"Separating and distorted nephroliths" signs of renal squamous cell carcinoma

To present the neglected radiographic signs of renal squamous cell carcinoma (RSCC). Twenty-eight cases of RSCC were retrospectively reviewed. Two radiographic signs were elaborated as follows: separating nephroliths sign was defined as change of distance or orientation between two or more renal stones on comparison of two sequential radiographs, while the distorted nephroliths sign was considered positive when a single radiograph showed irregularly marginated stone fragments in a cluster or linear pattern. The incidences of these signs were studied. Renal stones were present in 26 cases, 11 with calyceal stones, 3 with staghorn stone, and 12 with both calyceal and staghorn stones. Separating nephroliths sign was positive in 8 of 11 cases whose previous radiographs were available for comparison, and distorted nephroliths sign was seen in 3 of the remaining 15 cases. The overall positive rate was 39% among all cases of RSCC, or 42% when those 2 cases without renal stones were excluded. The separating and distorted nephroliths signs are not uncommon among cases of RSCC and may be useful for its earlier diagnosis.