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Add comprehensive documentation for adrenal conditions

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