Characteristics of the Peritumoral Pseudocapsule Vary Predictably With Histologic Subtype of T1 Renal Neoplasms

To determine characteristics of the peritumoral pseudocapsule (PC) between renal tumor subtypes.The peritumoral PCs of 160 pT1 renal tumors were examined, including 60 clear cell renal cell carcinomas (RCCs), 50 papillary RCCs, 25 chromophobe RCCs, and 25 oncocytoma. Pathologic features (presence or absence of PC, mean thickness, continuity, and invasion by tumor) were analyzed. PC thickness was measured using an ocular micrometer to the nearest 1/10 mm.A complete PC was found in 77% of clear cell tumors, 74% of papillary, 28% of chromophobe, and 4% of oncocytomas. Tumor PC was present but incomplete in 18% of clear cell, 18% of papillary, 44% of chromophobe, and 56% of oncocytoma. The PC was entirely absent in no clear cell tumors, 6% of papillary, 28% of chromophobe, and 40% of oncocytoma. Mean PC thickness and presence of invasion beyond the PC differed significantly by tumor subtype. Clear cell RCC possessed the thickest PC showing invasion through the capsule in 8% of tumors compared to 30% of papillary tumors. Complete PC invasion was not seen in chromophobe RCC or renal oncocytoma. Oncocytoma and chromophobe RCC characteristically exhibited an incomplete or absent PC.The characteristics of peritumoral PC vary predictably with histologic subtype of renal neoplasms. Clear cell RCC shows the most consistent PC, with a lower rate of invasion beyond it compared to papillary RCC. Chromophobe and oncocytoma characteristically have an incomplete or absent PC.