This article is more than 5 years old. Information may no longer be current.
Adrenal mass with macroscopic fat found during routine imaging
Click Here to Manage Email Alerts
A 55-year-old obese man was referred for the evaluation of a right adrenal mass. A CT of the abdomen was performed for abdominal pain and chronic constipation. The CT of the abdomen showed a round well-circumscribed suprarenal lesion measuring 3.8 cm x 3.2 cm x 3 cm. The mass was heterogeneous with internal areas of hypoattenuation consistent with fatty tissue and did not enhance with IV contrast (Figures 1A,B).
Stephanie L. Lee
His physical exam showed normal vital signs with a blood pressure of 124 mm Hg/76 mm Hg. Laboratory testing showed a serum sodium 142 mmol/L, blood urea nitrogen 16 mg/dL, creatinine 0.85 mg/dL, potassium 4.5 mmol/L, chlorine 102 mmol/L, C02 32.1 mmol/L, aldosterone 7 ng/dL with a non-suppressed plasma renin activity of 0.41 ng/mL/hour. A plasma-free metanephrine was normal at <25 pg/mL. An overnight 1 mg dexamethasone suppression test shows a normal morning cortisol of 0.2 mcg/dL. An MRI scan demonstrated the mass contained both microscopic intracellular and macroscopic fat deposits in the right adrenal gland diagnostic of an adrenal myelolipoma.
Fatty tissue, hematopoietic cells
An adrenal myelolipoma is a rare benign tumor. Adrenal myelolipoma is composed of mature fatty tissue with variable amount of hematopoietic cells. Tumor size varies from a few millimeters to >30 cm. Adrenal myelolipoma is typically not hormonally active but can coexist with other hormonally active tumors of the adrenal gland to produce excess adrenal cortical hormones and catecholamines.
Coronal CT scans of the abdomen before (A) and after (B) IV contrast. The adrenal malignancy (blue arrow) is located above the right kidney in the location of the adrenal gland. Macroscopic deposits fat is shown by the areas of hypoattentuation (yellow arrows). The adrenal malignancy in this patient did not show significant enhancement with contrast.
The diagnosis of adrenal myelolipoma is usually based on abdominal CAT scan or MRI scan. The mass is typically a well-encapsulated heterogeneous suprarenal mass of low density (–20 to –30 HU) equivalent to mature fat interspersed by denser myeloid tissue on CT scan. Although adrenal adenomas have low attenuation values, the density is not usually less than –20 HU. If the mass contains a lot of hematopoietic elements, the mass will appear more heterogeneous.
Fat has high signal intensity on T1- and T2-weighted images. Water and fat are additive on “in phase” sequences but cancel each other in “out of phase” sequences. This patient’s liver and right adrenal gland contain microscopic or intracellular fat and are hyperintense compared with the spleen in “in phase” (Figure 2A) and hypointense (signal dropout) compared with the spleen in “out phase” sequences (Figure 2B). Macroscopic fat is hyperintense on T1 images and hypointense on T2 MRI images with fat suppression sequences. The macroscopic fat is seen as a hyperintense band in Figure 3A in the adrenal gland but is hypointense (suppressed) with fat suppression imaging (Figure 3B).
Macroscopic fat in the adrenal mass on CT or MRI imaging is diagnostic for adrenal myelolipoma. Endocrine function of the mass should be performed to exclude exercise cortisol, aldosterone, adrenal androgens and catecholamines. In radiologically doubtful cases, a CT-guided fine needle aspiration will show fat and hematopoietic tissue, which is diagnostic for adrenal myelolipoma. It is important to exclude a pheochromocytoma before needle or open biopsy.
Axial MRI. T1 images of the abdomen show an enhancement of signal in the adrenal mass compared with spleen on the “in phase” images but signal dropout of both the liver and adrenal mass on “out of phase” images consistent with intracellular fat in a fatty liver and an adrenal malignancy.
Other characteristics
Myelolipomas primarily are found in the unilateral adrenal gland, but they have been reported in bilateral adrenal glands and in extra-adrenal sites such as the retroperitoneal, pelvic, renal, hepatic and gastric locations. In most cases, the tumors are asymptomatic and found — as with this patient — incidentally on abdominal images for other indications.
The size of the adrenal myelolipoma does not correlate with symptoms or risk for malignancy. Unlike other causes of asymptomatic adrenal incidentalomas, removal is not mandatory when the mass is >6 cm because the risk of malignancy is very low. Some papers recommend removal of asymptomatic adrenal myelolipoma when >10 cm to prevent hemorrhage or symptoms. When symptomatic, patient will complain of abdominal and flank pain and, with large tumor size, have a palpable mass causing compression of surrounding structures or necrosis/hemorrhage.
Axial MRI of the abdomen. A. A T1 image shows hyperintense linear macroscopic deposits of fat (red arrows). Enlarged image of the adrenal is indicated by the yellow arrow. B. In the T2 fat-suppression image, the signal of the macroscopic fat (red arrows) is suppressed with signal drop out. Enlarged image of the adrenal is indicated by the yellow arrow.
Adrenal myelolipoma can be confused with an adrenal malignancy especially if large (>6 cm). Surgery should be considered for abdominal or flank pain, large tumor size (>8, up to 10 cm), atypical radiologic appearance, and/or inferior vena cava compression. Large tumors can be excised surgically but are amenable to laparoscopic adrenalectomy.