Ultrasonographic evaluation of the canine urinary bladder following cystotomy for treatment of urolithiasis

Abigail D. Mariano Department of Clinical Sciences, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA 01536.

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Dominique G. Penninck Department of Clinical Sciences, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA 01536.

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James Sutherland-Smith Department of Clinical Sciences, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA 01536.

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Raymond K. Kudej Department of Clinical Sciences, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA 01536.

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Abstract

OBJECTIVE To describe the ultrasonographic appearance of the urinary bladder incision site in dogs that underwent cystotomy for treatment of urolithiasis.

DESIGN Prospective, longitudinal study.

ANIMALS 18 client-owned dogs.

PROCEDURES Dogs underwent urinary bladder ultrasonography at baseline (≤ 1 day before surgery) and at 1 day and approximately 2, 6, and 12 weeks after cystotomy for urocystolith removal. A baseline ratio between ventral (cystotomy site) and corresponding dorsal midline wall thickness was calculated and used to account for measurement variations attributable to bladder distension at subsequent visits. Patient signalment, weight, medications administered, urocystolith composition, and culture results were recorded. Clinical signs, reoccurrence of hyperechoic foci, and suture visualization were recorded at follow-up examinations. Variables were evaluated for association with cystotomy site thickening and resolution of thickening.

RESULTS Median wall thickness at the ventral aspect of the bladder was significantly greater than that of the corresponding dorsal aspect at baseline. Cystotomy site thickening peaked 1 day after surgery and decreased at subsequent visits in a linear manner. Twelve weeks after surgery, 5 of 10 clinically normal dogs evaluated had persistent cystotomy site thickening. Eleven of 18 dogs had reoccurrence of hyperechoic foci within the bladder at some time during the study (median time to first detection, 17 days after surgery).

CONCLUSIONS AND CLINICAL RELEVANCE Persistent cystotomy site thickening can be present up to 3 months after cystotomy for urolithiasis in dogs without lower urinary tract signs. Reoccurrence of hyperechoic foci in the bladder, although subclinical, was detected earlier and at a higher rate than anticipated.

Abstract

OBJECTIVE To describe the ultrasonographic appearance of the urinary bladder incision site in dogs that underwent cystotomy for treatment of urolithiasis.

DESIGN Prospective, longitudinal study.

ANIMALS 18 client-owned dogs.

PROCEDURES Dogs underwent urinary bladder ultrasonography at baseline (≤ 1 day before surgery) and at 1 day and approximately 2, 6, and 12 weeks after cystotomy for urocystolith removal. A baseline ratio between ventral (cystotomy site) and corresponding dorsal midline wall thickness was calculated and used to account for measurement variations attributable to bladder distension at subsequent visits. Patient signalment, weight, medications administered, urocystolith composition, and culture results were recorded. Clinical signs, reoccurrence of hyperechoic foci, and suture visualization were recorded at follow-up examinations. Variables were evaluated for association with cystotomy site thickening and resolution of thickening.

RESULTS Median wall thickness at the ventral aspect of the bladder was significantly greater than that of the corresponding dorsal aspect at baseline. Cystotomy site thickening peaked 1 day after surgery and decreased at subsequent visits in a linear manner. Twelve weeks after surgery, 5 of 10 clinically normal dogs evaluated had persistent cystotomy site thickening. Eleven of 18 dogs had reoccurrence of hyperechoic foci within the bladder at some time during the study (median time to first detection, 17 days after surgery).

CONCLUSIONS AND CLINICAL RELEVANCE Persistent cystotomy site thickening can be present up to 3 months after cystotomy for urolithiasis in dogs without lower urinary tract signs. Reoccurrence of hyperechoic foci in the bladder, although subclinical, was detected earlier and at a higher rate than anticipated.

Cystotomy is among the most common surgical procedures performed in dogs in general practice and referral hospitals. Indications for the surgery include urocystoliths, masses, congenital abnormalities, bladder rupture or trauma, and exploration for biopsy and culture. Removal of urocystoliths is the most common of these procedures.1–3 Although considered a routine procedure, complications of cystotomy can occur; in 1 study4 of dogs and cats, the incidence of complications was as high as 66/144 (45.8%), ranging from minor and self-limiting incidents to events requiring further surgical intervention. Complications include uroabdomen, urinary tract or surgical site infections, incomplete removal or reoccurrence of urocystoliths or neoplasia, ureteral damage, and lower urinary tract signs such as incontinence, hematuria, stranguria, and dysuria.1,3–6 Although most postoperative cystotomy complications can be managed medically, diagnostic procedures, especially ultrasonography, are frequently called upon to guide the treatment. Ultrasonography readily provides information on urinary bladder wall thickness, the distribution of lesions, and luminal contents.7–9 Despite the frequency of the cystotomy procedure and spectrum of complications, to the authors' knowledge, no study to date has investigated the expected appearance of the cystotomy site during the course of healing following urocystolith removal.

The purpose of the study reported here was to fill a gap in our knowledge of expected ultrasonographic findings for the urinary bladder following cystotomy for treatment of urolithiasis in dogs. An established pattern of expected changes, especially at the cystotomy site, could help clinicians to interpret ultrasonographic findings in a postoperative patient that does not show expected improvement in clinical signs (eg, dogs with persistent pollakiuria, stranguria, or hematuria). The main objective was to describe ultrasonographic findings for the bladder incision site immediately before and in the days and weeks following cystotomy. We hypothesized that dogs with urolithiasis that underwent surgery with a clinically uncomplicated recovery would have cystotomy site wall thickening, and that this change would be most pronounced on the first postoperative ultrasound examination but return to baseline (preoperative) or smaller measurements on subsequent examinations.

Materials and Methods

Dogs

Otherwise healthy dogs of any breed, age, weight, or sex undergoing cystotomy for urolith removal at the Cummings School of Veterinary Medicine at Tufts University between July 1, 2014, and September 30, 2015, were candidates for enrollment in the prospective study. Dogs with a previous history of bladder surgery were excluded to help limit the number of confounding variables in the recruited population. Dogs were required to undergo a preoperative ultrasound examination and ≥ 2 follow-up ultrasound examinations to participate in the study. The study was approved by the university's Clinical Studies Review Committee and conducted in accordance with the committee's requirements; full informed consent of the owners was obtained prior to enrollment of dogs in the study.

Cystotomy and perioperative procedures

Cystotomies were performed by surgical faculty and surgical residents. The approach to the bladder lumen was through a ventral midline incision with a length of 2 to 4 cm. Bladder closure was performed in each dog with 3-0 or 4-0 poliglecaprone 25a in a single layer, with a simple interrupted appositional pattern. The bladder approach, suture type, and closure pattern were each consistent with well-established surgical techniques.2,4,6,10–12 All animals received a single perioperative dose of cefazolin sodium (22 mg/kg [10 mg/lb], IV).13 Intraoperative culturette samples of the bladder mucosa and crushed urocystoliths were collected for culture to assess for presence or absence of a concurrent urinary tract infection.14 In addition, calculi were submitted for composition analysis. Administration of antimicrobials and anti-inflammatory medications was recorded. All dogs received IV opioid and fluid treatment for 36 hours after surgery, and oral analgesic medications were prescribed on discharge from the hospital. Owing to variable history, clinical findings, and clinician preference, the selection and use of preoperative and postoperative antimicrobials and anti-inflammatory drugs were not controlled. If patients had ongoing urinary tract signs, this was documented at subsequent visits for ultrasound examination.

Ultrasonographic measurements

Serial bladder wall measurements were performed by radiology faculty and radiology residents at the following time points: ≤ 1 day prior to surgery (ie, baseline), 1 day after surgery, and approximately 2, 6, and 12 weeks after surgery. To facilitate compliance, the actual examination times after hospital discharge were allowed to vary slightly. Information obtained from each ultrasound examination was provided to the respective primary care clinician. Additional data points were available for some dogs when additional follow-up was requested by the clinician. All ultrasound examinations were performed with 1 ultrasound unitb; a linear array (12- to 8-MHz) transducer was used for optimal bladder wall resolution, and a microconvex (8- to 5-MHz) transducer was used when additional penetration was needed. At each ultrasound examination, transverse and sagittal DICOM cine-loop videos and static images of the bladder were recorded for later review and measurement. Two board-certified veterinary radiologists reviewed all images on DICOM workstationsc and determined the imaging results by consensus. At baseline, bladder wall thickness was measured ventrally and dorsally near midline (measurements designated A and B, respectively), with the ventral bladder wall measured at the expected location of the cystotomy. Bladder wall thickness was defined as the distance between outer serosa and inner mucosa. Two measurements of each site were obtained, and the mean value was reported. On postoperative images, the cystotomy site was located, and the mean of the 2 maximum wall thickness measurements at the middle of the incision was reported as measurement A. The dorsal urinary bladder wall was measured opposite to the incision location and reported as measurement B. The presence of suture material and hyperechoic foci or other changes was also noted.

To account for variations of bladder distension on wall thickness measurements at the incision site, a ratio of the baseline measurements (A/B) was used as the reference ratio for future examinations. As previously described, the wall thicknesses A and B vary similarly at any given distension of the urinary bladder.15–19 Therefore, measurement B on subsequent examinations was used in an equation with the baseline reference ratio to solve for the expected measurement of A if a cystotomy had not been performed at that location. By subtracting the calculated A measurement from the actual A measurement, the degree of cystotomy site thickening was calculated. When the difference between measured and calculated thickness at the surgical site was 0 or became a negative number, this was considered to represent resolution of the cystotomy site thickening.

Statistical analysis

The data were analyzed with a statistical software program.d Quantitative data were tested for normality, and descriptive statistics were reported as median and IQR for nonparametric data. A χ2 likelihood ratio test was used to assess for associations between categorical factors (including medications given, presence of hyperechoic foci, and suture presence) and resolution of cystotomy site thickening or presence of clinical signs; between urocystolith type and postoperative presence (reoccurrence) of hyperechoic foci; and between urocystolith type and presence of infection at the time of surgery (ie, a positive culture result).

A Wilcoxon signed rank test was used to compare bladder wall thickness measurements at the ventral and dorsal locations (measurements A and B, respectively) at each ultrasound examination and to compare the differences in these measurements among various time points for each patient. Continuous variables were evaluated for relationships with categorical variables with the Mann-Whitney U test. This included associations of age and weight with resolution of cystotomy site thickening during the 12-week course of the study; associations of clinical signs, suture visualization, hyperechoic foci reoccurrence, urocystolith type, and medications with the degree of (calculated) cystotomy site thickening; and associations of urocystolith type, presence of infection at the time of surgery, and medications with time (in days) until resolution of cystotomy site thickening was detected. This test was also used to evaluate associations of urocystolith type with the time of hyperechoic foci reoccurrence and of suture dissolution time with presence or absence of recurrent hyperechoic foci. Values of P < 0.05 were considered significant.

Results

Eighteen dogs were enrolled in the study. Median age of the dogs was 9 years (IQR, 5.7 to 12.5 years), and median weight was 11.6 kg (25.5 lb; IQR, 5.7 to 25.6 kg [12.5 to 56.3 lb]). Twelve dogs were castrated males, 2 were sexually intact males, and 4 were spayed females. There were 2 Cocker Spaniels, 2 Pugs, and 1 each of the following breeds: Maltese, Dachshund, Toy Poodle, Dalmatian, Bichon Frise, Norfolk Terrier, American Staffordshire Terrier, and English Bulldog. The remaining 6 were mixed-breed dogs. Age and weight were not significantly (P = 0.190 and 0.161, respectively) associated with resolution of cystotomy site thickening.

Ultrasound data were obtained from 18 dogs at baseline, 1 day, and 2 weeks after surgery; from 15 dogs 6 weeks after surgery; and from 10 dogs 12 weeks after surgery. The timing of baseline ultrasound examinations ranged from 1 day prior to surgery (1 dog) to the day of surgery (17 dogs). Day 1 postoperative evaluations for all dogs took place 1 day after surgery. Median times for the 2-week, 6-week, and 12-week recheck examinations were 14 days (IQR, 12 to 16 days), 40 days (IQR, 39 to 43 days), and 82.5 days (IQR, 79 to 86 days), respectively.

Bladder wall thickness data were summarized (Table 1). At all baseline and postoperative ultrasound examinations, the median measured thickness for the ventral aspect of the urinary bladder wall was significantly (P ≤ 0.005 for all comparisons) greater than that for the dorsal aspect (Figure 1). Median cystotomy site thickening calculated on the basis of ultrasound measurements peaked on day 1 after surgery and then decreased linearly at subsequent ultrasound examinations over the 12 weeks of the study. Nine dogs had complete resolution of cystotomy site thickening during the study period; this was detected at a median of 77 days after surgery (IQR, 27 to 113 days). Median residual cystotomy site thickening for the 9 remaining dogs was 1.27 mm (IQR, 0.8 to 3.1 mm), with a median last day of follow-up 47 days (IQR, 28 to 83 days) after surgery. None of these dogs had clinical signs at the last follow-up visit.

Figure 1—
Figure 1—

Baseline sagittal ultrasound image of the urinary bladder in a dog with urolithiasis showing locations (arrowheads) for ventral (A) and dorsal (B) bladder wall measurements. The ventral aspect of the bladder wall is thicker than the corresponding dorsal region (measurements of 3.3 mm and 1.4 mm, respectively). Similar disparities in wall thicknesses at baseline were consistently identified in all 18 dogs undergoing cystotomy for treatment of urolithiasis in the present study. Notice the urolith (asterisk) associated with clean shadowing in the bladder lumen.

Citation: Journal of the American Veterinary Medical Association 252, 9; 10.2460/javma.252.9.1090

Table 1—

Median (IQR) urinary bladder wall thickness data for 18 client-owned dogs ≤ 1 day before (ie, baseline) and at predetermined time points after cystotomy for treatment of urolithiasis.

  Wall thickness (mm)   
Time pointNo. of dogs evaluatedVentral (A)Dorsal (B)A/B ratioEMA (mm)CST (mm)
Baseline183.4 (2.7–5.0)*1.6 (1.4–2.7)2.0 (1.2–2.7)NANA
1 d186.7 (6.0–8.3)*1.8 (1.4–3.8)3.6 (2.6–4.4)4.8 (3.2–6.3)2.8 (1.0 to 4.5)
2 wk187.5 (6.5–9.0)*3.0 (2.0–4.2)2.5 (1.8–3.7)4.8 (3.9–7.7)2.3 (1.1 to 3.4)
6 wk155.0 (3.4–5.7)*1.4 (1.1–1.7)3.1 (2.0–4.4)2.9 (1.9–4.3)1.3 (0.1 to 3.4)
12 wk102.4 (1.8–4.1)*1.6 (0.9–2.5)1.9 (1.6–2.4)2.9 (1.9–3.4)0.2 (−1.5 to 1.0)

To account for changes in wall thickness caused by distension, a ratio of baseline measurements (ventral midline wall thickness [measurement A]/dorsal midline wall thickness [measurement B]) was used as the reference ratio for all postoperative examinations. For each postoperative ultrasonogram, measurement B was used in an equation with the reference ratio to solve for the expected measurement of A; cystotomy site thickening was then calculated as (actual measurement A) – (expected measurement A). Actual examination times varied slightly for the 2-, 6-, and 12-week visits.

Value of measurement A is significantly greater than that of measurement B at the same time point.

The calculated value is significantly greater than 0 (ie, baseline measurement).

CST = Calculated cystotomy site thickening. EMA = Expected measurement A. NA = Not applicable.

At 2 weeks after surgery, 2 dogs had persistent urinary tract signs (pollakiuria [1 dog] and stranguria [1 dog]). The degree of cystotomy site thickening was not associated with the presence of clinical signs (P = 0.157). At 6 weeks after surgery, 3 dogs had urinary tract signs (pollakiuria [2 dogs] and stranguria [1 dog]). The dogs with clinical signs had a median cystotomy site thickening of 3.5 mm (individual values of 1.8, 3.5, and 6.5 mm), compared with a median of 0.7 mm (IQR, 0.1 to 1.7 mm) for dogs without clinical signs. However, this difference was not significant (P = 0.07). No dogs, including the 3 dogs with clinical signs at the 6-week examination, had persistent urinary tract signs at 12 weeks. This was the first postoperative examination time point at which median cystotomy site thickening did not differ significantly (P = 0.838) from baseline (Table 1; Figure 1).

Five of 18 dogs had positive culture results for bladder mucosa samples collected intraoperatively. Single isolates were identified in 4 dogs; these included Staphylococcus pseudintermedius (n = 3) and Escherichia coli (1). One dog had both E coli and Serratia marcescens identified. The presence of infection at the time of surgery was not associated with time to resolution of cystotomy site thickening (P = 0.99).

Twelve dogs were administered a course of antimicrobials for a median duration of 8.5 days (IQR, 7 to 12 days) beginning immediately after surgery. Nine dogs received NSAIDs for a median of 5 days (IQR, 3 to 7 days) after surgery. Neither antimicrobial nor NSAID administration was associated with the presence of clinical signs, the degree of cystotomy site thickening at any time point, or time to resolution of cystotomy site thickening (all P ≥ 0.059).

Four different urocystolith compositions were represented among the dogs. Eleven dogs had calcium oxalate, 3 dogs had struvite, 2 dogs had urate, and 2 dogs had cystine urocystoliths. There was no significant association of urocystolith type with presence of infection at the time of surgery or reoccurrence of hyperechoic foci within the bladder (P = 0.207 and 0.205, respectively). No association was detected between urocystolith type and degree of cystotomy site thickening at any time point, time to resolution of cystotomy site thickening, or time to reoccurrence of hyperechoic foci (all P ≥ 0.267).

Eleven dogs had reoccurrence of hyperechoic foci within the urinary bladder (range of sizes [largest diameter], < 1 to 2.5 mm) during the study. Median time to reoccurrence was 17 days after surgery (IQR, 12 to 38 days); the earliest reoccurrence was detected on day 10. Eight of 11 dogs with hyperechoic foci detected had calcium oxalate uroliths at the time of surgery. Three dogs had resolution of the hyperechoic foci on subsequent ultrasound examinations without surgical treatment. Reoccurrence of hyperechoic foci was not associated with the degree of cystotomy site thickening, presence of clinical signs at any time point, or time to resolution of cystotomy site thickening (all P ≥ 0.110).

Suture material was visualized as regularly spaced hyperechoic foci within the bladder wall by ultrasound in all dogs until 6 weeks after surgery (Figure 2). Ten dogs had ultrasound rechecks that followed healing through the dissolution of suture material. The median time for detection of dissolution was at the 12-week ultrasound examination, or 82 days (IQR, 74 to 84 days). Suture dissolution time was not associated with reoccurrence of hyperechoic foci within the bladder (P = 0.104). Suture was last visualized in 1 dog at 89 days after surgery; this dog did not have hyperechoic foci in the bladder lumen. The presence of suture material was not associated with clinical signs at any time point (all P ≥ 0.325). At 12 weeks after surgery, suture presence was associated with cystotomy site thickening (median bladder wall thickness, 1.3 mm when suture present vs −0.2 mm when suture not present; P = 0.044), but this was not found at any other time point (P ≥ 0.305 for all other comparisons). The presence of suture did not reach the threshold of significance (P = 0.053) for association with time to resolution of cystotomy site thickening.

Figure 2—
Figure 2—

Sagittal ultrasound image of the urinary bladder in a dog 2 weeks after cystotomy for treatment of urolithiasis. The cystotomy site at the ventral aspect of the bladder wall is identified (arrows). The cystotomy site is 7.1 mm thick, whereas the comparable region at the dorsal aspect is 3.1 mm thick. Notice the suture material (asterisks) visualized as regularly spaced, hyperechoic foci along the incision.

Citation: Journal of the American Veterinary Medical Association 252, 9; 10.2460/javma.252.9.1090

Of the 9 dogs that did not have resolution of cystotomy site thickening, 7 had reoccurrence of hyperechoic foci within the urinary bladder, persistent suture present, or both at the time of the last follow-up. Despite this, resolution of the cystotomy site thickening in patients over the course of the study was not found to be significantly (P = 0.598) associated with reoccurrence of hyperechoic foci or persistent suture visibility, whether considered alone or in combination.

Discussion

To our knowledge, the present study was the first to evaluate the urinary bladder by ultrasonography following surgery for urocystolith removal in dogs and to investigate associations between ultrasonographic appearance of the cystotomy site and clinical signs. We calculated cystotomy site thickening as the difference between the actual wall thickness measurement at the incision and an expected value determined on the basis of wall thickness ratios at baseline (prior to surgery). In our patient population, median cystotomy site thickening peaked at the first postoperative examination (1 day after surgery), with values decreasing at each subsequent examination (approx 2, 6, and 12 weeks after surgery) in a linear manner. Comparing data for dogs with and without reported persistent lower urinary tract signs, we did not detect an association between the degree of cystotomy site thickening and the presence of these signs at any time point; however, affected dogs comprised a very small subset (a maximum of 3) in our population. Clinical signs in all dogs had resolved by the 12-week ultrasound examination.

Results of a study20 evaluating incisional breaking strength and biochemical scar analysis in dogs revealed that the urinary bladder is among the fastest-healing organs and is the only organ reported to return to 100% strength ≤ 14 to 21 days after surgery. Although not described for dogs, rabbits have maximal swelling and edema at the bladder incision in the first 24 to 48 hours after surgery,21 which corresponds to the ultrasonographic cystotomy site thickness peak observed in our study. The maturation phase of bladder healing occurs up to 70 days after surgery, during which time the surgical scar matures and decreases in size.20,22,23 In our study, this phase was observed as a linear decrease in ultrasonographically determined cystotomy site thickening over time, with a median time to resolution of 77 days after surgery for the 9 dogs that had complete resolution during the study. The median follow-up period for the 9 dogs without resolution of cystotomy site thickening was only 47 days, so it was possible that resolution could have been detected if these dogs had been examined again at a later date.

Bladder wall thickness has historically been assessed by use of contrast-enhanced radiographic images and ultrasonographic measurements, with the latter being less invasive and more accurate.15,24–27 In our population of dogs with urocystoliths, ventral midline bladder wall measurements were consistently thicker than dorsal midline bladder wall measurements. This finding was significant (all P ≤ 0.005) at baseline as well as at all postoperative ultrasound examinations, including those for patients with resolution of cystotomy site thickening. The presence of urocystoliths and varying degrees of cystitis likely contributed to the unequal distribution of bladder wall thickness as well as the changes we assessed at cystotomy sites. The ventral surface of the bladder is the most dependent location, where the urocystoliths rest in a standing quadruped. A ventral distribution of cystitis is supported in the literature.7,28,29

Calcium oxalate, struvite, urate, and cystine urocystoliths were represented in our study. All patients had radiographs obtained immediately after surgery; these and ultrasound rechecks on day 1 after surgery revealed no remaining urocystoliths. More than half of the dogs in this study (11/18) had a reoccurrence of hyperechoic foci within the urinary bladder, first seen as early as 10 days, and at a median of 17 days, after surgery. Most (8/11) reoccurrences were in patients having calcium oxalate urocystoliths at the time of surgery. However, these foci were too small to result in urinary outflow obstruction, and no association was found between the presence of foci and the presence of clinical signs, degree of cystotomy site thickening, or time to resolution of cystotomy site thickening. Historically, urolithiasis reoccurrence depends on many factors including the presence of a urinary tract infection, dietary factors, urocystolith composition, breed, and the presence of a nidus (such as suture) within the bladder.20,30–34 In 1 study32 of dogs with urolithiasis of various compositions, there was an overall reoccurrence rate of 25% (111/438) over a 6.5-year period. Another studye identified a 3-year reoccurrence rate of 48% (16/33) in dogs with calcium oxalate urolithiasis. The timing of urolith formation varies with type; for example, infection-associated struvite urocystoliths can form in days to weeks,35,36 whereas calcium oxalate urocystoliths take months to years to develop.32,35,e Although our study found a high rate of hyperechoic foci development at an early postoperative stage, it is unknown how many, if any, of these foci later became sizeable urocystoliths resulting in clinical disease. It is conceivable that some of these foci had been present in the urethra, ureters, or kidneys immediately after surgery and that they were too small to be detected on postoperative radiographs, but subsequently entered the bladder. In the present study, 3 of 11 dogs had resolution of the hyperechoic foci on subsequent ultrasound examinations without surgical intervention. Given the small sizes of these foci, this may have been due to spontaneous voiding in the urine. These subjective findings suggested that early postoperative monitoring may reveal small subclinical hyperechoic foci. Although the consequences of such foci are unknown, if detected at this stage, further monitoring or possibly interventions such as voiding urohydropropulsion might be recommended at the clinician's discretion.

The ideal suture material for urinary bladder closure should be present long enough to retain strength during the healing phase and then dissolve completely so that it does not act as a nidus for urocystolith formation.31 In our study, suture material was best visualized by ultrasound examination at the 2-week recheck and persisted afterward in most dogs; dissolution (the time when suture could no longer be visualized) was detected a median of 82 days after surgery. The rate of degradation of suture material is affected by surgical technique, urine pH, presence of infection and bacterial species, medications given, and overall patient health.22,37–39 Poliglecaprone 25 suture causes minimal tissue reactivity,40,41 and histologic analysis in rats that underwent experimental cystotomy has shown that by 14 days after surgery, the bladder tissue reaction around the suture is declining.11 Other studies have shown that complete absorption of poliglecaprone 25 suture varies from 21 days when immersed in acidic, basic, or infected urine38 to 90 to 119 days in the subcutaneous and muscle tissue of rats.40,42 In our study, no statistical association was found between suture presence and presence of clinical signs or hyperechoic foci reoccurrence, but detectable suture was associated with a greater degree of cystotomy site thickening at the 12-week ultrasound examination, compared with that in dogs that did not have suture material detectable by ultrasound.

One limitation of our study was that no attempt was made to standardize the volume of fluid in the urinary bladder at each examination. In dogs, bladder wall thickness has been shown to increase with body weight and decrease with distension.15 Additionally, in people, it is well established that thicknesses at all locations in the bladder will vary together for a given degree of distension within a given patient.16–19 With this in mind, we used the ratio of the bladder wall thickness in 2 consistent locations to account for distension variability; however, the precise impact of cystitis in our population on this variation was unknown. When imaging the bladder by ultrasound, applying some pressure to the organ is necessary. Although the degree of pressure has the potential to affect measurements taken along the bladder wall, particularly at the ventral aspect, it is an unavoidable aspect of bladder ultrasonography in a clinical setting. Another limitation was the frequency of ultrasound monitoring at 2-week to 6-week intervals. This restricted the window for identifying significant changes to the timing of these ultrasound examinations, which may have led to an overestimation of the time to resolution of cystotomy site thickening, reoccurrence of hyperechoic foci, and suture dissolution. More frequent monitoring would be useful to determine timing of these milestones more precisely. At our hospital, poliglecaprone 25 is the standard suture choice for cystotomy closure. We therefore did not investigate other suture material choices, which could potentially have different ultrasonographic appearances or influences on the resolution of cystotomy site thickening as well as suture dissolution time. Variable preoperative and postoperative antimicrobial and anti-inflammatory drug protocols were used for dogs in our patient population, and further studies that control for and investigate the effects of these medications on clinical and ultrasonographic results may provide additional useful information for clinicians. Finally, the study included a small population of clinical patients, and smaller subsets of these dogs were compared for some analyses; thus, low statistical power may have resulted in an underestimation of some associations. Future investigation with a larger sample size may help to elucidate some of these potential associations.

Although our results suggested that persistent cystotomy site thickening and small hyperechoic foci are common subclinical findings in dogs following cystotomy with a ventral midline approach for treatment of urolithiasis, further follow-up may be indicated if clinical signs associated with the lower urinary tract are present, or may be necessary to monitor treatment efficacy. We speculated that our finding of greater preoperative ventral bladder wall thickness, compared with the corresponding region of the dorsal wall, was attributable to the presence of inflammation secondary to infection, urocystolith-associated trauma, or both; further studies should be considered to determine whether dorsal cystotomy site healing is similar to ventral cystotomy site healing in dogs with urolithiasis.

Acknowledgments

Funded by a Companion Animal Health Grant from Cummings School of Veterinary Medicine, Tufts University, North Grafton, Mass.

The authors declared that there were no conflicts of interest.

The authors thank Dr. Bruce Barton for assistance with statistical design and analysis.

ABBREVIATIONS

IQR

Interquartile (25th to 75th percentile) range

Footnotes

a.

Monocryl, Ethicon Inc, Somerville, NJ.

b.

Philips iU22, Philips Medical Systems, Bothell, Wash.

c.

Carestream Vue PACS, Carestream, Rochester, NY.

d.

SPSS for Windows, version 22.0, IBM Corp, Armonk, NY.

e.

Lulich JP, Perrine L, Osborne CA, et al. Postsurgical recurrence of calcium oxalate uroliths in dogs (abstr). J Vet Intern Med 1992,6:119.

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  • 12. Radasch RM, Merkley DF, Wilson JW, et al. Cystotomy closure: a comparison of the strength of appositional and inverting suture patterns. Vet Surg 1990;19:283288.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 13. Buote NJ, Kovak-McClaran JR, Loar AS, et al. The effect of preoperative antimicrobial administration on culture results in dogs undergoing cystotomy. J Am Vet Med Assoc 2012;241:11851189.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 14. Hamaide AJ, Martinez SA, Hauptman J, et al. Prospective comparison of four sampling methods (cystocentesis, bladder mucosal swab, bladder mucosal biopsy, and urolith culture) to identify urinary tract infections in dogs with urolithiasis. J Am Anim Hosp Assoc 1998;34:423430.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 15. Geisse AL, Lowry JE, Schaeffer DJ, et al. Sonographic evaluation of urinary bladder wall thickness in normal dogs. Vet Radiol Ultrasound 1997;38:132137.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 16. Kojima M, Inui E, Ochiai A, et al. Ultrasonic estimation of bladder weight as a measure of bladder hypertrophy in men with infravesical obstruction: a preliminary report. Urology 1996;47:942947.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 17. Kuzmić AC, Brkljacić B, Ivanković D. Sonographic measurement of detrusor muscle thickness in healthy children. Pediatr Nephrol 2001;16:11221125.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 18. Müller L, Jacobsson B, Mårild S, et al. Detrusor thickness in healthy children assessed by a standardized ultrasound method. J Urol 2001;166:23642367.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 19. Oelke M. International consultation on incontinence-research society (ICI-RS) report on non-invasive urodynamics: the need of standardization of ultrasound bladder and detrusor wall thickness measurements to quantify bladder wall hypertrophy. Neurourol Urodyn 2010;29:634639.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 20. Hastings JC, Van Winkle W, Barker E, et al. The effect of suture materials on healing wounds of the bladder. Surg Gynecol Obstet 1975;140:933937.

    • Search Google Scholar
    • Export Citation
  • 21. Rasmussen F. Healing of the urinary bladder wounds. Morphologic and biochemical studies. Proc Soc Exp Biol Med 1966;123:470475.

  • 22. Degner DA, Walshaw R. Healing response of the lower urinary tract. Vet Clin North Am Small Anim Pract 1996;26:197206.

  • 23. Bellah JR. Wound healing in the urinary tract. Semin Vet Med Surg (Small Anim) 1989;4:294303.

  • 24. Dinesh D, Behl SM, Singh P, et al. Diagnosis of urinary bladder diseases in dogs by using two-dimensional and three-dimensional ultrasonography. Vet World 2015;8:819822.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 25. Kundu P, Ghosh D. Ultrasonographic study of urinary bladder diseases in dogs. Indian J Vet Surg 2006;27:3334.

  • 26. Mahaffey MB, Barber DL, Barsanti JA, et al. Simultaneous double-contrast cystography and cystometry in dogs. Vet Radiol Ultrasound 1984;25:254259.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 27. Mahaffey MB, Barsanti JA, Crowell WA, et al. Cystography: effect of technique on diagnosis of cystitis in dogs. Vet Radiol Ultrasound 1989;30:261267.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 28. Martinez I, Mattoon JS, Eaton KA, et al. Polypoid cystitis in 17 dogs (1978–2001). J Vet Intern Med 2003;17:499509.

  • 29. Takiguchi M, Inaba M. Diagnostic ultrasound of polypoid cystitis in dogs. J Vet Med Sci 2005;67:5761.

  • 30. Allen HS, Swecker WS, Becvarova I, et al. Associations of diet and breed with recurrence of calcium oxalate cystic calculi in dogs. J Am Vet Med Assoc 2015;246:10981103.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 31. Appel SL, Lefebvre SL, Houston DM, et al. Evaluation of risk factors associated with suture-nidus cystoliths in dogs and cats: 176 cases (1999–2006). J Am Vet Med Assoc 2008;233:18891895.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 32. Brown NO, Parks JL, Greene RW. Recurrence of canine urolithiasis. J Am Vet Med Assoc 1977;170:419422.

  • 33. Clark WT. The distribution of canine urinary calculi and their recurrence following treatment. J Small Anim Pract 1974;15:437444.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 34. Julian TD, Ravitch MM. Closure of the urinary bladder with stainless steel and absorbable staples. Ann Surg 1986;204:186192.

  • 35. Koehler LA, Osborne CA, Beuttner MT, et al. Canine uroliths: frequently asked questions and their answers. Vet Clin North Am Small Anim Pract 2009;39:161181.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 36. Osborne CA. Improving management of urolithiasis: canine struvite uroliths. April 1, 2004. Available at: veterinarynews.dvm360.com/improving-management-urolithiasis-canine-struvite-uroliths. Accessed May 30, 2016.

    • Search Google Scholar
    • Export Citation
  • 37. Case GD, Glenn JF, Postlethwait RW. Comparison of absorbable sutures in the urinary bladder. Urology 1976;7:165168.

  • 38. Greenberg CB, Davidson EB, Bellmer DD, et al. Evaluation of the tensile strengths of four monofilament absorbable suture materials after immersion in canine urine with or without bacteria. Am J Vet Res 2004;65:847853.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 39. Schiller TD, Stone EA, Gupta BS. In vitro loss of tensile strength and elasticity of five absorbable suture materials in sterile and infected canine urine. Vet Surg 1993;22:208212.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 40. Bezwada RS, Jamiolkowski DD, Lee IY, et al. Monocryl suture, a new ultra-pliable absorbable monofilament suture. Biomaterials 1995;16:11411148.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 41. Nary Filho H, Matsumoto MA, Batista AC, et al. Comparative study of tissue response to poliglecaprone 25, polyglactin 910 and polytetrafluorethylene suture materials in rats. Braz Dent J 2002;13:8691.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 42. Molea G, Schonauer G, Bifulco G, et al. Comparative study on biocompatibility and absorption times of three absorbable monofilament suture materials (polydioxanone, poliglecaprone 25, glycomer 631). Br J Plast Surg 2000;53:137141.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Figure 1—

    Baseline sagittal ultrasound image of the urinary bladder in a dog with urolithiasis showing locations (arrowheads) for ventral (A) and dorsal (B) bladder wall measurements. The ventral aspect of the bladder wall is thicker than the corresponding dorsal region (measurements of 3.3 mm and 1.4 mm, respectively). Similar disparities in wall thicknesses at baseline were consistently identified in all 18 dogs undergoing cystotomy for treatment of urolithiasis in the present study. Notice the urolith (asterisk) associated with clean shadowing in the bladder lumen.

  • Figure 2—

    Sagittal ultrasound image of the urinary bladder in a dog 2 weeks after cystotomy for treatment of urolithiasis. The cystotomy site at the ventral aspect of the bladder wall is identified (arrows). The cystotomy site is 7.1 mm thick, whereas the comparable region at the dorsal aspect is 3.1 mm thick. Notice the suture material (asterisks) visualized as regularly spaced, hyperechoic foci along the incision.

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  • 11. Hildreth BE, Ellison GW, Roberts JF, et al. Biomechanical and histologic comparison of single-layer continuous Cushing and simple continuous appositional cystotomy closure by use of poliglecaprone 25 in rats with experimentally induced inflammation of the urinary bladder. Am J Vet Res 2006;67:686692.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 12. Radasch RM, Merkley DF, Wilson JW, et al. Cystotomy closure: a comparison of the strength of appositional and inverting suture patterns. Vet Surg 1990;19:283288.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 13. Buote NJ, Kovak-McClaran JR, Loar AS, et al. The effect of preoperative antimicrobial administration on culture results in dogs undergoing cystotomy. J Am Vet Med Assoc 2012;241:11851189.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 14. Hamaide AJ, Martinez SA, Hauptman J, et al. Prospective comparison of four sampling methods (cystocentesis, bladder mucosal swab, bladder mucosal biopsy, and urolith culture) to identify urinary tract infections in dogs with urolithiasis. J Am Anim Hosp Assoc 1998;34:423430.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 15. Geisse AL, Lowry JE, Schaeffer DJ, et al. Sonographic evaluation of urinary bladder wall thickness in normal dogs. Vet Radiol Ultrasound 1997;38:132137.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 16. Kojima M, Inui E, Ochiai A, et al. Ultrasonic estimation of bladder weight as a measure of bladder hypertrophy in men with infravesical obstruction: a preliminary report. Urology 1996;47:942947.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 17. Kuzmić AC, Brkljacić B, Ivanković D. Sonographic measurement of detrusor muscle thickness in healthy children. Pediatr Nephrol 2001;16:11221125.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 18. Müller L, Jacobsson B, Mårild S, et al. Detrusor thickness in healthy children assessed by a standardized ultrasound method. J Urol 2001;166:23642367.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 19. Oelke M. International consultation on incontinence-research society (ICI-RS) report on non-invasive urodynamics: the need of standardization of ultrasound bladder and detrusor wall thickness measurements to quantify bladder wall hypertrophy. Neurourol Urodyn 2010;29:634639.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 20. Hastings JC, Van Winkle W, Barker E, et al. The effect of suture materials on healing wounds of the bladder. Surg Gynecol Obstet 1975;140:933937.

    • Search Google Scholar
    • Export Citation
  • 21. Rasmussen F. Healing of the urinary bladder wounds. Morphologic and biochemical studies. Proc Soc Exp Biol Med 1966;123:470475.

  • 22. Degner DA, Walshaw R. Healing response of the lower urinary tract. Vet Clin North Am Small Anim Pract 1996;26:197206.

  • 23. Bellah JR. Wound healing in the urinary tract. Semin Vet Med Surg (Small Anim) 1989;4:294303.

  • 24. Dinesh D, Behl SM, Singh P, et al. Diagnosis of urinary bladder diseases in dogs by using two-dimensional and three-dimensional ultrasonography. Vet World 2015;8:819822.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 25. Kundu P, Ghosh D. Ultrasonographic study of urinary bladder diseases in dogs. Indian J Vet Surg 2006;27:3334.

  • 26. Mahaffey MB, Barber DL, Barsanti JA, et al. Simultaneous double-contrast cystography and cystometry in dogs. Vet Radiol Ultrasound 1984;25:254259.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 27. Mahaffey MB, Barsanti JA, Crowell WA, et al. Cystography: effect of technique on diagnosis of cystitis in dogs. Vet Radiol Ultrasound 1989;30:261267.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 28. Martinez I, Mattoon JS, Eaton KA, et al. Polypoid cystitis in 17 dogs (1978–2001). J Vet Intern Med 2003;17:499509.

  • 29. Takiguchi M, Inaba M. Diagnostic ultrasound of polypoid cystitis in dogs. J Vet Med Sci 2005;67:5761.

  • 30. Allen HS, Swecker WS, Becvarova I, et al. Associations of diet and breed with recurrence of calcium oxalate cystic calculi in dogs. J Am Vet Med Assoc 2015;246:10981103.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 31. Appel SL, Lefebvre SL, Houston DM, et al. Evaluation of risk factors associated with suture-nidus cystoliths in dogs and cats: 176 cases (1999–2006). J Am Vet Med Assoc 2008;233:18891895.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 32. Brown NO, Parks JL, Greene RW. Recurrence of canine urolithiasis. J Am Vet Med Assoc 1977;170:419422.

  • 33. Clark WT. The distribution of canine urinary calculi and their recurrence following treatment. J Small Anim Pract 1974;15:437444.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 34. Julian TD, Ravitch MM. Closure of the urinary bladder with stainless steel and absorbable staples. Ann Surg 1986;204:186192.

  • 35. Koehler LA, Osborne CA, Beuttner MT, et al. Canine uroliths: frequently asked questions and their answers. Vet Clin North Am Small Anim Pract 2009;39:161181.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 36. Osborne CA. Improving management of urolithiasis: canine struvite uroliths. April 1, 2004. Available at: veterinarynews.dvm360.com/improving-management-urolithiasis-canine-struvite-uroliths. Accessed May 30, 2016.

    • Search Google Scholar
    • Export Citation
  • 37. Case GD, Glenn JF, Postlethwait RW. Comparison of absorbable sutures in the urinary bladder. Urology 1976;7:165168.

  • 38. Greenberg CB, Davidson EB, Bellmer DD, et al. Evaluation of the tensile strengths of four monofilament absorbable suture materials after immersion in canine urine with or without bacteria. Am J Vet Res 2004;65:847853.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 39. Schiller TD, Stone EA, Gupta BS. In vitro loss of tensile strength and elasticity of five absorbable suture materials in sterile and infected canine urine. Vet Surg 1993;22:208212.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 40. Bezwada RS, Jamiolkowski DD, Lee IY, et al. Monocryl suture, a new ultra-pliable absorbable monofilament suture. Biomaterials 1995;16:11411148.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 41. Nary Filho H, Matsumoto MA, Batista AC, et al. Comparative study of tissue response to poliglecaprone 25, polyglactin 910 and polytetrafluorethylene suture materials in rats. Braz Dent J 2002;13:8691.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 42. Molea G, Schonauer G, Bifulco G, et al. Comparative study on biocompatibility and absorption times of three absorbable monofilament suture materials (polydioxanone, poliglecaprone 25, glycomer 631). Br J Plast Surg 2000;53:137141.

    • Crossref
    • Search Google Scholar
    • Export Citation

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