Vestibular, vaginal and urethral relationships in spayed and intact normal dogs

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Wang KY, Samii VF, Chew DJ, et al.

Theriogenology 2006;66:726-735.

The purpose of this study was to evaluate the urogenital anatomy in sound spayed and intact dogs. Fourteen intact and 12 spayed sound dogs had their lower urogenital tract evaluated with conventional vaginourethrography, computed tomography (CT) vaginourethrography and uroendoscopy under general anesthesia. Measurements for each of the three imaging modalities were made. Measurements included vaginal length, vaginal height, vaginal width, vestibule length, vestibule height, vestibule width, cingulum height, cingulum width, cingulum area, urethral length, urethral height, urethral width, angle of urethra to vestibule and angle of vagina to vestibule. Group comparisons were made between sound spayed and intact dogs. In general, most measurements were greater in intact dogs compared to spayed dogs regardless of imaging modality utilized. Group-weight interactions (P<0.01) were found on conventional vaginourethrograms (vaginal height and length and vestibule height, length and width) and CT vaginourethrograms (vaginal length, vestibule height, length and width, cingulum area, urethral width and angle of vagina to vestibule). A three-way interaction (P<0.01) for vaginal length, vaginal height and vestibule height was also identified. Vestibule length and height, cingulum height and urethral length were larger (P<0.01) with increasing dog weight and in intact dogs for both conventional and CT vaginourethrograms. No difference in vestibulovaginal ratio was observed between intact dogs and spayed dogs (P=0.0221). One of 14 intact dogs and 8 of 12 spayed dogs had vestibulovaginal ratios <0.33 on conventional vaginourethrograms. Anatomical differences in the lower urogenital tract between spayed and intact dogs emphasizes the need to establish normal reference ranges for spayed and intact dogs.