Approaches to nephron-sparing surgeries (NSS) of renal lesions include partial nephrectomy (PN) and tumor enucleation (TE). Our objective was to examine the pathology of the pseudocapsule and status of the surgical margin in small renal masses treated by NSS and to correlate these findings with the surgical and oncological outcomes. All consecutive renal TE and PN specimens obtained during the period between January 2012 and December 2014, of which clinical follow-up was available, were included in this study. Pathologic features and clinical data were reviewed and analyzed. A total of 117 NSS specimens (59 EN, 58 PN) were reviewed. Clear cell renal cell carcinomas and paraganglioma had the thickest pseudocapsules (0.36 mm), while angiomyolipomas did not form a well-defined pseudocapsule. Other tumors were intermediate in their characteristics. The positive margin rate for TE and PN was 17.2 and 0 %, respectively. Compared to PN, TE involved a significantly shorter procedure time, less blood loss, and fewer post-operative complications. None of the patients from either group was found to have a local recurrence after follow-up imaging. Although positive surgical margins were more frequently seen in TE specimens, local tumor recurrence was comparable to PN. Thus, TE is a reasonable choice for pT1 renal tumors, especially for those without a prominent infiltrative growth pattern.

Small renal tumors are usually enwrapped in a pseudocapsule with well-confined borders, a feature that facilitates the performance of nephron-sparing surgeries (NSS). Our study was designed to evaluate the histologic features of the pseudocapsule of small renal tumors. One hundred seventy-eight renal tumors (≤4 cm), which were surgically removed by total nephrectomy, partial nephrectomy, or enucleation procedures during 2002-2013, were re-examined microscopically. Special attention was paid to the completeness and thickness of the pseudocapsule as well as the extra-pseudocapsular extension (EPE); components of the pseudocapsule and the intra-pseudocapsular vasculature (size/number) were evaluated. The data were analyzed according to the histological tumor types, Fuhrman grades, and sizes. Student's t test and chi-square tests were used for statistical analysis. Among 178 renal tumors, clear cell renal carcinomas (RCC) showed the thickest pseudocapsule (average 0.23 mm), while oncocytoma showed the thinnest (average thickness of 0.09 mm). Chromophobe RCC had the highest rate of EPE and the highest percentage of tumors with larger (≥0.2 mm) intra-pseudocapsular arteries. The EPE rate was also related to the nuclear grade (p = 0.001). Muscular differentiation, reticulin, and collagen components were present in the fibrous stroma of the pseudocapsule. Our study suggests that clear cell RCC has the thickest pseudocapsule while oncocytoma has a poorly developed pseudocapsule, but shows the least infiltrative pattern. In small RCC (≤4.0 cm), the EPE rate is related to tumor grade but not to tumor size. Larger arterioles (≥0.2 mm) are encountered infrequently within the tumor pseudocapsule, with the highest percentage being found in chromophobe RCC and the lowest in papillary RCC.

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