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Myelolipoma of the Adrenal Gland
S.A. Rooholamini, M.D.*, C. Aoyama, M.D.†,
A.H. Au, M.D.*, J. Rahimian, Ph.D.*,
From the Departments of Radiological Sciences* and Pathology† Olive View-UCLA Medical Center, Sylmar, CA
CASE SUMMARY The patient is a 56-year-old man with left flank pain of one-month duration. The patient complains that he cannot bend to his left. He reports no headaches, palpitations, weight loss, or change in bowel habits. Physical examination revealed left flank fullness. The laboratory values, including 24-hour urinary VMA and metanephrine, are normal.
Figure 1. (A and B) Axial CT images of the abdomen at the level of the adrenal glands without (A) and with (B) contrast enhancement demonstrate a large bilobed space-occupying mass in the left adrenal bed.
Figure 2. (A, B, C and D) A large heterogeneous mass is present in the left adrenal bed containing fat and soft tissue densities and displacing the adjacent structures. The mass measures 16x9x11 cm. No significant enhancement is noted following intravenous administration of contrast material.
RADIOLOGIC FINDINGS Computed tomography of the abdomen reveals a large tumor in the left side of the abdomen posterior to the stomach and pancreas and medial to the spleen. The mass is bilobed and measures 16x9x11 cm, indents the stomach posteriorly and displaces it anteriorly. The mass compresses and displaces the pancreas anteriorly and the left kidney caudad. The splenic artery and vein are stretched and displaced anteriorly by the mass. The jejunal loops are also displaced anteromedially. The mass has a heterogeneous appearance containing fat and soft tissue densities. No calcifications are visible within the mass. The mass is rather well delineated and no stranding is visible around it. The right adrenal gland is seen and is normal. A normal left adrenal gland cannot be identified. The right kidney is normal. The left kidney is displaced inferiorly by the mass. Both kidneys demonstrate normal function. Following intravenous administration of contrast material, minimal enhancement of the soft tissue components of the mass occurs. There is no significant difference between the early and the late phases. There is no evidence for retroperitoneal lymphadenopathy or ascites.
DIAGNOSIS Adrenal myelolipoma, proven at surgery.
DISCUSSION Adrenal myelolipoma is a rare benign lesion, composed of mature adipose cells and hematopoietic tissue. It is most commonly seen in the 5th-7th decades of life, although it has been reported from 12-93 years of age. Most are asymptomatic and are found incidentally on CT, although larger lesions may cause pain or be associated with intratumoral hemorrhage (1,2). The tumors are functionally inactive. Myelolipomas have a characteristic appearance due to their high fat content. They are brightly echogenic on sonography. CT offers the most definitive radiologic diagnosis (1,3,4). Unenhanced scans are usually adequate to make the diagnosis. The demonstration of macroscopic fat in an adrenal mass on CT is usually sufficient to make the diagnosis (5). The attenuation value of the lipomatous component of myelolipomas is in the range of fatty tissue, or –30 to –100 Hounsfield units. Calcifications are sometimes noted (6). A myelolipoma may be homogeneous or may appear somewhat heterogeneous. On MRI, myelolipomas demonstrate hyperintensity of the lipomatous component on all pulse sequences, similar to the retroperitoneal and subcutaneous fat. Distinguishing a myelolipoma from a retroperitoneal lipoma or a liposarcoma can be difficult (6). A large mass arising from the left adrenal gland was found by surgery and excised in conjunction with left adrenalectomy. The tumor was bilobed and consisted of two large round pieces connected by a thin membranous tissue, weighing in total 623 gm and measuring 11x8x5 cm and 11.5x10x7 cm. The consistency of the tumor was very soft. Histological sections show the adrenal capsule, adrenal cortex, and myelolipoma, consisting of adipose tissue and bone marrow elements (figures 3, 4 and 5).
CONCLUSION Adrenal myelolipoma is an unusual benign nonfunctioning tumor composed of fat and bone marrow hematopoietic elements. The presence of fat helps in making a definitive diagnosis on computed tomography and magnetic resonance imaging.
REFERENCES 1. Musante F, Derchi LE, Zappasodi F, et al. Myelolipoma of the Adrenal Gland: Sonographic and CT Features. American Journal of Roentgenology 151:961-964, 1998. 2. Palmer WE, Gerare-McFraland EL, Chew FS. Adrenal Myelolipoma. American Journal of Roentgenology 156:724, 1991. 3. Vick CW, Zeman RK, Mannes E, et. Al. Adrenal Myelolipoma: CT and Ultrasound Findings. Urol. Radiol. 6:7-13, 1984. 4. Adusumilli S, Ramchandani P, et al. Adrenal Myelolipoma. www.emedicine.com/radio/ topic18.htm. 5. Fishman EK. www.CTisus.com. 6. Boland GWL. The Incidentally Detected Adrenal Mass: An Integrated Approach to Lesion Characterization. Applied Radiology 13-19, February 1999.
ACKNOWLEDGMENT The authors express their thanks to Paul Beers, Shervin Ghamghamy and René Retana for their valuable technical and secretarial work in the preparation of this manuscript.
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