[Characterization and staging of renal tumors: significance of MRI diagnostics]

Retrospective evaluation of MRI in the diagnosis of renal masses and determination of the correlation of MRI with histology or follow-up.

46 consecutive patients (13 female, 33 male, mean age 64.7 yrs) with suspected renal tumors were examined with a 1.5 T MR scanner using a standardized protocol (TSE T2fs, 2DGRE T1, dynam. ce3DGRE T1fs, ce2DGRE T1fs, ce3DGRE urogram).

142 renal lesions were found with diameters of < 2 cm up to 14 x 18 cm. A primary classification as solid and cystic lesions was performed according to MRI criteria. In 29 cases we found lesions bilaterally, in 17 patients only in one kidney, and in four cases we found multifocal renal tumors unilaterally (n = 3) or bilaterally (n = 1). In 22 patients with renal tumors, cystic lesions could be seen as well. In 19 cases these were uncomplicated cysts, and in 3 cases these were complicated cysts. 35/43 lesions were histologically proven solid vascularized tumors (29 renal cell carcinomas, 6 urothelial carcinomas), five additional masses with tumor signs in MRI appeared to be progressive during follow-up thus suggesting malignancy, and one case was a multifocal bilateral renal tumor. 3/43 lesions were initially reported as being suspected of malignancy but were proven during follow-up or histologically to be benign. Tumor thrombus was depicted in MRI in the renal vein in 5 cases, stretching into the IVC in 4 cases and proven histologically in 4 and 3 cases, respectively. Of these solid masses, 99 cystic lesions could be differentiated clearly in MRI (88 simple cysts, 11 complicated cysts) that remained unchanged during follow-up (6 - 65 months) or were proven to be cysts histologically. In 17 cases these cysts were bilateral, in 19 cases unilateral, and 33 kidneys showed multicystic changes. In characterizing renal masses, MRI showed a positive predictive value of 93 % for the diagnosis of a malignant tumor. The T-stage of histologically proven renal cell carcinomas using MRI was correct in 89 %.

MRI is a valid modality for characterizing and staging renal masses using a suitable sequence protocol that includes dynamic ce studies. Venous tumor invasion can be depicted safely. MRI can be employed alternatively to state-of-the-art ceCT and additionally to CT in unclear cases.