What type of MRI (Magnetic Resonance Imaging) is used for evaluating adrenal neoplasms?

Chemical-Shift MRI is the Preferred MRI Technique for Adrenal Neoplasm Evaluation

Chemical-shift MRI is the most appropriate MRI technique for evaluating adrenal neoplasms, with high sensitivity and specificity for differentiating benign from malignant lesions. 1

Imaging Approach to Adrenal Neoplasms

Initial Imaging

• Non-contrast CT is typically the first-line imaging modality for adrenal masses
  • Hounsfield Units (HU) < 10 on unenhanced CT strongly indicates a benign adenoma 1, 2
  • HU > 10 requires further characterization

MRI Techniques for Adrenal Neoplasm Characterization

1. Chemical-Shift MRI (First Choice)

   • Works by detecting intracytoplasmic lipid content in adrenal lesions 1
   • Most benign adenomas contain lipid, while most malignant tumors do not
   • Shows signal intensity loss in opposed-phase images for benign adenomas 2
   • High sensitivity (96%) and specificity (100%) for differentiating benign from malignant lesions 1
   • Rated with an appropriateness score of 8/9 by the American College of Radiology 1

2. Dynamic Enhanced MRI (Limited Role)

   • Based on differences in timing and intensity of enhancement after gadolinium administration
   • Shows mixed results in the literature (91% accuracy in some studies, but significant overlap between benign and malignant lesions in others) 1
   • Rated with a lower appropriateness score of 2/9 by the American College of Radiology 1

Clinical Scenarios and MRI Selection

For Patients Without History of Malignancy

• Chemical-shift MRI is recommended when non-contrast CT is equivocal (HU > 10) 1
• Particularly useful for adrenal masses discovered incidentally on other imaging studies

For Patients With History of Malignancy

• Chemical-shift MRI is indicated if a lesion is identified only on contrast-enhanced CT and further characterization is required 1
• Note: If the lesion is indeterminate on non-contrast CT, MRI is unlikely to add significant information 1

Advantages of MRI Over CT for Adrenal Imaging

• Superior tissue contrast allowing better characterization of indeterminate lesions 3
• No ionizing radiation exposure
• Better visualization of local invasion and involvement of the inferior vena cava 1
• Can detect signal intensity characteristics that suggest malignancy (inhomogeneous appearance with irregular margins) 1

Pitfalls and Limitations

• Chemical-shift MRI may be less reliable for characterizing borderline tumors (epithelial tumors with high malignant potential) 4
• Some adenomas may not contain sufficient lipid to show the characteristic signal drop on opposed-phase images 4
• MRI is more expensive and less widely available than CT 3
• Some patients cannot tolerate the longer imaging time required for MRI 5

Important Considerations

• Adrenal mass biopsy is rarely indicated and should not be routinely performed due to risk of tumor seeding and complications 2
• Always rule out pheochromocytoma before any invasive procedure through measurement of plasma-free or urinary-fractionated metanephrines 1
• For suspected malignant adrenal masses, cross-sectional imaging of the chest, abdomen, and pelvis is required preoperatively to assess for metastatic disease 1

In summary, when MRI is indicated for adrenal neoplasm evaluation, chemical-shift MRI is the technique of choice due to its high sensitivity and specificity for differentiating benign from malignant lesions, with dynamic enhanced MRI playing a more limited role in specific clinical scenarios.