Claws are the intraaxial tails...

VRU 2023 - 64(4): 706-712

January 19, 2024

Background: The “claw sign” is a radiographic sign studied in human imaging to determine if a mass arises from a solid structure or organ versus a close adjacent location, resulting in distortion of the outline of an organ.

Study: The study was a retrospective, secondary analysis, cross-sectional study that included 27 dogs with histologically confirmed diagnosis of either glioma or meningioma and available 3T MRI data. The study aimed to report the sensitivity, specificity, and inter- and intraobserver variabilities of the “claw sign” using kappa statistics.

Methods: The “claw sign” was defined as the thinning of brain parenchyma adjacent to the mass at the pial surface of the brain, forming an acute angle with a sharp point. Five blinded image evaluators, three radiologists and two neurologists, were asked to rate cases as positive, negative, or indeterminate for the “claw sign” on postcontrast T1-weighted images in two separate randomized sessions.

Results: The sensitivity and specificity of the “claw sign” for the diagnosis of glioma were 85.5% and 80%, respectively. The interobserver agreement was moderate (κ = 0.48), and the intraobserver agreement was substantial (κ = 0.72).

Limitations: The study had some limitations, such as the low number of cases, the lack of standardization of MRI parameters, the potential bias of image evaluators by other MRI features, and the restriction of the study population to only glioma and meningioma cases.

Conclusions: The study concluded that the “claw sign” may be supportive but not pathognomonic for intra-axial localization in cases of canine glioma on MRI, and that it should not be used alone and should be used cautiously in some brain regions.

Examples of cases where the “claw sign” was present with strong evaluator agreement. Postcontrast T1-weighted (T1W) transverse image (A), postcontrast T1W dorsal image (B), and postcontrast T1W transverse images (C and D) of 4 dogs with peripherally located, contrasting enhancing glioma. The white arrow heads in A-D point out the acute angle formed with the meninges and thinning of the brain parenchyma. The dogs are a 10-year-old intact male French bulldog with a high grade oligodendroglioma of the left cerebrum (A), a 6-year-old spayed female boxer with a grade III oligodendroglioma of the left cerebrum (B), an 11-year-old spayed female American pit bull terrier with a high grade oligodendroglioma of the right cerebrum (C), and an 8-year-old castrated male boxer with a grade IV astrocytoma (formerly known as glioblastoma multiforme) of the left cerebrum (D). For the cases in A, B and D, all 5 evaluators across both sessions rated them positive for the “claw sign”. For the first session for case C, all 5 evaluators rated the case as positive for the “claw sign”. For the second session for case C, 4 evaluators rated the case as positive for the “claw sign” and one evaluator rated the case as indeterminate.

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