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Difficulty: MediumInterpreting Imaging Results

A 60-year-old man presents to the clinic for a follow-up evaluation. Two weeks ago, he was evaluated in the emergency department for severe left lower quadrant abdominal pain and was diagnosed with acute uncomplicated diverticulitis. A contrast-enhanced computed tomography (CT) scan of the abdomen and pelvis performed at that time confirmed the diverticulitis and incidentally noted a 3.2-cm, well-circumscribed mass in the right adrenal gland. He has completed a course of oral antibiotics, and his abdominal pain has completely resolved. He has no history of hypertension, palpitations, or weight loss. Blood pressure is 122/78 mm Hg, and pulse is 74/min. Physical examination is unremarkable. Upon review of the initial CT scan report, the adrenal mass has a pre-contrast attenuation of 6 Hounsfield units (HU) and demonstrates an absolute contrast washout of 70% at 15 minutes. Based on the interpretation of these imaging findings, which of the following represents the most accurate diagnosis and the most appropriate next step in management?

  1. The mass is consistent with a benign lipid-rich adenoma; biochemical testing to evaluate for hormone hypersecretion should be performedAnswer
  2. B
    The imaging characteristics suggest an indeterminate lesion; a CT-guided percutaneous biopsy should be performed to exclude malignancy
  3. C
    The mass features are concerning for metastasis; a whole-body positron emission tomography (PET) scan should be ordered to locate a primary tumor
  4. D
    The findings are highly suspicious for adrenocortical carcinoma; the patient should be referred for immediate surgical resection
  5. E
    The mass represents a benign simple cyst; routine clinical observation without further laboratory testing is indicated

Answer

The mass is consistent with a benign lipid-rich adenoma; biochemical testing to evaluate for hormone hypersecretion should be performed
The correct answer accurately interprets the lesion as a benign lipid-rich adenoma based on its low pre-contrast attenuation (less than 10 Hounsfield units) and rapid contrast washout (absolute washout greater than 60%). Despite this definitively benign radiologic appearance, standard of care dictates that all adrenal incidentalomas require biochemical evaluation (e.g., 1-mg overnight dexamethasone suppression test, plasma free metanephrines, and potentially an aldosterone-to-renin ratio) to rule out subclinical hormone hypersecretion.

Step-by-Step Solution

1
Interpret the specific imaging characteristics of the adrenal mass provided in the CT report.
The mass has a low pre-contrast attenuation (6 HU) and rapid absolute contrast washout (70%).
These specific Hounsfield unit and washout parameters are the established radiographic criteria used to definitively identify a lesion as a benign, lipid-rich adrenal adenoma.
2
Determine the required follow-up for a radiographically benign adrenal incidentaloma.
Biochemical testing is indicated to rule out functional status.
Even when cross-sectional imaging strongly suggests a benign etiology, clinical guidelines mandate that all adrenal incidentalomas must be evaluated for subclinical hormone hypersecretion (e.g., cortisol, catecholamines, aldosterone) before they can be considered completely harmless.

Key Concept

Interpretation of adrenal mass imaging characteristics (Hounsfield units and contrast washout) and subsequent management of adrenal incidentalomas.
Estimated Time:1m 30s
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Interpreting Imaging Results

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