Incidental adrenal mass found on CT scan

Issue: December 2011

ByGayatri Kuraganti, MD

ByStephanie L. Lee, MD, PhD, ECNU

A 43-year-old woman was referred for an incidentally identified right 2.5 cm × 3 cm adrenal mass found on a CT scan. We performed adrenal testing in the morning that was normal with a cortisol 11.3 mcg/dL, total testosterone 24 ng/dL, aldosterone 9.87 ng/dL, renin direct 11 mcU/mL, dehydroepiandrosterone sulphate 24.8 mcg/dL and plasma metanephrine 0.56 nmol/L. Twenty-four hour urine collections showed normal levels of adrenal cortex and medulla hormones.

Gayatri Kuraganti

Stephanie L. Lee

One year before, a trauma CT scan after a motor vehicle accident showed a “bruised 3-cm adrenal” gland. An adrenal MRI was ordered that showed a 3.8 cm × 2.5 cm × 4 cm right adrenal mass (Figure 1). The mass was intermediate in signal in both T1 and T2. Out-of-phase sequence showed signal dropout to suggest an adenoma. There was no evidence of hemosiderin to suggest resolving hemorrhage. Because there was no growth of the adrenal mass in the 15 months between her prior CT and MRI scans and her biochemical testing was negative, it was elected to follow her clinically.

CT scan with adrenal protocol ordered

One year later, biochemical testing for both adrenal cortical and medullary function was again found to be normal. A CT scan with adrenal protocol was ordered (Figures 2 and 3). The mass in the right adrenal gland measured 3.7 cm. The adrenal nodule on the unenhanced images had a density of 5 Hounsfield units (HU). The mass enhanced 60 seconds after rapid IV contrast bolus to 70 HU. After a 5-minute delay, the contrast washed out of the mass to approximately 35 HU (approximately 50% washout). Repeat CT scan imaging 3 years after diagnosis showed no growth of the adrenal mass with a 60% washout after contrast.

Adrenal incidentaloma (AI) is an accidentally discovered adrenal mass on a radiological examination performed for an unrelated symptom. The frequency of AI increases from about 0.2% to 7% with aging. Common causes of AI include nonfunctioning, benign cortical adenomas or hypersecretory tumors such as Cushing’s syndrome, pheochromocytoma and aldosterone-secreting adenoma. Other rare etiologies include primary adrenocortical carcinoma, metastasis and various rare benign tumors.

Patients with AI should undergo clinical, biochemical and radiological evaluations. The history and physical exam should focus on signs and symptoms of a functional adrenal tumor. Imaging evaluation of AI depends on the size and appearance on imaging studies. Twenty-five percent of masses larger than 4 cm were adrenal cancer in one large study. Given the high mortality associated with adrenal carcinoma, most experts recommend surgery for lesions larger than 4 cm regardless of the biochemical or image characteristics. Benign tumors are distinguished from carcinoma on CT scan based on lipid content and rapidity of washout of contrast medium. The cytoplasmic fat in adenomas results in low attenuation on non-enhanced CT, whereas non-adenomas have a higher attenuation.

Figure 1. Axial MRI scan of the adrenal gland. The density of the adrenal mass (yellow arrow) is intermediate between the liver and cerebrospinal fluid on T1- (A) and T2- (B) weight images. There is signal drop out (decrease in density) when the in-phase (C) and out-of-phase (D) images are compared, suggesting a high fat content. These characteristics are typical of a benign adenoma.

Reprinted with permission: Stephanie L. Lee, MD, PhD

Figure 2. Coronal CT scan with contrast of the adrenal. The right adrenal mass superior to the right kidney is hypointense compared with the liver after IV contrast (red arrow).
For a larger image, click here.

Figure 3. Axial CT scan with adrenal protocol. A. Unenhanced adrenal mass (red arrow) with a low density of 5 Hounsfield units (HU). B. Peak density of 70 HU obtained 1 minute after IV contrast bolus. C. Reduction of >50% of density (35 HU) after 5 to 10 minutes of washout is consistent with a benign adenoma.

‘Adrenal CT protocol’

The HU scale is a semi-quantitative measurement of attenuation. An adrenal mass with less than 10 HU on unenhanced CT is an adenoma (74% sensitivity and 96% specificity). But about 25% to 30% of adenomas are lipid poor and have attenuation values of more than 10 HU. An “adrenal CT protocol” includes an IV contrast bolus with an immediate and 10-minute delayed adrenal imaging to determine the maximum rise of HU attenuation and the rapidity of washout. On delayed contrast enhanced CT, adrenal adenomas typically exhibit rapid contrast washout as demonstrated by this patient (Figure 3), but non-adenomas have a delayed contrast material washout. Contrast washout of more than 50% on the delayed scan has been reported to be 100% sensitive and specific for adenoma, but less than 50% washout is suggestive of carcinoma, metastasis or pheochromocytoma. Generally, malignancy is suggested on CT by a large mass (4-6 cm) with an irregular border, inhomogeneity/necrosis, a washout of contrast after 10 minutes of less than 50% and calcifications. It is recommended that repeat imaging should be performed at 3 to 6 months and then annually for 1 to 2 years. Current practice is to remove any tumor that grows by more than 1 cm in diameter during the follow-up period. For all adrenal tumors, hormonal evaluation should be performed at the diagnosis and then annually for 5 years.

When an AI cannot be adequately characterized by CT, MRI should be performed with T1 and T2 weighted images and chemical shift imaging (in-phase and out-of-phase; Figure 1). Primary adrenal carcinomas are characterized by intermediate to high signal intensity on T1 and T2 weighted images compared with liver and cerebrospinal fluid, heterogeneity on T2 weighted images due to hemorrhage or necrosis and avid enhancement with delayed washout. FDG-PET scan has high sensitivity for malignancy. Because of cost and lack of extensive experience, this test is not routinely recommended.

Gayatri Kuraganti, MD, is a resident in internal medicine at St. Vincent Hospital in Worcester, Mass. Stephanie L. Lee, MD, PhD, is director of the Thyroid Health Center at Boston Medical Center and associate professor of medicine at Boston University School of Medicine.

For more information:

Hamrahian AH. J Clin Endocrinol Metab. 2005;90:871-877.

Nieman LK. J Clin Endocrinol Metab. 2010. 95:4106-4113.

Young WF Jr. N Engl J Med. 2007;356:601-610.

Zeiger MA. Endocr Pract. 2009;15(Suppl 1):1-20.

Disclosure: Drs. Kuraganti and Lee report no relevant financial disclosures.