4.5 Adrenal gland Flashcards
Adrenal gland anatomy and blood supply
4-6 cm long, limbs 3-6 mm thick
Cortex (90% of gland) from mesoderm, divided into zona glomerulosa (aldosterone), fasiculata (cortisol), reticularis (epiandrosterone)
Medulla from neuroectoderm, secretes adrenaline and noradrenaline
Adrenal arteries: superior (inferior phrenic), middle (aorta), inferior (renal)
Adrenal venous drainage - right to IVC, left to left renal vein
Radioisotope studies for functional adrenal lesions
I-131 MIBG or Indium 111 Octreotide to investigate adrenal functional lesions
Adrenal adenoma - prevalence, CT/MR
2-10% at autopsy, 1% at abdominal CT; majority non-functioning
If no malignancy, lesion less than 1.5 cm almost always adenoma
If less than 10 HU at CT Sn 71% Sp 98% for adenoma
Wash out by >60% (absolute) (less than 30 HU) or >40% relative (to enhanced) at 15 minute CT
MR - if non-functioning, isointense T1W and iso-/hyperintense on T2W to liver, with drop off on out of phase
Adrenal myelolipoma - imaging, complication
Rare, benign, encapsulated, always non-functioning
Can haemorrhage spontaneously and become necrotic
Demonstrate intralesional fat
US: hyperechoic
CT: heterogeneous ± calcification (20%; especially post haemorrhage)
MR: high T1W if fat or haemorrhage, drop off out of phase if fat
Adrenal cysts - cause, size
May be large (>3 cm), peripheral / curvilinear calcification in 15%
45% endothelial, 40% pseudocysts (due to haemorrhage / infarct / cystic degeneration; show irregular walls / septations)
5% echinococcus, 10% epithelial cyst
Adrenal haemorrhage - bilaterality and causes
20% bilateral; may calcify even at > 1 year post haemorrhage
Spontaneous, especially if coagulopathic;
Post-traumatic (right > left), burns, sepsis (DIC - Waterhouse Freidrichsen)
Post adrenal venography (10% risk)
Haemorrhagic metastases (melanoma)
Phaeochromocytoma - origin, location, CFs
Catecholamine secreting from chromaffin cells of medulla
85% adrenal, 8% paraaortic, 5% organ of Zuckerkandl, 1% urinary bladder
Cause headaches, palpitations, sweating, tremor, anxiety, HTN (but only 0.1% HTN caused by phaeo)
Rule of tens: 10% bilateral / familial / malignant / extra-adrenal
98% intra-abdominal
If extra-adrenal, called paragangliomas, 40% malignant, most common at organ of Zuckerkandl (aortic bifurcation)
Phaeochromocytoma - imaging, biochemical
Increased vanilmandelic acid on 24 hour urine (50%)
Usually > 3 cm, solid, hypervascular; rarely calcified / cystic
Uptake on MIBG (80% Sn), octreotide, PET
Enhances strongly on CT; ‘light bulb’ very high signal on T2W MR
Bx: may precipitate hypertensive crisis
Phaeochromocytoma - syndrome associations
Syndromes: MEN (5%; usually bilateral and almost always intraadrenal) 2 and 3, NF, vHL, Sturge-Weber, Carney’s Triad, tuberous sclerosis
Adrenal carcinoma - association, CFs
Rare, can be functioning (causes Cushing’s, virilisation) or non-functioning
Association with MEN 1
Bimodal peak - paediatric and 40 y/o
Generally large (>12 cm), haemorrhage is poor prognostic indicator
20-30% calcified, generally heterogeneous enhancement on CT
Metastasis by haematogenous / lymphatic spread
Adrenal Metastasis - cause, imaging
If known malignancy, 38-57% adrenal nodules are metastatic (usually lung, breast, renal, melanoma)
Frequently bilateral; generally large, heterogenous and poorly marginated
Delayed washout on CT, no drop off on chemical shift imaging
PET most accurate - uptake > liver on PET (but clear cell renal, carcinoid and bronchoalveolar may be false negative)
Adrenal lymphoma - type, bilaterality
NHL most commonly, 70% bilateral
Cushing’s Syndrome - cause, CFs, imaging
Due to glucocorticoid excess
Obese, bruising, striae, wasting, DM (10-15%), osteoporosis, HTN
70% due to adrenal hyperplasia: 90% ACTH pituitary adenoma, 10% ectopic ACTH (lung, islet cell pancreatic, ovarian)
20% adrenal adenomas (2-4 cm)
10 % adrenal cortical carcinoma (but only 10% of these cause Cushing’s)
Cortisol producing adenomas are characteristically low density on CT with remainder of gland atrophic
If adrenal hyperplasia due to ACTH secretion, causes diffuse bilateral enlargement
Adrenal vein sampling sometimes used if no cause on CT
Nonspecific adrenal hyperplasia - associations
Acromegaly (100%), hyperthyroidism (40%), HTN (15%)
Conn’s Syndrome - cause, CFs
Due to aldosterone excess; F > M, usually 40 y/o
HTN, hypokalaemia, polyuria, hypernatraemia
Primary (Conn’s disease): 75% due to aldosterone-secreting adenoma (small, low attenuation, eccentric); 25% adrenal cortical hyperplasia
Secondary: RAS, reninoma
