Adrenal myelolipoma – an incidental finding

Clinical History

Patient was sent to perform adrenal CT for evaluation of difficult-to-control hypertension. No relevant symptoms.

Imaging Findings

Unenhanced and contrast-enhanced CT examination reveal a well-circumscribed, heterogeneous mass in the right adrenal gland measuring 48 mm, with areas of fat density interspersed with areas of soft tissue density.
The left adrenal gland has normal size and shape.

Discussion

Adrenal myelolipoma is an uncommon, benign and non-functioning neoplasm found in less than 1% of autopsies. [1] Extra-adrenal myelolipoma is significantly less common and is typically located in the retroperitoneum, most commonly in the presacral space. [2]
Myelolipomas usually originate in normal adrenal gland and are composed of variable amounts of mature fat and haematopoietic elements similar to bone marrow. [1, 2] In most cases they are asymptomatic and constitute an incidental finding. Adrenal myelolipomas range from 1-15 cm in size. The larger ones can rupture and haemorrhage, or cause vague symptoms or pain. [1]
On ultrasound, myelolipomas are highly echogenic or hypoechoic depending on the relative amounts of fat. The limits are poorly defined due to the presence of surrounding retroperitoneal fat. [2]
CT allows characterisation of almost all lesions. [3] Myelolipomas appear as well-circumscribed masses, sometimes with a thin capsule and have fat densities (less than -20 HU). Adrenal myelolipomas usually have 50-90% of fat, but this value can vary from almost all fat to only small foci of fat in a soft tissue mass. [1] Acute haemorrhage appears as high-density areas and calcification can occur in 20-30% of cases. [1, 3] Enhancement following administration of contrast material may occur in the soft tissue component. [3]
MRI may occasionally be useful by demonstrating high fat signal intensity on T1- and T2- weighted images, which is reduced on fat-suppression images. [3] Myeloid elements have low-signal intensity on T1-weighted images and intermediate signal intensity on T2-weighted. [2] Lesions enhance brightly after intravenous administration of gadolinium. [1]
In nearly all cases, diagnosis can be made confidently based on CT or MRI alone. The presence of fat is the key to diagnosis [1], and encapsulated adrenal lesions containing both fat and soft tissue can be confidently diagnosed as myelolipomas. Diagnosis of extra-adrenal myelolipoma is more challenging. [2] If necessary, biopsy can be performed revealing fat and myeloid elements which confirm the diagnosis. [1]
Definite diagnosis is important because the surgical resection is not indicated in the majority of cases. Resection is indicated in symptomatic cases, when there is increase in size during follow-up or in those larger than 7 cm because of the risk of rupture and haemorrhage. Myelolipomas smaller than 4 cm should be monitored, and the management of intermediate-sized lesions is individualised. When surgical resection is performed, laparoscopic resection should be preferred and is curative. [2]
In the presented case, follow-up was preferred.

Differential Diagnosis List

Final Diagnosis

Adrenal myelolipoma

URL:	https://www.eurorad.org/case/10321
DOI:	10.1594/EURORAD/CASE.10321
ISSN:	1563-4086