Triple-Phase Computed Tomography for Differentiating Canine Cutaneous and Subcutaneous Mast Cell Tumors From Benign Lesions: A Size-Based Evaluation.

Canine cutaneous and subcutaneous mast cell tumors (MCTs) have highly variable clinical presentation, often mimicking benign lesions. This retrospective case-control study aimed to identify triple-phase computed tomography (CT) features that distinguish MCTs from benign lesions, with an emphasis on tumor size. Twenty-three MCTs (10 large [≥3 cm]; 13 small [<3 cm]) and seven benign lesions were included. Qualitative features and CT attenuation values were compared among three groups by size and type. Large MCTs were primarily characterized by qualitative CT features. Significant differences among the three groups were observed in heterogeneous enhancement patterns, feeding vessels, infiltration, necrosis, and fat stranding. These features were most frequently observed in large MCTs. In contrast, small MCTs lacked these features but showed significantly higher CT attenuation values in the portal venous and equilibrium phases than benign lesions (p = 0.025 and 0.034, respectively). Receiver operating characteristic curve analysis for discriminating small MCTs from benign lesions yielded optimal cutoff values of 68.7 Hounsfield units (HU) for the portal venous phase (area under the curve [AUC] = 0.88; sensitivity, 92%; specificity, 71%) and 74.7 HU for the equilibrium phase (AUC = 0.85; sensitivity, 92%; specificity, 57%). In conclusion, despite the limited sample size, these findings suggest that triple-phase CT has clinical utility for differentiating MCTs from benign lesions. Qualitative patterns are particularly informative for large MCTs, whereas CT attenuation values in the portal venous and equilibrium phases may serve as objective adjunct indicators for identifying small MCTs that lack distinct morphological features.