Upper Respiratory Tract Dimensions in Chihuahuas and Pomeranians

VRU 62(2): 201-210

Author

Ryan Appleby
July 04, 2023

Background: Chihuahuas and Pomeranians are often afflicted with obstructive upper respiratory tract disease. Previous computed tomographic (CT) studies have described the dimensions and abnormalities of different parts of the upper respiratory tract in brachycephalic dogs. However, Chihuahuas and Pomeranians were not included.

Study: The objective of this study was to determine the transverse-sectional (TSA) dimensions of the nasopharynx, cricoid, and trachea of Chihuahuas and Pomeranians, and investigate whether or not Chihuahuas and Pomeranians had smaller airway dimensions than another non-brachycephalic breed (Dachshund).

Methods: A retrospective, descriptive, single-center cross-sectional cohort study was performed. CT studies of 88 dogs were included (42 Chihuahuas, 29 Dachshunds, and 17 Pomeranians). The TSA of the rostral, mid, and caudal aspect of the nasopharynx, the cricoid and trachea at the level of C4 were determined.

Results: The rostral nasopharynx was the smallest part of the upper airways in Chihuahuas and Pomeranians. Chihuahuas had significantly smaller rostral nasopharynx TSA/weight ratios compared to Dachshunds. The rostral nasopharynx TSA/cricoid ratio and the rostral nasoharynx/trachea ratio for Chihuahuas were significantly smaller than both that of Pomeranians and Dachshunds. Pomeranians had significantly smaller cricoid TSA/weight ratios compared to Chihuahuas and Dachshunds.

Limitations: This study has several limitations. There were differences in group size of the different breeds. Since this was a retrospective study, the number of dogs for each breed was based on the number of patients that were seen at the veterinary institution in a certain period of time.

Conclusions: This study demonstrated that the nasopharynx is narrow in Chihuahuas and Pomeranians, with the smallest dimensions located at the rostral part of the nasopharynx.

Location of performed measurements in one of the Chihuahuas on a sagittal image (A) and transverse images (B–D) in bone algorithm with window width of 1500 and window level of 300). A, from left to right, The TSA of the rostral nasopharynx (solid line), the middle nasopharynx (dotted line), caudal nasopharynx (dashed line), the cricoid height (line with squares), and trachea height (closely spaced dashed line) were measured. The corresponding TSA in mm2 (black and white hatch pattern) of the measurement of the rostral nasopharynx performed just caudal to the choanae, at the level of the pterygoid bone (B). The TSA in mm2 of the middle part of the nasopharynx performed at the level of the biggest transverse-sectional area of the tympanic bulla (C), and the TSA in mm2 of the caudal aspect of the nasopharynx performed at the end of the soft palate, at the level of the intrapharyngeal opening (D)

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