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---
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title: "Adrenal Adenoma"
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docid: "e2916d86-5f9f-4dd3-9576-1a7b89d8dda0"
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breadcrumbs:
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- "Genitourinary"
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- "Diagnosis"
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- "Adrenal"
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- "Benign Neoplasms"
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- "Adrenal Adenoma"
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---
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# KEY FACTS
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- ## Imaging
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- Well-circumscribed, uniform, low-attenuation, small adrenal mass
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- Low attenuation due to abundant intracytoplasmic lipid
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- Imaging features of typical lipid-rich adenomas
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- NECT: < 10 HU (71% sensitivity, 98% specificity)
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- MR: Significant decrease in signal on out-of-phase T1WI due to intravoxel lipid and water
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- May show focal areas of heterogeneous attenuation or absence of signal loss due to degeneration, hemorrhage, and fibrin deposition
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- Clinical context key to differentiate from collision tumor: Unlikely in absence of extraadrenal malignancy
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- Lipid-poor adenomas (10-40% cases): Utilize relative or absolute CT contrast washout kinetics for diagnosis
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- Accounts for vast majority of adrenal "incidentalomas"
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- Imaging intensive algorithm suggested for incidental adrenal lesions, though overwhelming majority are benign and hormonally inactive
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- Primary hyperaldosteronism (Conn syndrome): 80% due to unilateral, typically small (< 2 cm) adenoma
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- Cushing syndrome: 80-85% due to adrenal hyperplasia
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- Typically shows FDG uptake < that of liver on PET/CT
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- ## Top Differential Diagnoses
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- Adrenal metastases and lymphoma
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- Adrenal (macronodular) hyperplasia
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- Pheochromocytoma
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- Adrenal carcinoma
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- Adrenal myelolipoma
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- Gastric diverticulum
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- Adrenal cyst
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- ## Diagnostic Checklist
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- Asymptomatic mass: Usually nonfunctioning adenoma, even in patients with known cancer
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- NECT and MR are equally accurate for diagnosis of lipid-rich adenoma
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- Utilize dedicated CECT adrenal protocol with 15-minute delayed imaging for diagnosis of potential lipid-poor adenomas
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# TERMINOLOGY
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- ## Definitions
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- Benign adrenal cortical tumor
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# IMAGING
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- ## General Features
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- ### Best diagnostic clue
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- Imaging strategies target typical adenoma histology: Abundant intracytoplasmic lipid
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- Low attenuation (< 10 HU) on NECT
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- Significant loss of signal on out-of-phase T1WI MR (intravoxel fat and water)
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- ### Size
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- Cushing syndrome adenoma: 2-5 cm
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- Conn syndrome adenoma: Classically < 2 cm (20% < 1 cm)
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- Vast majority of incidental, hormonally inactive adrenal adenomas are small (< 2 cm)
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- ### Morphology
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- Usually round to oval suprarenal mass
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- Key concepts
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- Most common adrenal cortex tumor (10% bilateral)
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- Accounts for > 90% of all "incidentalomas"
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- May occur in up to 9% of general population, diagnosed on 5% of CT exams with various indications
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- Lipid-rich adrenal adenoma: 60-90% of adenomas
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- Lipid-poor adrenal adenoma: 10-40% of adenomas
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- Increased incidence in patients with diabetes and hypertension
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- NECT (or chemical shift MR): Study of choice to diagnose incidental adrenal masses
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- Classified into 2 types based on function
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- Nonhyperfunctioning: Normal hormone levels
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- Hyperfunctioning: Primary hyperaldosteronism, Cushing syndrome, hyperandrogenism
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- **Cushing syndrome**
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- 15-25% of cases are due to autonomous adrenal adenoma
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- 80-85% of cases are due to**adrenal hyperplasia**
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- Adenomas usually > 2 cm
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- **Primary hyperaldosteronism (Conn syndrome)**
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- 80% of cases are due to****adrenal adenoma
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- 20% of cases are due to adrenal hyperplasia
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- Adenomas are often small (< 2 cm)
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- ## CT Findings
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- ### NECT
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- Smooth, well defined, round or oval in shape
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- Homogeneous soft tissue mass of 0-20 HU
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- **Lipid-rich adrenal adenoma** (60-90% of cases)
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- Uniform low attenuation
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- Metaanalysis of < 10 HU threshold: 71% sensitivity, 98% specificity
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- Sensitivity may increase to almost 90% with histogram analysis (identify negative pixels), though variable results and scanner dependent
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- **Lipid-poor adrenal adenoma** (10-40% of cases)
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- Attenuation varies from 10-30 HU
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- Difficult to differentiate from metastases on NECT
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- Cushing syndrome due to adrenal adenoma
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- Remainder of ipsilateral gland and contralateral adrenal gland may be atrophic due to ↓ ACTH levels
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- ↑ cortisol: Feedback inhibition on pituitary ACTH
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- ACTH-independent macronodular hyperplasia: Multiple, bilateral, functioning adrenal adenomas
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- Conn syndrome due to adrenal adenoma
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- Remainder of ipsilateral gland and contralateral adrenal gland appear normal
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- Large adenomas
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- More heterogeneous than small adenomas
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- ± hemorrhage, cystic degeneration, calcification
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- Growth should raise suspicion for malignancy
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- ### CECT
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- Enhancing adrenal mass that deenhances rapidly
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- Dedicated adrenal CT exam incorporates initial dynamic enhanced phase (~ 70-second delay) and 15-minute delay
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- Relative percentage washout = dynamic enhanced (HU) - delayed (HU) / dynamic enhanced HU
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- Relative percentage washout > 40%: 96% sensitivity, 100% specificity
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- Absolute percentage washout (if NECT available) = dynamic enhanced (HU) - delayed (HU) / dynamic enhanced (HU) - unenhanced (HU)
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- Absolute percentage washout > 60%: 86-88% sensitivity, 92-96% specificity
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- 10-minute delay utilized by some centers, but shorter delay may decrease sensitivity
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- Adrenal washout calculators readily available online
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- Utilize technique for indeterminate, potentially lipid-poor adenomas
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- Clinical context critical: Rapid washout can be seen with pheochromocytomas, renal cell, hepatocellular carcinoma, and hypervascular metastases
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- Dual-energy CT and iodine subtraction techniques can generate virtual noncontrast (VNC) images
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- May identify lipid-rich adenomas and obviate need for additional imaging
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- Iodine:VNC ratio ≥ 6.7 has sensitivity and specificity of 95% for adenoma (higher ratios in adenoma compared to metastasis)
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- ## MR Findings
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- T1WI and T2WI
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- Low to intermediate signal
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- Chemical shift (in- and out-of-phase) imaging
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- Mainstay of MR diagnosis
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- Sensitivity and specificity equivalent to NECT
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- Signal loss on out-of-phase T1WI due to intravoxel water and fat protons
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- Inverse relationship between percentage of lipid-rich cells and relative ↓ signal on out-of-phase imaging
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- May not identify lipid-poor adenomas
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- Visual inspection of signal in phase (SIP) and out of phase (SOP), though quantitative analysis may be helpful
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- Adrenal to spleen chemical shift imaging (CSI) ratio: Lesion:spleen SOP/adrenal/spleen SIP
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- < .71 = adenoma
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- Adrenal signal intensity index: 100 x (SIP - SOP) / SIP
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- > 16.5% = adenoma
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- Beware technical pitfalls
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- Sampling of 1st echo pair at 3T is challenging
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- India ink artifact mimics signal loss, particularly in small adrenal lesions
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- Other primary or secondary adrenal lesions may contain lipid
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- Adenomas and metastases may coexist in same gland (collision tumor)
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- T1 C+ MR
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- Rapid, uniform enhancement and deenhancement
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- Ancillary MR techniques
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- Diffusion MR: Not specific (ADC overlap between adenomas and metastases)
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- MR spectroscopy: Choline:creatinine and choline:lipid ratio discriminatory threshold ratios may aid in adrenal lesion characterization, though larger studies needed
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- ## Ultrasonographic Findings
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- ### Grayscale ultrasound
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- Nonspecific, solid suprarenal mass
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- Right suprarenal mass seen more clearly left due to acoustic window provided by liver
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- ## Angiographic Findings
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- Conventional
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- Adrenal arteriography
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- Catheterization of renal or inferior adrenal arteries shows vascular supply of adrenal tumors
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- Adenomas are usually hypo- to moderately vascular
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- No arterial encasement or venous laking or puddling, which are malignant vascular features
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- Adrenal venography
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- Most commonly to obtain adrenal vein samples
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- Advocated for patients with primary hyperaldosteronism triaged to adrenalectomy
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- Technically difficult study but may confirm laterality of small, aldosterone-secreting adenoma
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- Technical approach and criteria for positive study varies; ACTH stimulation may increase accuracy
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- Adrenal adenoma is seen as filling defect within adrenal gland displacing adjacent vessels
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- Circumferential vein frequently seen around adrenal adenoma
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- ## Nuclear Medicine Findings
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- PET/CT
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- Utilized as part of malignancy staging
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- Markedly increased F-18 FDG uptake characteristic of metastases
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- Adenomas may also accumulate F-18 FDG, typically less intense than liver
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- Potential false-negatives: Metastases from primary carcinomas that are non-FDG avid (e.g., neuroendocrine tumors)
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- SUV thresholds published but adenomas typically less intense than liver
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- Adrenocortical scintigraphy by using NP-59
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- NP-59 is cholesterol analog that binds to low-density lipoprotein receptors of adrenal cortex
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- NP-59 used and dexamethasone: Accentuate uptake in non-ACTH-dependent adrenal tissues (adenoma)
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- Normal NP-59: When both adrenal glands are seen 5 days after injection or thereafter
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- Adrenal adenoma: Unilateral early adrenal visualization before day 5 after NP-59 injection
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- Adrenal hyperplasia: Bilateral early adrenal visualization before day 5 after NP-59 injection
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- ## Imaging Recommendations
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- NECT is initial study of choice to confirm diagnosis of lipid-rich adrenal adenoma
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- ROI should encompass lesion: Attenuation < 10 HU is diagnostic
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- In- and out-of-phase MR equivalent to NECT for lipid-rich lesions
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- Signal dropout on out-of-phase T1WI MR: Qualitative assessment typically suffices
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- CECT, including 15-minute delayed phase, used for potential lipid-poor adenomas: Calculate either relative or absolute washout
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# DIFFERENTIAL DIAGNOSIS
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- [Adrenal Metastases and Lymphoma](/document/adrenal-lymphoma/44639c90-bd04-4e2a-a470-2c28a0e2ff78)
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- Adrenal metastases
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- Unilateral or bilateral masses ± central necrosis, hemorrhage
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- Usually known to have malignancy elsewhere
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- NECT: Metastases mimic lipid-poor adenoma
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- CECT: Hypo- or hypervascular and prolonged washout pattern
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- Adrenal lymphoma
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- Usually spread to adrenal gland from retroperitoneal tumor
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- Unilateral or bilateral masses
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- Unilateral primary lymphoma (non-Hodgkin) can mimic adenoma
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- Hypovascular; moderate enhancement with contrast
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- [Adrenal Myelolipoma](/document/adrenal-myelolipoma/5813a554-06a4-4696-af71-7ce50693039d)
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- Small or large, asymptomatic adrenal mass
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- Intramural macroscopic fatty elements on imaging
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- [Adrenal Hyperplasia](/document/adrenal-hyperplasia/90d09395-41d4-49b4-bb1d-4cb00b8bc272)
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- Adrenal glands are often symmetrically enlarged
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- Width of adrenal gland limbs > 10 mm (diagnostic)
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- No discrete mass or nodule seen as rule
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- Dominant macronodule of macronodular hyperplasia mimics small adrenal adenomas
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- Cortisol-secreting adenoma: Remainder of ipsilateral and contralateral glands, atrophic (↓ ACTH)
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- Macronodular hyperplasia: Both glands are enlarged (due to elevated ACTH levels)
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- No obvious enhancement and washout pattern seen
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- [Pheochromocytoma](/document/pheochromocytoma/7d3c4062-643c-4030-8783-f85184ad8132)
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- Tumor > 3 cm in most cases; classically T2 hyperintense
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- Highly vascular tumor prone to hemorrhage, necrosis
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- Bilateral adrenal tumors in multiple endocrine neoplasia (MEN) syndromes
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- [Unilateral Adrenal Hemorrhage](/document/adrenal-hemorrhage/5812e5c4-ca8a-4af5-884b-f75795bcde0f)
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- Chronic hematoma: Well-defined, round, low-density, mass-like lesion simulating adenoma
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- [Adrenal Carcinoma](/document/adrenal-cortical-carcinoma/bdc7a08b-a64f-4bd2-9dfc-24331728e85e)
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- Rare, unilateral, invasive and enhancing mass
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- > 6 cm when initially diagnosed
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- [Gastric Diverticulum](/document/gastric-diverticulum/eeb101f0-8bdf-4771-b44a-fe6e73b3a463)
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- Abnormal, rounded soft tissue lesion in left suprarenal area; mimics adrenal mass
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- Diverticular contents do not enhance, whereas adenomas do
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- Distend stomach with gas and fluid; scan in prone position to distend diverticulum
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- [Ganglioneuroma](/document/pheochromocytoma/7d3c4062-643c-4030-8783-f85184ad8132)
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- Younger patients; mean age: 27 years
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- Larger mass; average tumor size: 8 cm
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- ## Adrenal Cyst
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- Attenuation similar to lipid-rich adenoma
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- Lack of enhancement, rim calcification may suggest diagnosis
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# PATHOLOGY
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- ## General Features
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- ### Etiology
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- Unknown
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- ### Associated abnormalities
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- MEN syndromes
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- Most adrenals with adenoma have normal function
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- Occasionally adenoma causes adrenal hyperfunction
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- Normal adrenocortical secretory hormones
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- Cortisol, aldosterone, androgens
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- ## Gross Pathologic & Surgical Features
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- Well-delineated, tan-yellow, ovoid mass
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- 3 microscopic patterns
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- Pure (fasciculata- or reticularis-type cells), mixed, or hybrid
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- May have focal areas of degeneration, hemorrhage, and fibrin deposition
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- ## Microscopic Features
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- 70% of adenomas: High % of intracytoplasmic lipid
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- 30% of adenomas: Low % of intracytoplasmic lipid
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# CLINICAL ISSUES
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- ## Presentation
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- ### Most common signs/symptoms
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- Asymptomatic incidental CT finding
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- Conn syndrome: Hypertension and weakness
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- Cushing syndrome: Moon facies, truncal obesity, purple striae, and buffalo hump
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- Virilization in women
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- Lab data: ↑ aldosterone, cortisol, &/or androgens
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- Diagnosis: Clinical, biochemical, imaging, histology
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- ## Demographics
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- ### Age
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- Prevalence of adenoma increases with age
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- Peak at 60-69 years, decreasing thereafter
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- ### Epidemiology
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- Most common adrenal tumor of all incidentalomas
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- ↑ incidence in patients with diabetes or hypertension
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- Occurs in up to 9% of population (postmortem data)
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- ## Natural History & Prognosis
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- Prognosis: Excellent when incidental and nonhyperfunctioning
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- ## Treatment
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- No treatment when asymptomatic incidental finding
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- Laparoscopic removal of gland if hyperfunctioning
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# DIAGNOSTIC CHECKLIST
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- ## Consider
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- Asymptomatic mass: Usually nonhyperfunctioning adenoma, even in patient with known cancer
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- ## Image Interpretation Pearls
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- Well-defined, low-density (< 10 HU) suprarenal mass
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- Enhances with washout pattern > 50% within 15 minutes
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- Out-of-phase T1WI MR: Signal dropout, lipid-rich mass
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