Surgical correction of EU alone had a successful outcome, defined as complete long-term urinary continence, in 47% of cases in this study population. This is in accordance with earlier studies reporting postoperative incontinence rates varying between 25 and 82% [1, 2, 8,9,10,11, 13,14,15]. Three dogs still required medication after surgery to remain continent, with an overall success rate of 53% for long-term continence.
In the model of best fit, ureteral or renal pyelum dilation and male sex were significantly associated with a higher chance of becoming continent post-operatively, whereas a more severe pre-operative incontinence score was a negative prognostic indicator for postoperative continence.
It has been reported that Siberian huskies have a significantly lower and Labrador retrievers a significantly higher rate of successful outcome of surgery [2, 9, 18]. Labrador retrievers did not have a better outcome than any of the other breeds included in our study. No Siberian huskies were included in our study population. An interesting finding in the study of Weigand et al.  was that Labrador retrievers more often presented with a dilated ureter or renal pyelum than other breeds. This was not confirmed in our study. It has been suggested that normal vesico-urethral sphincter function could cause more pronounced ureteral or pyelum dilation in dogs with EU. An ectopic ureter passing through a well-functioning vesico-urethral sphincter may be prone to become temporarily or partially obstructed leading to hydroureter or dilated renal pelvis, as was hypothesised by Wiegand et al. . Good sphincter function is probably beneficial after correction of the EU, where it contributes to the continence of the dog post-surgically. The results of our study fit this hypothesis, where dogs with pre-operative dilation of ureters or renal pelvis had a higher chance of becoming continent post-operatively.
Preoperative urethral pressure profiling was previously reported to be a potential useful tool in predicting postoperative incontinence due to concurrent functional abnormalities of the urinary tract, such as urinary sphincter mechanism incompetence [19, 20]. However, this has not been validated in a larger group of dogs. In future studies, it would be interesting to assess urethral pressure profiling values in combination with incontinence severity before and after surgery.
The results of the study from Wiegand et al.  also reported that female dogs have a higher risk of postoperative incontinence than males, which was confirmed in our study, although another study  did not find a difference. Due to increased urethral length in male dogs, passive urinary incontinence may not be apparent or only present later in life. Therefore, the prevalence of ureteral ectopia in male dogs may be underestimated and is often diagnosed at an older age. Male dogs may also have a better clinical outcome after surgery due to this increased length [2, 10, 21]. The realisation that especially male dogs with EU may remain asymptomatic or do not show urinary incontinence until a later age, has led to an increase in the number of male dogs being diagnosed with EU [2, 22]. This is reflected in a different female to male ratio found in this study, which was approximately 2.1:1, compared to the ratio reported by Wiegand et al. , who showed a female to male ratio of 6.2:1. This higher prevalence is likely due to increased education as well as improved diagnostic modalities.
The severity of urinary incontinence, subjectively scored by the owner, was a negative prognostic factor for continence after surgery for EU in our study. This result seems logical, but recall bias may be a limitation of subjective scoring of incontinence by owners, due to the retrospective study design. It is possible that owners of dogs in which surgery was effective, scored preoperative severity of incontinence differently compared to owners of dogs that remained incontinent after surgery. The severity of urinary incontinence may also show variation due to fluctuations in water uptake, concurrent bacterial infections, medical treatment and oestrous cycle. Despite these limitations, when incontinence is observed over a longer period of time, the owners’ perception of the severity of incontinence becomes more reliable and clinically relevant. In future studies, a validated scoring system of urinary incontinence should be used prospectively in order to confirm the findings of this study.
Neutering before or after EU correction has been discussed as a risk factor for urinary incontinence in dogs with EU . A recent publication by Hoey et al.  did not show a significant increase in incontinence scores if neutering of female dogs was performed after surgical correction of EU, but in the study of Dekerle et al. , 3 of the 5 dogs that were spayed after EU correction had recurrence of urinary incontinence. Results of our study did not show a significant increase in the risk of postoperative urinary incontinence in dogs with EU that were already neutered at the time of surgical correction. Interestingly, 3 intact dogs started showing signs of urinary incontinence related to EU only after they were neutered. Neutering may have been an additional causative factor in the development of urinary incontinence in these dogs, as it can decrease urethral tone . However, the number of dogs that were neutered either before or after EU correction may have been too small to identify neuter status as a prognostic factor (type 2 error).
Although recently endoscopic laser ablation was identified as a technique with a more favourable outcome , surgical technique was not included as a dependent variable in this study because only 1 of 69 intramural EU was treated with laser ablation. Although the choice of surgical technique is often elective in intramural EU and not specifically case related, in the future prediction modelling surgical technique should be considered as a confounder for outcome.