From the Guidelines
For the surveillance of adrenal masses, a structured approach is recommended, starting with non-contrast CT as the first-line imaging modality to distinguish benign lesions from those requiring further investigation, followed by washout CT or chemical-shift MRI for indeterminate masses. This approach is based on the most recent guidelines from 2023, as outlined in the study by 1. The key principle is to balance the need for early detection of potential malignancy with the avoidance of unnecessary procedures for benign, non-functioning adenomas.
Initial Assessment and Surveillance Strategy
- For small adrenal masses (<4 cm) with benign characteristics (low attenuation <10 Hounsfield units on unenhanced CT), follow-up imaging is recommended at 6,12, and 24 months, as suggested by 1.
- Masses with indeterminate features or those between 4-6 cm should be imaged more frequently, at 3-6 month intervals for the first year, then annually for an additional 1-2 years.
- The preferred initial imaging modality is non-contrast CT due to its ability to assess size and density characteristics, as per the guidelines 1.
Choice of Imaging Modality
- Non-contrast CT is the first-line imaging modality for its ability to distinguish benign from potentially malignant lesions based on density characteristics.
- MRI with chemical shift imaging is an alternative, particularly for patients who cannot undergo CT or when there are concerns about radiation exposure, as noted in 1.
- PET/CT may be considered for masses suspicious for malignancy, given its utility in detecting metabolic activity indicative of cancer.
Rationale and Outcome
The rationale behind this surveillance strategy is to detect growth or changes in appearance that might indicate malignant transformation while minimizing unnecessary procedures for benign lesions. Most benign adrenal masses are known to grow slowly or not at all, whereas malignant lesions typically demonstrate more rapid growth or changes in imaging characteristics, as implied by the management strategies outlined in 1. This approach prioritizes morbidity, mortality, and quality of life by ensuring that patients with potentially malignant lesions are identified and treated promptly, while those with benign lesions are not subjected to unnecessary interventions.
From the Research
Imaging Modalities for Adrenal Mass Surveillance
The following imaging modalities are recommended for surveillance of adrenal masses:
- Computed Tomography (CT) 2, 3, 4, 5
- Magnetic Resonance Imaging (MRI) 2, 3, 4, 6
- Contrast-enhanced sonography 2, 6
- Duplex and Doppler sonography 2
Characteristics of Adrenal Masses on Imaging
Imaging characteristics of adrenal masses can help differentiate between benign and malignant lesions:
- Size: larger masses are more likely to be malignant 2, 5
- Contrast enhancement: early arterial or arterial contrast enhancement and rapid washout are seen in malignant lesions 2
- Attenuation values: masses with attenuation values of >10 Hounsfield units may require further characterization using MRI 4
- Signal loss on chemical shift analysis: can help diagnose lipid-rich adenoma and myelolipoma 3
Comparison of Imaging Modalities
The sensitivity and specificity of different imaging modalities for characterizing adrenal masses are: