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.