Detection of pseudocapsule of renal cell carcinoma with MR imaging and CT.

OBJECTIVE

A pseudocapsule surrounding a renal cell carcinoma is a pathologic feature seen frequently in the early stages of this disease. Partial nephrectomy or simple enucleation may be indicated when a pseudocapsule is detected. The purpose of this study is to analyze the roles of MR imaging and CT in showing the pseudocapsule in renal cell carcinomas.

SUBJECTS AND METHODS

MR imaging and CT appearances of the kidneys in 52 patients with 54 renal cell carcinomas--and 40 patients with 45 other renal masses for comparison--were prospectively analyzed and correlated with pathologic results. The frequency of a pseudocapsule in renal cell carcinomas and in various renal tumors was analyzed. We compared the detectability of a pseudocapsule in renal cell carcinomas with MR imaging on T1-weighted spin-echo, T2-weighted spin-echo, and contrast-enhanced T1-weighted spin-echo sequences, and on contrast-enhanced CT.

RESULTS

At pathologic evaluation, a pseudocapsule was seen in 66% (19 of 29) of tumors 4 cm or less in diameter and in 28% (7 or 25) of tumors larger than 4 cm in diameter. All tumors with a pseudocapsule were low histologic grade. Large renal cell carcinomas and other tumors appeared expansile but not encapsulated. A rim corresponding to the pseudocapsule was seen around the tumor in seven lesions on T1-weighted images, 26 lesions on T2-weighted images, and 11 lesions on postcontrast T1-weighted images. T2-weighted imaging was the most sensitive technique for visualization of the pseudocapsule (sensitivity, 68%; specificity, 91%). All pseudocapsules detected on T1-weighted images or postcontrast T1-weighted images could be detected on T2-weighted images. With postcontrast images, enhancement of the pseudocapsule resulted in poor contrast relative to the surrounding tissue. At contrast-enhanced CT, the pseudocapsule was not visible in any tumors. In all MR imaging sequences and in CT, a pseudocapsule were not found in other pathologic conditions except oncocytoma.

CONCLUSION

A pseudocapsule was seen in 66% of renal cell carcinomas 4 cm in diameter or smaller. T2-weighted MR imaging is the most sensitive technique for showing this feature.