RESUMEN
Objective To study the clinical and histopathologic features of small renal carcinoma (diameter≤4 cm)and provide theoretical basis for evaluating the safety,efficacy and prognosis of nephron sparing surgery.Methods This retrospective study collected the pathological data of 490 patients with small renal cell carcinoma,who were treated in our hospital,from May 2000 to October 2014.We recorded and analyzed the tumor size,histological subtype,Fuhrman grading,pathological stage,the existence of mulifocality,vascular invasion,tumor psuedocapsule,hemorrhage or necrosis and distant metastasis.Results The median diameter of tumor was (3.2 ± 0.6) cm,ranged 0.6 to 4.0 cm.Of all the subjects,422 (86.1％) were clear cell carcinoma,32 (6.5％) were chromophobe cell carcinoma,23 (4.7％) were papillary carcinoma and 13 (2.7％) were other rare types.Among the 422 clear cell carcinoma cases,27 were Fuhrman grade Ⅰ,157 were Ⅰ-Ⅱ grade,210 were grade Ⅱ,21 were Ⅱ-Ⅲ grade,7 were grade Ⅲ and no one was grade Ⅳ.Multifocal tumors were found in 18 cases (3.7％) and tumor embolus of renal vein was found in 6 cases (1.2％).Intact psuedocapsule were found in 326 (66.5％) tumors with the thickness ranged from 0.2 to 1.0 mm.Tumor infiltration without the psuedocapsule penetration were found in 82 cases (16.7％),penetrated into the psuedocapsule were found in 11 cases (2.2％),infringement of perirenal fat were found in 9 cases (1.8％).Hemorrhage and necrosis were found in 240 cases (48.9％),synchronous lung metastases occurred in 3 patients (0.6％).Logistic regression analysis revealed that tumor invasion and pseudocapsule penetration were related to Fuhrman Ⅱ-Ⅲ,Ⅲ and tumor diameter (P =0.04).Moreover,tumor size was related with histological grade and renal capsule invasion (P =0.02).Nevertheless,there was no relationship among tumor size,renal vein embolus or mulifocality (P =0.35).Conclusions Although most small renal tumors are high differentiation and low grade,but rare cases are aggressive with infringement of perirenal fat or early distant metastasis,suggesting heterogeneity in its biological behavior.Most small renal tumors have obvious psuedocapsule.When the tumor size is greater than 3.0 cm and its Fuhrman classification was high,the psuedocapsule and perirenal fat are more likely to be infiltrated.Nephron sparing surgery should remove the tumor and its surface adipose tissue entirely.