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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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---
title: "Adrenal Cyst"
docid: "c5d717a3-3d6e-4e86-9efe-1ad0ec14740f"
breadcrumbs:
- "Genitourinary"
- "Diagnosis"
- "Adrenal"
- "Benign Neoplasms"
- "Adrenal Cyst"
---
# KEY FACTS
- ## Imaging
- "Adrenal cyst" is descriptive term, not pathological diagnosis
- True adrenal cysts
- Majority are endothelial cysts (lymphangiomas)
- Epithelial cysts exceedingly rare
- Simple, or minimally complex, adrenal cyst, thin rim calcification, no enhancement
- Pseudocysts
- Prior hemorrhage inferred
- Nonenhancing but complex contents and wall calcification
- Relevant history (extraadrenal malignancy, rapid growth), biochemical evaluation (cortisol, metanephrines): Consider underlying adrenal neoplasm
- Enhancing soft tissue components may suggest adrenal mass hemorrhage and pseudocyst formation
- Parasitic (echinococcal) cyst
- Rare outside endemic areas
- Typically in setting of generalized echinococcus
- ## Top Differential Diagnoses
- Adrenal adenoma
- CECT: Enhancing mass without visible wall or peripheral calcifications
- Gastric diverticulum
- Air-, fluid-, or contrast-filled mass with no enhancement of contents
- Adrenal myelolipoma
- Macroscopic fat
- Necrotic adrenal tumor
- Complex wall with heterogeneous contents
- Retroperitoneal bronchogenic cyst
- ## Clinical Issues
- No treatment required usually
- Imaging surveillance performed, although intensity and length of follow-up not defined
- Biochemical evaluation (cortisol, metanephrines) routinely performed to exclude underlying adrenal neoplasm
- Surgical resection for complex cyst with enhancing components, or symptomatic cyst
- ## Diagnostic Checklist
- Complicated cyst has high attenuation, thick enhancing wall, &/or septations
# TERMINOLOGY
- ## Definitions
- "Adrenal cyst" is descriptive term, not pathological diagnosis
- Can mean true cyst, pseudocyst, or cystic mass
# IMAGING
- ## General Features
- ### Best diagnostic clue
- Well-defined, nonenhancing, water-density adrenal mass ± calcifications
- ### Location
- Suprarenal
- Unilateral > bilateral (8-10% of cases)
- ### Size
- < 5 cm (50%), up to 20 cm
- ## CT Findings
- ### NECT
- Unilocular or multilocular mass
- Well-defined, round to oval, homogeneous mass usually with water (0 HU) or near-water density
- Higher- or mixed-attenuation mass (hemorrhage, intracystic debris, crystals)
- Wall usually very thin
- ↑ wall thickness, up to 3 mm for complex cysts
- Calcifications
- Rim-like or nodular (51-69%)
- Centrally in intracystic septation (19%)
- Punctate within intracystic hemorrhage (5%)
- ### CECT
- No central enhancement ± wall enhancement
- Coronal reformats helpful to determine organ of origin if large cyst
- ## MR Findings
- ### T1WI
- Homogeneous, hypointense mass
- Hyperintense mass (hemorrhage)
- ### T2WI
- Hyperintense mass
- ## Ultrasonographic Findings
- Simple or septated suprarenal cyst
- Shadowing from calcification
- Real-time examination helpful to differentiate adrenal cyst from adjacent (renal, pancreatic) cyst
- ## Imaging Recommendations
- ### Best imaging tool
- CECT or MR; US for confirmation
# DIFFERENTIAL DIAGNOSIS
- [Adrenal Adenoma](/document/adrenal-adenoma/e2916d86-5f9f-4dd3-9576-1a7b89d8dda0)
- NECT: Lipid-rich adenoma (< 10 HU) mimics adrenal cyst
- Peripheral or septal calcification favors adrenal cyst
- CECT: **Enhancing mass** without visible wall or peripheral calcifications
- Assess washout kinetics to diagnose lipid-poor adenoma
- MR: Signal suppression at out-of-phase, chemical-shift imaging
- US: Solid adrenal lesion
- [Gastric Diverticulum](/document/gastric-diverticulum/eeb101f0-8bdf-4771-b44a-fe6e73b3a463)
- May simulate left adrenal cyst
- Air-, fluid-, or contrast-filled suprarenal mass
- No enhancement
- Normal adjacent adrenal gland
- [Adrenal Myelolipoma](/document/adrenal-myelolipoma/5813a554-06a4-4696-af71-7ce50693039d)
- Fat (not fluid) attenuation mass
- ## Necrotic Adrenal Tumor
- Primary (pheochromocytoma or carcinoma) or metastatic
- Clinical history, biochemical evaluation, lesion complexity suggest correct diagnosis
- Enhancing soft tissue components
- ## Retroperitoneal Bronchogenic Cyst
- Rare, benign, suprarenal fluid or soft tissue attenuation lesion
- Adjacent to but separate from adrenal gland
- ## Renal Cyst
- Coronal MR/CT or US useful to determine organ of origin of large, retroperitoneal cystic lesions
# PATHOLOGY
- ## General Features
- ### Etiology
- Congenital (endothelial, epithelial) cysts
- Acquired (post hemorrhagic, inflammatory) pseudocysts
- Cystic, hemorrhagic degeneration of underlying adrenal neoplasm
- ## Staging, Grading, & Classification
- Accepted classification scheme
- Pseudocyst
- Most common type of cystic adrenal lesion in surgical series
- No epithelial or endothelial lining: Fibrous cyst wall
- Potentially as complication of prior trauma or hemorrhage though history of such often not elicited
- May be associated with underlying adrenal neoplasm (pheochromocytoma, adrenal carcinoma, myelolipoma)
- Attenuation and complexity at imaging varies depending upon hemorrhagic component
- Wall and septal calcification common
- Endothelial cyst
- Subtypes: Lymphangiomatous and hemangiomatous
- True cyst: Endothelial lining
- Originate from preexisting vascular malformation or obstructed, ectatic lymphatic channels
- Thin rim calcification typical
- Epithelial cyst
- Extremely rare: No acinar structures within normal adrenal gland
- Mesothelial origin suggested (mesothelial cells potentially incorporated within adrenal gland during embryogenesis)
- Parasitic (hydatid) cyst
# CLINICAL ISSUES
- ## Presentation
- ### Most common signs/symptoms
- Typically asymptomatic
- Larger cysts may be symptomatic
- Abdominal pain
- Hemorrhage
- Clinical history (malignancy, hypertension) elicited
- May indicate cystic degeneration of underlying adrenal neoplasm (e.g., metastasis, pheochromocytoma)
- Diagnosis
- Usually incidental finding at imaging
- Endocrine-biochemical evaluation performed to exclude underlying functional adrenal tumor
- ## Demographics
- ### Age
- Any, though patients 20-50 years of age most common
- ### Sex
- M:F = 1:3
- ### Epidemiology
- Uncommon entity: Autopsy incidence 0.064-0.18%
- Accounts for 1% of incidental adrenal lesions in large imaging series
- ## Natural History & Prognosis
- Complications
- Hypertension, infection, rupture, hemorrhage
- Excellent prognosis for vast majority of incidental, benign adrenal cysts
- Prognosis for pseudocysts secondary to adrenal neoplasm depends upon tumor histology
- ## Treatment
- No treatment required usually
- Imaging follow-up typically performed
- Intensity and length of surveillance not defined
- Cysts may enlarge over time
- Endocrine evaluation (cortisol, metanephrine, etc.) performed
- Surgical resection if symptomatic, underlying adrenal neoplasm
- Laparoscopic resection preferred
# DIAGNOSTIC CHECKLIST
- ## Consider
- Complicated cyst may suggest underlying adrenal neoplasm
- Clinical history, biochemical evaluation, and prior imaging helpful
- ## Image Interpretation Pearls
- Simple adrenal cyst: Scant septation, no enhancement, thin rim calcification
- Likely benign endothelial cyst or pseudocyst
- Coronal imaging helpful to determine organ of origin (and exclude exophytic renal or pancreatic cyst)
- Complicated cyst: High attenuation, thick enhancing wall, &/or septations
- Complexity may suggest underlying adrenal neoplasm and secondary pseudocyst
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---
title: "Adrenal Myelolipoma"
docid: "5813a554-06a4-4696-af71-7ce50693039d"
breadcrumbs:
- "Genitourinary"
- "Diagnosis"
- "Adrenal"
- "Benign Neoplasms"
- "Adrenal Myelolipoma"
---
# KEY FACTS
- ## Terminology
- Uncommon benign tumor composed of mature fat tissue and hematopoietic elements (myeloid and erythroid cells)
- ## Imaging
- Benign, nonfunctioning adrenal tumor
- Accounts for 7-15% of incidental adrenal masses, usually in older population
- Typically unilateral and very rarely bilateral
- Large tumors can mimic retroperitoneal lipomas, liposarcomas
- Asymptomatic, though larger tumors may hemorrhage
- CT
- Lesion containing fat attenuation (-30 to -90 HU)
- Usually well-defined mass with recognizable pseudocapsule (remaining adrenal)
- Punctate calcifications seen in 24% of cases
- Coronal reconstruction helpful to differentiate from exophytic renal angiomyolipoma
- MR
- Tumor with major fat component
- T1WI in phase: Typically hyperintense
- FS sequences: Loss of signal
- ## Top Differential Diagnoses
- Adrenal adenoma
- Intracellular lipid vs. macroscopic fat
- Adrenal metastases and lymphoma
- Retroperitoneal liposarcoma
- Involving perirenal space, may simulate adrenal (or renal) fatty tumor
- Pheochromocytoma
- Highly vascular, prone to hemorrhage and necrosis
- Adrenal carcinoma
- Renal angiomyelolipoma
- Coronal CT reconstruction or MR useful to determine organ of origin
# TERMINOLOGY
- ## Definitions
- Uncommon benign tumor composed of mature adipose tissue and hematopoietic elements
# IMAGING
- ## General Features
- ### Best diagnostic clue
- Suprarenal mass containing fat
- ### Location
- Suprarenal
- Rare extraadrenal myelolipomas (presacral, retroperitoneal)
- ### Size
- Usually 2-10 cm, rarely 10-20 cm
- Key concepts
- Benign neoplasm of adrenal gland
- Autopsy prevalence rate of 0.2-0.4%
- Accounts for 7-15% of adrenal "incidentalomas"
- Usually unilateral incidental finding in older patient
- Larger tumors can bleed spontaneously
- Most are nonfunctioning (do not secrete hormones)
- Large myelolipomas can mimic retroperitoneal lipoma or liposarcoma
- ## CT Findings
- CT appearance depends on histologic composition
- Most tumors are heterogeneous adrenal masses composed of varying percentages of fat
- Low-attenuation suprarenal lesion containing fat density (-30 to -90 HU)
- Average NECT attenuation value of tumor: -74 HU in one series
- Interspersed soft tissue attenuation components: Myeloid elements, hemorrhage
- Presence of macroscopic fat within tumor is diagnostic
- Punctate calcifications seen in 24% of cases
- Usually well-defined mass with recognizable pseudocapsule (remnant adrenal)
- Coronal reconstructions may help determine organ of origin: Adrenal myelolipoma vs. exophytic renal angiomyelolipoma
- ## MR Findings
- MR appearance depends on histologic composition
- Tumor with major fat component
- T1WI in phase: Typically hyperintense
- T1WI out phase: Persistent hyperintensity of macroscopic fat
- T1WI FS: Confirmatory suppression of signal
- Bone marrow elements (myeloid and erythroid cells)
- Low signal on T1WI, moderate signal on T2WI
- Hemorrhage: Varying T1, T2 signal depending on age of blood
- ## Ultrasonographic Findings
- ### Grayscale ultrasound
- Well-defined, echogenic mass (↑ fat tissue)
- Often overlooked: Lack of mass effect and isoechogenicity relative to retroperitoneal fat
- Heterogeneous mass (↑ myeloid cells)
- ## Angiographic Findings
- Conventional
- Differentiate myelolipoma from retroperitoneal liposarcoma by determining origin of blood supply and vascularity of tumors
- ## Nuclear Medicine Findings
- Typically not metabolically active, though uptake reported at FDG PET
- ## Imaging Recommendations
- Helical NECT or MR with FS sequence
# DIFFERENTIAL DIAGNOSIS
- [Adrenal Adenoma](/document/adrenal-adenoma/e2916d86-5f9f-4dd3-9576-1a7b89d8dda0)
- Lipid-rich adenoma: ↓ attenuation (< 10 HU) at NECT
- Can contain small amounts of macroscopic fat due to lipomatous metaplasia
- CECT: Washout 15 minutes post injection: > 50%
- Relative washout: > 40%
- Absolute washout: > 60%
- [Metastases and Lymphoma, Adrenal](/document/adrenal-lymphoma/44639c90-bd04-4e2a-a470-2c28a0e2ff78)
- Bilateral lesions: Clinical history paramount
- Metastases: Soft tissue attenuation (signal)
- Lymphoma: May maintain adreniform shape, adjacent retroperitoneal adenopathy
- [Liposarcoma, Retroperitoneal](/document/retroperitoneal-sarcoma/c1466b30-b730-41c4-a065-2c2de018a5f7)
- Retroperitoneal primary sarcoma involving perirenal space may simulate adrenal (or renal) fatty tumor
- [Pheochromocytoma](/document/pheochromocytoma/7d3c4062-643c-4030-8783-f85184ad8132)
- Highly vascular, prone to hemorrhage and necrosis
- Hyperintense on T2WI, bilateral in multiple endocrine neoplasia syndromes (MEN) syndromes
- Clinical history (labile hypertension) and urinary catecholamines
- [Adrenal Carcinoma](/document/adrenal-cortical-carcinoma/bdc7a08b-a64f-4bd2-9dfc-24331728e85e)
- Rare, unilateral, invasive, enhancing mass
- Venous invasion, distant metastases
- May contain fat: Engulfed retroperitoneal fat vs. lipomatous metaplasia
- ## Renal Angiomyelolipoma
- Exophytic upper pole angiomyolipoma may mimic
- Coronal reconstruction/MR helpful to determine organ of origin
# PATHOLOGY
- ## General Features
- ### Etiology
- Unknown
- Best hypothesis: Reticuloendothelial cell metaplasia of capillaries in adrenal (stress/infection/necrosis)
- Secondary hypothesis: Myelolipoma represents site of extramedullary hematopoiesis
- ### Associated abnormalities
- Adrenal collision tumors (coexistent myelolipoma and adenoma typical)
- Large, bilateral myelolipomas reported with longstanding, poorly treated congenital adrenal hyperplasia
- ## Gross Pathologic & Surgical Features
- Cut section: Fat, soft tissue components
- ## Microscopic Features
- Mature fat cells and megakaryocytes; no malignant cells
- Calcification
- Hemorrhage within larger lesions
# CLINICAL ISSUES
- ## Presentation
- ### Most common signs/symptoms
- Asymptomatic
- Usually incidental finding on CT, MR
- Typically biochemically nonfunctioning
- Symptomatic
- Acute abdomen: Flank pain due to rupture and hemorrhage
- Case reports of hormonally active tumors: Cushing, Conn syndromes, virilization
- Diagnosis: Pathognomonic MR/CT features
- Biopsy reserved for larger, atypical lesions, though prone to sampling error
- ## Demographics
- ### Age
- Usually older patients (50-70 years old)
- ### Epidemiology
- Autopsy incidence: 0.2-0.4%
- ## Natural History & Prognosis
- Complication: Rupture with hemorrhage (rare)
- Prognosis: Excellent
- ## Treatment
- When diagnosis is certain, surgery not needed for lesions < 5-7 cm
- Surgery reserved for larger, symptomatic, or atypical lesions
- Surgical series have confirmed utility of laparoscopic resection
# DIAGNOSTIC CHECKLIST
- ## Consider
- Differentiate from other tumors (lipid-rich adenoma)
- Key is presence of imaging-apparent adipose tissue; avoid further work-up for incidental mass
- ## Image Interpretation Pearls
- Well-defined, heterogeneous, fat-attenuation tumor on CT
- T1 hyperintense, signal loss with fat suppression
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---
title: "Adrenal"
docid: "082ca43c-db5c-4770-aeed-0c6ea317e8fc"
breadcrumbs:
- "Genitourinary"
- "Anatomy"
- "Adrenal"
---
# TERMINOLOGY
- ## Abbreviations
- Adrenal corticotrophic hormone (ACTH)
# GROSS ANATOMY
- ## Overview
- Adrenal (**suprarenal**) glands are part of endocrine and neurological systems
- Essentially different organs within same structure, composed of thick outer cortex and thin inner medulla
- Lie within**perirenal space**bilaterally, bounded by**renal** (**perirenal**)**fascia**, above/medial to kidneys
- Composed of "body" and 2 limbs (medial and lateral)
- ## Anatomic Relationships
- Right adrenal is usually more apical in location
- Lies anterolateral to right crus of diaphragm, medial to liver, and posterior to inferior vena cava (IVC)
- Often pyramidal in shape with inverted V shape on transverse section
- Left adrenal is usually more caudal and lies medial to upper pole of left kidney, lateral to left crus of diaphragm, and posterior to splenic vein and pancreas
- Often crescentic in shape with λ or triangular shape on transverse section
- ## Divisions
- **Adrenal cortex**
- Embryologically derived from mesoderm
- Divided into 3 distinct zones (zona glomerulosa, zona fasciculata, and zona reticularis)
- Secretes **mineralocorticoids**(aldosterone) from zona glomerulosa, **glucocorticoids**(cortisol) from zona fasciculata, and **androgens**from zona reticularis
- **Adrenal medulla**
- Embryologically derived from neural crest
- Part of sympathetic nervous system
- **Chromaffin cells** secrete **catecholamines** (mostly epinephrine) into bloodstream
- **Vessels**,**nerves**, and **lymphatics**
- Arteries
- **Superior adrenal arteries**: Typically 6-8; from inferior phrenic arteries
- **Middle adrenal artery**: 1; from abdominal aorta
- **Inferior adrenal artery**: 1; from renal arteries
- Veins
- **Right adrenal vein** drains into IVC
- **Left adrenal vein** drains into left renal vein (usually after joining left inferior phrenic vein)
- Nerves
- Extensive sympathetic connection to adrenal medulla
- Presynaptic sympathetic fibers from paravertebral ganglia end directly on secretory cells of medulla
- Lymphatics
- Drain to **lumbar** (**aortic** and **caval**) **nodes**
# ANATOMY IMAGING ISSUES
- ## Multimodality Imaging Appearance
- No consensus on "normal" size or thickness of adrenals but average thickness of ~ 3 mm for medial/lateral limbs
- While not based on any strong evidence, > 10-mm thickness can be used as threshold for hyperplasia
- MR: Generally isointense to liver on T1 MR and isointense to slightly hyperintense to liver on T2 MR
- Ultrasound: Easiest to visualize in newborns (as result of physiologic enlargement) and become progressively more difficult to visualize with age
- Right adrenal gland easier to visualize than left (due to lack of liver as acoustic window and overlying bowel gas)
- Adrenal glands in adults usually hypoechoic (juxtaposed against hyperechoic periadrenal fat), although medulla can rarely be discretely seen and appears hyperechoic
- ## Key Concepts
- **Adrenal** (**cortical**) **adenomas**
- Very common (at least 2% of general population) but usually cause no symptoms
- Mostly "nonfunctioning" but identical to "functional" adenomas that cause Cushing/Conn syndrome
- Most adenomas contain abundant lipid (precursor to steroid hormones), allowing definitive diagnosis using CT/MR sequences that highlight lipid
- Lipid is intracellular/intercellular (not macroscopic deposits of fat)
- Best CT technique: Nonenhanced CT with nodule measuring < 10 HU; or multiphase-enhanced CT with nodule demonstrating "washout" kinetics
- Best MR technique: Chemical-shift MR with signal dropout within nodule on opposed-phase images
- Standard imaging features for diagnosis of adenoma should be used for nodules measuring < 4 cm, while lesions > 4 cm should raise concern for malignancy
- **Pheochromocytoma** (tumor of adrenal medulla)
- Signs: Headache, palpitations, excessive perspiration
- 90% arise in adrenal, 90% unilateral, 90% benign
- Similar tumor arising in other chromaffin cells of sympathetic ganglia is called **paraganglioma**
- More common with multiple endocrine neoplasia, neurofibromatosis, and von Hippel-Lindau
- Often markedly hypervascular in arterial phase
- **Adrenal myelolipoma**
- Uncommon benign tumor (usually incidental finding) composed of mature adipose and hematopoietic tissue
- Characterized by presence of **macroscopic fat**
- May have internal soft tissue component or calcification
- **Adrenocortical carcinoma**
- Highly aggressive malignancy with poor prognosis
- Large, heterogeneous mass (often with necrosis, hemorrhage, or calcification) with frequent local invasion, vascular invasion, and distant metastases
- **Cushing syndrome** (excess cortisol)
- Signs: Truncal obesity, hirsutism, hypertension
- Causes: Pituitary tumors (→ adrenal corticotrophic hormone), exogenous (medications) > adrenal adenoma > carcinoma
- **Conn syndrome** (excess aldosterone)
- Signs: Hypertension, hypokalemic alkalosis
- Causes: Adrenal adenomas > hyperplasia > carcinoma
- **Addison syndrome**(adrenal insufficiency)
- Signs: Hypotension, weight loss, altered pigmentation
- Causes: Autoimmune disease > adrenal metastases > adrenal hemorrhage > adrenal infection
# CLINICAL IMPLICATIONS
- ## Clinical Importance
- Rich adrenal blood supply due to endocrine function
- Results in adrenal glands being common site for hematologic **metastases** (lung, breast, melanoma, etc.)
- Adrenal glands respond to stress (trauma, sepsis, surgery, etc.) by secreting ↑ cortisol and epinephrine
- Overwhelming stress may result in **adrenal hemorrhage**or acute adrenal insufficiency (addisonian crisis)
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