Adrenal incidentaloma
An adrenal incidentaloma is a mass in the adrenal gland discovered on a scan performed for an unrelated reason. They are common — found in several per cent of abdominal CT scans, and more frequently with increasing age — and the great majority are harmless, non-functioning adenomas requiring nothing more than reassurance. The work of the clinic is answering two questions properly, and only two: is it producing hormones, and is it cancer? Everything else follows from those answers, and a patient who has had both questions addressed clearly can usually be discharged with confidence.
How they form
The adrenal gland has two functionally distinct parts, and lesions arise from both:
- The cortex, derived from mesoderm, with three zones producing different hormones: the zona glomerulosa (aldosterone, controlling salt and blood pressure), the zona fasciculata (cortisol), and the zona reticularis (androgens).
- The medulla, derived from neural crest cells, producing adrenaline and noradrenaline.
The commonest incidentaloma by far is a non-functioning cortical adenoma — a benign proliferation of cortical cells that produces no excess hormone. These are rich in intracytoplasmic lipid, which is the basis of the single most useful radiological test: lipid gives them low attenuation on unenhanced CT, and a value of 10 Hounsfield units or less is essentially diagnostic of a benign adenoma. This one measurement resolves the majority of cases.
Other lesions found incidentally include:
- Functioning adenomas — producing cortisol (Cushing's syndrome or, far more often, mild autonomous cortisol secretion) or aldosterone (primary aldosteronism)
- Phaeochromocytoma — arising from the medulla, producing catecholamines. A meaningful proportion are found incidentally and are biochemically silent or only mildly symptomatic, which is why every incidentaloma is screened for it.
- Myelolipoma — a benign mixture of mature fat and bone marrow elements, with a characteristic and reassuring appearance of macroscopic fat on CT
- Adrenal cyst, haematoma, granuloma
- Adrenocortical carcinoma — rare, but the possibility that drives the assessment
- Metastasis — the adrenal is a common site for metastasis from lung, breast, kidney, melanoma and gastrointestinal primaries. In a patient with a known cancer, an adrenal mass is a metastasis until proved otherwise, and the probabilities are reversed.
Symptoms
By definition, incidentalomas are found without symptoms prompting the scan. However, a careful history and examination frequently uncover features that were not previously connected:
- Hypertension — particularly resistant hypertension requiring several drugs, or of early onset
- Low potassium, with muscle weakness and cramps — suggesting aldosterone excess
- weight gain, easy bruising, thin skin, purple stretch marks, proximal muscle weakness, new or worsening diabetes, osteoporosis — suggesting cortisol excess
- episodic headache, sweating, palpitations and pallor, often with paroxysmal hypertension — suggesting phaeochromocytoma
- virilisation in women or rapid onset of any of these — raising the possibility of adrenocortical carcinoma
Mild autonomous cortisol secretion deserves particular mention, because it is far commoner than full Cushing's syndrome and is easily overlooked. Patients have no classical physical features but do have the metabolic consequences — hypertension, type 2 diabetes, obesity, osteoporosis and an increased cardiovascular risk. Recognising it matters because these are treatable consequences.
How the assessment is done
The assessment is standardised and should be completed in every patient.
Is it functioning? — biochemical testing
- 1mg overnight dexamethasone suppression test — in all patients. Dexamethasone given at night should suppress morning cortisol below 50 nmol/L; failure to suppress indicates autonomous cortisol production.
- Plasma or 24-hour urinary metanephrines — in all patients, to exclude phaeochromocytoma. This must be done before any biopsy or surgery, because manipulating an unsuspected phaeochromocytoma can precipitate a hypertensive crisis.
- Aldosterone-to-renin ratio — in patients with hypertension or low potassium.
- Sex hormones and steroid precursors — where adrenocortical carcinoma is suspected or there are virilising features.
Is it malignant? — imaging
- Unenhanced CT with Hounsfield unit measurement — the key investigation. ≤10 HU and homogeneous indicates a benign lipid-rich adenoma with very high reliability.
- Size — the risk of malignancy rises with size. Lesions above 4cm warrant closer attention; above 6cm the risk is substantial.
- Features suggesting malignancy — irregular margins, heterogeneity, necrosis, calcification, local invasion, rapid growth, and delayed washout of contrast (benign adenomas wash out contrast rapidly; malignant lesions and phaeochromocytomas do not).
- Chemical shift MRI — an alternative means of demonstrating intracellular lipid, useful where CT is equivocal or radiation is a concern.
- PET-CT — particularly useful in patients with a known cancer, to distinguish metastasis from adenoma.
The rule about biopsy
Adrenal biopsy is rarely indicated and is potentially dangerous. It is useful in only one situation: a patient with a known extra-adrenal cancer in whom establishing whether the adrenal lesion is a metastasis would change management, and only after phaeochromocytoma has been excluded biochemically. Biopsy cannot reliably distinguish adrenocortical carcinoma from adenoma, and biopsying a phaeochromocytoma or an adrenocortical carcinoma may cause a hypertensive crisis or seed tumour along the needle track respectively.
Management
Reassurance and discharge
A homogeneous lesion under 4cm with an unenhanced attenuation of 10 HU or less and normal biochemistry is benign. Current guidance is that such lesions require no further imaging and no further follow-up — a change from older practice of repeated scanning, which generated anxiety, radiation and cost without benefit. This should be stated clearly to the patient rather than leaving them with an open-ended sense of uncertainty.
Surveillance
For lesions that are indeterminate on imaging, repeat imaging at six to twelve months to confirm stability. Repeat biochemical testing where mild cortisol excess was borderline, or where new hypertension or diabetes develops.
Surgery
Adrenalectomy is indicated for:
- any functioning tumour — phaeochromocytoma, aldosterone-producing adenoma, cortisol-producing adenoma causing Cushing's syndrome
- mild autonomous cortisol secretion in younger patients with hypertension, diabetes or osteoporosis that may improve with removal — an individualised decision
- lesions suspicious for malignancy on imaging
- lesions above 4cm, particularly if indeterminate, and generally all lesions above 6cm
- growth of more than about 1cm on surveillance
Laparoscopic adrenalectomy is the standard approach, by transperitoneal or posterior retroperitoneoscopic route, and is associated with short hospital stay and rapid recovery. Open surgery is preferred where adrenocortical carcinoma is suspected, because capsular rupture during laparoscopic removal seeds the tumour and worsens the outlook substantially.
Preparation matters: phaeochromocytoma requires alpha-blockade for two to three weeks beforehand; patients with cortisol-secreting tumours require perioperative and postoperative steroid cover, since the contralateral gland is suppressed and will take months to recover.
Recovery
After laparoscopic adrenalectomy, hospital stay is typically one to two nights and return to normal activity two to four weeks. Patients who had cortisol excess require tapering steroid replacement over months, with clear instructions about sick-day dosing, and should carry a steroid card.
When to seek an opinion
Any adrenal mass should have the standard biochemical screen performed. Resistant hypertension, unexplained low potassium, new-onset diabetes with weight gain and easy bruising, or episodic headache with sweating and palpitations all warrant assessment for an adrenal cause even without a known mass.
Common questions
A lump was found on my adrenal gland by accident. Is it cancer?
Almost certainly not. These are common findings, particularly with age, and the great majority are harmless non-functioning growths. Two questions need answering — whether it produces hormones, and whether it has any features suggesting cancer — and both can usually be settled with a blood test, a urine test and one specific type of CT measurement.
What is the significance of the "Hounsfield units" on my scan?
It is a measure of density. Benign adrenal growths are rich in fat within their cells, which makes them appear less dense. A value of ten or below on a scan taken without contrast is essentially diagnostic of a harmless growth, and it settles the question in most people without any further testing.
Why do I need urine and blood tests if I feel completely well?
Because some of these growths produce hormones in amounts too small to cause obvious symptoms but large enough to raise blood pressure, cause diabetes, weaken bones or — in one particular type — cause a dangerous surge in blood pressure if the gland is operated on or biopsied. The tests are simple and they change what happens next.
Do I need repeat scans every year?
If the growth is small, uniform and has the typical low-density appearance, and your hormone tests are normal, then no — current guidance is that no further scans are needed. This is a change from older practice, which involved repeated scanning that caused anxiety and radiation exposure without any benefit. You should be told this clearly rather than left wondering.
Should it be biopsied?
Almost never. A biopsy cannot reliably distinguish a benign adrenal growth from a cancerous one, and it is hazardous if the growth turns out to be the hormone-producing type. The only situation where it helps is when you already have a cancer elsewhere and knowing whether this is a deposit from it would change your treatment.
When does it need removing?
If it produces hormones, if it has features on the scan suggesting it may be cancerous, if it is larger than about four centimetres, or if it grows on repeat scanning. Otherwise it is left alone.
Can I live with one adrenal gland?
Yes, entirely normally. The remaining gland takes over completely. The exception is where the removed gland was producing excess cortisol, in which case the other gland has become dormant and needs several months of steroid tablets, gradually reduced, while it recovers. That period needs careful supervision and clear instructions about what to do if you become ill.
Could this be a spread from another cancer?
If you have a known cancer, this is a genuine possibility and is assessed specifically, often with a PET scan or occasionally a biopsy. If you have no history of cancer, it is very unlikely, and the usual assessment applies.
Related conditions
Other conditions of the adrenal glands covered on this site:
- Primary aldosteronism (Conn's syndrome)
- Cushing's syndrome
- Phaeochromocytoma and paraganglioma
- Adrenocortical carcinoma
- Adrenal metastases
This page provides general information and does not replace an individual medical consultation. Assessment and treatment are decided for each patient after review of their history, examination and investigations.