Next Imaging for Incidentally Discovered Adrenal Mass on Lung CT
Obtain a dedicated non-contrast CT of the abdomen to measure the adrenal mass density in Hounsfield Units (HU), as this is the essential first step to determine if the lesion is a benign lipid-rich adenoma or requires further characterization. 1, 2
Initial Imaging Algorithm
The American College of Radiology assigns non-contrast CT the highest appropriateness rating (8 out of 9) for evaluating incidentally discovered adrenal masses 1. This test serves as the critical decision point:
- If the mass measures <10 HU and appears homogeneous and well-circumscribed, it is definitively a benign lipid-rich adenoma requiring no further imaging workup 2
- If the mass measures >10 HU, proceed immediately to second-line imaging with either delayed contrast-enhanced CT (washout protocol) or chemical shift MRI to further characterize the lesion 1, 2
Context: Lung CT and Cancer History
Since this mass was discovered on lung CT, you must determine whether the patient has a known malignancy or is being evaluated for suspected lung cancer. This distinction fundamentally changes the approach:
For Patients WITHOUT Known Malignancy:
- Most small adrenal masses (<3 cm) are benign, and the non-contrast CT approach described above is appropriate 1
- If non-contrast CT shows >10 HU, chemical shift MRI is particularly useful if the lesion was only identified on the initial contrast-enhanced lung CT 1
For Patients WITH Known or Suspected Lung Cancer:
- The same non-contrast CT is still the first step (appropriateness rating 8/9) 1
- However, if non-contrast CT is indeterminate (>10 HU), FDG-PET has higher utility (appropriateness rating 6/9) specifically for lung cancer, colon cancer, lymphoma, and neuroendocrine tumors, as metastases typically show uptake values >4 1
- In oncology patients, even smaller adrenal lesions are suspect, with metastatic risk ranging from 25-72% depending on the primary tumor 3
Size-Based Considerations
The size of the adrenal mass influences urgency and subsequent management:
- <3 cm: Most are benign; extensive workup usually not justified in patients without cancer history 1
- 3-5 cm: Requires second-line imaging (washout CT or chemical shift MRI) regardless of HU measurement 1, 4
- ≥4 cm: Even if radiologically benign (<10 HU), requires repeat imaging in 6-12 months 1, 4
- >5 cm: Should be removed due to higher malignancy risk 1, 4
Critical Pitfall to Avoid
Do not proceed directly to adrenal biopsy. Biopsy is rarely indicated and carries unnecessary risks including tumor seeding and potential hypertensive crisis if an undiagnosed pheochromocytoma is present 2, 3. The ACR guidelines assign biopsy an appropriateness rating of 8/9, but only after non-invasive imaging techniques are equivocal and there is high suspicion for metastatic disease 1.
Concurrent Hormonal Evaluation
While obtaining the non-contrast CT, simultaneously initiate hormonal workup regardless of imaging characteristics, as approximately 5% of radiologically benign incidentalomas have subclinical hormone production requiring treatment 2, 3. This is particularly important before any consideration of biopsy, as undiagnosed pheochromocytoma must be excluded 1, 2.