrenal Myelolipoma vs. Adrenocortical Adenoma with Lipomatous Metaplasia: The Importance of Differentiation

Introduction:
Adrenocortical adenomas (ACAs) are benign neoplasms of the adrenal gland and are the most common cause of ACTH-independent Cushing’s syndrome. ACAs can be difficult to differentiate from adrenal myelolipomas on imaging however doing so can impact clinical decision making, as illustrated by this case.

Case Description:
A 52-year-old female with a history of type 2 diabetes and hypertension presented with a six-year history of progressive muscle cramping, proximal upper and lower extremity muscle weakness, abdominal weight gain, easy bruising, and rounded face. She was found to have left 6.8 x 6.2 cm adrenal incidentaloma (AI) with atrophy of the contralateral adrenal gland. Workup for hypercortisolism demonstrated elevated late-night salivary cortisol levels: 0.150, 0.114, and 0.184 (ref: 0.010 – 0.090 ug/mL) and two separate non-suppressive cortisol levels with 1 mg dexamethasone suppression test (cortisol levels 11.7 and 11.2 respectively). An 8 AM cortisol level was 12.3 with ACTH <1.5 (ref: 7.2 – 63.3 pg/mL).

The CT imaging report described the lesion as having several small areas with macroscopic fat consistent with a myelolipoma. Myelolipomas are usually clinically silent, so the lesion was not felt to be the source of the hypercortisolism and so adrenal vein sampling for cortisol-producing lesion localization was proposed. The patient was referred to another endocrinology for a second opinion. Imaging was reviewed and not felt to be consistent with a myelolipoma. Because of this, and the contralateral adrenal gland atrophy, it was determined that the adrenal lesion was the cause of the hypercortisolism and adrenal vein lateralization testing would not be necessary. The patient underwent uncomplicated left adrenalectomy and pathology demonstrated an adrenocorticoid adenoma with lipomatous metaplasia. The patient had significant symptom relief post-operatively and is clinically doing well.

Discussion:
Typical imaging features of ACAs are homogenous, small, and well-circumscribed. They most commonly occur in women between the 4^th and 8^th decade of life, are associated with hypertension and diabetes, and typically occur in the left adrenal gland. However, they can have atypical imaging features, particularly with regards to lipid content making it hard to differentiate them from adrenal myelolipomas. Though there have been some reports of adrenal myelolipomas secreting excess adrenal hormone these neoplasms are typically though of as clinically silent.

This case highlights the importance of personal review of patient imaging as well as maintaining a suspicion for atypical appearing ACAs to avoid misclassifying an adenoma or delay in diagnosis or treatment of a functioning tumor.