A 48-year-old woman is evaluated in the clinic following a minor motor vehicle collision 2… — USMLE Step 3

A 48-year-old woman is evaluated in the clinic following a minor motor vehicle collision $2$ weeks ago. During her emergency department visit, a computed tomography (CT) scan of the abdomen and pelvis without contrast was performed to evaluate right-sided abdominal pain. The scan revealed no acute intra-abdominal injuries, but an incidental $2.8$ cm, well-circumscribed, homogeneous mass with an attenuation of $8$ Hounsfield units was identified in the right adrenal gland. The patient reports she feels well and has fully recovered from her mild abdominal wall contusion. She has no history of headaches, palpitations, episodic sweating, unexplained weight gain, or muscle weakness. Her medical history is significant for essential hypertension diagnosed $3$ years ago, which is well-controlled with amlodipine. She takes no other medications. Vital signs are a blood pressure of $128/82$ mmHg, a heart rate of $74$ /min, and a BMI of $25 \text{ kg/m}^2$ . Physical examination reveals no abdominal bruits, purple striae, facial plethora, or central adiposity. Which of the following is the most appropriate next step in the diagnostic workup for this patient's adrenal finding?

A
Measurement of basal morning serum cortisol and plasma adrenocorticotropic hormone (ACTH) levels
B
CT-guided fine-needle aspiration biopsy of the right adrenal mass
Measurement of plasma free metanephrines, an overnight $1$ -mg dexamethasone suppression test, and a plasma aldosterone-to-renin ratioAnswer
D
Repeat unenhanced computed tomography of the abdomen in $6$ to $12$ months
E
Whole-body $^{18}$ F-fluorodeoxyglucose positron emission tomography (FDG-PET) scan

Answer

Measurement of plasma free metanephrines, an overnight 1-mg dexamethasone suppression test, and a plasma aldosterone-to-renin ratio

The correct answer involves performing a comprehensive biochemical evaluation. When an adrenal mass

>1

cm is incidentally discovered on imaging performed for other reasons (an adrenal incidentaloma), the initial diagnostic workup must assess two domains: malignant potential and functional status (hormonal hypersecretion). Although this patient's mass has definitively benign imaging characteristics (size

<4

cm, homogeneous, and lipid-rich with an attenuation

<10

Hounsfield units), which effectively rules out a malignant primary tumor or metastasis, the mass must still be evaluated for hormonal activity. The standard sequence of screening tests for an adrenal incidentaloma includes an overnight

1

-mg dexamethasone suppression test to screen for autonomous cortisol secretion (subclinical Cushing syndrome) and measurement of plasma free metanephrines or

24

-hour urine fractionated metanephrines to screen for a pheochromocytoma. Furthermore, because this patient has a history of hypertension, screening for primary aldosteronism with a plasma aldosterone-to-renin ratio is also strictly indicated. Performing this biochemical workup is the mandatory immediate next step before deciding on long-term observation or surgical intervention.

Step-by-Step Solution

Analyze the clinical presentation and imaging findings.

The patient has an incidentally discovered

2.8

cm adrenal mass with benign imaging characteristics (

<10

Hounsfield units, well-circumscribed), known as an adrenal incidentaloma.

To determine the risk of malignancy based on size and density criteria established by imaging protocols.

Determine the required evaluation for all new adrenal incidentalomas.

Regardless of benign imaging appearance, all adrenal incidentalomas require biochemical testing to rule out silent hormonal hypersecretion.

Functioning adenomas (such as those causing subclinical Cushing syndrome or pheochromocytomas) can lack classical symptoms but still cause significant long-term cardiovascular morbidity if left untreated.

Select the appropriate biochemical screening tests based on the patient's history.

The correct sequence includes testing for pheochromocytoma (metanephrines), hypercortisolism (

1

-mg dexamethasone suppression test), and primary aldosteronism (aldosterone-to-renin ratio, indicated strictly because the patient has a history of hypertension).

These are the highly sensitive first-line screening tests recommended by endocrine guidelines for the initial evaluation of adrenal incidentalomas.

Key Concept

All incidentally discovered adrenal masses

>1

cm require immediate biochemical evaluation for hormonal hypersecretion (hypercortisolism, pheochromocytoma, and, if hypertensive, primary aldosteronism), regardless of whether the imaging characteristics appear benign.

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