Ultrasonographic assessment of bladder neck mobility in continent bitches and bitches with urinary incontinence attributable to urethral sphincter mechanism incompetence.

Objective: To determine bladder neck positional changes between standing and recumbent positions in bitches and whether change is related to continence status or general anesthesia, or both, and to evaluate reproducibility of measurements.
Animals: 45 continent animals and 46 incontinent bitches with urethral sphincter mechanism incompetence (SMI).
Procedure: Distance between the bladder neck and perineal skin was measured ultrasonographically via the perineum while each dog was conscious in standing and right lateral recumbency and in right lateral recumbency under general anesthesia. Measurements of the bladder neck position obtained in right lateral recumbency under anesthesia were compared with radiographic measurements of the same parameter. Reproducibility of the ultrasonographic measurements of the distance between bladder neck and perineum was assessed on 3 occasions for each position in 50 dogs.
Results: In all dogs, differences in bladder neck position between standing and recumbent conscious-associated positions were not significant. However, caudal bladder neck movement between standing conscious- and recumbent anesthesia-associated positions and between recumbent conscious- and anesthesia-associated positions was significant for all dogs. Incontinent bitches had greater degree of caudal bladder movement during anesthesia. Mean difference in bladder neck positions between recumbent conscious- and recumbent anesthesia-associated positions was 0.24 cm in continent, compared with 0.73 cm in incontinent, bitches. Radiographic measurements were significantly greater than ultrasonographic measurements. Differences between repeated measurements for standing position were not significant, but those for recumbent conscious- and recumbent anesthesia-associated positions were significant.
Conclusions: Additional vesicourethral support mechanisms in continent dogs, are deficient in bitches with SMI, allowing the bladder neck to move further caudad.