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Basics ⬇

Outline

BASICS

Definition!!navigator!!

In rectal prolapse, tissue protrudes through the anus. Depending on the layers involved, it can be categorized into 4 types:

  • Type 1 = rectal mucosa and submucosa protrude
  • Type 2 = prolapse of all layers of the rectal ampulla
  • Type 3 = in addition to a type 2 prolapse there is intussusception of peritoneal rectum or small colon into the rectum. The intussuscepted part does not protrude through the anus
  • Type 4 = intussusception of the peritoneal rectum and varying lengths of the small colon through the anus

Pathophysiology!!navigator!!

Rectal prolapse results from an increase in pressure gradient between the abdominal cavity and the anus (i.e. straining), which causes the rectal mucosa and submucosa to glide backward over the muscularis layer. Unreduced prolapses become edematous and cyanotic owing to compromise of venous outflow. With type 3 and 4 prolapses, the entire rectum disengages from the perirectal tissues, resulting in complete displacement of the rectum as well as the distal small colon. Because the mesocolon of the distal small colon is relatively short, caudal displacement and tearing of the mesocolon during prolapse often result in avulsion of the colonic blood supply. If the blood supply to the small colon is disrupted, ischemic necrosis ensues.

Systems Affected!!navigator!!

  • Gastrointestinal—rectal impaction, small colon necrosis, or peritonitis
  • Behavioral—straining or mild to moderate abdominal pain
  • Cardiovascular—circulatory shock may be evident in horses with thrombosis or rupture of the small colonic vasculature or as a result of endotoxemia caused by small colon necrosis

Signalment!!navigator!!

More common in adult horses and mares. Type 4 rectal prolapse is seen with dystocia in mares.

Signs!!navigator!!

Historical Findings

Prolonged straining due to diarrhea or colic; dystocia.

Physical Examination Findings

Palpation and inspection are simple means of differentiating between the 4 types of rectal prolapses. Types 1, 2, and 3 are continuous with the mucocutaneous junction of the anus. Characteristic findings include:

  • Type 1—a circular, doughnut-shaped, edematous swelling at the anus that is usually most prominent ventrally
  • Type 2—a larger, cauliflower-shaped swelling that is often thicker ventrally than dorsally
  • Type 3—appears similar to type 2, but the invaginated peritoneal rectum or small colon can be palpated within the rectal lumen. This invaginated part (intussusceptum) does not protrude through the anus
  • Type 4—a palpable trench exists between the prolapse and the anus, and can be appreciated by sliding a finger underneath the prolapse and past the normal mucocutaneous junction. Usually has a tube-like appearance

Causes!!navigator!!

Rectal prolapse is most often associated with straining secondary to a variety of conditions:

  • Parturition
  • Dystocia
  • Uterine prolapse
  • Diarrhea
  • Constipation
  • Colitis
  • Proctitis
  • Rectal masses—neoplasms (leiomyoma, lipoma), foreign bodies, abscesses, polyps, hematomas
  • Grade 2 rectal tears
  • Intestinal parasitism
  • Urethral obstruction—urolithiasis

In many cases, however, a cause cannot be identified.

Risk Factors!!navigator!!

Any condition that induces straining. Poor body condition owing to loss of tone in the anal sphincter or decreased elasticity of the connective tissue may increase risk. Type 1 rectal prolapses are often seen in horses with severe diarrhea, and type 4 rectal prolapses are most often associated with dystocia in broodmares.

Diagnosis ⬆ ⬇

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DIAGNOSIS

Differential Diagnosis!!navigator!!

Prolapsed tissues may be mistaken for a neoplastic mass. Visual inspection and palpation can differentiate between the 2 conditions. Evaginated rectal tissues are obvious with a prolapse, whereas a neoplasm arises from a localized aspect of the rectal or perirectal tissues.

CBC/Biochemistry/Urinalysis!!navigator!!

Systemic abnormalities corresponding to the inciting cause may be identified. Early in the course of type 3 and 4 prolapses, leukocytosis and neutrophilia with a left shift may be observed, as well as increases in packed cell volume, fibrinogen, TP, sodium, and potassium levels. With longer duration, leukopenia and neutropenia ensue. Chronicity may lead to decreases in potassium, sodium, and chloride levels and increases in blood urea nitrogen, creatinine, and bilirubin.

Other Laboratory Tests!!navigator!!

Abdominocentesis to assess if compromise to the small colon has occurred. Peritoneal fluid in horses with type 3 or 4 prolapse may have an increase in white blood cell count or TP level. These abnormal findings may not develop until necrosis of gut wall, leakage, and peritonitis have occurred.

Imaging!!navigator!!

Transabdominal ultrasonography may be used to identify possible free fluid in the abdomen and evaluate motility of the intestine.

Other Diagnostic Procedures!!navigator!!

A flank laparotomy, ventral midline celiotomy, or laparoscopy can be used to assess the degree of compromise to the mesocolon and small colon in type 3 and 4 prolapse; however, access to the terminal small colon can be challenging with a flank or ventral midline laparotomy. In the standing horse, laparoscopy provides superior visualization and selection of the most appropriate surgical procedure in a minimally invasive manner.

Treatment ⬆ ⬇

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TREATMENT

  • The first step in the treatment of rectal prolapse is to prevent straining. The specific cause of the prolapse should therefore be identified and addressed. Epidural anesthesia is an effective means of alleviating tenesmus. Alternatively, heavy sedation, use of lidocaine gel, or a lidocaine enema may provide some relief
  • Early type 1 and 2 rectal prolapses without extensive edema, trauma, or contamination usually respond to conservative therapy aimed at reduction of tissue edema, manual reduction of the prolapse, and placement of a purse-string suture in the anus to prevent recurrence, and treatment of the primary cause for the prolapse:
    • Reduction of edema—application of topical glycerin, or mannitol, or magnesium sulfate, and lidocaine jelly or lidocaine enema (12 mL of lidocaine in 50 mL of water)
    • Reduce or prevent straining via epidural anesthesia
    • Purse-string suture—use of a large (size 1–3), nonabsorbable (nylon, polypropylene, umbilical tape, caprolactam) material; placed using 4 wide bites located 1–2 cm from the anus. Following placement, the external anal sphincter should be dilatable to a diameter of 2–3 cm to permit defecation to some degree although normal defecation will be impaired. Therefore, suture opening every 2–4 h to allow defecation or manual removal of feces is recommended It is usually advised to remove the suture within 48–72 h to minimize complications
    • The horse should be taken off feed for the first 24 h. Thereafter, mineral oil or other laxatives should be administered for at least 1 week and the horse should be fed a laxative diet for at least 2 weeks
    • Horses should be kept cross-tied in a box stall for the first week to prevent recumbency (increased abdominal pressure when recumbent)
  • Type 1 and 2 prolapses that are chronic in nature or that have failed to respond to conservative therapy can be treated successfully by submucosal resection or by full-thickness partial rectal amputation. Both procedures can be performed in the standing, sedated horse using epidural anesthesia. Submucosal resection is preferred over full-thickness rectal amputation because the rectal vasculature and muscular layers are preserved, an aseptic peritoneal environment is maintained, there is decreased risk of postoperative perirectal abscess formation or of rectal stricture, and postoperative tenesmus is decreased
  • Type 3 and 4 rectal prolapses require referral to a surgical facility as the damage to the mesocolon can be serious. Balanced polyionic IV fluid therapy may be required by horses with type 3 or 4 prolapses for treatment of hypovolemia or endotoxemic shock. The fluid rate should be based on the horse's hydration status and clinical condition

Client Education!!navigator!!

Horses with type 4 rectal prolapse have a serious condition carrying a guarded to poor prognosis for survival. Depending on the length of intussuscepted tissues, severity of small colon mesenteric damage, chronicity of the prolapse, the horse's medical status and value, and the owner's intentions for the horse, euthanasia may be warranted. If the owner wishes to pursue treatment, factors that require discussion include cost, the need for extensive postoperative care, and multiple possible complications following resection/anastomosis or colostomy. Horses undergoing colostomy may require a second procedure for revision, although permanent colostomy after resecting the rectum and distal small colon involved in a type 4 rectal prolapse may be indicated.

Surgical Considerations!!navigator!!

Notable hemorrhage may occur during submucosal resection or full-thickness rectal partial amputation, but can be controlled with electrocautery or ligation.

Medications ⬆ ⬇

MEDICATIONS

Drug(s) of Choice

  • Sedation may be achieved with xylazine (0.2–1.1 mg/kg IV) or detomidine (0.005–0.02 mg/kg IV). Both duration and quality of sedation may be enhanced by the coadministration of butorphanol tartrate (0.1 mg/kg IV)
  • Epidural administration of a variety of agents may provide anesthesia for initial evaluation and treatment, as well as analgesia for prevention of postoperative straining (for details and dosages, see chapter Rectal tears)

Follow-up ⬆ ⬇

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FOLLOW-UP

Patient Monitoring!!navigator!!

Following treatment, the patient should be observed regularly for evidence of tenesmus, rectal impaction, or relapse. Purse-string sutures should be removed within 24–48 h to minimize complications. In grade III and IV, serial abdominocentesis is advised.

Prevention/Avoidance!!navigator!!

Prompt recognition and treatment of factors predisposing to tenesmus reduce the likelihood of rectal prolapse.

Possible Complications!!navigator!!

  • Rectal impaction
  • Re-prolapse
  • Dehiscence of suture lines
  • Perirectal abscess formation
  • Rectal stricture
  • Ischemic necrosis of the small colon
  • Complications associated with colostomy, celiotomy, or resection/anastomosis procedures

Expected Course and Prognosis!!navigator!!

The prognosis for type 1 and 2 rectal prolapses is favorable, whereas the prognosis for type 3 and 4 prolapses is guarded to poor.

Miscellaneous ⬆ ⬇

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MISCELLANEOUS

Associated Conditions!!navigator!!

  • Endotoxemia
  • Laminitis
  • Uterine prolapse

Abbreviations!!navigator!!

TP = total protein

Suggested Reading ⬆ ⬇

Espinosa Buschiazzo CA, Cancela MCJ, Simian MV. Permanent colostomy after small colon prolapse in a parturient mare. Equine Vet Educ 2010;22:223–227.

Freeman DE. Rectum and anus. In: Auer JA, Stick JA, eds. Equine Surgery, 4e. St. Louis, MO: WB Saunders, 2012:494–505.

Author(s) ⬆

Author: Luis M. Rubio-Martinez

Consulting Editors: Henry Stämpfli and Olimpo Oliver-Espinosa

Acknowledgment: The author and editors acknowledge the prior contribution of Judith B. Koenig and Annette M. Sysel.