Surgical treatment of type II atresia ani and rectocutaneous fistula in a male kitten

Abstract

Case summary

A 4-week-old, male domestic shorthair kitten presented with congenital abnormalities of the rectum and perineal region, including defecation through an aberrant opening within the scrotal area. Positive-contrast radiography and ultrasonography confirmed type II anal atresia with a ventral rectocutaneous fistula. An abnormally positioned urethra was also identified, coursing dorsally to the penile structure. Surgical transposition of the fistulous tract and reconstruction of the anal sphincter were performed using a fistula-flap technique to restore normal defecation. Recovery was uneventful, and spontaneous defecation resumed within 2 weeks. At a 20-month follow-up, the patient remained clinically well.

Relevance and novel information

This case represents the first documented use of a fistula-flap technique to successfully correct type II atresia ani with rectocutaneous fistula in a male feline patient, demonstrating that the technique can be safely adapted to different anorectal malformation patterns.

Introduction

The cloaca is a transient embryonic structure that serves as a common opening for the gastrointestinal, urinary and reproductive tracts. Abnormal embryonic development in this region is believed to result in congenital anorectal malformations in neonatal puppies and kittens.^1–3 The true incidence is unknown, as many affected neonates are euthanased before the diagnosis is made.^4,5 In dogs, the incidence is estimated at 0.007% based on data from the Veterinary Medical Database. ⁶ To date, no data have been published on the incidence of this condition in cats.

Atresia ani is one of the most frequently reported congenital perineal anomalies in small animals. It is classified into four types (I–IV) depending on the degree of rectoanal separation, ranging from anal stenosis to complete imperforation, with varying degrees of proximity between the anal membrane and the rectum.^4–6 The condition is fairly frequently associated with rectovaginal or rectovestibular fistulas, particularly in female animals.^2,3,6 Cases of type II atresia ani with rectovaginal fistula have also been reported in a male pseudohermaphrodite kitten. ¹¹ Congenital rectocutaneous fistulae are rarely seen in the human medical literature, often associated with atresia ani.^7,8 and comparable cases have been described in guinea pigs. ⁹ In cats, the available literature on anorectal malformations is largely limited to isolated case reports^10–15 and small case series,^16,17 with rectocutaneous fistula documented only rarely.^18,19

Clinical signs of a maldeveloped anal area include tenesmus, discomfort, abdominal distension and vomiting. These become more pronounced once the diet is transitioned to solids and can be accompanied by perineal bulging, a lack of defecation or defecation from an abnormal orifice. Megacolon may be present in more severe cases.^17,20–22

Diagnosis is typically based on physical examination and positive contrast radiography or CT. These imaging techniques not only help delineate the terminal colon and possible fistulous tracts but also aid in planning surgical intervention.^3,6

Balloon dilatation has been reported as an effective treatment for isolated anal stenosis.^20,23 For more complex cases of atresia, including types II, III and IV, surgical management typically involves reconstruction of the anal opening with emphasis on preservation of the sphincter mechanism. Techniques include perineal anoplasty, involving excision of the fibrous tissue at the blind rectal pouch and mobilisation of the proximal rectum, which is then sutured to the perineal skin to create a neo-anus. In selected patients, a fistula flap can be incorporated into the reconstruction to facilitate anoplasty and restore mucocutaneous continuity.^1,2,24 In cases with multiple fistulas, abnormal fistulous tracts or distorted perineal anatomy, combined techniques may be required. ¹⁸

Case description

History

A stray kitten estimated to be 4 weeks old was referred for treatment of type II atresia ani. It had been intermittently vomiting and straining to defecate. Tenesmus was addressed by introducing of lactulose (0.5–1 ml PO q8h, 3.3 g/5 ml, Laxatract syrup; Dechra) to achieve a softer faecal consistency.

Clinical findings

On examination, the patient was alert, weighed 800 g, and had mild hypogastric abdominal distension with discomfort on palpation. The anal dimple was evident yet occluded by an imperforate membrane. Ventral to this, a midline perineal cutaneous opening was identified between two lateral skin pouches, consistent with incomplete fusion of the scrotum at the median raphe and a cutaneous fistula. This anomalous orifice functioned as a pathway for faecal passage. In addition, ventrally, a structure partially covered by the prepuce was observed, presumed to be a penis (Figure 1).

Figure 1

(a) Preoperative and (b) postoperative appearance of the perineal region. The rectocutaneous fistula (a) is located ventral to the imperforate anal dimple and dorsal to the penile structure, which is covered by a skin flap lacking the normal urethral opening. (b) After surgery, a new anal opening was created within the site of the anal dimple, and the fistulous tract was utilised as a flap to establish a continuous faecal passage. A urinary catheter was placed to visualise the urethra during surgery and was used to perform a positive contrast lower urinary tract study postoperatively

Diagnostics

After 3 weeks of medical management, the kitten was readmitted for further evaluation and surgical intervention. The patient was premedicated with acepromazine (0.01 mg/kg IV, ACP; Elanco) and methadone (0.3 mg/kg IV, Comfortan; Dechra). Anaesthesia was induced with propofol (2–4 mg/kg IV, PropoFlo Plus; Zoetis) and maintained with isoflurane (Isoflo; Zoetis) in oxygen via endotracheal intubation to allow abdominal and perineal ultrasonography, followed by positive contrast radiography. Ultrasonography identified two small testes within the inguinal canals. The terminal rectum ended blindly, with mild caudal dilation and faecal accumulation. Positive contrast fistulography using a non-ionic low osmolar iodine contrast medium, iohexol (300 mg/ml, diluted at 50% with saline solution, Omniaque; GE Healthcare), confirmed a blind-ending rectum with a ventral rectocutaneous fistula opening at the perineal midline (Figure 2). The structure partially covered by the prepuce was ultrasonographically consistent with penile tissue, with a dorsally positioned urethral opening, consistent with penile hypospadias.

Figure 2

(a,b) Preoperative images of the fistulogram. (a) A blind-ending rectum was identified (white arrowhead), preventing the faecal material from advancing to the location where the anus is expected (white arrow). (b) The contrast medium delineates a thin fistulous tract (white arrow) after removal of the catheter

Treatment

Under the same anaesthetic event, the patient underwent surgical intervention. Cefuroxime (22 mg/kg IV, Zinacef; GlaxoSmithKline) was administered approximately 30 mins before surgery. The patient was positioned in sternal recumbency with the pelvis elevated and pelvic limbs extended beyond the edge of the surgical table. The tail was secured dorsally over the back, and the perineal region was clipped and aseptically prepared. A 3.0 Fr × 11 cm semi-rigid urinary catheter (SurgiVet Slippery Sam Tomcat Urethral Catheter; Smiths Medical PM) was advanced into the urethra and maintained in situ to facilitate intraoperative identification of this structure.

The rectocutaneous fistula was dissected from surrounding tissues and transposed dorsally, where a vertical incision was made at the imperforate anal site. Stay sutures were placed to improve tissue handling. The fistula was preserved and used as a flap for anal canal and opening reconstruction, with the rectal attachment maintained. The neo-anus was created by suturing the fistula flap to the perianal skin using simple interrupted 5–0 polydioxanone sutures (PDS; Ethicon).

Postoperative radiographs were acquired (Figure 3). The previously administered contrast media delineated the walls of the caudal portion of the descending colon and rectum, with no evidence of a persistent rectocutaneous fistulous tract. A 1 ml syringe was introduced via the neo-anus to allow visualisation of its path and margins, which appeared well-defined and smooth. A 3 Fr urinary catheter was replaced for a positive retrograde cystography, which confirmed an unremarkable urinary bladder and proximal urethra with no communication between the lower urinary tract and rectum.

Figure 3

(a–c) Postoperative radiographs of positive colonography. (a) The colon was smoothly delineated by the contrast media administered during the fistulography. (b) Positive colonography via the neo-anus delineated the caudal rectal wall (white arrowhead); there was no evidence of a persistent rectocutaneous fistulous tract. (c) A 1 ml syringe was introduced via the neo-anus to allow visualisation and delineation of its path and margins (white arrows). A Foley catheter delineated the urethral path towards the urinary bladder (white arrowhead); both were unremarkable

Postoperative recovery was uneventful, with spontaneous defecation observed shortly after surgery. The patient was discharged 5 days postoperatively with continued oral lactulose and a 7-day course of amoxicillin–clavulanate (15 mg/kg PO q12h, Synulox Palatable Drops; Zoetis).

Outcome

Mild faecal incontinence was noted immediately postoperatively but improved over time. Lactulose administration resulted in persistently soft stools, leading to perianal and caudal thigh dermatitis, which resolved with topical antimicrobial and anti-inflammatory therapy q12h (Isaderm Gel; Dechra). Stool quality normalised within 2 weeks after gradual tapering and discontinuation of lactulose. At 20 months postoperatively, the patient was continent, with only rare involuntary passage of small faecal fragments that did not affect quality of life. No urinary abnormalities were reported during the follow-up period.

Discussion

This report describes a case of type II atresia ani with concurrent rectocutaneous fistula and hypospadias in a male kitten. Surgical correction using a fistula-flap technique and perineal anoplasty restored normal defecation, with a favourable long-term outcome and only mild intermittent faecal incontinence at the 20-month follow-up.

Congenital anorectal malformations are infrequently reported in cats, and the true incidence is unknown. Most published feline cases involve atresia ani with rectovestibular or rectovaginal fistulae in female cats.^10,21 Rectocutaneous fistulae in male kittens are particularly rare,^18,19 with very few veterinary reports and only occasional analogues described in humans^7,8 and guinea pigs. ⁹ This case, therefore, provides valuable documentation of a complex congenital malformation in a male feline patient.

Positive-contrast radiography was essential for delineating the blind-ending rectum and surgical planning. Advanced imaging, including CT or endoscopy, could have provided additional anatomic detail but may be challenging in paediatric patients due to size-related limitations and resource-limited settings, as in this case, managed by a private animal welfare organisation.

The fistula-flap technique described by Jardel et al ¹ was successfully adapted in this patient despite anatomical differences, preserving the mucocutaneous junction, reducing neo-orifice tension and possibly contributing to the favourable continence outcome. The potential functional benefit of using the fistulous tract as a flap may relate to its muscular composition. Histopathological and manometric studies in paediatric patients and porcine models have shown that fistulous connections between the intestine and urogenital tract may contain fibres consistent with the internal anal sphincter.^25–27 In cats, no histological evidence of this has been reported. In the present case, the presence of internal anal sphincter tissue or epithelialisation of the reconstructed anal canal could not be confirmed. Nevertheless, the favourable long-term outcome observed is consistent with appropriate healing of the newly formed anal canal and anocutaneous junction, and the absence of major postoperative complications compares favourably with previously reported outcomes.^28,29 Secondary perianal dermatitis highlights the importance of proactive postoperative management.

Both testes were located within the inguinal canals and were later removed by the referring veterinarians via inguinal castration at 7 months of age, consistent with suspected cryptorchidism. Atresia ani and rectovaginal fistula are frequently associated with additional congenital abnormalities; in human medicine, approximately one-third of patients with anorectal malformations have concurrent defects. ³⁰ Similar associations have been reported in veterinary species, including partial caudal vertebral agenesis in dogs with rectovaginal fistula^30,31 and sacrocaudal dysgenesis or hydrocephalus in cats. ²⁹ In the present case, cryptorchidism remained presumptive because of the patient’s young age, although testicular descent had not occurred by the time of neutering.

An additional challenge in this case was concurrent hypospadias. Similar anomalies have been reported in male pseudohermaphroditic kittens and patients with disorders of sex differentiation, ³² in Boston Terriers with anovaginal clefts ³³ and in a puppy with atresia ani. ¹⁶ To the authors’ knowledge, only one other feline patient has been reported with concurrent hypospadias and atresia ani. ³⁴ This case reinforces the importance of thorough evaluation for concurrent urogenital or anogenital anomalies in all animals diagnosed with atresia ani. The clinical significance of this anatomical variation remains unclear but is considered low in the absence of associated morbidity. Nevertheless, ongoing monitoring is warranted, as it could theoretically predispose the patient to later disorders, mainly feline lower urinary tract disease.

The limitations of this report include reliance on caretaker observations for continence assessment and the absence of a standardised continence scoring system, which may underestimate subtle sphincter dysfunction. Despite this, the patient maintained an excellent quality of life with his indoor lifestyle.

Conclusions

This case demonstrates that surgical correction of type II atresia ani with rectocutaneous fistula using a fistula-flap technique can achieve anatomical and functional restoration. Early diagnosis, careful surgical planning and proactive postoperative management are essential for favourable long-term outcomes.