eMedicine Specialties > Radiology > Genitourinary

Adrenal Adenoma

Author: Perry J Horwich, MD, Staff Physician, Instructor of Radiology, Department of Radiology, Beth Israel - Deaconess Medical Center
Coauthor(s): Stephen A Okon, MD, Consulting Staff, Assistant Professor of Radiology, Department of Radiology, Beth Israel Medical Center
Contributor Information and Disclosures

Updated: May 4, 2009

Introduction

Background

Adrenal cortical adenoma is a common benign tumor arising from the cortex of the adrenal gland. It commonly occurs in adults, but it can be found in persons of any age. Adrenal cortical adenomas are not considered to have the potential for malignant transformation.

The adrenal gland is the fourth most common site of metastasis, and adrenal metastases may be found in as many as 25% of patients with known primary lesions. Therefore, radiologists frequently face the task of determining whether an adrenal mass is benign or malignant. The question can directly affect the clinical management of the case. For instance, the workup for an otherwise resectable lung cancer may reveal the presence of an adrenal mass and suggest the possibility of metastatic disease.

The differential diagnosis of adrenal masses includes many primary, metastatic, benign, and malignant entities, most of which are not discussed at length here. Instead, this article includes practical information that pertains specifically to adrenal adenomas.

Frequency

United States

Adrenal masses are a common finding on cross-sectional abdominal images. In about 1-5% of all cases, abdomen CT scans that are obtained for reasons other than the evaluation for possible adrenal neoplasm demonstrate an adrenal mass; the majority of these are adrenal adenomas. On autopsy, 2-10% of cases involve a benign cortical adrenal adenoma.

International

An Italian study of incidentally discovered adrenal masses among subjects undergoing chest CT scan found that the prevalence of adrenal adenomas was approximately 4%.¹

Sex

Evidence suggests that the incidence in teenage girls is slightly higher that that of teenage boys, but no sex-related predilection is found in adults.

Age

Adrenal cortical adenoma commonly occurs in adults, but it can be present in individuals of any age.

Presentation

Anatomy

The adrenal glands are located in the perirenal space near the upper pole of each kidney. Their appearance varies: they may be shaped like the letter H, L, Y, T, or V. Typically, they are less than 4 cm in length and less than 1.0 cm in width.

Pathophysiology

Benign adrenal cortical adenomas are commonly smaller than 6 cm in diameter on initial presentation, but they may be larger. Correlation with the clinical presentation and, if necessary, serum chemical and urinalysis results should be used to determine whether an adrenal cortical adenoma is functional. Nonfunctional adrenal cortical adenomas are not premalignant, and surgical excision is not indicated.

Histologically, adrenal cortical adenomas can be differentiated on the basis of intracytoplasmic lipid content. Approximately 70% of all adrenal cortical adenomas have a high percentage of intracytoplasmic lipid; the remaining 30% do not.

The presence of intracytoplasmic lipid is fairly specific for adrenal cortical adenomas; other processes, such as metastasis, hemorrhage, and other primary adrenal neoplasms, have distinctly different imaging characteristics. This unique characteristic allows clinicians to distinguish adenomas from other processes that affect the adrenal gland, by using imaging techniques that demonstrate lipid. The major exception is clear cell carcinoma of the kidney, which contains an abundance of intracytoplasmic lipid; when these metastasize to the adrenal gland, their appearance can be identical to that of a lipid-rich adenoma. Note that on CT scans and MRIs, the appearance of intracytoplasmic lipid is different from that of macroscopic fat, as in the case of a myelolipoma.

Preferred Examination

The modalities of choice in the evaluation of an adrenal mass are CT, MRI, and positron emission tomography (PET). Ultrasonography has a role in the evaluation of a potential adrenal mass in infants, but no appearance is specific for benign adrenal adenoma.^{2,3,4,5,6,7,8,9,10,11,12}

How should the radiologist proceed in evaluating an incidental small adrenal mass? Two important questions must be answered:

• First, does the patient have a hormonal or biochemical abnormality that may be caused by an enlarged adrenal gland? If this is the case, the lesion should be surgically removed regardless of the imaging features.
• Second, does the patient have a known malignancy? In the absence of a known malignancy, the probability that a small, well-circumscribed adrenal mass is malignant is nearly zero. The characterization of an adrenal mass is critical in patients with a known malignancy, in whom the diagnosis of an adrenal metastasis precludes curative surgery.

The authors of a prominent review article suggest that CT without intravenous contrast enhancement should be the initial study.² If the adrenal mass is less than 10 Hounsfield units (HU), a diagnosis of adrenal adenoma can be made. If the adrenal mass is more than 10 HU, CT with intravenously administered contrast material should follow, and the washout should be calculated; benign lesions typically demonstrate more than 50% washout. In cases in which CT findings are equivocal, chemical shift MRI should be performed. When the findings of both modalities are inconclusive, biopsy is advised only when a known extra-adrenal malignancy is present.

Limitations of Techniques

Obvious considerations include the availability and cost of CT and MRI. A delay in CT imaging can potentially diminish the efficiency of the CT schedule, result in multiple examinations, and expose the patient to ionizing radiation. MRI examination may enable diagnosis without exposing the patient to ionizing radiation; however, MRI may not be as available as CT and can be more expensive.

Differential Diagnoses

Other Problems to Be Considered

Adrenal hemorrhage
Adrenal hyperplasia
Adrenal cyst
Infection (eg, tuberculosis, meningococci)

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