Adrenal incidentaloma - investigation and treatment

(Aotea News, August 2010)

Michael Crooke
Chemical Pathologist

An adrenal incidentaloma is an adrenal mass greater than 1cm in diameter, serendipitously discovered by radiologic examination in the course of investigating some other condition.

The prevalence has been stated to be around 3–4 per cent on abdominal CT but improved modern imaging may show a higher prevalence, as rates as high as 9–12 per cent have been noted in autopsy series.

How to investigate an adrenal incidentalom

Two questions need to be answered:

  • Is the mass malignant
  • Is there excessive secretion of hormones?

Imaging characteristics and size are pointers to malignancy. Tumours over 4–5cm are more likely to be malignant but even if the imaging characteristics suggest a benign adenoma these larger tumours should be considered for surgery. Nearly 90 per cent of incidentalomas are benign.

All patients should be evaluated for abnormal hormone secretion, irrespective of whether the imaging characteristics suggest carcinoma or benign adenoma. Even if there are no obvious clinical features, 10–15 per cent of adrenal incidentalomas will show abnormal secretion.

Phaeochromocytoma and subclinical Cushing’s syndrome are the most frequent endocrine problems in incidentalomas. In a hypertensive patient, primary hyperaldosteronism also should be considered. Hormonal hypofunction is very rare.

Investigation of hormonal secretion is as follows:

  • For Cushing’s syndrome there is a range of possible investigations, but for adrenal incidentaloma the overnight 1mg Dexamethasone suppression test is the best. The Dexamethasone is taken at 11.00pm and serum cortisol is measured at 8.00am the following morning. Results: <50nmol/L exclude Cushing’s syndrome, <100 excludes with high probability, 100–135 is equivocal and over 135nmol/L is consistent with Cushing’s syndrome.
  • For phaeochromocytoma 24-hour urinary catecholamines and/or metanephrines remain the best initial tests. Plasma metanephrines may be useful in difficult cases but are not a first line test and should be ordered only after discussion. Plasma catecholamines are not a useful test.
  • The plasma aldosterone, renin ratio, taken before 10.00am, is the best screening test for primary hyperaldosteronism. Aldactone or amiloride within six weeks invalidate the test. It is not absolutely necessary to stop ACE inhibitors and diuretics, although interpretation is easier if they can be stopped for two weeks before testing. Calcium channel blockers and alpha blockers do not affect the test. A ratio >800–1000 with aldosterone over 400 is strongly suggestive of abnormal secretion and referral for confirmatory tests is indicated.

What are the appropriate treatments?

For proven phaeochromocytoma, surgery is the appropriate treatment, irrespective of the size of the tumour. The surgical option should be offered in primary hyperaldosteronism but medical management may be appropriate in some cases.

The optimal management of subclinical Cushing’s syndrome associated with adrenal incidentaloma is not established but if surgery is not offered long-term follow up is required.

The effectiveness of long-term follow up of non-secreting benign adrenal incidentalomas is not established but it is generally agreed that there should be repeat imaging at six to 12 months and thereafter according to clinical judgement.

If the original imaging is suggestive but not definite for malignancy, repeat imaging should be at three months.

Biochemical monitoring should be repeated annually for up to four years before it is concluded that the tumour will remain non-secretory.