Combrink Lisa, Beviss-Challinor Kenneth B
Department of Radiology, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa.
Department of Radiodiagnosis, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa.
SA J Radiol. 2021 Feb 26;25(1):2012. doi: 10.4102/sajr.v25i1.2012. eCollection 2021.
The claw sign is advocated as a discriminant of renal versus non-renal origin of tumours. The accuracy of the claw sign on magnetic resonance imaging (MRI) is unknown and is potentially hindered by the inferior spatial resolution and the larger tumour sizes at presentation in developing countries.
To define and evaluate the claw sign in differentiating renal from non-renal retroperitoneal masses in children undergoing MRI.
A definition of the claw sign was proposed. Magnetic resonance imaging studies, clinical and laboratory records of 53 children were reviewed to test the diagnostic accuracy, inter- and intra-observer reliability. Three tumour-mass interface characteristics, inherent to the claw sign, were tested: (1) a smooth tapering kidney edge blending continuously with the tumour, (2) absence of infolding of the kidney and (3) an obtuse superficial angle.
The sensitivity, specificity, negative predictive value and positive predictive values of the claw sign were 97%, 74%, 83% and 94%. The Cohen's kappa values for intra-rater reliability were 0.72 (95% confidence interval 0.54-0.86) for the first reader and 0.83 (0.66-1.00) for the second reader. The Cohen's kappa values for inter-rater reliability were 0.67 (0.50-0.85) and 0.65 (0.44-0.86) for the second reading respectively ( < 0.0001).
The three tumour-mass interface characteristics investigated are all important characteristics of the claw sign. Intra- and inter-rater reliability is moderate to strong for all characteristics and overall impression of the claw sign. The claw sign is therefore sensitive in the accurate placement of an intra-renal mass but lacks specificity.
爪征被认为是区分肿瘤肾源性与非肾源性的一个指标。磁共振成像（MRI）中爪征的准确性尚不清楚，在发展中国家，由于空间分辨率较低以及就诊时肿瘤尺寸较大，其准确性可能受到影响。
在接受MRI检查的儿童中定义并评估爪征在区分肾性与非肾性腹膜后肿块方面的作用。
提出了爪征的定义。回顾了53例儿童的磁共振成像研究、临床及实验室记录，以测试其诊断准确性、观察者间及观察者内可靠性。测试了爪征固有的三个肿瘤-肿块界面特征：（1）肾脏边缘光滑渐细并与肿瘤连续融合；（2）肾脏无内褶；（3）表面钝角。
爪征的敏感性、特异性、阴性预测值和阳性预测值分别为97%、74%、83%和94%。第一位读者观察者内可靠性的Cohen's kappa值为0.72（95%置信区间0.54 - 0.86），第二位读者为0.83（0.66 - 1.00）。第二次阅读时观察者间可靠性的Cohen's kappa值分别为0.67（0.50 - 0.85）和0.65（0.44 - 0.86）（P < 0.0001）。
所研究的三个肿瘤-肿块界面特征均为爪征的重要特征。所有特征及爪征总体印象的观察者内和观察者间可靠性为中度至高度。因此，爪征在准确判断肾内肿块位置方面较为敏感，但缺乏特异性。
