When to Order Imaging for Adrenal Mass Evaluation: ACR Appropriateness Decoded
When to Order Imaging for Adrenal Mass Evaluation: ACR Appropriateness Decoded
An incidental adrenal mass appears on a computed tomography (CT) scan ordered for an unrelated reason—a common clinical scenario that presents a distinct diagnostic challenge. Is it a benign adenoma or something more concerning? The next step in the workup depends on the mass’s size, its imaging features, and the patient’s clinical history, particularly any history of malignancy. Choosing the right follow-up imaging is critical for accurate characterization while avoiding unnecessary radiation exposure and cost. This guide synthesizes the American College of Radiology (ACR) Appropriateness Criteria to help you navigate the evaluation of an indeterminate adrenal mass, ensuring you order the most effective study for your patient.
What Does ACR Adrenal Mass Evaluation Cover?
The ACR Appropriateness Criteria for Adrenal Mass Evaluation focus specifically on the workup of an adrenal mass that is discovered incidentally and is considered indeterminate on initial imaging. An “indeterminate” mass is one that does not have classic benign features, such as the macroscopic fat seen in a myelolipoma or the simple fluid characteristics of a cyst. On a non-contrast CT, this typically means a lesion with a density greater than 10 Hounsfield Units (HU).
These guidelines apply to adult and pediatric patients and stratify recommendations based on three key factors: the size of the mass, the presence of a known primary malignancy elsewhere in the body, and the need for follow-up versus initial characterization. The criteria do not cover the evaluation of a suspected functional (hormone-secreting) adrenal mass, where biochemical testing is the primary next step. They also do not apply to patients with a known primary adrenal carcinoma or pheochromocytoma, as these conditions have distinct management pathways.
What Imaging Should I Order for Adrenal Mass Evaluation? Recommendations by Clinical Scenario
The ACR provides specific imaging recommendations tailored to different clinical presentations. The choice of modality—typically a dedicated multiphase CT or magnetic resonance imaging (MRI)—is designed to characterize the lesion by assessing for intracellular lipid (common in benign adenomas) or specific enhancement and washout patterns.
For an indeterminate adrenal mass less than 1 cm in a patient with no history of malignancy, the ACR rates all further imaging modalities as Usually Not Appropriate. These sub-centimeter nodules are overwhelmingly benign, and the consensus is that they do not warrant a diagnostic workup.
When an indeterminate mass is between 1 cm and 4 cm without a history of malignancy, dedicated adrenal imaging is recommended. For a mass between 1-2 cm requiring follow-up at 12 months, a CT abdomen without IV contrast or an MRI abdomen without IV contrast are both rated Usually Appropriate. For initial characterization of a mass between 2-4 cm, a multiphase CT abdomen without and with IV contrast (an adrenal protocol study) or an MRI abdomen without and with IV contrast are Usually Appropriate. These studies can differentiate lipid-poor adenomas from other lesions.
In a patient with a known history of malignancy and an adrenal mass less than 4 cm, the primary goal is to distinguish a metastasis from a benign incidentaloma. In this context, FDG-PET/CT skull base to mid-thigh, CT abdomen without and with IV contrast, and MRI abdomen without and with IV contrast are all considered Usually Appropriate. PET/CT is particularly valuable for its ability to assess metabolic activity and stage disease simultaneously.
For large masses—greater than or equal to 4 cm—the management approach often shifts. In a patient with no history of malignancy, the ACR rates further imaging for characterization as Usually Not Appropriate, as these lesions have a higher risk of malignancy and often proceed to surgical consultation based on size alone. However, in a patient with a known malignancy, a large adrenal mass is highly suspicious for a metastasis. Here, both FDG-PET/CT and image-guided biopsy are rated Usually Appropriate to confirm the diagnosis and guide systemic therapy.
ACR Imaging Recommendations Table
| Clinical Scenario | Top Procedure | ACR Rating | Adult RRL | Pediatric RRL |
|---|---|---|---|---|
| Indeterminate adrenal mass, <1 cm on initial imaging. No history of malignancy. | Further imaging is usually not appropriate. | Usually Not Appropriate | Varies | Varies |
| Indeterminate adrenal mass, 1 to 2 cm on initial imaging. No history of malignancy. Follow-up imaging in 12 months. | CT abdomen without IV contrast | Usually Appropriate | ☢ ☢ ☢ 1-10 mSv | ☢ ☢ ☢ ☢ 3-10 mSv [ped] |
| Indeterminate adrenal mass, >2 cm and <4 cm on initial imaging. No history of malignancy. Adrenal specific imaging. | CT abdomen without and with IV contrast | Usually Appropriate | ☢ ☢ ☢ ☢ 10-30 mSv | ☢ ☢ ☢ ☢ ☢ 10-30 mSv [ped] |
| Indeterminate adrenal mass, ≥4 cm on initial imaging. No history of malignancy. Adrenal specific imaging. | Further imaging is usually not appropriate. | Usually Not Appropriate | Varies | Varies |
| Adrenal mass, <4 cm on initial imaging. No diagnostic benign imaging features. History of malignancy. Adrenal specific imaging. | FDG-PET/CT skull base to mid-thigh | Usually Appropriate | ☢ ☢ ☢ ☢ 10-30 mSv | ☢ ☢ ☢ ☢ 3-10 mSv [ped] |
| Adrenal mass, ≥4 cm on initial imaging. No diagnostic benign imaging features. History of malignancy. Adrenal specific imaging. | FDG-PET/CT skull base to mid-thigh | Usually Appropriate | ☢ ☢ ☢ ☢ 10-30 mSv | ☢ ☢ ☢ ☢ 3-10 mSv [ped] |
Adult vs. Pediatric Adrenal Mass Evaluation Imaging: Radiation Dose Tradeoffs
While adrenal masses are less common in children, the principles of evaluation are similar, with a heightened emphasis on minimizing radiation exposure. The principle of As Low As Reasonably Achievable (ALARA) is paramount in pediatric imaging. For any CT scan, the pediatric relative radiation level (RRL) is often in a higher tier than the adult equivalent for the same millisievert (mSv) range, reflecting the increased lifetime risk of radiation-induced malignancy in younger patients.
For this reason, MRI is often a preferred modality for adrenal characterization in children when it can provide equivalent diagnostic information. An MRI of the abdomen, whether with or without contrast, involves no ionizing radiation (0 mSv). When CT is necessary, protocols should be specifically tailored to pediatric patients to reduce the dose. The decision between CT and MRI must balance the need for a definitive diagnosis with the long-term risks of radiation, a conversation that is crucial to have with the patient’s family.
Imaging Protocol Details for Adrenal Mass Evaluation
Once you’ve decided on the right study, the specific imaging protocol is essential for obtaining diagnostic-quality images. A standard contrast-enhanced CT of the abdomen is often insufficient for full adrenal characterization. Our protocol guides provide detailed, scannable information on technique, contrast timing, and key interpretation principles for the studies recommended in these guidelines.
Tools to Help You Order the Right Study
Navigating imaging guidelines can be complex. To streamline the process of ordering the correct study and managing patient care, several resources are available. These tools are designed to bring evidence-based guidelines directly into the clinical workflow.
The ACR Appropriateness Criteria Lookup provides a quick way to access the latest ACR recommendations for thousands of clinical scenarios beyond just adrenal mass evaluation. It helps ensure the imaging you order is aligned with national standards.
For detailed procedural steps, the Imaging Protocol Library offers a comprehensive collection of protocols for CT, MRI, and other modalities. This resource is useful for understanding the technical requirements of the studies you order, facilitating communication with radiology departments.
To help discuss radiation exposure with patients, the Radiation Dose Calculator can estimate cumulative radiation dose from various imaging studies. This supports shared decision-making and helps in tracking a patient’s total exposure over time.
What defines an “indeterminate” adrenal mass on imaging?
An adrenal mass is typically considered indeterminate if it does not show classic benign features on initial imaging. On a non-contrast CT, a benign adenoma is usually low density (≤10 Hounsfield Units) due to its high intracellular fat content. A mass with a density >10 HU is considered indeterminate and requires further characterization with a dedicated adrenal protocol CT or MRI.
Why is image-guided biopsy often rated “Usually Not Appropriate”?
Biopsy of an adrenal mass carries significant risks. First, if the mass is a pheochromocytoma, a biopsy can precipitate a life-threatening hypertensive crisis. All patients should undergo biochemical screening to rule out pheochromocytoma before a biopsy is considered. Second, there is a risk of seeding tumor cells along the needle tract if the mass is an adrenal cortical carcinoma. Biopsy is typically reserved for specific situations, such as confirming a suspected metastasis in a patient with a known primary cancer when the result will change management.
What is the difference between a CT adrenal protocol and a standard contrast-enhanced CT?
A dedicated CT adrenal protocol is a multiphase study designed to assess the enhancement and washout characteristics of an adrenal mass. It includes a non-contrast phase to measure baseline density, a portal-venous phase (60-80 seconds post-injection) to assess peak enhancement, and a delayed phase (15 minutes post-injection) to calculate contrast washout. Benign adenomas typically wash out contrast rapidly, while malignant lesions tend to retain it. A standard CT of the abdomen usually only includes a single portal-venous phase, which is insufficient for this characterization.
When should I suspect a pheochromocytoma?
Pheochromocytoma should be suspected in patients with an adrenal mass who present with clinical symptoms like paroxysmal hypertension, headaches, palpitations, and sweating. On imaging, these tumors are often highly vascular and may appear complex or cystic. However, they can have a variable appearance. The definitive diagnosis is made with biochemical testing (plasma free metanephrines or 24-hour urinary fractionated metanephrines), which should be performed before any invasive procedure, including biopsy.
For a small adrenal mass (<1 cm), is any follow-up ever needed?
According to the ACR Appropriateness Criteria, indeterminate adrenal masses less than 1 cm in patients without a cancer history are considered benign and do not require any imaging follow-up. The risk of malignancy in these small lesions is extremely low. Follow-up is generally not recommended unless there are specific clinical concerns, such as evidence of hormonal overproduction.
Why is the 4 cm size threshold so important in these guidelines?
The 4 cm size threshold is a critical factor because the risk of an adrenal mass being malignant, particularly adrenal cortical carcinoma, increases significantly with size. While most adrenal masses of any size are benign adenomas, a mass larger than 4 cm raises enough suspicion for malignancy that management often shifts from imaging characterization to surgical consultation for potential resection, regardless of its imaging features.
Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 12, 2026
