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867.e2 Rectoanal Congenital Anomalies/Atresia Ani

Rectoanal Congenital Anomalies/Atresia Ani Client Education
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• ± Rectovaginal or urethrorectal fistula
BASIC INFORMATION
pouch, which is brought through the skin
• Other congenital abnormalities sometimes careful dissection exposes the distal rectal
Definition identified (e.g., cleft palates, open fontanelles, incision and incised. The rectum is then
A rare congenital absence or closure of the anus hypospadias) sutured to the surrounding subcutaneous
tissue and skin.
Synonyms Etiology and Pathophysiology • Type IV atresia ani: an abdominal approach
Rectal atresia, segmental rectal aplasia • At 7 weeks of embryologic development, may be needed to mobilize the distal colon
the urorectal fold grows caudally, separat- and rectum.
Epidemiology ing the urogenital and rectal tracts and
SPECIES, AGE, SEX their shared cloaca. The anal membrane Chronic Treatment
Congenital rectal abnormalities are rare, with a eventually thins and ruptures, forming an • Bougienage for continued anal stenosis
reported 0.007% incidence among dogs. True anus. • Additional surgery such as anoplasty revision
incidences are hard to determine because most • Atresia ani is caused by a failure of the urorec- or subtotal colectomy
affected dogs and cats are euthanized. Females tal fold to completely separate the primitive
are 1.79 times more likely to develop atresia ani, cloaca or failure of the anal membrane to Nutrition/Diet
with poodles and Boston terriers predisposed. perforate after anal formation. • Diets should be selected that produce soft
Newborn puppies and kittens are clinically stools.
normal for the first 2-4 weeks of life, with an DIAGNOSIS • Stool softeners (e.g., lactulose) as needed to
age range of 4-24 weeks at presentation. decrease straining
Diagnostic Overview
GENETICS, BREED PREDISPOSITION The diagnosis is suspected in dogs and cats Possible Complications
• Miniature/toy poodle around the age of weaning based on lack of • Wound dehiscence and sepsis
• Boston terrier defecation, abdominal distention, and absence • Incontinence from inadequate external anal
• Miniature schnauzer or lack of patency of the anus. Abdominal sphincter function
radiographs are useful. • Secondary colonic atony from prolonged
ASSOCIATED DISORDERS distention
Many animals with atresia ani have multiple Differential Diagnosis • Anal stricture
congenital anomalies such as vaginal abnor- • Rectovaginal or urethrorectal fistula: can
malities, tail malformations, a short colon, occur simultaneously with atresia ani Recommended Monitoring
absence of anal sac ducts, incomplete or absent • Parasitism: unthrifty nature, abdominal Weight gain, ability to defecate without
external anal sphincter, and rectovaginal and distention tenesmus, evidence of megacolon
urethrorectal fistulas. Rectovaginal fistulas were
documented in 8 of 12 patients with atresia Initial Database PROGNOSIS & OUTCOME
ani in one report. • CBC/serum biochemistry profile
• Abdominal radiography • Often poor with high surgical mortality
Clinical Presentation ○ Determine the degree of colonic distention. rate
DISEASE FORMS/SUBTYPES ○ Determine position of terminal rectum • Better prognosis for types I and II than types
Atresia ani is classified as four anatomic types: within the pelvic canal (gas may accumu- III or IV
• Type I: congenital stenosis of the anus late in the colon and rectum). Elevation of • High incidence of fecal incontinence after
• Type II: the rectum ends as a blind pouch the animal’s hindquarters during a lateral surgery
immediately cranial to the imperforate anus radiograph or horizontal beam radiography • In one study, 4 of 6 dogs could pass feces
• Type III: imperforate anus, with the blind is useful to encourage gas migration to normally during a 1- to 5-year follow-up
end of the rectum located farther cranially the area. period.
than type II
• Type IV: discontinuity of the proximal Advanced or Confirmatory Testing PEARLS & CONSIDERATIONS
rectum with normal anal and terminal rectal Positive contrast radiography to determine
development location of rectovaginal or urethrorectal fistula, Comments
if applicable • Meticulous dissection is essential because
HISTORY, CHIEF COMPLAINT the rectal tissue is thin and friable from
Animals with type I atresia ani are normal until TREATMENT prolonged distention.
weaning, at which time clinical signs of constipa- • It is crucial to preserve the external anal
tion and tenesmus develop. Those with types II, Treatment Overview sphincter to minimize chances of permanent
III, and IV are clinically normal for the first 2-4 Surgical repair is indicated, but postoperative fecal incontinence.
weeks of life and then become weak, anorexic, complications are frequent and numerous. • Repeated procedures may be necessary.
or restless and develop abdominal enlargement. • Delay in the diagnosis is common. Chronic
Defecation is absent or from the vagina. Acute General Treatment distention of the colon and rectum often
• Correction of dehydration leads to megacolon.
PHYSICAL EXAM FINDINGS • Type I atresia ani: general anesthesia then
• Perineal swelling, anal membrane protru- gentle bougienage or total removal of the Technician Tips
sion, restlessness, arched back, abdominal stenosed portion of the rectum Every time you obtain a rectal temperature,
enlargement, anal dimple, vomiting, and • Type II or III atresia ani: a vertical skin also examine for normal rectoanal conformation
dehydration incision is made over the anal dimple, and and tone.

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