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Approach to the Adrenal Incidentaloma

Dr. Anthony Glover and Prof. Stan Sidhu
University of Sydney Endocrine Surgical Unit and Kolling Institute of Medical Research, Royal North Shore Hospital.

An adrenal incidentaloma is a mass lesion greater than 1cm in diameter discovered by chance during radiologic examination.  Diagnosis of adrenal incidentaloma is becoming more common due to the use of modern imaging techniques such as computed tomography (CT).

While around 90% of adrenal incidentalomas are benign,1 the diagnostic work-up of an adrenal incidentaloma must include the consideration of whether the lesion secretes hormones (functional lesion) and whether the lesion is or could be malignant.  These guidelines (Fig 1) present general advice for patients presenting with a single adrenal incidentaloma.  Referral to an endocrinologist or endocrine surgeon is recommended for clinicians unfamiliar with the work-up or for those with bilateral adrenal masses.

Diagram showing suggested approach to the adrenal incidentaloma
Figure 1

Approximately 10% of adrenal incidentalomas are functional and can produce excess steroids, mineralocorticoids, sex hormones or catecholamines.1 If on focused history (including family history) and examination, hormone excess is suspected, subsequent investigations are tailored for that excess.  For asymptomatic patients, subclinical Cushing’s syndrome and pre-symptomatic pheochromocytoma should be excluded.  Subclinical Cushing’s syndrome is investigated using the 1mg overnight dexamethasone suppression test.  For subclinical pheochromocytoma, investigation is by measurement of 24-hour urinary fractionated metanephrines and catecholamines.  If these tests are positive then referral to an endocrinologist or endocrine surgeon should take place.

For patients with symptoms suggestive of a functional lesion, referral to an endocrinologist or endocrine surgeon should take place.  General guidelines for the work-up of these patients are as follows:

  1. Pheochromocytoma: assessment of plasma metanephrines should be performed.
  2. Conn’s syndrome (mineralocorticoid producing adenoma): a mid-morning plasma paired aldosterone/renin ratio screen should be performed.  If this screen is abnormal, hypertension should be controlled with Prasozin and medications reviewed to assess for any that could cause a false negatives result (such as spironolactone & beta-blockers).  Further assessment of Conn’s syndrome is performed using adrenal vein sampling by a specialised unit.
  3. Cushing’s syndrome (cortisol producing adenoma): 24-hour urinary free cortisol.

In the absence of a diagnosis of pre-existing malignancy, less than 5% of adrenal incidentalomas are malignant.1 However due to the aggressive nature of adrenocortical carcinoma and the poor outcomes seen with advanced disease it is essential this diagnosis is considered in patients presenting with an adrenal incidentaloma.2 The maximum diameter of the adrenal mass is predictive of malignancy, with a size of over 4cm being recommended for surgical excision due to a risk of malignancy of over 20%.3 However size alone is not the only criteria for assessment. The radiographic characteristics of the lesion and any change in size over time are other important factors to be considered.  CT with 2-3mm cuts of the adrenal mass should be performed and assessment of radiograph attenuation performed using Hounsfield unit (HU) values.  On CT, a homogenous adrenal mass with a smooth border and an attenuation value of < 10 HU is most likely to be benign.4

For patients with an adrenal incidentaloma that are non-functional and not suspicious for malignancy and less than 4cm in a size, the role of further follow- should be tailored according to the patient.   The practice of our unit and other specialist units is for interval assessment and imaging (such as at one year) to assess for any new symptoms, change in size or in radiographic characteristics.4

References

  1. Cawood, T. J., Hunt, P. J., O'Shea, D., Cole, D. & Soule, S. Recommended evaluation of adrenal incidentalomas is costly, has high false-positive rates and confers a risk of fatal cancer that is similar to the risk of the adrenal lesion becoming malignant; time for a rethink? European Journal of Endocrinology 161, 513–527 (2009).
  2. Ip, J. C. Y. et al. Improving Outcomes in Adrenocortical Cancer: An Australian Perspective. Ann Surg Oncol (2014). doi:10.1245/s10434-014-4133-4
  3. Mantero, F. et al. A Survey on Adrenal Incidentaloma in Italy. The Journal of Clinical Endocrinology & Metabolism 85, 637–644 (2000).
  4. Nieman, L. K. Approach to the Patient with an Adrenal Incidentaloma. The Journal of Clinical Endocrinology & Metabolism 95, 4106–4113 (2013).

Note

  • Imaging of adrenal incidentaloma should be with fine cut adrenal CT with assessment of the lesion including pre-contrast and delayed contrast phases, unless contraindicated.
  • Investigations for subclinical Cushing’ syndrome is by the 1mg overnight dexamethasone suppression test and for subclinical pheochromoctyoma is by the 24-hour urinary fractionated metanephrines and catecholamines.
  • HU - Hounsfield unit assessment of radiograph attenuation.

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