Papillary renal carcinoma: diagnostic approach by chemical shift gradient-echo and echo-planar MR imaging

PURPOSE: To elucidate whether MRI can detect fat in interstitial histiocytes and hemosiderin (Hs) deposition (both of which are histological characteristics of papillary renal carcinoma (RCpap)) within RCpap. MATERIALS AND METHODS: Preoperative MR images of nine surgically confirmed RCpap and 57 clear cell renal carcinoma (RCcc) cases were retrospectively studied. Solid components of the lesions were evaluated. For fat detection, signal reduction on opposed-phase images of chemical shift MRI (CSI) was used. For Hs detection, signal reduction on echo-planar images or in-phase images of CSI was used. The prevalence of fat and Hs detection was compared between RCpap and RCcc. RESULTS: In five of nine RCpap (54%), and 38 of 57 RCcc (67%), the presence of fat within the tumor was suggested by CSI (P = 0.71). Hs deposition within tumors was suggested by either EPI or CSI in nine of nine RCpap (100%), and 28 of 57 RCcc (51%) (P = 0.0036). Hs in RCpap was observed without or apart from necrosis or hemorrhage, whereas Hs in RCcc was located predominantly around necrosis. CONCLUSION: Detecting intratumoral Hs by EPI or CSI, particularly that unrelated to necrosis or hemorrhage, may help differentiate RCpap from RCcc.