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.
Homogeneous, well-defined, 7-HU ovoid mass is seen in the right adrenal gland; this finding is diagnostic of a benign adrenal adenoma. (Image was obtained in the same patient as in Image 2 in Multimedia.)
Homogeneously enhancing ovoid mass is seen in the left adrenal gland. (Image was obtained in the same patient as in Images 6 and 8 in Multimedia.)
Adrenal cortical adenoma can be diagnosed with a high degree of accuracy: the specificity of imaging studies ranges from 95-99%, and the sensitivity is greater than 90%. These impressive percentages are a result of the relatively high prevalence of adrenal adenomas in the general population and the extensive radiologic research with imaging methods, primarily CT and MRI.
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
| Adrenal Carcinoma | Neuroblastoma |
| Adrenal Hemorrhage | Pheochromocytoma |
| Adrenal Metastases | |
| Adrenal Myelolipoma | |
| Hyperaldosteronism |
Other Problems to Be Considered
Adrenal hemorrhage
Adrenal hyperplasia
Adrenal cyst
Infection (eg, tuberculosis, meningococci)
More on Adrenal Adenoma |
Overview: Adrenal Adenoma |
| Imaging: Adrenal Adenoma |
| Follow-up: Adrenal Adenoma |
| Multimedia: Adrenal Adenoma |
| References |
| Further Reading |
| Next Page » |
References
Bovio S, Cataldi A, Reimondo G, Sperone P, Novello S, Berruti A, et al. Prevalence of adrenal incidentaloma in a contemporary computerized tomography series. J Endocrinol Invest. Apr 2006;29(4):298-302. [Medline].
Boland GW, Lee MJ, Gazelle GS, Halpern EF, McNicholas MM, Mueller PR. Characterization of adrenal masses using unenhanced CT: an analysis of the CT literature. AJR Am J Roentgenol. Jul 1998;171(1):201-4. [Medline].
Ho LM, Paulson EK, Brady MJ, Wong TZ, Schindera ST. Lipid-poor adenomas on unenhanced CT: does histogram analysis increase sensitivity compared with a mean attenuation threshold?. AJR Am J Roentgenol. Jul 2008;191(1):234-8. [Medline].
Halefoglu AM, Bas N, Yasar A, Basak M. Differentiation of adrenal adenomas from nonadenomas using CT histogram analysis method: A prospective study. Eur J Radiol. Jan 21 2009;[Medline].
Krestin GP, Steinbrich W, Friedmann G. Adrenal masses: evaluation with fast gradient-echo MR imaging and Gd-DTPA-enhanced dynamic studies. Radiology. Jun 1989;171(3):675-80. [Medline].
Khati NJ, Javitt MC, Schwartz AM. Adrenal adenoma and hematoma mimicking a collision tumor at MR imaging. Radiographics. Jan-Feb 1999;19(1):235-9. [Medline].
Yoh T, Hosono M, Komeya Y, Im SW, Ashikaga R, Shimono T, et al. Quantitative evaluation of norcholesterol scintigraphy, CT attenuation value, and chemical-shift MR imaging for characterizing adrenal adenomas. Ann Nucl Med. Jul 2008;22(6):513-9. [Medline].
Korobkin M. CT characterization of adrenal masses: the time has come. Radiology. Dec 2000;217(3):629-32. [Medline].
Liang HL, Pan HB, Lee YH, et al. Small functional adrenal cortical adenoma: treatment with CT-guided percutaneous acetic acid injection--report of three cases. Radiology. Nov 1999;213(2):612-5. [Medline].
Mayo-Smith WW, Boland GW, Noto RB, Lee MJ. State-of-the-art adrenal imaging. Radiographics. Jul-Aug 2001;21(4):995-1012. [Medline].
Otal P, Escourrou G, Mazerolles C, et al. Imaging features of uncommon adrenal masses with histopathologic correlation. Radiographics. May-Jun 1999;19(3):569-81. [Medline].
Boland GW, Blake MA, Hahn PF, Mayo-Smith WW. Incidental adrenal lesions: principles, techniques, and algorithms for imaging characterization. Radiology. Dec 2008;249(3):756-75. [Medline].
Pena CS, Boland GW, Hahn PF, et al. Characterization of indeterminate (lipid-poor) adrenal masses: use of washout characteristics at contrast-enhanced CT. Radiology. Dec 2000;217(3):798-802. [Medline].
Hood MN, Ho VB, Smirniotopoulos JG, Szumowski J. Chemical shift: the artifact and clinical tool revisited. Radiographics. Mar-Apr 1999;19(2):357-71. [Medline].
Clinical Trials (PDQ®). Adrenal Scans With Radioiodine-Labeled Norcholesterol (NP-59). National Cancer Institute. Available at http://www.cancer.gov/search/ViewClinicalTrials.aspx?cdrid=585137&version=HealthProfessional&protocolsearchid=5407345#ContactInfo_CDR0000585137. Accessed November 10, 2008.
Doppman JL, Gill JR Jr. Hyperaldosteronism: sampling the adrenal veins. Radiology. Feb 1996;198(2):309-12. [Medline].
Katz DS, Math KR, Groskin SA, eds. Radiology Secrets. Hanley & Belfus Inc;1998.
Mittelstaedt CA. Abdominal Ultrasound. 5th ed. 1989.
Newhouse JH, Heffess CS, Wagner BJ, et al. Large degenerated adrenal adenomas: radiologic-pathologic correlation. Radiology. Feb 1999;210(2):385-91. [Medline].
NIH state-of-the-science statement on management of the clinically inapparent adrenal mass ("incidentaloma"). NIH Consens State Sci Statements. Feb 4-6 2002;19(2):1-25. [Medline].
Siegal MJ. Pediatric Sonography. 2nd ed. Lippincott-Raven;1995.
Further Reading
Related eMedicine topics
Adrenal Adenoma (Endocrinology)
Adrenal Carcinoma
Adrenal Metastases
Adrenal Surgery
Clinical guidelines
ACR Appropriateness Criteria® incidentally discovered adrenal mass. American College of Radiology - Medical Specialty Society. 2000 (revised 2007). 8 pages. NGC:005995
Stereotactic radiosurgery for patients with pituitary adenomas. IRSA - Professional Association. 2004 Apr. 12 pages. NGC:003598
Clinical trials
Study of Adrenal Gland Tumors
Adrenal Scans With Radioiodine-Labeled Norcholesterol (NP-59)
Adrenal Tumors - Pathogenesis and Therapy
Keywords
adrenal adenoma, adrenal cortical nodular hyperplasia, adrenal tumor, adrenal gland tumor, benign adrenal tumor, adrenal cortical adenoma




Overview: Adrenal Adenoma