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Diagnostic yield of uroendoscopy compared to ultrasonography for evaluating lower urinary tract disorders in dogs

Abstract Background Cystourethroscopy and vaginoscopy (uroendoscopy) is often used in the diagnostic evaluation of dogs with lower urinary tract disorders (LUTD). Objective/Hypothesis To evaluate if uroendoscopy is warranted in dogs with various LUTD, the agreement between uroendoscopic and ultrasonographic diagnoses were compared. Dogs with recurrent urinary tract infections (rUTI) will have the highest diagnostic agreement between uroendoscopy and ultrasonography (US) compared to dogs presenting for other LUTD. Animals Two hundred thirty‐seven dogs presenting between 2014 and 2019 with lower urinary tract signs (LUTS) that had US within 60 days preceding uroendoscopy. Methods Retrospective study. Dogs were categorized by primary indication for ultrasound. Pertinent uroendoscopic findings were recorded and agreements (κ analysis) between the final uroendoscopic diagnosis were compared with the final ultrasonographic diagnosis. Results Pertinent uroendoscopic findings were recorded for 69/237 (29%) cases. For dogs presenting primarily for urinary incontinence (UI), agreement between uroendoscopy and US was 71% (46/65; κ = 0.47, 95% CI 0.28‐0.66), for dogs with stranguria, 58% (29/50; κ = 0.47, 95% CI 0.31‐0.62) and for dogs with rUTI the agreement was substantial at 87% (26/30; κ = 0.70, 95% CI 0.43‐0.98). Urethral strictures were the majority (14/21; 67%) of pertinent uroendoscopic findings for dogs with stranguria, of which 12 were male dogs. Conclusions and Clinical Importance Agreement between uroendoscopy and US was moderate for all dogs. Based on these data, recommendation for uroendoscopy should be tailored to individual clinical presentation and signalment; transabdominal US is not the preferred modality for urethral lesions.


| INTRODUCTION
Common lower urinary tract signs (LUTS) in dogs include stranguria, periuria, pollakiuria, dysuria, urinary incontinence (UI), hematuria; no one sign is specific for any specific disorder. Imaging modalities such as planar radiography, contrast radiography, ultrasonography (US), computed tomography (CT) and cystourethroscopy/vaginoscopy (uroendoscopy) are frequently performed for evaluating dogs with chronic LUTS. Uroendoscopy is also performed for interventional procedures such as laser lithotripsy of cystic calculi or ablation of ectopic ureters. Radiographs and US are often performed early in the diagnostic plan, as both modalities are more readily available, less invasive and less expensive compared to uroendoscopy or CT, yet the latter are considered by many to be superior for the diagnosis of some lower urinary tract disorders (LUTD). [1][2][3][4] Cystourethroscopy and CT, for example, have greater sensitivity for identifying ectopic ureters compared with excretory urography and are considered better modalities for identifying the ureters within the lower urinary tract. [2][3] The utility of uroendoscopy in dogs with recurrent urinary tract infection (rUTI) is less clear. In dogs with rUTI, nonspecific cystourethroscopic and vaginoscopic findings such as mucosal edema, lymphoid follicles and vestibulovaginal septal remnants were noted in 45/53 (85%) cases, but no comparisons were made between endoscopic and ultrasonographic findings in that study. 4 In addition, that study did not determine if these findings were clinically relevant or related to the LUTS for which the dog was being evaluated. In 163 women with rUTI, cystourethroscopy rarely (3.8%) identified a unique lesion (ie, pertinent uroendoscopic finding) that was not previously identified by US (111 women) or contrast CT (22 women). 5 In 118 women with rUTI, only 8% of women (9/118) had pertinent uroendoscopic findings and 7 women were >50 years of age, suggesting that signalment should be considered when recommending cystourethroscopy in women with rUTI. 6 Furthermore, when imaging studies (primarily US) were considered normal, the cystourethroscopic examination was also likely to be normal, with a negative predictive value of 99%. 6 These data suggest that cystourethroscopy should not be part of the diagnostic workup for women without risk factors for rUTI, and uroendoscopy rarely provides additional information in the face of unremarkable imaging. 6 Uroendoscopy and US diagnoses comparisons in dogs with rUTI as well as other LUTD or chronic LUTS have not been critically evaluated.
The objective of this study was to compare the agreement between the uroendoscopy diagnosis and the US diagnosis in dogs presenting for a variety of LUTS and LUTD. We hypothesized that dogs with rUTI would have the highest agreement between uroendoscopy and US compared to dogs presenting for other LUTD. We also aimed to evaluate the overall pertinent lower urinary tract (LUT) uroendoscopic findings in dogs with LUTD, which included findings on uroendoscopy that were not identified on US as well as the absence of abnormalities on uroendoscopy that were identified on US. To determine if uroendoscopy provided adjunct clinical pertinent LUT findings in each dog (and not in agreement with the US diagnosis), ultrasonographic upper urinary tract and prostatic changes were not recorded because uroendoscopy cannot be utilized to evaluate these anatomical locations. [5][6] Similar to human studies, nonspecific, subjective findings noted on uroendoscopy suggestive of inflammation such as bladder mucosal edema, glomerulations, or lymphoid follicles, and findings that do not alter the management of the case or provide a definitive diagnosis, were not recorded in the data set. [5][6][7][8] Overt urogenital abnormalities such as foreign bodies were recorded, but hymenal remnants and paramesonephric septal remnants were not retrieved from the uroendoscopic reports because US cannot reliably visualize this area. If an abnormality was suspected on US but not confirmed with uroendoscopy, the diagnoses were considered a nonagreement. If an abnormality was suspected via US and confirmed with uroendoscopy, the diagnoses were considered an agreement. Urethral findings noted on uroendoscopy were recorded, because although transabdominal US is not ideal for urethral examination, the extraabdominal portion of the urethra is often assessed during US for various LUTD.

| Data collection
Based on the history and US request report, indications for transabdominal US were categorized as follows: (1) UI (unconscious urine leaking), (2) stranguria without other LUTS or concurrent urinary tract infection (UTI), (3) rUTI without concurrent UI as defined above (if UI was the primary reason for US, but concurrent subclinical bacteriuria/UTI was noted, the dog was classified in the UI category), (4) urolithiasis, (5) suspected mass lesion(s) that were noted by the referring veterinarian via cursory bladder US or suspected due to signalment and physical examination findings, (6) hematuria only without other LUTS or concurrent UTI, (7) multiple LUTS with an undefined cause, and

| Agreements between uroendoscopy and US among various indications for uroendoscopy
The most common clinical indications for requesting US were UI, stranguria and evaluation for rUTI. The agreement between the uroendoscopic and ultrasonographic diagnoses among the different indications for US was fair to substantial for all dogs (   Table 3.

| Urinary incontinence
The median age of all dogs presenting for UI was 1.5 years (range, 0.25-14). When evaluating all cases, ectopic ureters were suspected during US examination in 11 dogs, but not confirmed by uroendoscopy; 8 of these dogs were ≤2 years of age. Four dogs with normal

| Recurrent urinary tract infections
The median age of all dogs presenting for rUTI was 3 (range, 0.33-11).
Uroendoscopy provided pertinent clinical findings compared to US in only 4/30 (13%) dogs. In 1 dog, the ultrasonographer suspected a urachal remnant, which was not detected by uroendoscopy and in 3 dogs,  (1) Note: These include findings noted during the uroendoscopy that were not reported via US as well as the absence of abnormalities on uroendoscopy that were noted during the US. Dogs were categorized by the primary indication for their ultrasound examination as deemed by the attending clinician.

| Nonlower urinary tract related concerns
The median age of dogs that initially had US performed for nonlower urinary tract related concerns was 6 years (range, 0.5-15). A variety of pertinent uroendoscopic diagnoses were noted (

| Mass lesions and urolithiasis
The median age of all dogs presenting for mass lesions and urolithiasis

| Hematuria
The median age of all dogs presenting for only hematuria was 5 (range, uroendoscopy was not routinely performed at the time of that publication. 11 In our study, ectopic ureters were suspected in 11 dogs presenting for UI based on the US report, which were not confirmed by uroendoscopy. Sonographically, ureteral jets are not always present during US, rendering the identification of the exact location of the ureterovesicular junctions more difficult. Intravenous furosemide might improve ureteral jet detection but is not routinely used in our institution. 12 Uroendoscopy is more sensitive for detecting ectopic ureters and should be recommended to confirm or refute the diagnosis, particularly in younger, female dogs with a history of UI. Moreover, if confirmed, laser ablation to correct the abnormality can be performed during the same anesthetic episode. [13][14] Clinicians also perform fluoroscopic contrast retrograde ureterograms and cystourethrograms which could provide more accurate assessments of the LUT but investigating this imaging modality was beyond the scope of this study. Of the 50 dogs presenting for stranguria, 21 (42%) had pertinent findings identified on uroendoscopy that were in disagreement with US. The kappa agreement between uroendoscopy and US was considered substantial for female dogs, but only fair for male dogs. The majority of these cases (67%) had a urethral stricture identified, of which 12 were male dogs. Standard transabdominal US is not the preferred imaging modality to diagnose urethral strictures in dogs, so the larger number of cases with pertinent uroendoscopic urethral lesions was expected. In men, the diagnosis of urethral stricture is confirmed by cystourethroscopy, retrograde urethrogram/voiding cystourethrogram or by the passage of a urethral catheter, and measurement of the stricture length should be obtained by 1 of the imaging studies. 15 Uroendoscopy is also considered a confirmatory study for suspected urethral strictures in women. 16 Transabdominal US of the urethra is limited by interference of the pubis. 17 Other techniques such as transrectal US and contrast enhanced transperineal US are more sensitive for lesions of the intrapelvic urethra and adjacent structures, however, these techniques were not employed in this study, affecting the agreement between uroendoscopy and US in these dogs. 18,19 The absence of abnormalities on uroendoscopy in stranguric dogs should be considered relevant, as this allows the clinician to exclude a mechanical obstruction as the reason for the clinical signs. Contrast urethrography could also be considered for these cases, but we did not evaluate that imaging modality in this study.
While we noted pertinent uroendoscopic findings in only 4/30 (13%) dogs presenting for rUTI, this is higher than reported for women using similar criteria where cystourethroscopy identified 9 (5.5%) cases that had "significant clinical findings," including 5 (3.8%) that were uniquely identified on cystourethroscopy and missed on other imaging (primarily US) modalities. 5 When imaging was unremarkable, only 6.1% of the women who underwent cystourethroscopy had abnormal findings. Clinical risk factors were not associated with higher risk of having an abnormal cystourethroscopy and the authors concluded cystourethroscopy was a low yield diagnostic test in this human population. 5 Similar findings were noted in a retrospective study of women undergoing cystourethroscopy for rUTI; 9/118 (8%) women had pertinent abnormalities on their cystourethroscopy not reported on US, and most were older than 50 years of age, suggesting that women without risk factors for rUTI and normal imaging could omit cystourethroscopy as part of their diagnostic workup entirely. 6 Our canine population had a higher percentage (13%) of pertinent uroendoscopic findings, however we had a much lower case number and further data should be investigated. In humans, flexible cystourethroscopy is often utilized for women 6 and men, while rigid cystourethroscopy is utilized for female dogs and flexible cystourethroscopy for male dogs in this study. It is possible that the use of rigid cystourethroscopy in female dogs might provide better visualization and lead to a lower agreement in our canine population.
Cystourethroscopic anomalies are reported in 45/53 (85%) dogs evaluated for rUTI, however many of these abnormalities could be considered nonspecific (eg, bladder and urethral mucosal edema and lymphoid follicles) regardless of the severity, rather than a pertinent uroendoscopic finding that would likely alter case managment. 4,20 Common findings in cystourethroscopy include vestibulovaginal abnormalities, such as vestibulovaginal stenosis. The latter has been reported as a potential contributing comorbidity in dogs with rUTI but was not included as a pertinent finding in our study. Although a vestibulovaginal ratio of <0.2 is considered a "contributing factor" for LUTS (eg, UI, UTI, vaginitis), 21  This study had several limitations. As a retrospective study there was some case selection bias, where the clinician recommended uroendoscopy expecting to find abnormalities that had not already been noted via US. On this assumption we expected the agreements to be lower, but the agreements were higher in some categories even with this biased selection. This study also excluded cases that had sonographic diagnosis of disease in which uroendoscopy was not chosen (eg, gross neoplasia with a cytologic diagnosis). A variety of radiologists, imaging residents, and uroendoscopists performed the procedures, interpreted the findings, and wrote the available reports.
However, only cases that had an US or uroendoscopy completed by or reviewed by a boarded radiologist or internist, respectively, were included. While this does increase the variability, this was thought to represent and reflect real-life practice similar to human studies. [5][6] As mentioned previously, for some cases uroendoscopy may have been recommended and pursued for interventional therapies (eg, ectopic ureter laser ablation or laser lithotripsy) in addition to or in lieu of investigating anatomical abnormalities or obtaining a definitive diagnosis. A complete evaluation of the urethra is difficult using noncontrast enhanced transabdominal US. Finally, several of the categories evaluated in this study had small case numbers.

| CONCLUSION
Based on the low agreements in some categories of LUTD we evaluated, uroendoscopy can be a clinically useful adjunct diagnostic. However, because the agreement was variable, a tailored case approach is important when determining whether to recommend uroendoscopy for each dog that presents for LUTS.

ACKNOWLEDGMENT
No funding was received for this study.