A 55-year-old man visits his primary care physician to discuss the results of a recent ima… — USMLE Step 3

A $55$ -year-old man visits his primary care physician to discuss the results of a recent imaging study. Two days ago, he was evaluated in the emergency department for severe, colicky left flank pain and was diagnosed with a $4$ -mm ureteral stone, which he has since passed. The unenhanced computed tomography (CT) scan of the abdomen and pelvis obtained during that visit confirmed the stone but also revealed an incidental $3.4$ -cm nodule in the right adrenal gland. The patient has a history of essential hypertension managed with lisinopril and amlodipine. He reports feeling well and denies headaches, palpitations, episodic sweating, or unexplained weight changes. His blood pressure today is $132/82$ mmHg, and his heart rate is $76$ /min. The physician reviews the CT scan images and notes that the right adrenal mass is well-circumscribed and homogeneous. A region of interest placed over the mass reveals an attenuation value of $6$ Hounsfield Units (HU). Based on the interpretation of these imaging findings, which of the following is the most appropriate next step in management?

Biochemical evaluation for hormone hypersecretionAnswer
B
Contrast-enhanced CT of the abdomen with adrenal washout protocol
C
Image-guided percutaneous core needle biopsy of the mass
D
Referral for laparoscopic right adrenalectomy
E
Reassurance and repeat abdominal CT scan in $12$ months

Answer

Biochemical evaluation for hormone hypersecretion

Adrenal incidentalomas are discovered in approximately

5\%

7\%

of abdominal CT scans. Evaluation focuses on two main goals: ruling out malignancy (via imaging) and ruling out autonomous hormone secretion (via biochemical testing). The most critical imaging parameter on an unenhanced CT scan is the attenuation value, measured in Hounsfield Units (HU). An unenhanced attenuation of

< 10

HU is highly specific for a benign, lipid-rich adrenal adenoma. Because this patient's mass has an attenuation of

6

HU, the imaging definitively points to a benign lesion, and no further imaging characterization is required. However, regardless of how benign an incidentaloma appears on imaging, up to

15\%

of these masses secrete hormones (such as cortisol, catecholamines, or aldosterone). Therefore, the correct next step is to perform a comprehensive biochemical evaluation. This typically includes a

1

-mg overnight dexamethasone suppression test, plasma free metanephrines, and a plasma aldosterone-to-renin ratio (given his hypertension).

Step-by-Step Solution

Analyze the imaging findings provided in the stem.

The unenhanced CT shows a

3.4

-cm homogeneous right adrenal mass with an attenuation of

6

HU.

To determine the malignant potential of the adrenal incidentaloma based on radiological criteria.

Interpret the clinical significance of the Hounsfield Units.

An unenhanced attenuation value of

< 10

HU is highly specific for a lipid-rich adrenal adenoma, which is benign.

To decide whether further characterizing imaging (like a washout protocol or MRI) is necessary.

Determine the required management for a benign-appearing adrenal incidentaloma.

Proceed with biochemical testing to rule out pheochromocytoma, subclinical Cushing syndrome, and primary aldosteronism.

Up to

15\%

of radiologically benign incidentalomas are functional and require medical or surgical intervention.

Key Concept

Adrenal Incidentaloma Management

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