Complex renal cysts: Findings on MR imaging

OBJECTIVE. We retrospectively evaluated our experience with complex cystic renal masses on MR imaging, using T1-weighted, T2-weighted, and gadolinium- enhanced images, to determine whether imaging features could permit distinc tion between benign and malignant lesions. MATERIALS AND METHODS. Thirty-seven patients with complex cystic renal lesi ons were included in this retrospective study. The patients selected had un dergone T1-weighted, T2-weighted, and gadolinium-enhanced MR imaging examin ations using 1.5-T scanners, with at least one of the following findings: c yst fluid of heterogeneous signal intensity, mural irregularity, septa, mur al masses or nodules, increased mural thickness, or intense mural enhanceme nt. The diagnosis was established by histology in 19 patients and by follow -up studies in the remaining 18 patients. RESULTS. Fifty-five complex renal cystic lesions were present in the 37 pat ients. Among the 55 lesions, of 37 that contained fluid of a heterogeneous signal intensity, eight were malignant (22%); of 16 with irregular walls, 1 9 were malignant (63%); of four with septa, two were malignant (50%); of fo ur with mural masses or nodules, three were malignant (75%); of 14 with a t hick wall (>2 mm), 10 were malignant (71%); and of 32 with intense mural en hancement, 14 were malignant (44%). As independent variables, mural irregul arity mural masses or nodules, increased mural thickness, and intense mural enhancement each were highly associated with malignancy (p = .0003-.0022). The combination of mural irregularity and intense mural enhancement had th e highest correlation with malignancy (p = .0002), CONCLUSION, The combination of mural irregularity and intense mural enhance ment is a strong predictor of malignancy in renal cystic lesions. However, the appearance of benign and malignant lesions may overlap, suggesting that distinct separation of these entities is not currently possible in all cas es with MR imaging.