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Difficulty: HardDiagnostic Workup and Test Sequencing

A 55-year-old woman comes to the office to discuss the results of a recent imaging study. She visited an urgent care clinic two weeks ago for acute right flank pain. An unenhanced CT scan of the abdomen and pelvis showed a 3.0-mm nonobstructing right renal calculus and an incidental 3.2-cm homogenous, lipid-rich mass in the left adrenal gland. Her flank pain has since resolved. Her medical history is significant for hypertension diagnosed six months ago, which is currently managed with amlodipine. Her blood pressure today is 148/92 mmHg, pulse is 78/min, and BMI is 29 kg/m². Physical examination is unremarkable, with no abdominal striae, proximal muscle weakness, or hirsutism. Serum potassium is 3.8 mEq/L. Which of the following is the most appropriate next step in the diagnostic evaluation of this patient?

  1. Overnight 1-mg dexamethasone suppression test, plasma free metanephrines, and plasma aldosterone-to-renin ratioAnswer
  2. B
    CT-guided fine-needle aspiration of the adrenal mass
  3. C
    Magnetic resonance imaging of the abdomen with intravenous contrast
  4. D
    Repeat unenhanced CT scan of the abdomen in 6 to 12 months
  5. E
    24-hour urine collection for fractionated metanephrines and catecholamines only

Answer

The correct approach is to perform a comprehensive biochemical evaluation using an overnight 1-mg dexamethasone suppression test, plasma free metanephrines, and a plasma aldosterone-to-renin ratio.
The initial management of an incidentally discovered adrenal mass (incidentaloma) focuses on evaluating its functional status and assessing its malignant potential. Because this mass is small (<4 cm) and possesses benign radiologic features (homogenous, lipid-rich on unenhanced CT), immediate surgical removal or further radiologic characterization with MRI is not indicated. However, a biochemical evaluation is mandatory. All patients with an adrenal incidentaloma require screening for autonomous cortisol secretion (e.g., 1-mg overnight dexamethasone suppression test) and pheochromocytoma (e.g., plasma free metanephrines or 24-hour urine fractionated metanephrines). Furthermore, because this patient has a history of hypertension, screening for primary aldosteronism using a plasma aldosterone-to-renin ratio is also required.

Step-by-Step Solution

1
Analyze the clinical presentation.
The patient has an incidentally discovered 3.2-cm adrenal mass (incidentaloma) with benign imaging characteristics (lipid-rich, homogenous) and a history of hypertension.
Identifying the incidental nature, size, imaging characteristics, and comorbid hypertension dictates the required diagnostic pathways.
2
Evaluate the need for immediate surgical or further radiologic investigation.
The mass is less than 4 cm and has benign radiologic features on the unenhanced CT.
Masses >4 cm or those with heterogeneous, lipid-poor features on imaging have a higher suspicion for malignancy and may require distinct management.
3
Determine the necessary biochemical screening tests.
Screening for subclinical Cushing syndrome and pheochromocytoma is required for all patients. Screening for primary aldosteronism is added due to the presence of hypertension.
All adrenal incidentalomas must be evaluated for functional status (hormone hypersecretion) regardless of the presence of typical clinical symptoms.

Key Concept

Diagnostic Workup of Adrenal Incidentaloma
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Topics

Diagnostic Workup and Test Sequencing

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