CT-Based Reference Ranges for Canine Pyloric Thickness: Influence of Body Size and Normalization With Aortic Diameter

Pyloric wall thickness reflects pyloric pathology. Prior related studies included small samples and did not consistently measure perpendicular to the pyloric axis. This multicenter retrospective study established body-weight (BW)-specific computed tomography (CT) reference ranges for pyloric thickness, measured in both cross-sectional and transverse planes, in clinically normal dogs and evaluated relationships with BW, age, breed, and sex. Multiplanar reconstruction (MPR) was used to obtain a true cross-sectional plane, and the transverse plane was used for practicality. CT images of 229 dogs were analyzed to measure pyloric thickness and calculate the pyloric thickness-to-aortic diameter (P/Ao) ratio. Consistent differences were observed between planes. Pyloric thickness showed a positive correlation with BW, with significant differences across BW groups. No significant association was found with age, nor based on neutering status, nor among breeds with similar BW. A minor difference between sexes was observed only in the transverse plane, likely reflecting oblique slicing. In the cross-sectional plane, mean (±standard deviation [SD]) pyloric thickness was 3.61 ± 0.76, 4.21 ± 0.87, 5.10 ± 1.14, and 6.93 ± 1.18 mm for dogs weighing <5, 5-10, 10-20, and ≥20 kg, respectively. In the transverse plane, the corresponding values were 4.03 ± 0.82, 4.80 ± 1.03, 6.02 ± 1.40, and 7.75 ± 1.33 mm. P/Ao ratio was independent of BW, with means (±SD) of 0.74 ± 0.18 and 0.83 ± 0.20 in the cross-sectional and transverse planes, respectively. Therefore, BW-specific reference ranges may be used routinely, whereas the BW-independent P/Ao ratio may facilitate assessment when BW is unavailable.