ADRENAL GLANDS

Cortex - derived from mesothelium
Medulla - derived from neural crest cells
Avg thickness ~3 mm for medial/lateral limbs; >10 mm can be used as hyperplasia threshold

Adrenal cortex:

Consists 3 layers that synthesize distinct hormones derived from cholesterol (superficial -> deep):
- Zona glomerulosa (mineralocorticoids) - produces aldosterone
- Zona fasciculata (glucocorticoids) - responds to ACTH to produce GC
- Zona reticularis (androgens) - produces androgens
Adrenal hyperplasia, adenoma, and cortical carcinoma are lesions that can be diagnosed on imaging.

Adrenal medulla:

Secrete catecholamines into bloodstream; norepinephrine and epinephrine derived from tyrosine.
Masses that arise in medulla include...
- Pheochromocytomas
- Neuroblastic tumors (ganglioneuroma, ganglioneuroblastoma, neuroblastoma)

Arteries:

Superior adrenal: 6-8; from inferior phrenic arteries
Middle adrenal: 1; from abdominal aorta
Inferior adrenal: 1; from renal arteries

Veins:

Right AG drains into IVC
L adrenal drains into L renal vein

Presynaptic SNS fibers from paravertebral ganglia end directly on secretory cells of medulla.

APPROACH TO ADRENAL LESIONS

nandra-et-al-2020-technical-and-interpretive-pitfalls-in-adrenal-imaging.pdf

BIOCHEMICAL APPROACH

HYPERFUNCTION

Cushing syndrome:

Excess cortisol via...

- Exogenous admin
- Endogenous production 2/2...
  - Pituitary dz: Cushing dz
  - Nonpituitary dz:
    - Idiopathic adrenal hyperplasia
    - Adrenal adenoma
    - Ectopic/paraneoplastic ACTH (SCLC)

Conn syndrome:

Excess aldosterone production (usually 2/2 adrenal adenoma) -> HTN and hypokalemia.
Adenomas implicated in CS are typically small and may be difficult to detect on CT.
Localizing side of excess hormone production w/ venous sampling may be a helpful diagnostic adjunct.

Adrenal cortical carcinoma:

Very rare malignancy that arises from the cortex
Typically causes an increase in levels of all cortical adrenal hormones and their precursors.

Pheochromocytoma

Usually arise from adrenal medulla
Can be assoc w/ excess catecholamine production.
Sx: episodic HA, tachycardia, diaphoresis, and uncontrolled HTN

HYPOFUNCTION

Substantial destruction of adrenal tissue is required to produce adrenal insufficiency.

Addison dz
- NOT an imaging diagnosis
- Chronic adrenocortical insufficiency
- Can be 2/2 autoimmune destruction and AGs or by prior infection.
Waterhouse-Friderichsen syndrome
- Post-hemorrhagic adrenal failure 2/2 Neisseria Meningitidis bacteremia
Idiopathic adrenal hemorrhage:
- Usually unilateral and rarely causes adrenal hypofunction

INDETERMINATE ADRENAL MASS

RSNA ADRENAL NEOPLASMS

RADASS ADRENAL INCIDENTALOMA

RADASS ADRENAL LESIONS

ADRENAL WASHOUT CT

Most useful for distinguishing AA from emts in patients w/ known nonhypervascular primary malignancy.
Washout CT findings should not be stand-alone features for diagnosis of lipid-poor adenoma; other features such as mass size, heterogeneity, and clinical context should be considered.

Adrenal protocol: 3 phases
- NECT
  - If <10 HU on NECT = AA -> no further WU
  - If >10 HU on NECT -> 60 sec + delayed CECT
- CECT - adrenal parenchymal phase @ 60 sec
- Delayed CECT 15 min
If NECT images are unavailable, relative washout calculation can still be performed.

AAs demonstrate rapid washout
Adrenal mets demonstrate slow washout: <60% absolute; <40% relative)
In a pt w/ a known primary malignancy, lesions that do not demonstrate benign washout kinetics are suspicious for, but not diagnostic of, mets.

CT WASHOUT CALCULATOR

Some malignant adrenal mass may rarely contain intracytoplasmic lipid and lose signal on OOP:

Well differentiated adrenocortical carcinoma
Metastatic clear cell RCC
metastatic HCC
Liposarcoma

Adrenal Adenoma

Benign tumor of adrenal cortex
Usually incidental but can occasionally produce excess aldosterone -> secondary HTN (Conn syndrome)
Majority of AAs have 2 properties that allow for imaging diagnosis: Microscopic fat and/or rapid washout characteristics on CECT.
- Nodule <=10 HU on NECT can be reliably diagnosed as AA
  - 75% of AAs measure <10HU on NECT = lipid-rich
  - 25% of AAs measure >10 HU on NECT (lipid-poor) and require CECT to assess washout characteristics.
- AA washout characteristics: absolute WO >60% or a relative WO >40%
- If nodule does not meet CT density or WO criteria for AA, it is considered indeterminate.
  - In practice, an indeterminate adrenal nodule in a patient w/o known malignancy most likely represents a lipid-poor adenoma and advanced imaging is usually NOT required.
- If dx is requried for further management (lung CA w/o known mets), further WU is based on lesion size, hx of malignancy, and availability of prior imaging. In some cases, FDG PET/CT and BX are helpful.
- BX is indicated for an adrenal mass that remains indeterminate after comprehensive imaging workup, particulalry in the context of underlying malignancy.
Collision tumor: coexistence of 2 tumors w/n an adrenal mass, such as mets w/n an adrenal adenoma or myelolipoma.
- If a lesion appears heterogeneous or shows an interval increase in size, then a collision tumor should be considered in patients w/ a known primary malignancy, even if a portion of the lesion is <10 HU.
MRI - chemical shift imaging
- Lipid rich adenomas contain intracytoplasmic lipid which MRI can detect by taking advantage of the fact that protons resonate at different frequencies in fat and in water.

MYELOLIPOMA

benign neoplasm consisting of myeloid cells (erythrocyte precursors) and fat cells.
In rare cases, they can be extraadrenal and are pathologically indistinguishable from extramedullary hematopoiesis which occurs in patients w heme dz
Adrenal mass w/ macroscopic/gross fat is diagnostic of myelolipoma
Usually incidental and can be large (>4 cm) at time of diagnosis.
Few reports of adrenocortical carcinoma and metastatic carcinoma w/ macroscopic fat.
A retroperitoneal liposarcoma may mimic a myelolipoma, although liposarcoma typically presents as a large mass that may displace, rather than arise from, the AG.
Adrenal myelolipoma and renal AML are NOT the same. These entities are unrelated but both diagnosed by the presence of macroscopic fat.

ADRENAL CYST

Relatively uncomm on but have typical characteristics of benign cysts that occur elsewhere in the body: internal fluid content w/ thin, smooth, nonenhancing wall.

Endothelial adrenal cyst: MC (45%) type and may be lymphatic or angiomatous in origin.
Pseudocyst: 2/2 adrenal hemorrhage represents 39% and lack epithelial lining. peripheral calcs may be present.
Epithelial cysts: rare, 9%

Occasionally an AC may have a complex appearance and can be difficult to differentiate from a cystic/necrotic neoplasm. -> percutaneous aspiration or surgical resection may be considered.

Small, asx simple cysts can be ignored.

A cyst may rarely grow so large as to cause sx, such as dull pain or compression of the stomach/duodneum.
VERY rarely, hydatic dz may affect the AGs and produce a complex cystic lesion w/ an internal membrane.

PHEOCHROMOCYTOMA

Intra-adrenal paraganglioma; neuroendocrine tumor that typically originates from the adrenal medulla.

Composed of chromaffin cells that secrete catecholamines and cause uncontrolled secondary HTN and episodic headaches/diaphoresis.
Hereditary type: small bilateral adrenal lesions in young patient.
Sporadic type: large > 3 cm, unilateral mass in older pt
Syndromes:
- MEN2A/B: b/l intraadrenal pheos
- NF1
- vHL
- Carney's triad (gastric leiomyosarcoma, pulmonary chondroma, paraganglioma)
- Hereditary paraganglioma-pheochromocytoma syndrome: SDHD gene mutation.
90% RULE: 90% arise in adrenal, 90% unilateral, ~90% are benign
- Called paraganglioma when tumor arises in other chromaffin cells of sympathetic ganglia. Typically subdiaphragmatic but can be anywhere along sympathetic chain from neck to bladder.
- Organ of Zuckerkandl (along Ao bifurcation to level of bladder) and urinary bladder are relatively common sites.
  - If urinary bladder is involved, it can produce post-micturation syncope.

PHEOCHROMOCYTOMA STATDx

IMAGING FEATURES

CANNOT be distinguished from other tumors by imaging alone. Need clinical hx and lab values (urinary and plasma fractionated metanephrines)
Highly vascular and prone to hemorrhage

US: hypoechoic suprarenal lesion +/- cystic change
NECT: >10 HU
CECT:
- Delayed washout kinetics typically similar to adrenal CA and mets, but rapid washout like adenoma is possible.
- Heterogeneous enhancement 2/2 necrosis, cystic degeneration, hemorrhage.
MR: Variable T1/T2 signal 2/2 hemorrhage, cystic degeneration, necrosis; T2 light bulb hyperintensity
Ga-68 DOTATATE: ectopic, recurrent and metastatic tumors. (see below)

ADRENOCORTICAL CARCINOMA

ADRENAL CORTICAL CARCINOMA STATdx

Very rare w prevalence approx 1/1,000,000. Highly aggressive w/ poor prognosis
~66% are functional producing a disordered array of hormones that may manifest as Cushing syndrome, hyperaldosteronism, and virilization.

Imaging:

Large >4 cm and unilateral; irregular tumor margins
Central necrosis/hemorrhage w/ heterogeneous enhancement.
Calcification is common. Fat is rare.
Early local vascular invasion of renal vein or IVC
20% have distant mets at presentation lungs, liver nodes, bone.

ADRENAL METS

4th MC site of hematogenous mets after lungs, liver and bone.

Adrenal mets are present >25% of patients w known primary malignancy.

Melanoma (50%), lung/breast (30-40%), renal/GIT (10-20%)
Rich adrenal blood supply for endocrine function. As a result, adrenal glands are common site for hematologic mets (lung, breast, melanoma)
Unilateral or bilateral; central necrosis +/- hemorrhage
Usually <5 cm, larger if melanoma.
Must differentiate b/n isolated benign adrenal lesion (typically adenoma) and mets during initial staging:

Most mets show prolonged washout pattern unlike adenoma.
Rapid washout if hypervascular mets.

DIFFUSE ADRENAL DISORDERS

ADRENAL HEMORRHAGE

ADRENAL HEMORRHAGE STATdx

Can be spontaneous but in adults is usually due to anticoagulation or an underlying malignancy.
Hemorrhage can appear mass-like and is often heterogeneous on CT but does not enhancement of postcontrast images.
When prior imaging is available, it should be suspected in the event of rapid onset of an adrenal mass.
In this context F/U imaging can be helpful to confirm resolution and/or interval decrease in size.

ADRENAL CALCIFICATION

Not infrequent but rarely cause adrenal hypofunction.
Can be 2/2 hemorrhage, granulomatosis w polyangiitis, TB, and histoplasmosis.

ADRENAL HYPERPLASIA

ADRENAL HYPERPLASIA STATdx

Enlargment of adrenal glands

Adrenal body > 10 mm, limbs >5 mm
Typically bilateral and smooth w/ maintained shape
Majority are nonfunctional. minority demonstrate subclinical or clinical adrenal dysfunction.

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