Average HU of -63

Nonfunctioning adrenal tumor discovered on an imaging study performed for indications exclusive of adrenal related conditions.

“ The prevalence of adrenal incidentalomas has increased, and our result of 5% prevalence corroborates the 4.4% reported from a recent series compared with the 1-2% reported in the older literature.”
The Incidental Adrenal Mass on CT: Prevalence of Adrenal Disease in 1,049 Consecutive Adrenal masses in Patients with No Known Malignancy
Song JH et al.
AJR 2008; 190:1163-1168

“ In 973 consecutive patients with an incidental adrenal mass and no history of cancer, no malignant lesions were identified. Adenomas (75%) and myelolipomas (6%) were the most common lesions.”
The Incidental Adrenal Mass on CT: Prevalence of Adrenal Disease in 1,049 Consecutive Adrenal masses in Patients with No Known Malignancy
Song JH et al.
AJR 2008; 190:1163-1168

“ All of the incidentally detected adrenal masses with a CT attenuation of >10 HU were benign in patients with no known malignancy. Follow-up imaging to characterize an incidental mass appears to have a limited role in this patient cohort.”
The Incidental Indeterminate Adrenal Mass on CT (>10H) in Patients Without Cancer: Is Further Imaging Necessary? Follow-Up of 321 Consecutive Indeterminate Adrenal Masses
Song JH et al.
AJR 2007; 189:1119-1123

OBJECTIVE. The purpose of this study was to determine the rate of malignancy in incidentally detected bilateral adrenal masses in patients with no known history of cancer. 
CONCLUSION. No case of malignancy was found in 322 incidentally detected bilateral adrenal nodules at CT of patients without known cancer. Imaging follow-up of such lesions may be unnecessary. 
Incidentally Detected Bilateral Adrenal Nodules in Patients Without Cancer: Is Further Workup Necessary? 
Corwin MT et al.
AJR 2018; 210:780–784

“We found no cases of malignancy in 322 incidentally detected bilateral adrenal nodules at CT examinations of 161 patients who had no known cancer. Imaging follow-up of such lesions may be unnecessary.” 
Incidentally Detected Bilateral Adrenal Nodules in Patients Without Cancer: Is Further Workup Necessary? 
Corwin MT et al.
AJR 2018; 210:780–784

“Our study adds to the growing body of evidence that small incidentally detected adrenal nodules in patients without a history of cancer are highly likely benign and may require no further imaging follow-up. Specifically, our findings suggest this approach applies to the case of bilateral nodules. This finding of our study is important because the increased use and resolution of CT have led to an increase in incidental findings unrelated to the original clinical indication. This can lead to extensive further cascades of imaging and interventional workups that can be costly and cause morbidity and psychologic stress.” 
Incidentally Detected Bilateral Adrenal Nodules in Patients Without Cancer: Is Further Workup Necessary? 
Corwin MT et al.
AJR 2018; 210:780–784

“Adrenal incidentalomas (AIs) are found in approximately 4% of patients undergoing abdominal imaging, with peak prevalence in the sixth and seventh decades of life. Detection of AI warrants clinical, biochemical, and radiological evaluation to establish its secretory status and risk of malignancy. Careful review of the lipid content, size, and imaging phenotype of an adrenal mass is needed to evaluate the risk for malignancy. Identification of an AI may be an opportunity to identify an underlying secretory tumor that may have been otherwise unrecognized. A practical approach to investigation and follow-up of AIs is presented in this article.”
Adrenal Incidentalomas: A Disease of Modern Technology Offering Opportunities for Improved Patient Care.
Ioachimescu AG et al.
Endocrinol Metab Clin North Am. 2015 Jun;44(2):335-354.

“Detection of AI warrants clinical, biochemical, and radiological evaluation to establish its secretory status and risk of malignancy. Careful review of the lipid content, size, and imaging phenotype of an adrenal mass is needed to evaluate the risk for malignancy. Identification of an AI may be an opportunity to identify an underlying secretory tumor that may have been otherwise unrecognized.”
Adrenal Incidentalomas: A Disease of Modern Technology Offering Opportunities for Improved Patient Care.
Ioachimescu AG et al.
Endocrinol Metab Clin North Am. 2015 Jun;44(2):335-354.

“Adrenal incidentalomas are defined as nodules greater than 1 cm incidentally discovered during imaging performed for nonadrenal disorders. Adrenal nodules are common, occurring in 4.4% of patients undergoing computed tomography (CT), and in 6% of the population in a large autopsy series. Because the prevalence of adrenal nodules increases with age, and as cross-sectional imaging use continues to expand, the overall number of incidental adrenal nodules detected is expected to increase.”
Incidental Adrenal Nodules 
Daniel I. Glazer, Michael T. Corwin, William W. Mayo-Smith
Radiol Clin N Am 59 (2021) 591–601

”Most incidentally detected adrenal nodules are benign, most commonly nonfunctioning adenomas. Although almost all small adrenal nodules can safely be ignored, a small percent- age of incidentally discovered adrenal nodules require further work-up to determine if they represent clinically relevant neoplasms (adrenocortical carcinoma [ACC], metastases, or pheo- chromocytoma).”
Incidental Adrenal Nodules 
Daniel I. Glazer, Michael T. Corwin, William W. Mayo-Smith
Radiol Clin N Am 59 (2021) 591–601

“ In clinical practice therefore, 10 HU is the most widely used threshold value for the diagnosis of lipid-rich adrenal adenoma.”
Adrenal Imaging
Blake MA et al.
AJR 2010; 194:1450-1460

Mean 0
SD 21
Minimum -56
Maximum 59

0 HU to 64 HU

31 HU at 10 minutes
S/P injection

“Myelolipoma is an uncommon benign tumor composed of mature adipose cells and hematopoietic tissue. The prevalence in autopsy series is between 0.08% and 0.2% . Typically, myelolipoma arises in the adrenal gland. Extra-adrenal myelolipoma is rare and is found most commonly in the presacral and other retroperitoneal areas . Usually asymptomatic and discovered incidentally at cross-sectional imaging, myelolipoma occasionally causes discomfort due to compression or hemorrhage.”
CT and MR Imaging of Extrahepatic Fatty Masses of the Abdomen and Pelvis: Techniques, Diagnosis, Differential Diagnosis, and Pitfalls
Pereira JM et al.
RadioGraphics January 2005 vol. 25 no. 1 69-85

“The prevalence of malignancy in patients with adrenal tumors of 4 cm or more in diameter was 31%. Older age, male sex, nonincidental mode of discovery, larger tumor size, and higher unenhanced CT attenuation were associated with an increased risk for malignancy. Clinical context should guide management in patients with adrenal tumors of 4 cm or more in diameter.”
Clinical, Biochemical, and Radiological Characteristics of a Single-Center Retrospective Cohort of 705 Large Adrenal Tumors
Nicole M. Iñiguez-Ariza et al.
Mayo Clin Proc Innov Qual Outcomes. 2018 Mar; 2(1): 30–39.