Ultrasonographic Renal Subcapsular Thickening in Cats with Primary and Metastatic Carcinoma

TL;DR

This study describes ultrasound features of kidney subcapsular thickening in cats with primary and metastatic cancer, helping improve diagnosis.

Contribution

First report on ultrasonographic subcapsular thickening in feline kidneys caused by metastatic carcinoma.

Findings

Metastatic subcapsular thickening in cats is thin, focal, and hypoechoic, while primary is circumferential and heterogeneous.

Hyperechoic renal parenchyma with hypoechoic striations was observed in most affected kidneys.

Renal metastases, especially from lung cancer, should be considered in differential diagnosis for subcapsular thickening.

Abstract

Renal subcapsular thickening is an ultrasonographic finding often related to lymphoma or feline infectious peritonitis in cats. Although a previous study reported that other renal neoplasia may cause subcapsular thickening, detailed information is lacking. Therefore, the purpose of this study is to describe ultrasonographic findings in renal subcapsular thickening and renal parenchyma in cats diagnosed with primary and metastatic carcinoma in the kidney. Nine kidneys from six cats met the inclusion criteria, including one primary renal carcinoma, four metastatic carcinomas, and four presumed metastatic carcinomas in kidneys from primary pulmonary carcinomas. In our study population, metastatic subcapsular thickening lesions were relatively thin, focal, homogeneous, and hypoechoic, whereas the primary ones were circumferential and heterogeneous. Additionally, hyperechoic renal parenchyma was observed in seven kidneys, three of which had concurrent hypoechoic striations. This is the first report documenting ultrasonographic subcapsular thickening in feline kidneys affected by metastatic carcinoma. Renal metastases, especially those arising from pulmonary carcinoma, should be included in the differential diagnosis when subcapsular thickening with the aforementioned ultrasonographic features is observed. The ultrasonographic findings of primary renal carcinoma may vary and require further investigation.

Ultrasonographic subcapsular thickening caused by renal neoplasia other than lymphoma has been previously reported in cats; however, detailed information is lacking. This study aims to describe ultrasonographic findings in renal subcapsular thickening and renal parenchyma in cats diagnosed or presumed with primary and metastatic carcinoma in the kidney. Ultrasound reports were retrospectively searched from 3 veterinary hospitals and 6 cats with 9 affected kidneys were included. Renal lesions were confirmed either cytologically or histopathologically as primary renal carcinoma with metastasis in the contralateral kidney (in 1 case), or metastatic pulmonary carcinoma (in 3 cases). Two patients were cytologically diagnosed with pulmonary carcinoma with concurrent renal subcapsular thickening. Eight kidneys affected by metastatic carcinomas showed relatively thin, focal, and homogeneously hypoechoic subcapsular thickening while a single kidney affected by primary renal carcinoma showed markedly thick, circumferential, and heterogeneously mixed iso- to hypoechoic lesion. The renal parenchyma, especially when just beneath the subcapsular lesion, exhibited at least one abnormality in all affected kidneys, most characterized by hyperechoic renal cortex with concurrent hypoechoic striations. This is the first report describing metastatic carcinoma causing renal ultrasonographic subcapsular thickening in cats. Our results suggest that renal carcinoma should be included in differential diagnoses when ultrasonographic subcapsular thickening is present in cats.

Figures