eMedicine Specialties > Radiology > Genitourinary

Adrenal Myelolipoma

Author: Parvati Ramchandani, MD, Associate Professor of Radiology, University of Pennsylvania School of Medicine; Consulting Staff, Section of Genitourinary Radiology, Department of Radiology, Hospital of the University of Pennsylvania at Philadelphia
Contributor Information and Disclosures

Updated: Jan 15, 2010

Introduction

Background

Adrenal myelolipoma is a rare benign neoplasm composed of mature adipose tissue and a variable amount of hematopoietic elements. Most lesions are small and asymptomatic, discovered incidentally at autopsy or on imaging studies performed for other reasons. Most tumors are unilateral but show no predilection to one particular side. Tumor size varies from several millimeters to more than 30 cm.

Adrenal myelolipoma images are provided below:

Contrast-enhanced CT in a 64-year-old man confirm...

Contrast-enhanced CT in a 64-year-old man confirms the presence of chunky calcification and a large amount of macroscopic fat in the left adrenal mass, which is diagnostic of a myelolipoma. Courtesy of P. Ramchandani, MD.

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Contrast-enhanced CT in a 64-year-old man confirm...

Contrast-enhanced CT in a 64-year-old man confirms the presence of chunky calcification and a large amount of macroscopic fat in the left adrenal mass, which is diagnostic of a myelolipoma. Courtesy of P. Ramchandani, MD.


Unenhanced CT in an asymptomatic man reveals a 6-...

Unenhanced CT in an asymptomatic man reveals a 6-cm right adrenal mass with density measurements that range from -14 to -27 Hounsfield units, consistent with myelolipoma. Courtesy of P. Ramchandani, MD.

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Unenhanced CT in an asymptomatic man reveals a 6-...

Unenhanced CT in an asymptomatic man reveals a 6-cm right adrenal mass with density measurements that range from -14 to -27 Hounsfield units, consistent with myelolipoma. Courtesy of P. Ramchandani, MD.


Coronal fat-saturated gadolinium-enhanced T1-weig...

Coronal fat-saturated gadolinium-enhanced T1-weighted gradient-echo image shows that the left adrenal myelolipoma is avascular, as reflected by its lack of enhancement. Courtesy of S. Adusumilli, MD.

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Coronal fat-saturated gadolinium-enhanced T1-weig...

Coronal fat-saturated gadolinium-enhanced T1-weighted gradient-echo image shows that the left adrenal myelolipoma is avascular, as reflected by its lack of enhancement. Courtesy of S. Adusumilli, MD.


Recent studies

Yip et al in a study of 196 adrenalectomies in 192 patients from 2000 to 2008 found that CT or MR characteristics predicted the presence of benign lesions with 100% specificity. Histopathology confirmed that all 66 adrenal masses with imaging characteristics suggesting benign adenoma were indeed benign lesions and included 61 benign adrenal adenomas and 5 benign nonadenomatous lesions (3 myelolipomas, 1 composite myelolipoma/adenoma, and 1 ganglioliponeuroma). The authors stated that to exclude malignancy, adrenal masses with non-benign imaging characteristics should be resected.1

Lamas et al reported on 2 cases of large mixed adrenal tumors that had a heterogeneous appearance and areas of fat density on imaging and resulted in autonomous cortisol production leading to Cushing syndrome. The patients underwent adrenalectomy, and histology identified adrenocortical adenomas with widespread myelolipomatous metaplasia. The authors noted that although adrenal myelolipomas are usually asymptomatic, nonfunctioning adrenal incidentalomas, there have been a few reports of myelolipomatous masses that are associated with adrenocortical hypersecretion.2

Montone et al presented pathologic and radiographic features of 3 patients with adrenocortical neoplasms. Two patients had imaging findings that were compatible with adrenal myelolipoma. Pathologically, 2 of the lesions were classified as adrenocortical neoplasms of uncertain malignant potential, and 1 lesion was classified as an adrenocortical adenoma. All 3 lesions contained myelolipomatous foci throughout the neoplasm, and 2 of the tumors contained several pure lipomatous foci. The authors noted that imaging studies may result in a false diagnosis of a benign adrenal myelolipoma and, as a result, undertreatment.3

Pathophysiology

Several explanations of this neoplasm's development have been offered. One theory by D. C. Collins suggests that a myelolipoma represents a site of extramedullary hematopoiesis.4 The most widely accepted theory, as cited by Meaglia and Schmidt in a 1992 study of the natural history of adrenal myelolipoma, is the existence of metaplasia of the reticuloendothelial cells of blood capillaries in the adrenal gland in response to stimuli such as necrosis, infection, or stress.5

Frequency

United States

Incidence varies from 0.08-0.4% at autopsy.

Mortality/Morbidity

No death rate has been reported in the literature because of the rarity of this lesion. Myelolipomas do not undergo malignant transformation.

The primary complication, which is uncommon, is spontaneous rupture of the mass, resulting in retroperitoneal hemorrhage. Rupture and hemorrhage also can occur following blunt trauma.

Race

As reported by Han et al in a series of 20 patients, 85% of patients with adrenal myelolipoma were white.6

Sex

Mostly, the male-to-female ratio is 1:1; however, a study conducted by Han et al in 1997 reported a male-to-female ratio of 2:3.6

Age

Lesions most commonly occur in patients in their fifth to seventh decades, although they have been seen in patients aged 12-93 years.

Anatomy

Most myelolipoma lesions occur within the adrenal gland. Rarely, myelolipomas can exist in extraadrenal locations, such as the presacral retroperitoneum, perirenal and pararenal retroperitoneum, mediastinum, liver, and muscle fascia. Kammen et al reported a rare case of an extra-adrenal myelolipoma that presented as a fat-containing retroperitoneal mass not contiguous with the adrenal gland.7

Presentation

Most myelolipomas are asymptomatic and hormonally nonfunctional. Occasionally, patients present with nonspecific abdominal or flank pain secondary to intratumoral or peritumoral hemorrhage, tumor necrosis, or mechanical compression from tumor bulk. Other rare presenting symptoms include hematuria and abdominal mass.8,9

In a review of the literature, Hisamatsu et al documented 25 cases of endocrine dysfunction associated with adrenal myelolipomas, including conditions such as Cushing syndrome,2 Conn syndrome,10 and congenital adrenal hyperplasia.11,12 In 85% of these patients, the abnormality involves the pituitary adrenal axis. In patients with associated endocrine dysfunction, stimulation with cortisol or adrenocorticotropin hormone has been suggested to be involved in the pathogenesis of myelolipomas.

Patients with small asymptomatic myelolipomas are monitored clinically for symptoms, and routine follow-up radiologic tests appear unnecessary for such lesions.13 Symptomatic tumors are treated by adrenalectomy. Transcatheter embolization prior to surgical resection has been used successfully to achieve hemostasis in cases of ruptured myelolipomas leading to retroperitoneal hemorrhage. Occasionally, large silent tumors are excised to prevent the occurrence of rupture.

Preferred Examination

The fatty component of a myelolipoma is macroscopic in most patients and is diagnostic when discovered on cross-sectional imaging.

The preferred imaging modality is CT, which shows focal fatty density within the mass. MRI also accurately depicts both microscopic and macroscopic fat using chemical shift imaging and explicit fat saturation technique, respectively. Myelolipomas may be discovered incidentally on ultrasound (US), which otherwise is not used routinely to characterize adrenal neoplasms.

Limitations of Techniques

Occasionally, myelolipomas can enlarge enough to make the organ of origin difficult to discern on CT, resulting in a differential diagnosis that includes renal angiomyolipoma and retroperitoneal liposarcoma or lipoma. In these patients, the multiplanar capability of MRI can help define the tissue planes and confirm that the mass is adrenal in origin.

Some myelolipomas may have a larger amount of hematopoietic tissue and no recognizable fat, making them impossible to distinguish from well-differentiated retroperitoneal malignancies or other adrenal tumors on CT or MRI. Percutaneous biopsy may be necessary to establish a diagnosis.

Differential Diagnoses

Adrenal Adenoma
Adrenal Carcinoma
Angiomyolipoma, Kidney
Liposarcoma, Soft Tissue

More on Adrenal Myelolipoma

Overview: Adrenal Myelolipoma
Imaging: Adrenal Myelolipoma
Follow-up: Adrenal Myelolipoma
Multimedia: Adrenal Myelolipoma
References
Further Reading
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References

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Further Reading

Related eMedicine topics

 Adrenal Adenoma (Endocrinology)

Adrenal Adenoma (Radiology)

Adrenal Metastases

Adrenal Carcinoma


Clinical guidelines
ACR Appropriateness Criteria® incidentally discovered adrenal mass.
American College of Radiology - Medical Specialty Society. 2000 (revised 2007). 8 pages. NGC:005995

The diagnosis of Cushing's syndrome: an Endocrine Society clinical practice guideline.
The Endocrine Society - Disease Specific Society. 2008. 29 pages. NGC:006662

Clinical trials
Adrenal Tumors - Pathogenesis and Therapy

Adrenal Scans With Radioiodine-Labeled Norcholesterol (NP-59)

Study of Adrenal Gland Tumors

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Keywords

myelolipoma, adrenal gland myelolipoma, adrenal tumors, adrenal gland tumors, adrenal neoplasms, adrenal gland neoplasms

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Contributor Information and Disclosures

Author

Parvati Ramchandani, MD, Associate Professor of Radiology, University of Pennsylvania School of Medicine; Consulting Staff, Section of Genitourinary Radiology, Department of Radiology, Hospital of the University of Pennsylvania at Philadelphia
Parvati Ramchandani, MD is a member of the following medical societies: American Association for Women Radiologists, American College of Radiology, American Roentgen Ray Society, Radiological Society of North America, and Society of Uroradiology
Disclosure: Nothing to disclose.

Pharmacy Editor

Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand
Disclosure: Nothing to disclose.

Managing Editor

Arnold C Friedman, MD, FACR, Associate Chairman, Department of Radiology, University of Florida Health Science Center; Chief, Department of Radiology, Shands-Jacksonville Hospital
Arnold C Friedman, MD, FACR is a member of the following medical societies: American College of Radiology, American Institute of Ultrasound in Medicine, American Roentgen Ray Society, Association of University Radiologists, and Radiological Society of North America
Disclosure: Nothing to disclose.

CME Editor

Robert M Krasny, MD, Resolution Imaging Medical Corporation
Robert M Krasny, MD is a member of the following medical societies: American Roentgen Ray Society and Radiological Society of North America
Disclosure: Nothing to disclose.

Chief Editor

Eugene C Lin, MD, Consulting Radiologist, Virginia Mason Medical Center; Clinical Assistant Professor of Radiology, University of Washington School of Medicine
Eugene C Lin, MD is a member of the following medical societies: American College of Nuclear Medicine, American College of Radiology, Radiological Society of North America, and Society of Nuclear Medicine
Disclosure: Nothing to disclose.

 
 
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