MRI Renal Protocol for Exophytic Cysts

Indications for MRI

The American College of Radiology recommends ordering an MRI renal protocol when a cyst shows concerning features or cannot be definitively characterized as benign on initial imaging, with a sensitivity of 91.8% and specificity of 68.1% for diagnosing renal cell carcinoma 1, 2, 4, 5
The presence of an angular interface with renal parenchyma on T2-weighted imaging is 78% sensitive and 100% specific for benignity in exophytic masses ≥2 cm, making this a powerful discriminator when present 1, 4

MRI demonstrates superior specificity (68.1%) compared to CT (27.7%) for diagnosing renal cell carcinoma, while maintaining equivalent sensitivity (91.8% vs 94.5%) 2, 4, 5
MRI has significantly higher specificity for characterizing small cysts compared to CT, particularly in cysts <1.5 cm where CT pseudoenhancement is problematic 2, 3, 5

Indeterminate enhancement on CT, where MRI is more sensitive to contrast enhancement and avoids pseudoenhancement artifacts 2, 3, 5
Small lesions <1.5 cm, where MRI has higher specificity for characterizing small cysts compared to CT 2, 3, 5
Complex features present, such as multiple or thickened septa, mural irregularity or nodularity, heterogeneous signal intensity, or inability to definitively classify as Bosniak I or II on initial imaging 1, 3, 5
Patient-specific factors, such as contraindication to iodinated contrast or need for surveillance of previously identified complex cysts 1, 3, 4