Adrenal Adenoma

Adrenal adenoma is a benign adrenocortical tumour, most often found incidentally on imaging done for another reason. Most are non-functioning, and some secrete cortisol, aldosterone or (rarely) sex steroids.

Adrenal masses are found in 3 to 5% of adults on imaging, rising to 10% in older people. About 70 to 80% are non-functioning adenomas, 5 to 30% show mild autonomous cortisol secretion, 1 to 10% secrete aldosterone, and 1 to 5% are phaeochromocytomas. Adrenocortical carcinoma is under 2% of incidentalomas.

Malignancy risk rises with size, with irregular margins, heterogeneity and high unenhanced density.

Pathophysiology

Most adenomas are monoclonal tumours with somatic variants (CTNNB1, PRKACA, KCNJ5, CACNA1D, ATP1A1) which cause autonomous hormone production.

Lipid rich adenomas have low CT attenuation, which allows separation from other masses.

• Usually asymptomatic.
• Hormone excess: Cushing syndrome, hypertension with hypokalaemia (aldosterone), or virilisation (rare).
• Ask about episodic headache, sweating and palpitations to exclude phaeochromocytoma.

Red flags.

• Size over 4 cm, irregular margins or heterogeneity.
• Rapid growth, weight loss, pain or known cancer in another organ.
• Paroxysmal hypertension, sweating and palpitations.

• Unenhanced CT: homogeneous, under 10 Hounsfield units and under 4 cm indicates a benign lipid rich adenoma and needs no more imaging.
• Indeterminate lesions (over 10 Hounsfield units): contrast washout CT (absolute washout over 60% or relative over 40% at 15 minutes suggests adenoma), MRI with chemical shift, or fluorodeoxyglucose PET-CT.
• Hormones in every patient: 1 mg overnight dexamethasone test (cortisol under 50 nmol/L, 1.8 micrograms/dL, excludes autonomous secretion). Plasma free or urinary metanephrines unless under 10 Hounsfield units. Aldosterone to renin ratio if hypertensive or hypokalaemic. Sex steroids and precursors if virilisation or a large mass.

Differential diagnosis.

• Phaeochromocytoma, adrenocortical carcinoma and metastasis.
• Myelolipoma, adrenal cyst, haemorrhage and ganglioneuroma.
• Granulomatous infection and lymphoma.

• Non-functioning benign adenoma: no further imaging or hormone testing if under 4 cm and under 10 Hounsfield units. Indeterminate lesions: repeat imaging at 6 to 12 months and resect if growth exceeds 20% (and at least 5 mm).
• Functioning adenoma: unilateral laparoscopic adrenalectomy. Cortisol secreting: cover with hydrocortisone 100 mg intravenously at induction then 200 mg over 24 hours, then taper, with replacement until recovery.
• Aldosterone secreting: before surgery, spironolactone 12.5 to 25 mg daily titrated to 100 mg daily with potassium and eGFR checks. Adrenal vein sampling is advised before surgery in patients over 35 years.
• Phaeochromocytoma: alpha blockade for 7 to 14 days (doxazosin 2 to 16 mg daily or phenoxybenzamine 10 mg twice daily increasing as tolerated), then a beta blocker, with generous sodium and fluid intake.
• Surgery for tumours over 4 cm with suspicious features, and adrenal carcinoma needs open or oncological resection in a specialist centre.

Special groups. Older adults and those with limited life expectancy: avoid repeated imaging for small, benign looking lesions.

Monitoring. Indeterminate lesions: repeat unenhanced CT or MRI at 6 to 12 months. Autonomous cortisol secretion: yearly clinical review and comorbidity assessment.

Referral and escalation. Endocrinology for all functioning or indeterminate lesions; multidisciplinary review and adrenal surgery for lesions over 4 cm, suspected carcinoma or phaeochromocytoma.