Elizabeth Lee Carpenter MD, Presenter: Nothing to Disclose

Morton Arthur Bosniak MD, Abstract Co-Author: Nothing to Disclose

James S. Babb PhD, Abstract Co-Author: Nothing to Disclose

Nicole Maria Hindman MD, Abstract Co-Author: Nothing to Disclose

To determine whether there are significant differences in the MRI findings of papillary renal cell carcinomas (pRCC) and lipid poor angiomyolipomas (lpAML), so that a different approach can be used in the treatment of these two lesions, since one is benign and the other is malignant.

This retrospective study was HIPAA-compliant and approved by our IRB with waiver of informed consent. The pathology and radiology databases at our institution were searched to identify all cases of histologically-proven AMLs (without macroscopic fat on MRI) and pRCCs with preoperative imaging by MRI. MR images were reviewed in 12 pathologically-proven lpAMLs in 12 patients (2:10 M:F) and in 42 pathologically proven pRCCs in 37 patients (33:4 M:F). Images were analyzed independently by two blinded radiologists for lesion homogeneity, T1 and T2 signal intensity relative to renal cortex, and vascularity on arterial and nephrographic phases.

Logistic regression for correlated data was used to identify predictors of malignancy for lesions 2.0cm or smaller and lesions >2.0 cm. Interobserver agreement for lesion homogeneity and T2 signal was excellent (κ 0.97 and 0.99); very good for T1, arterial and nephrographic vascularity (κ 0.79, 0.73 and 0.61). When small, lpAML and pRCC cannot be differentiated on the basis of MRI findings as they both can show homogeneous low signal intensity on T2 and most are not distinguishable from renal parenchyma on T1. Vascular phases are variable and not diagnostic. However, pRCC lesions >2.0 cm are readily distinguishable because they demonstrate either heterogeneous T2 signal (p=0.009) and/or areas of very high T1 signal (p=0.001) and hypovascularity on arterial and nephrographic images (p=0.009 and 0.048). LpAMLs of all sizes are almost always homogeneous on T2 with isointensity to the renal parenchyma on T1.  

Lesions that are homogeneously low signal on T2 and isointense to renal cortex on T1 should be biopsied prior to surgery/ablation to avoid unnecessary treatment of benign lpAMLs, and to confirm the need for appropriate management of pRCC.  Vascular masses with heterogeneous low signal on T2 and/or high signal on T1 are diagnostic of pRCC.

Lesions with homogeneous low signal on T2 and isointensity on T1 should be biopsied prior to intervention to avoid unnecessary treatment of benign lpAMLs, and for appropriate management of pRCC.

Carpenter, E, Bosniak, M, Babb, J, Hindman, N, Comparison of the MRI Findings of Papillary Renal Cell Carcinomas and Lipid Poor (Non-macroscopic Fat Containing) Angiomyolipomas.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9001303.html