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.
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.
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
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.
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
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
For a larger image, click here.
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
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.
- Nieman LK. J Clin Endocrinol Metab. 2010.
- 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