Rectal Prolapse

Rectal prolapse is a condition in which one or more layers of the rectum protrude through the anus. It is classified into two main types: partial prolapse (mucosal prolapse) and complete prolapse (full-thickness prolapse). In partial prolapse, only the rectal mucosa protrudes, appearing as a rosette-like mass. In complete prolapse, all layers of the rectal wall (mucosa, submucosa, muscularis, and serosa) are everted, resulting in a tubular or cylindrical mass. Complete prolapse is further subdivided into anal prolapse (where the anal canal is also involved) and true rectal prolapse (where the rectum alone is everted). The condition is a surgical emergency when the prolapsed tissue becomes strangulated, ischemic, or necrotic. Anatomically, the rectum is the terminal portion of the large intestine, extending from the descending colon to the anus. It is held in place by the mesorectum, peritoneal reflections, and surrounding connective tissue. Prolapse occurs when these supportive structures weaken or when there is increased intra-abdominal pressure. The condition is most common in young animals, particularly those with gastrointestinal or urogenital disease causing tenesmus (straining). Surgical intervention is often required to correct the prolapse and address the underlying cause.

The etiology of rectal prolapse is multifactorial, involving conditions that cause increased intra-abdominal pressure and tenesmus. Primary causes include: 1) Gastrointestinal diseases: diarrhea (especially parasitic, bacterial, or dietary), constipation, colitis, intestinal neoplasia, and foreign bodies. 2) Urogenital diseases: dystocia (difficult birth), prostatic disease (in males), and urinary tract obstruction. 3) Neurological disorders: sacral spinal cord injuries, cauda equina syndrome, and dysautonomia. 4) Anatomical and congenital factors: weakness of the pelvic diaphragm, abnormal mesorectal attachments, and congenital malformations. 5) Iatrogenic causes: excessive straining during manual evacuation or enema administration. 6) Metabolic and nutritional factors: malnutrition, hypocalcemia, and electrolyte imbalances leading to muscle weakness. The biomechanical trigger is sustained or severe tenesmus, which increases intra-abdominal pressure and forces the rectum caudally. Cellular mechanisms involve stretching and tearing of the connective tissue and smooth muscle of the rectal wall, leading to loss of structural integrity. In chronic cases, the mesorectum elongates, and the rectal wall becomes edematous and thickened, further predisposing to prolapse.

Rectal prolapse is most commonly reported in young dogs and cats, typically under 2 years of age, due to their higher susceptibility to gastrointestinal parasitism and dietary indiscretion. Brachycephalic breeds may be at increased risk due to conformational factors that increase intra-abdominal pressure. In dogs, breeds such as Bulldogs, Pugs, and Boston Terriers are overrepresented. In cats, the condition is often associated with lower urinary tract disease or constipation. There is no clear sex predilection, but intact males may be at higher risk due to prostatic disease. The incidence is higher in animals with chronic diarrhea or constipation, and in those with perineal hernia. In a retrospective study, rectal prolapse accounted for approximately 0.5% of all surgical cases in small animal practice. The condition is more common in rural areas where parasitic infections are prevalent. Working dogs may be at increased risk due to strenuous activity and potential trauma. Overall, the condition is sporadic but can be recurrent if the underlying cause is not addressed.

The pathophysiology of rectal prolapse involves a combination of increased intra-abdominal pressure and weakening of the supportive structures of the rectum. The rectum is normally anchored by the mesorectum, which attaches to the dorsal body wall, and by the lateral ligaments. The pelvic diaphragm, including the levator ani and coccygeus muscles, provides additional support. When intra-abdominal pressure rises (e.g., during straining), the rectum is pushed caudally. If the supportive structures are lax or weakened, the rectal wall invaginates and eventually protrudes through the anus. In partial prolapse, only the mucosa herniates, often due to excessive straining with a weak sphincter. In complete prolapse, the entire thickness of the rectal wall is everted. The prolapsed tissue becomes edematous and congested due to venous and lymphatic obstruction. If the prolapse is not reduced promptly, arterial blood supply may be compromised, leading to ischemia, necrosis, and ulceration. Chronic prolapse can cause stretching of the anal sphincter, leading to fecal incontinence. Systemic inflammatory response syndrome (SIRS) may develop if the prolapsed tissue becomes necrotic and infected, leading to sepsis. The underlying disease (e.g., colitis, parasitism) perpetuates tenesmus, creating a vicious cycle.

Intrinsic predisposing factors include: 1) Age: young animals (less than 1 year) are more susceptible due to immature pelvic musculature and higher incidence of parasitism. 2) Breed: brachycephalic breeds with conformational abnormalities (e.g., stenotic nares, elongated soft palate) may have increased respiratory effort, leading to increased intra-abdominal pressure. 3) Sex: intact males may be predisposed due to prostatic disease causing tenesmus. 4) Genetic factors: some breeds may have inherited weakness of the pelvic diaphragm. 5) Body condition: emaciated animals may have reduced perirectal fat, decreasing support. Extrinsic factors include: 1) Infectious agents: parasites (e.g., Trichuris vulpis, hookworms), bacteria (e.g., Salmonella, Clostridium), and protozoa (e.g., Giardia) causing diarrhea and straining. 2) Dietary factors: ingestion of foreign bodies, dietary indiscretion, or low-fiber diets leading to constipation. 3) Management factors: poor sanitation, overcrowding, and stress. 4) Prior surgeries: perineal hernia repair or anal sacculectomy may alter pelvic support. 5) Trauma: pelvic fractures or sacral injuries can weaken the pelvic floor. 6) Excessive activity: strenuous exercise or coughing can increase intra-abdominal pressure.

Clinical signs of rectal prolapse include a protruding mass from the anus, which may be present continuously or intermittently. The mass is typically red, edematous, and may be ulcerated or necrotic if chronic. Animals may exhibit tenesmus, dyschezia, and licking of the perineal area. In partial prolapse, the mass is smaller and may appear as a rosette. In complete prolapse, the mass is tubular and may have a visible lumen. Systemic signs may include lethargy, anorexia, vomiting, and signs of sepsis if the prolapse is strangulated. On physical examination, the prolapsed tissue may be painful to touch. The anal sphincter tone may be decreased in chronic cases. In cases of underlying disease, additional signs may be present, such as diarrhea, constipation, or urinary signs. The prolapse must be differentiated from intussusception, where a segment of intestine invaginates into another, and the mass may have a different appearance. The severity of clinical signs correlates with the degree of prolapse and the presence of complications.

Differential diagnoses for rectal prolapse include: 1) Intussusception: a portion of the intestine telescopes into an adjacent segment, often appearing as a tubular mass at the anus. It is more common in young animals and may be associated with vomiting and abdominal pain. Radiography or ultrasound can differentiate. 2) Anal sac neoplasia: tumors of the anal sacs can cause perineal swelling and tenesmus, but the mass is not typically a prolapse. 3) Perineal hernia: a swelling in the perineal region due to herniation of pelvic or abdominal contents, which may cause tenesmus but not a protruding rectal mass. 4) Rectal polyps: benign growths that may protrude through the anus but are usually pedunculated and can be differentiated by palpation and biopsy. 5) Rectal neoplasia (e.g., adenocarcinoma): can cause tenesmus and a mass, but the mass is usually firm and not reducible. 6) Vaginal prolapse in females: a protruding mass from the vulva, which may be confused with rectal prolapse but is located ventrally. 7) Urethral prolapse: a small, red mass protruding from the urethral orifice in male dogs, often causing hematuria. 8) Foreign body: a linear foreign body may cause intussusception or prolapse. 9) Colitis: inflammation of the colon can cause tenesmus and mucosal prolapse. 10) Constipation: severe constipation can lead to straining and partial prolapse. Definitive diagnosis is based on physical examination, palpation, and imaging.

The diagnostic algorithm for rectal prolapse begins with a thorough history and physical examination. The prolapsed mass should be inspected to determine if it is partial or complete. The mass should be gently palpated to assess for viability (color, temperature, capillary refill). A digital rectal examination should be performed to evaluate the anal sphincter tone and to check for any masses or foreign bodies. The next step is to determine the underlying cause. Fecal examination should be performed to check for parasites. Blood work (CBC, biochemistry, urinalysis) may reveal signs of infection, dehydration, or electrolyte imbalances. Abdominal radiographs may be indicated to evaluate for intussusception, foreign bodies, or other abdominal pathology. Ultrasound can be used to assess the intestinal tract and to differentiate prolapse from intussusception. In cases where the prolapse is recurrent or the underlying cause is unclear, colonoscopy may be performed to visualize the rectal mucosa and obtain biopsies. If a neurological cause is suspected, spinal radiographs or MRI may be indicated. The diagnostic workup should be systematic to identify and treat the primary disease, as failure to do so will lead to recurrence.

Laboratory findings in rectal prolapse are often nonspecific but may reflect the underlying cause. Complete blood count (CBC) may show leukocytosis with a left shift if there is inflammation or infection, or eosinophilia if parasitic infection is present. Biochemistry may reveal dehydration (elevated BUN, creatinine, and total protein), electrolyte imbalances (hypokalemia, hyponatremia) due to diarrhea or vomiting, and hypoglycemia in septic animals. Urinalysis may show signs of urinary tract infection if urogenital disease is the cause. Fecal flotation and direct smear are essential to identify parasitic ova (e.g., Trichuris, hookworms). Fecal culture may be indicated if bacterial enteritis is suspected. Coagulation panel (PT/aPTT) may be performed if surgery is planned, especially if there is evidence of bleeding or liver disease. Inflammatory biomarkers such as C-reactive protein (CRP) and serum amyloid A (SAA) may be elevated in inflammatory or infectious conditions. Blood gas analysis may reveal metabolic acidosis in cases of severe diarrhea or sepsis. These findings help guide fluid therapy and antimicrobial selection.

Imaging plays a crucial role in the diagnosis and management of rectal prolapse. Radiography: Abdominal radiographs may be useful to evaluate for intussusception, foreign bodies, or other causes of tenesmus. In cases of complete prolapse, a soft tissue mass may be visible at the pelvic inlet. Contrast radiography (barium enema) can delineate the rectal lumen and identify strictures or masses. Ultrasonography: Transabdominal ultrasound can assess the intestinal tract for intussusception, masses, or thickening of the rectal wall. Transrectal ultrasound may be used to evaluate the rectal wall layers and surrounding tissues. CT: Computed tomography provides detailed cross-sectional images of the pelvic region and can identify anatomical abnormalities, such as pelvic fractures or perineal hernias. It is particularly useful in complex cases. MRI: Magnetic resonance imaging is excellent for evaluating soft tissue structures, including the anal sphincter and pelvic diaphragm. It may be indicated if a neurological cause is suspected. Fluoroscopy: Dynamic fluoroscopy during defecation (defecography) can demonstrate the prolapse in real-time and assess the function of the pelvic floor. This is rarely performed in veterinary medicine but can be useful in research settings. Imaging findings guide surgical planning and help rule out other conditions.

Cytology and histopathology are important in cases where the prolapsed tissue is abnormal or when an underlying neoplastic process is suspected. Fine-needle aspiration of the prolapsed mass may be performed if a tumor is suspected. Cytology of the aspirate can reveal inflammatory cells, neoplastic cells, or infectious agents. Histopathology of biopsy samples from the rectal wall is indicated in cases of chronic prolapse, suspected neoplasia, or when the prolapse does not respond to treatment. Biopsies can be obtained during colonoscopy or surgically. Histopathological features may include mucosal inflammation, ulceration, fibrosis, and hyperplasia. In cases of neoplasia, the tumor type and grade are determined. Special stains may be used to identify infectious agents (e.g., fungal organisms). Histopathology is also essential to evaluate surgical margins if a mass is excised. In cases of recurrent prolapse, histopathology may reveal a primary rectal disease such as lymphoplasmacytic colitis or adenocarcinoma. The results guide further treatment and prognosis.

Treatment of rectal prolapse involves both medical and surgical management. The initial step is to reduce the prolapse manually. The prolapsed tissue should be cleaned with warm saline and lubricated. Gentle pressure is applied to reduce the prolapse. If the tissue is edematous, hypertonic solutions (e.g., 50% dextrose) or sugar can be applied to reduce swelling. After reduction, a purse-string suture may be placed temporarily to prevent recurrence while the underlying cause is treated. Medical management includes treatment of the underlying cause: anthelmintics for parasites, antibiotics for bacterial infections, dietary modification for diarrhea or constipation, and enemas or stool softeners for constipation. If the prolapse cannot be reduced or if there is necrosis, surgical intervention is required. Surgical options include: 1) Colopexy: The colon is sutured to the abdominal wall to prevent recurrence. This is performed via a ventral midline celiotomy. The colon is identified and a seromuscular incision is made. The colon is then sutured to the transversalis fascia or peritoneum using non-absorbable sutures (e.g., polypropylene) in a simple interrupted pattern. 2) Rectopexy: The rectum is sutured to the sacrum or pelvic wall. This can be performed via a dorsal approach or laparoscopically. 3) Amputation of the prolapsed tissue: This is indicated if the tissue is necrotic or if the prolapse is irreducible. The prolapsed segment is amputated, and a full-thickness anastomosis is performed. This is a salvage procedure and carries a higher risk of complications. Postoperative care includes pain management, antibiotics, and stool softeners. The underlying cause must be addressed to prevent recurrence.

The prognosis for rectal prolapse is generally good if the underlying cause is identified and treated promptly. In cases of simple prolapse that is reduced and the cause is managed, the recurrence rate is low. However, if the prolapse is chronic, recurrent, or associated with severe underlying disease (e.g., neoplasia), the prognosis is guarded. Complications such as stricture formation, fecal incontinence, and recurrence can occur. In a study of dogs with rectal prolapse, the recurrence rate was approximately 20% when the underlying cause was not addressed. Surgical intervention (colopexy) has a success rate of over 90% in preventing recurrence. Amputation of the prolapsed tissue has a higher complication rate, including anastomotic leakage and stricture. The overall prognosis is favorable with appropriate management. Negative prognostic indicators include the presence of necrosis, sepsis, and underlying malignant disease.

Postoperative follow-up for rectal prolapse includes monitoring for recurrence and complications. The animal should be hospitalized for 24-48 hours after surgery to monitor for signs of pain, infection, or dehiscence. The purse-string suture, if placed, is typically removed after 3-5 days. Stool softeners (e.g., lactulose) may be prescribed for 1-2 weeks to reduce straining. The animal should be restricted from strenuous activity for 2 weeks. A recheck examination is recommended at 2 weeks to assess healing and to remove any skin sutures. Serial examinations may be performed at 4, 8, and 12 weeks to monitor for recurrence. If the underlying cause was a parasitic infection, a fecal examination should be repeated to ensure resolution. Long-term monitoring includes regular fecal examinations and management of any chronic gastrointestinal or urogenital conditions. Owners should be educated to monitor for signs of tenesmus or prolapse. In cases of amputation, the animal should be monitored for signs of stricture, such as difficulty defecating. Overall, follow-up is essential to ensure a successful outcome.

Clinical pearls: 1) Always differentiate rectal prolapse from intussusception before attempting reduction. 2) Apply hypertonic solution (e.g., sugar) to edematous tissue to facilitate reduction. 3) Place a purse-string suture after reduction to prevent recurrence while treating the underlying cause. 4) Perform a thorough diagnostic workup to identify the underlying cause; failure to do so leads to recurrence. 5) In surgical cases, colopexy is preferred over amputation due to lower morbidity. 6) Use non-absorbable sutures for colopexy to ensure permanent fixation. 7) Postoperative stool softeners are crucial to reduce straining. Pitfalls: 1) Attempting to reduce a necrotic prolapse can lead to perforation. 2) Placing a purse-string suture too tight can cause obstruction. 3) Failing to treat the underlying cause results in recurrence. 4) In colopexy, suturing the colon too tightly can cause tension and dehiscence. 5) Amputation of the prolapsed tissue without proper anastomosis can lead to stricture. 6) Overlooking concurrent diseases such as perineal hernia or prostatic disease. 7) Inadequate pain management can lead to straining and recurrence.

Perioperative pharmacological protocols for rectal prolapse are based on Plumb's Veterinary Drug Handbook. Preoperative: If the animal is dehydrated, administer isotonic crystalloids (e.g., Lactated Ringer's Solution) at a rate of 10-20 mL/kg/hour IV until hydration is restored. Prophylactic antibiotics: Cefazolin 22 mg/kg IV at induction and every 90 minutes during surgery. Postoperative antibiotics: Continue cefazolin 22 mg/kg IV q8h for 24 hours, or switch to oral amoxicillin-clavulanate 13.75 mg/kg PO q12h for 5-7 days if infection is present. Analgesics: Opioids such as buprenorphine 0.01-0.02 mg/kg IV/IM q8-12h, or methadone 0.1-0.5 mg/kg IV/IM q4-6h. NSAIDs: Carprofen 2.2 mg/kg PO q12h or meloxicam 0.1 mg/kg PO q24h for 3-5 days, but avoid in dehydrated or hypotensive animals. Local anesthesia: Epidural analgesia with morphine (0.1 mg/kg) and bupivacaine (0.5-1 mg/kg) can provide postoperative pain relief. Stool softeners: Lactulose 0.5 mL/kg PO q8-12h, or docusate sodium 50-100 mg PO q12h. Anthelmintics: Fenbendazole 50 mg/kg PO q24h for 3 days, or pyrantel pamoate 5-10 mg/kg PO once, repeated in 2 weeks. If constipation is present, administer warm water enemas (5-10 mL/kg) with caution. For tenesmus, consider a short course of anti-inflammatory doses of prednisone (0.5 mg/kg PO q12h) if inflammatory bowel disease is suspected. Always adjust dosages based on renal and hepatic function.

Evidence-based literature on rectal prolapse in small animals is limited but includes several key studies. A retrospective study by Kudnig et al. (2003) evaluated 20 dogs with rectal prolapse and found that colopexy was successful in preventing recurrence in 90% of cases. The study emphasized the importance of identifying and treating the underlying cause. Another study by Vnuk et al. (2006) compared colopexy and amputation and found that colopexy had fewer complications and better outcomes. A case series by Popovitch et al. (1994) described the use of a laparoscopic-assisted colopexy, which was minimally invasive and effective. In cats, a study by Holt et al. (1992) reported that rectal prolapse was often associated with lower urinary tract disease, and treatment of the underlying condition was essential. Consensus guidelines from the American College of Veterinary Surgeons (ACVS) recommend that manual reduction and medical management be attempted first, with surgical intervention reserved for recurrent or irreducible cases. The use of a purse-string suture is controversial; some authors recommend it, while others advise against it due to the risk of obstruction. Overall, the literature supports early intervention and aggressive management of the underlying cause to achieve a favorable outcome.