From the Guidelines
A hypodense adrenal mass seen on CT should typically be further evaluated with MRI with chemical shift imaging, which can be performed without contrast, as it helps distinguish between benign adenomas and potentially malignant lesions. The use of chemical shift imaging is supported by studies such as 1, which shows that this technique can effectively characterize adrenal masses, especially those with densities between 10 and 30 HU on CT. According to 1, chemical shift imaging has better sensitivity and specificity than non-enhanced CT for differentiating adenomas from non-adenomas.
The approach of using MRI with chemical shift imaging without contrast is particularly valuable for indeterminate adrenal masses, as it can help detect intracellular lipid content, which is typically present in benign adenomas but absent in malignant lesions. This distinction is crucial for patient management decisions, especially for masses measuring between 1-4 cm. While contrast-enhanced MRI can provide additional information on enhancement patterns and washout characteristics, the initial evaluation with chemical shift imaging can be done without contrast, as suggested by the appropriateness criteria in 1 and 1.
It's worth noting that more recent studies, such as 1, emphasize the importance of accurate characterization of adrenal masses, especially in the context of non-small cell lung cancer, where the presence of an adrenal mass could indicate metastasis. However, the specific recommendation for the use of MRI with or without contrast in this context is guided by the principles outlined in the earlier studies, which prioritize the use of chemical shift imaging for its ability to distinguish between benign and malignant lesions.
In terms of the technical aspects of the MRI protocol, the use of gadolinium-based contrast agents is common in abdominal MRI, but for the initial evaluation of a hypodense adrenal mass with chemical shift imaging, the focus is on the non-contrast sequences that allow for the detection of intracellular lipid. The administration of contrast may be considered in subsequent evaluations or based on specific clinical indications but is not necessary for the initial characterization of the mass using chemical shift imaging.
Overall, the approach to evaluating a hypodense adrenal mass seen on CT with MRI prioritizes the use of chemical shift imaging without contrast as the initial step, given its effectiveness in distinguishing between benign and potentially malignant lesions, which is critical for determining the appropriate management strategy and impacting patient outcomes in terms of morbidity, mortality, and quality of life.
From the Research
Imaging Modalities for Hypodense Mass Adrenal Gland
- The choice between MRI with contrast or without contrast for a hypodense mass in the adrenal gland seen on CT depends on various factors, including the size and attenuation of the mass on unenhanced CT 2, 3, 4.
- For adrenal masses with low attenuation on unenhanced CT (≤10 HU), MRI without contrast can be useful in characterizing the lesion, particularly using chemical shift imaging to detect signal loss, which is indicative of an adenoma 3, 5.
- However, for masses with higher attenuation on unenhanced CT (>10 HU), the utility of MRI without contrast may be limited, and contrast-enhanced MRI or CT may be more helpful in characterizing the lesion 4, 6.
- Chemical shift MRI can be useful in evaluating adrenal lesions with an unenhanced CT attenuation density less than 30 HU, but its utility decreases for lesions with higher attenuation densities 4.
- Washout CT has been shown to be more accurate than MRI in characterizing lipid-poor adrenal adenomas, particularly for lesions with higher attenuation values on unenhanced CT 6.
Considerations for Imaging Protocols
- The imaging protocol should be tailored to the individual patient and the specific characteristics of the adrenal mass, taking into account the size, attenuation, and other imaging features 2, 5.
- A combination of imaging modalities, including CT and MRI, may be necessary to accurately characterize the adrenal mass and guide management decisions 2, 6.
- The use of contrast agents, such as gadolinium, should be carefully considered, particularly in patients with renal impairment or other contraindications to contrast administration 5, 6.