American Journal of Roentgenology, Vol 166, 1151-1155, Copyright © 1996 by American Roentgen Ray Society

ARTICLES

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

Y Yamashita, S Honda, T Nishiharu, J Urata and M Takahashi
Department of Radiology, Kumamoto University School of Medicine, Japan.

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.
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