Urologic Imaging

What Is the Best Imaging for a Small Adrenal Mass in a Patient with Cancer History?

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What Is the Best Imaging for a Small Adrenal Mass in a Patient with Cancer History?

It’s late in the afternoon clinic, and you’re reviewing surveillance imaging for a 65-year-old patient with a history of non-small cell lung cancer. The chest CT is stable from a pulmonary standpoint, but the radiologist notes a new, indeterminate 2.8 cm left adrenal mass. It has no macroscopic fat or other features to confirm it’s a benign myelolipoma. The immediate clinical question is pressing: is this a metastasis, or is it one of the extremely common benign adrenal adenomas? Choosing the right next imaging study is critical for staging and subsequent management. For this specific scenario, the American College of Radiology (ACR) finds that MRI abdomen without and with IV contrast is Usually Appropriate.

Who Fits This Clinical Scenario?

This guidance applies to a very specific patient population: those with an adrenal mass found on initial imaging (like CT or ultrasound) that meets all the following criteria:

  • Size: The mass is less than 4 cm in its greatest dimension.
  • Indeterminate Features: The initial study does not show features diagnostic of a benign lesion. For example, it does not contain bulk fat (suggesting a myelolipoma) or measure simple fluid density (suggesting a cyst).
  • Clinical Context: The patient has a known history of an extra-adrenal malignancy (e.g., lung, breast, renal, or melanoma).

This workflow is distinct from other similar presentations. This article does not apply if:

  • There is no history of malignancy. An incidental adrenal mass in a patient without a cancer history is evaluated differently, with the workup stratified by size.
  • The mass is 4 cm or larger. Larger masses carry a higher risk of being a primary adrenocortical carcinoma (ACC), which alters the diagnostic algorithm and often leads to a more aggressive workup.
  • The mass has classic benign features. A mass with macroscopic fat on CT is almost certainly a myelolipoma and typically requires no further imaging workup.

What Diagnoses Are You Working Up in This Scenario?

In a patient with a known malignancy, an indeterminate adrenal mass raises a focused but critical differential. The primary goal of imaging is to distinguish a consequential metastatic deposit from a benign incidentaloma, which can be found in up to 5% of the general population and does not change the patient’s cancer staging or management.

Adrenal Metastasis
This is the most significant concern. The adrenal glands are a common site for hematogenous spread from other cancers. The most frequent primary tumors to metastasize to the adrenals are lung cancer, breast cancer, renal cell carcinoma, and melanoma. Confirming an adrenal metastasis can upstage the patient’s disease and dramatically alter their treatment plan, potentially shifting from curative-intent therapy to palliative care.

Lipid-Poor Adenoma
Benign adrenal adenomas are extremely common and are the most likely finding overall, even in patients with cancer. While many adenomas are “lipid-rich” and easily characterized on non-contrast CT, a subset are “lipid-poor.” These lesions do not contain enough intracellular fat to have the characteristic low density on CT, making them appear indeterminate and difficult to distinguish from metastases on initial imaging alone.

Pheochromocytoma
Though less common, this catecholamine-secreting tumor is a crucial “can’t-miss” diagnosis. Pheochromocytomas can mimic the imaging appearance of metastases, often appearing avidly enhancing. While many patients present with classic symptoms of adrenergic excess (palpitations, headache, sweating), some are asymptomatic. Biochemical testing is essential if there is any clinical or imaging suspicion.

Adrenocortical Carcinoma (ACC)
A primary adrenal cancer is rare, particularly for masses under 4 cm. However, it remains in the differential for any solid adrenal mass. ACCs are typically aggressive, and early detection is key. They are less likely than a metastasis in this specific clinical context but cannot be entirely excluded by imaging alone if features are aggressive.

Why Is Adrenal MRI the Recommended Study for This Presentation?

When faced with an indeterminate adrenal mass under 4 cm in a patient with a known malignancy, the ACR designates MRI abdomen without and with IV contrast as a Usually Appropriate study. Its diagnostic power in this scenario comes from its unique ability to assess tissue composition, not just density or morphology.

The key MRI sequence is chemical shift imaging, which includes “in-phase” and “out-of-phase” acquisitions. This technique can detect the presence of microscopic, intracellular lipid. Benign adrenal adenomas (even lipid-poor ones) typically contain enough intracellular fat to cause a signal drop on out-of-phase images compared to in-phase images. In contrast, metastases, pheochromocytomas, and adrenocortical carcinomas are composed of cells that lack this lipid and therefore do not demonstrate this signal drop. This single characteristic provides high sensitivity and specificity for differentiating benign adenomas from malignant lesions.

While MRI is a top choice, two other studies are also rated Usually Appropriate:

  • CT abdomen without and with IV contrast: This is a robust alternative. A dedicated adrenal protocol CT involves a non-contrast scan, a post-contrast scan (typically at 60-70 seconds), and a delayed scan (at 15 minutes). This allows for calculation of contrast washout. Adenomas typically enhance and then wash out contrast rapidly, while metastases tend to wash out more slowly. However, this protocol involves a significant radiation dose (☢☢☢☢ 10-30 mSv), whereas MRI has no ionizing radiation (0 mSv).
  • FDG-PET/CT skull base to mid-thigh: This study is highly valuable for evaluating metabolic activity and is often used for systemic cancer staging. A highly FDG-avid adrenal lesion in a cancer patient is very suspicious for a metastasis. However, some benign adenomas can be metabolically active, and very small lesions may be falsely negative due to resolution limits. It is an excellent choice when the clinical question involves overall staging, not just characterizing the adrenal lesion in isolation. It also carries a high radiation dose (☢☢☢☢ 10-30 mSv).

Conversely, a CT abdomen with IV contrast alone is rated Usually Not Appropriate. Without the non-contrast images to establish a baseline density and the delayed images to assess washout, the study is non-diagnostic for adrenal characterization and provides very little useful information beyond what was seen on the initial scan.

What’s Next After Adrenal MRI? Downstream Workflow

The results of the adrenal MRI will guide the subsequent management plan, which hinges on whether the lesion can be confidently characterized as benign or remains suspicious for malignancy.

If the MRI suggests a benign adenoma:
If the mass demonstrates the classic signal drop on out-of-phase chemical shift imaging, it can be confidently diagnosed as a benign adenoma. In this case, no further imaging or intervention for the adrenal lesion is needed. The patient’s cancer staging is not affected, and they can continue with their planned oncologic treatment. This is the most common and favorable outcome.

If the MRI is suspicious for metastasis:
If the mass does not show signal drop on chemical shift imaging and has other features concerning for malignancy (e.g., restricted diffusion, avid enhancement with slow washout), it is considered highly suspicious for a metastasis. The next step depends on the overall clinical picture. If this is the only site of potential metastatic disease, an image-guided biopsy (May be appropriate) may be pursued to obtain a tissue diagnosis before altering a curative-intent treatment plan. If there is already evidence of widespread metastatic disease elsewhere, a biopsy may be unnecessary, as the adrenal finding would be consistent with the patient’s overall stage.

If the MRI remains indeterminate:
Occasionally, a lesion may have equivocal features on MRI. In this situation, the next step is often a different imaging modality to provide complementary information. An FDG-PET/CT (Usually Appropriate) is an excellent problem-solving tool to assess the lesion’s metabolic activity. A metabolically “cold” lesion is likely benign, while a “hot” lesion increases suspicion for metastasis and may prompt a biopsy.

Pitfalls to Avoid (and When to Get Help)

Navigating this clinical scenario requires careful attention to detail to avoid common missteps that can delay diagnosis or lead to unnecessary procedures.

  • Assuming the mass is a metastasis: Remember that benign adenomas are far more common than adrenal metastases, even in patients with cancer. A dedicated characterization study is almost always warranted.
  • Ordering the wrong protocol: Simply ordering a “CT abdomen with contrast” is insufficient. You must specify an “adrenal protocol” to ensure non-contrast and delayed phases are performed. For MRI, ensure the order includes chemical shift (in/out-of-phase) sequences.
  • Ignoring biochemical screening: If a lesion has imaging features suggestive of a pheochromocytoma (e.g., very bright on T2-weighted MRI, cystic/hemorrhagic changes), biochemical testing for plasma or urine metanephrines should be performed before any biopsy is considered.
  • Biopsy before characterization: Biopsy of an adrenal mass carries risks, including bleeding and, critically, the risk of precipitating a hypertensive crisis if the lesion is an unsuspected pheochromocytoma. Imaging characterization should always be the first step.

If the imaging results remain indeterminate after both MRI and PET/CT, or if biopsy is considered high-risk, escalation to a multidisciplinary tumor board including radiology, oncology, endocrinology, and surgery is the appropriate next step.

Related ACR Topics and Tools

The ACR Appropriateness Criteria are a powerful resource for evidence-based imaging decisions. For a comprehensive overview of all clinical variants related to adrenal masses, from incidentalomas in patients without cancer to large, symptomatic masses, please see our parent guide. You can also use the tools below to explore adjacent scenarios or technical details.

Frequently Asked Questions

Why is MRI preferred over a dedicated adrenal protocol CT if both are ‘Usually Appropriate’?

While both are excellent studies, MRI is often preferred because it involves no ionizing radiation (0 mSv vs. 10-30 mSv for a multi-phase CT). Additionally, MRI’s chemical shift imaging is a direct and highly specific method for detecting intracellular lipid to confirm a benign adenoma. CT relies on indirect measures like density and contrast washout, which can sometimes overlap between benign and malignant lesions.

What if my patient has a contraindication to MRI, like a non-compatible pacemaker?

If MRI is contraindicated, a dedicated adrenal protocol CT (without and with IV contrast, including delayed images) is the best alternative and is also rated ‘Usually Appropriate’ by the ACR. If the patient also has a severe contrast allergy or renal failure, an FDG-PET/CT may be considered, though its primary role is metabolic assessment and staging.

Does the type of primary cancer matter when choosing the imaging test?

Generally, no. The imaging workup to differentiate a metastasis from a benign adenoma is the same regardless of the primary cancer type (e.g., lung, breast, melanoma). The key is the presence of a known extra-adrenal malignancy, which raises the pre-test probability of metastasis. However, if the primary cancer is known to be very FDG-avid, a PET/CT might be chosen earlier in the workup, especially if systemic restaging is also needed.

Is a biopsy always needed if the MRI suggests a metastasis?

Not always. A biopsy is typically performed when confirming the adrenal lesion as metastatic would be the sole factor that changes the patient’s management from a curative to a palliative pathway. If the patient already has known metastatic disease in other organs (e.g., liver, bone), a new adrenal lesion with imaging features of a metastasis is often presumed to be malignant without biopsy, as it doesn’t change the overall stage or treatment plan.

What if the adrenal mass is found to be functional on biochemical testing?

If blood or urine tests suggest the adrenal mass is producing excess hormones (e.g., cortisol in Cushing’s syndrome, or metanephrines in a pheochromocytoma), the patient should be referred to an endocrinologist. The management will then be guided by the specific hormonal excess, which often takes precedence over the concern for malignancy. For instance, a suspected pheochromocytoma must be managed with appropriate alpha- and beta-blockade before any surgical consideration.

Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 29, 2026