From the Guidelines
For an adrenal mass, I recommend ordering a dedicated adrenal MRI protocol that includes T1-weighted, T2-weighted, and chemical shift imaging sequences, as this provides the best characterization of the mass and guides management decisions 1. The protocol should include in-phase and opposed-phase gradient echo sequences, which are crucial for detecting intracellular lipid content to differentiate benign adrenal adenomas from other lesions.
- Dynamic contrast-enhanced sequences following gadolinium administration should be included to assess enhancement patterns and washout characteristics.
- Diffusion-weighted imaging (DWI) is also valuable to evaluate for restricted diffusion, which may suggest malignancy. The examination should cover both adrenal glands with thin slices (3-5 mm) and should be performed before and after intravenous contrast administration. This comprehensive protocol allows for characterization of adrenal masses based on their signal intensity, enhancement pattern, and chemical composition. Adenomas typically show signal dropout on opposed-phase images due to intracellular lipid, while malignant lesions often demonstrate heterogeneous enhancement, delayed washout, and restricted diffusion. The choice of MRI over CT is preferred in cases where pheochromocytoma is suspected due to the risk of hypertensive crisis with CT contrast agents 1. However, CT can be used as a first-line imaging modality for suspected adrenocortical carcinoma due to its lower cost and equivalent diagnostic accuracy for benign tumors 1. It's essential to note that while imaging can provide valuable information, it may not always determine the exact entity of the mass, and clinical correlation with hormonal workup and other diagnostic tests is necessary for accurate diagnosis and management 1.
From the Research
MRI Protocol for Adrenal Mass
To evaluate an adrenal mass, the following MRI protocol can be considered:
- T2-weighted fast spin-echo imaging
- Unenhanced and gadolinium-enhanced T1-weighted spin-echo imaging
- Chemical-shift imaging
- Dynamic gadolinium-enhanced studies
Key Imaging Features
The key imaging features to look for in an adrenal mass include:
- Size: lesions <3 cm are likely benign, while those >6 cm are at high risk of malignancy 2
- Enhancement pattern: rapid contrast enhancement followed by rapid washout suggests a benign lesion, while gradual persistent enhancement may indicate a ganglioneuroma, myelolipoma with infarction, or angiomyolipoma with minimal fat 3
- Signal intensity: adrenal carcinomas and pheochromocytomas typically present as inhomogeneous lesions with intermediate-to-high intensity on T2 images 2
- Chemical-shift imaging: significant differences between adenomas and nonadenomas can be seen, with adenomas showing a signal intensity loss on opposed-phase images 4
Diagnostic Accuracy
The diagnostic accuracy of MRI in characterizing adrenal masses is high, with a sensitivity of 91%, specificity of 94%, and accuracy of 93% 4. However, some lesions may remain indeterminate, and histologic sampling may be necessary for definitive diagnosis. Contrast-enhanced ultrasound (CEUS) may also be used as a screening modality to differentiate benign vs malignant adrenal masses, especially in patients with renal dysfunction or allergy to CT contrast 5.