Case report

A 52-year-old man with a history of traveling to remote locations presented to his primary care physician describing intermittent midabdominal discomfort, which had started approximately 2 to 3 weeks earlier. A physical examination and routine laboratory analysis were unremarkable. Contrast-enhanced computed tomography (CT) scans of the abdomen and pelvis showed a lesion in the left adrenal gland (Figures).

Challenge: What is the lesion in the left adrenal gland most consistent with?

1. Adrenal cortical carcinoma
2. Adrenal adenoma
3. Adrenal myelolipoma
4. Adrenal metastasis

Answer: Myelolipoma

Myelolipomas are benign adrenal tumors comprised of fat and bone marrow elements. They were once considered rare, with autopsy series reporting an incidence between 0.08% and 0.20%.¹ The advent of routine CT scanning has shown these tumors to be more common.² Macroscopic fat is a distinguishing characteristic of myelolipomas on CT scans. This differentiates them from adrenal adenomas, which contain microscopic fat. Adrenal myelolipomas almost always have areas of macroscopic fat with correspondingly low Hounsfield Units (HU), typically between -20 and -30 HU, which is slightly higher than that of the surrounding retroperitoneal fat.¹

As the "myelo" in "myelolipoma" suggests, these tumors also contain hematopoietic elements that resemble bone, and calcifications are observed in approximately 20% of these lesions.¹ Although myelolipomas are typically located in the adrenal glands, extra-adrenal lesions have been identified in the mediastinum, liver, and muscle fascia, and in the presacral, perirenal, and pararenal retroperitoneum.^1,3,4 Myelolipomas are not typically associated with other disease processes.¹

Clinically, myelolipomas are usually asymptomatic and hormonally nonfunctional. Larger tumors can exhibit symptoms secondary to tumor necrosis and mechanical compression, but the greatest clinical concern is hemorrhage. When these lesions grow larger than 10 cm, the risk of hemorrhage increases, and massive retroperitoneal hemorrhage and hypotensive shock are possible.⁵ Rarely, myelolipomas can be hormonally active, causing Cushing's syndrome, Conn's syndrome, and congenital adrenal hyperplasia.^1,6

The natural history of adrenal myelolipomas varies. Myelolipomas are known to enlarge, but their growth rate and size vary and do not correspond with symptoms.⁷ Most patients with these lesions are asymptomatic and can be monitored with CT scanning and treated conservatively.^7,8 Symptomatic tumors should be managed with adrenalectomy. Large tumors (>5 cm) also should be resected because of the risk of hemorrhage.^2,8 In cases where there is concern regarding intraoperative hemorrhage, preoperative transcatheter embolization can be performed.¹

References

1. Adusumilli S, Ramchandani P. Adrenal myelolipoma. e-medicine. Available at: www.emedicine.com/radio/topic18.htm. Accessed October 22, 2007.
2. Tanaka T, Matsuo N, Ishikura H, et al. Adrenal myelolipoma: a case report and review of the literature. Jpn J Surg. 1989;19(5):597-606.
3. Chen KT, Felix EL, Flam MS. Extraadrenal myelolipoma. Am J Clin Pathol. 1982;78(3):386-389.
4. Singla AK, Kechejian G, Lopez MJ. Giant presacral myelolipoma. Am Surg. 2003;69(4):334-338.
5. Kenney PJ, Wagner BJ, Rao P, et al. Myelolipoma: CT and pathological features. Radiology. 1998;208(1):87-95.
6. Hisamatsu H, Sakai H, Tsuda S, et al. Combined adrenal adenoma and myelolipoma in a patient with Cushing's syndrome: case report and review of literature. Int J Urol. 2004;11(6):416-418.
7. Han M, Burnett AL, Fishman EK, et al. The natural history and treatment of adrenal myelolipoma. J Urol. 1997;157(4):1213-1216.
8. El-Mekresh MM, Abdel-Gawad M, El-Diasty T, et al. Clinical, radiological and histological features of adrenal myelolipoma: review and experience with a further eight cases. Br J Urol. 1996;78(3):345-350.