Comparison of urethral length and orifice diameter in cats undergoing transpelvic or subpubic urethrostomy for perineal urethrostomy revision (cadaveric study)

Abstract

Objectives

Stenosis is a postoperative complication reported in 12–17% of male cats that undergo perineal urethrostomy (PU). This study compared two different revision techniques for failed perineal urethrostomies. The first objective was to evaluate the feasibility of performing a transpelvic urethrostomy (TPU) after a previous, correctly performed PU in male cats. The second objective was to determine the residual urethral length, orifice diameter, and the position of the orifice relative to the pubic brim and anus after PU, TPU and subpubic urethrostomy (SPU).

Methods

Twenty male cat cadavers were randomly divided into two groups: TPU and SPU. In group TPU, PU was followed by TPU; in group SPU, PU was followed by SPU. After each procedure, the urethral orifice cross-section size was estimated by inserting the largest possible urinary catheter without resistance. Residual urethral length was measured both on contrast radiographs and after anatomical dissection.

Results

In all cats, TPU could be performed following a technically correct PU. The TPU resulted in a 1.5-times longer residual urethral length than SPU, based on contrast radiographs (P = 0.001) and confirmed by anatomical dissection (P <0.001). Relative to the initial urethral length, PU, TPU and SPU resulted in a reduction of 24%, 36% and 56%, respectively. The urethral orifice diameter after TPU did not differ from SPU (P = 1.000), and it was not statistically significantly different between TPU and PU (P = 0.317) or between SPU and PU (P = 0.655). The urethral orifice was located further away from the pubis (P <0.001) and closer to the anus (P <0.001) after TPU than after SPU.

Conclusions and relevance

Both TPU and SPU are possible revision surgeries following PU. As TPU preserves a significantly longer urethral length and requires less tissue dissection, the risk of urinary tract infections, urinary dermatitis and urinary incontinence might be less following TPU than SPU.

Keywords

Transpelvic urethrostomy subpubic urethrostomy perineal urethrostomy cadaveric study

Introduction

Perineal urethrostomy (PU) is the traditional surgical approach in male cats suffering repeated obstructive feline lower urinary tract disease (FLUTD) or irreversible trauma to the penile urethra. However, postoperative stenosis of the urethral orifice is one of the most frequent complications and is reported in 12–17% of cats.^1,2 A study on surgical revision of stenosed PU found that in 8/11 cats, the original dissection did not involve the urethra to the level of the bulbourethral glands, where the average internal diameter is nearly twice that of the penile urethra.^3,4 In such cases, a revision PU can be performed by further dissection and mobilisation of the urethra to just proximal to the bulbourethral glands. Other reasons for PU urethral orifice stenosis include automutilation, lower urinary tract infections, traumatic tissue handling, poor mucosa to skin apposition and/or subcutaneous leakage after traumatic catheterisation.⁴ In those cases, alternative revision techniques such as prepubic (PPU), subpubic (SPU) or transpelvic (TPU) urethrostomy need to be considered.^4–10

PPU results in a urethral orifice immediately cranial to the brim of the pubis.^5,10,11 Because of its location, it is associated with high rates of complications such as ascending infection, urinary outflow obstruction due to kinking of the urethra, urinary incontinence and peristomal dermatitis; therefore, it is not commonly performed.^5,10,11 With SPU, a pubic flap is created through a pubic osteotomy. The postprostatic urethra is transposed and tunnelled subcutaneously allowing the urethrostomy opening to be placed caudal to the inguinal fat pad.⁶ This position permits free caudal flow of the urine without scalding the inguinal and thigh regions. To the best of our knowledge, no new data have been published about SPU since the original single case report in 1989.⁶ In 2004, TPU was described as a primary or salvage procedure for FLUTD.⁷ This technique involves an ischial ostectomy and thereby eliminates the need for transposition of the urethra, decreasing the risk of iatrogenic disruption of its vascular and/or nerve supply.⁷

The first objective of this study was to evaluate the feasibility of performing TPU in male cats that underwent a technically correct PU. The second objective was to compare the residual urethral length, urethral orifice diameter and position of the orifice after TPU vs SPU revision surgery. It was hypothesised that TPU would result in a longer residual urethra, that there would be no difference in size of the urethral orifice and that TPU would result in a urethral orifice closer to the anus than SPU.

Materials and methods

Twenty cadavers of adult male cats that died or were euthanased for reasons unrelated to this study were collected and randomly assigned to one of two groups (‘group TPU’ and ‘group SPU’). Body weight and body condition score (BCS; 9-point scale) were determined. Cadavers were stored at −18°C and thawed at room temperature for 24–48 h, depending on size and BCS prior to the study. The distance from the anal orifice to the preputium and from the preputium to the pubic brim was measured with a flexible scale. A native laterolateral digital radiograph (Agfa CR 10-X; Verachtert Digital) was taken to exclude gross bony abnormalities and to screen for the presence of radiopaque uroliths.

Retrograde catheterisation of the urethra was performed using a 1.3 mm Tomcat catheter (Buster Cat Catheter; Kruuse). The bladder was emptied through the catheter and 40 ml of 1:2 diluted contrast medium (Iomeron 300 mg I/mL; Bracco Imaging) was instilled to perform a cystourethrography. A 23 G needle was positioned through the prepuce and perineal skin at the level of the urethral opening to facilitate later identification of the caudal end of the urethra on the radiographic images. A lateral radiograph was taken with a probe with radiopaque markings introduced in the rectum to allow for accurate measurements of the urethra on the digital images (Figure 1a). The contrast solution was evacuated from the bladder and the lower urinary tract was thoroughly flushed with saline. The perineal skin was cleaned with water and soap to remove all contamination with contrast solution. This cleaning process was repeated after each following contrast radiograph.

Figure 1

Cystourethrographies with a radiographic marker in the rectum (1 unit = 1 cm). A needle is positioned at the urethral orifice to facilitate identification of the caudal end of the urethra. (a) Preoperative situation. (b) After perineal urethrostomy. (c) After transpelvic urethrostomy. (d) After subpubic urethrostomy

With the urinary catheter still in place, a modified Wilson & Harrison PU was performed with the cats in a perineal position.¹² The urethra was dissected until just proximal of the bulbourethral glands and the urethral mucosa was sutured to the skin with 5-0 nylon (Ethicon). The post-PU urethral orifice cross-section was assessed by inserting soft, kink-resistant PVC catheters (Kruuse) of increasing diameter. The size of the largest urinary catheter that was easily inserted was recorded and this catheter was used to perform a new retrograde cystourethrogram (Figure 1b). Subsequently, all cats were placed in dorsal recumbency with the hindlimbs in a neutral, frog-leg position.

In cats belonging to group TPU, a TPU was performed.⁷ Briefly, a midline incision was made starting from the cranial brim of the pubis, extending caudally to end as an elliptical skin incision around the previously created PU orifice. An area 10 mm wide × 12 mm long was removed from the caudal aspect of the ischium using Kerrison rongeurs size 4 (Aesculap). The pelvic urethra dorsal to this bony defect was incised longitudinally at its ventral aspect and sutured to the skin with simple interrupted sutures (5-0 nylon). The most caudal portion of the urethra, including the PU urethral orifice, was amputated and its length was recorded.

In group SPU, cats underwent a SPU with minor modifications to the described technique.⁶ Briefly, a caudal coeliotomy from 5 cm cranial to the pubis until the pubic brim was performed. The skin was retracted caudally to expose the pubis. The prepubic tendon was partially incised and reflected laterally, and the adductor muscles and cranial portion of the gracilis muscles were subperiosteally elevated from the symphysis pubis to expose the pubic rami. An 8 mm osteotome and mallet were used to osteotomise the pubic rami 10 mm lateral to the pubic symphysis. A third transverse osteotomy was made through the body of the pubic bone across the pubic symphysis. The T-shape flap that was created through the osteotomies was rotated ventrally, after which the intrapelvic urethra could be visualised. The urethra was transected as caudal as possible and two stay sutures (4-0 nylon) were placed on both lateral sides of the orifice to retract the urethra cranially and the pubic flap was hinged back into its original location. The muscular aponeuroses of the adductor and gracilis muscles were repositioned over the flap with a continuous suture (3-0 polydioxanone). Caudal traction was applied to the stay sutures in the urethra to determine the ideal urethral orifice location. The goal was to create the urethral orifice as caudal as possible, while avoiding excessive tension on the urethra. A 10 mm midline skin incision was created, and curved Kelly forceps were tunnelled from caudal to cranial through the subcutaneous fat and were used to grasp the stay sutures and pull the urethra in its subpubic position. The urethra was spatulated over 5 mm on its ventral aspect. The urethral mucosa was apposed to the skin with simple interrupted sutures (5-0 nylon). The abdomen was closed in a routine fashion.

All procedures were performed by the same surgeon (SD). After TPU or SPU, the urethral orifice diameter was measured as described above. The distances from anus to the centre of the urethral orifice and from the centre of the urethral orifice to the pubic brim were measured. A final retrograde cystourethrogram was performed (Figure 1c,d). In cats that underwent SPU, the caudal proportion of urethra that was left in situ was dissected and its length was measured. Finally, a coeliotomy was performed in all cats and the bladder and urethra were dissected and removed ‘en bloc’ to determine the residual urethral length.

The course of the urethra and its length were analysed on all radiographs using dedicated imaging software (ClearCanvas Workstation 2.0).

Statistical analyses

Statistical analyses were performed using SPSS Statistics 27 (IBM). Shapiro–Wilk tests were performed to assess the normality of the data. The body weight of both groups was assessed using independent t-tests. All other parameters between both groups were assessed using the Mann–Whitney U-test. Wilcoxon signed rank tests were used to assess the difference in urethral orifice diameter and the distance between the urethral orifice and the anus within cats between PU on the one side and TPU or SPU on the other side. P values were considered to be statistically significant if they were <0.05.

Results

Mean body weight, median BCS, preoperative urethral length, and distance from pubis to prepuce and from prepuce to anus were not statistically different between groups (Table 1). Mineralisations in the urinary tract were not seen on any of the radiographs, and all cadavers were successfully catheterised through the penile orifice. There was no statistically significant difference between either group regarding median urethral orifice size, urethral length, and distance from pubis to prepuce or from prepuce to anus after PU (Table 2). PU resulted in a median reduction of 24% length vs the natural urethral length.

Table 1

Baseline values of the male cat cadavers used in this study

	Group TPU (n = 10)	Group SPU (n = 10)	P value
Body weight (kg)	4.9 ± 1.6	4.5 ± 1.3	0.951
BCS (9-point scale)	5 (1–8)	5.5 (2–7)	0.631
Urethral length on cystourethrography (mm)	97 (55–129)	82 (68–112)	0.353
Distance from pubis to prepuce (mm)	46 (33–69)*	42 (32–68)^†	0.321
Distance from prepuce to anus (mm)	38 (33–46)	44 (29–47)	0.123

Data are presented as mean ± SD or median (range)

TPU = transpelvic urethrostomy; SPU = subpubic urethrostomy; BCS = body condition score

n = 9

†

n = 8

Table 2

Measurements recorded after perineal urethrostomy

	Group TPU (n = 10)	Group SPU (n = 10)	P value
Urethral orifice diameter (Fr)	10 (10–12)	11 (8–12)	1.000
Urethral length on cystourethrography (mm)	73 (47–92)	68.5 (51–102)	0.796
Distance from pubis to urethral orifice (mm)	67 (52–78)*	56.5 (46–82)^†	0.114
Distance from urethral orifice to anus (mm)	23.5 (18–28)	23 (12–25)	0.247

Data are presented as median (range)

TPU = transpelvic urethrostomy; SPU = subpubic urethrostomy

n = 9

†

n = 8

It was technically feasible on all occasions to perform a TPU, despite the preceding PU. A statistically significantly longer urethral length could be preserved after TPU compared with SPU (Table 3). TPU resulted in a 36% reduction in urethral length vs the initial urethral length, whereas SPU resulted in a 56% reduction in urethral length. The median urethral orifice diameter did not differ between TPU and SPU (Table 3). When comparing the urethral orifice diameter between PU and TPU and between PU and SPU, no statistically significant differences were found (P = 0.317 and P = 0.655, respectively). Finally, TPU resulted in a urethral orifice that was statistically significantly closer to the anus compared with SPU (Table 3). When the distance from the urethral orifice to the anus was compared between PU and TPU and between PU and SPU, both TPU and SPU resulted in a urethral orifice that was statistically significantly further away from the anus compared with PU (P = 0.005 and P = 0.005, respectively).

Table 3

Measurements recorded after transpelvic (TPU) and subpubic urethrostomy (SPU)

	Group TPU (n = 10)	Group SPU (n = 10)	P value
Urethral length on cystourethrography (mm)	59 (40–76)	39 (27–63)	0.001
Urethral length on anatomical dissection (mm)	53 (34–67)	33 (18–48)	<0.001
Length of removed part of distal urethra (mm)	7 (2–13)*	17 (11–29)^†	0.002
Urethral orifice diameter (Fr)	10 (10–12)	11 (8–12)	1.000
Distance from pubis to urethral orifice (mm)	48 (37–64)*	18 (13–25)*	<0.001
Distance from urethral orifice to anus (mm)	34 (20–40)	57.5 (38–92)	<0.001

Data are presented as median (range)

n = 9

†

n = 7

Discussion

To our knowledge, this is the first study to directly compare residual urethral length, urethral orifice diameter and distance from the urethral orifice to the anus after TPU and SPU. Although both TPU and SPU shortened the urethra, this was far less pronounced for TPU. TPU resulted in a urethra that was 1.5-times longer than SPU but resulted in a urethral orifice closer to the anus than SPU. The urethral orifice diameter was similar for both TPU and SPU, and neither was different from PU.

When TPU was originally described by Bernarde and Viguier in 2004, it was introduced as a primary urinary diversion solution.⁷ Yet, there were two cats included in that study cohort that underwent TPU as a salvage procedure after a failed PU. Nevertheless, it was not specified whether PU revision surgery with further dissection up to the bulbourethral glands would still have been an option in those cats. Indeed, improper surgical technique is the cause of the vast majority of, but not all, cases of PU stenosis, and there are only anecdotical reports of how to approach the latter group of cats surgically. Based on the results of this cadaveric study, revision by performing a TPU is a surgical option in failed PU cats, even after a previous technically correct PU. Of note, in some cases, the resected piece of urethra between PU and TPU was as short as a few millimetres. In the cadavers, it was impossible to mimic the stenosis of the urethral orifice that would have occurred after the original PU in clinical cases that require revision. Nevertheless, it is our clinical experience with revisions of failed PU that the obstruction is caused by a stenosis of the urethral orifice itself rather than a stricture of the more proximal urethral segment. We therefore expect that, in most clinical cases, a TPU would be a valuable salvage procedure.

A recent study described stenosis in 16% of cats after TPU was used as a first-line surgery in male cats presented with FLUTD.¹³ This percentage is similar to what has been reported after PU.^1,2 However, the authors reported that cases that developed stenosis were difficult to manage, with 60% of cats requiring multiple revision surgeries. The high number of recurrent stenoses might have been due to insufficient remaining urethral tissue to create a tension-free stoma in that location. In order to reach a sufficient amount of healthy urethra, the ischiatic ostectomy can be extended cranially. However, fracturing of the pubis has been described as a complication after ostectomy of 50% of the length of the pelvic floor.¹⁴ Therefore, in cases with a more proximal obstruction, SPU can be considered a reasonable alternative.

Urinary tract infection (UTI) is a common complication, reported in 22–53% of cats that undergo PU.^1,13,15–17 Further shortening of the urethra might increase the risk of UTI even more. In our study, PU resulted in a reduction of urethral length of one-quarter vs the length before PU. TPU resulted in a reduction of one-third in urethral length vs the initial urethral length, whereas SPU resulted in a reduction of more than half the initial urethral length. It is therefore expected that SPU will result in a higher prevalence of UTI than TPU. On the contrary, TPU resulted in a urethral orifice closer to the anus than SPU. Yet, in a recent study, most UTIs in cats that underwent PU were caused by normal skin flora rather than intestinal flora, and the prevalence of UTI was much higher after PPU than after PU.¹⁵ The proximity of the anus to the urethral orifice might therefore be less important than the remaining urethral length. The impact of urethral orifice position and residual urethral length on the prevalence of UTI after TPU and SPU needs further investigation in clinical patients.

The position of the urethral orifice might also have an impact on the development of peristomal dermatitis and urinary incontinence. A recent study compared the short- and long-term complications after PPU and TPU.¹⁸ Urinary dermatitis and urinary incontinence were not observed in cats after TPU but were reported after PPU in 18% and 13% of cats, respectively.¹⁸ The SPU procedure is a modification of the PPU, maintaining a longer urethral segment.⁶ During SPU, the goal is to create a urethral orifice as caudal as possible, while avoiding excessive tension on the urethra. Using the described modification, we were able to create the new orifice at a median distance of 18 mm caudal to the pubic brim. Therefore, SPU might be associated with less peristomal dermatitis and urinary incontinence than PPU. In order to transpose the urethra to a subpubic location, more dissection and manipulation of the urethra was required during SPU vs TPU. Possible damage to the innervation could result in a higher risk of incontinence after TPU than after SPU. The resulting effect of the manipulation during surgery and the final location of the urethral orifice on the postoperative incidence of urinary dermatitis and incontinence needs further clinical research.

A trend for shorter surgical time for TPU vs SPU was noted, although not evaluated statistically due to the incomplete data set. Overall, the TPU procedure was perceived as more straightforward and technically less demanding than SPU.

The sample population in this study was small. Some data regarding the distance between the pubis and the urethral orifice were lacking from the first three cats as we only started collecting them from cat 4 onwards. The length of the excised part of urethra during TPU and SPU was also only recorded from cat 5 onwards.

As already indicated, several limitations inherent to a cadaveric study are acknowledged. In addition, information on the clinical history of the cats was lacking. We assumed that the cats did not have any clinical signs related to FLUTD. However, in one cadaver, a small urolith was detected in the urinary bladder at the time of the anatomical dissection at the end of all procedures, which was not visible on native radiographs. Nevertheless, it is unlikely that this will have influenced any of the data obtained.

Conclusions

In cats with a previous PU, TPU not only requires less dissection and manipulation of the remaining urethral segment, but it also preserves a longer residual urethra than SPU. Therefore, in the case of a stenotic PU, a subsequent TPU seems preferable to SPU. In cases with a more proximally located obstruction, a SPU might be indicated.

Footnotes

Accepted: 15 October 2022

Author note

These findings were presented as a clinical research abstract at the 31st European College of Veterinary Surgeons Annual Scientific Meeting in July 2022.

Conflict of interest

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Ethical approval

The work described in this manuscript involved the use of non-experimental (owned or unowned) animals. Established internationally recognised high standards (‘best practice’) of veterinary clinical care for the individual patient were always followed and/or this work involved the use of cadavers. Ethical approval from a committee was therefore not specifically required for publication in JFMS. Although not required, where ethical approval was still obtained, it is stated in the manuscript.

Informed consent

Informed consent (verbal or written) was obtained from the owner or legal custodian of all animal(s) described in this work (experimental or non-experimental animals, including cadavers) for all procedure(s) undertaken (prospective or retrospective studies). No animals or people are identifiable within this publication, and therefore additional informed consent for publication was not required.

ORCID iD

Sieglinde David

Stella Minnoye

Hilde de Rooster

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