Association between open fontanelle and occipital malformation, ventriculomegaly, and atlanto-occipital overlapping in dogs using MDCT imaging.

Occipital malformation (OM) is a congenital cranial abnormality predominantly affecting brachycephalic dogs, frequently associated with atlanto-occipital overlap (AOO), ventriculomegaly, and open fontanelle (OF). This study aims to evaluate the associative value of OF as a marker for OM, ventriculomegaly, AOO, and incomplete cranial ossification using multidetector computed tomography (MDCT). A retrospective observational study was conducted on 399 client-owned dogs with various breeds and skull types that underwent head CT imaging between November 2022 and November 2024. Dogs were classified by skull morphology. Associations between OF and structural abnormalities were determined using odds ratios (OR) and diagnostic performance metric analyses. OF demonstrated strong associations (p < 0.01) with AOO (OR = 56.43, Sp = 99.55%, Sn = 20.34%, PPV = 97.30%, NPV = 61.05%), OM (OR = 43.30, Sp = 99.22%, Sn = 25.35%, PPV = 94.74%, NPV = 70.64%), and incomplete parietal ossification (OR = 34.82, Sp = 99.60%, Sn = 11.97%, PPV = 94.44%, NPV = 67.19%). Significant associations were also found with incomplete occipital ossification (OR = 20.99, Sp = 80.76%, Sn = 83.33%, PPV = 26.04%, NPV = 98.35%) and ventriculomegaly (OR = 5.38, Sp = 72.10%, Sn = 65.57%, PPV = 19.84%, NPV = 95.60%). Dogs with OF and concurrent OM or AOO exhibited a high prevalence of ventriculomegaly, most commonly of moderate severity. The highest proportion of moderate ventriculomegaly (72.22%) occurred in dogs with concurrent AOO. In conclusion, OF demonstrates a strong association and high specificity for concurrent cranial abnormalities, such as OM and AOO. MDCT provides an effective, non-invasive modality for early detection, enabling timely clinical management to prevent neurological deterioration.