Original Research

Magnetic resonance imaging for paediatric retroperitoneal masses: Diagnostic accuracy of the claw sign

Lisa Combrink, Kenneth B. Beviss-Challinor
South African Journal of Radiology | Vol 25, No 1 | a2012 | DOI: https://doi.org/10.4102/sajr.v25i1.2012 | © 2021 Lisa Combrink, Kenneth B. Beviss-Challinor | This work is licensed under CC Attribution 4.0
Submitted: 05 October 2020 | Published: 26 February 2021

About the author(s)

Lisa Combrink, Department of Radiology, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa
Kenneth B. Beviss-Challinor, Department of Radiodiagnosis, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa


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Abstract

Background: 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.

Objectives: To define and evaluate the claw sign in differentiating renal from non-renal retroperitoneal masses in children undergoing MRI.

Methods: 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.

Results: 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 (p < 0.0001).

Conclusion: 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.


Keywords

claw sign; diagnostic accuracy; radiology; radiodiagnosis; paediatrics.

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