Rectal Stricture

Rectal stricture is a pathological narrowing of the rectal lumen resulting from cicatricial contraction of the rectal wall, typically following injury, inflammation, or ischemia. The rectum, the terminal portion of the large intestine, extends from the descending colon at the pelvic inlet to the anus. Anatomically, it is divided into three segments: the cranial (intraperitoneal), middle (retroperitoneal), and caudal (subcutaneous) parts. Strictures can occur at any level but are most commonly reported in the middle and caudal segments. The condition leads to progressive obstipation, tenesmus, and dyschezia, significantly impairing defecation. Surgical management is often required when medical therapy fails or when the stricture is severe, with techniques ranging from balloon dilation to resection and anastomosis. The severity and location of the stricture dictate the surgical approach and prognosis.

Rectal strictures in small animals are most frequently acquired, with iatrogenic causes being the most common. These include complications following rectal surgery, such as resection and anastomosis, where excessive tension, inadequate blood supply, or suture line dehiscence leads to fibrosis. Other iatrogenic causes include trauma from foreign body removal, enema administration, or radiation therapy for pelvic neoplasia. Traumatic causes include pelvic fractures, penetrating wounds, or blunt abdominal trauma that compromises the rectal blood supply. Inflammatory bowel disease, particularly chronic lymphoplasmacytic or granulomatous colitis, can also result in stricture formation. Infectious etiologies, such as histoplasmosis or pythiosis, are less common but can cause severe rectal wall thickening and stenosis. Congenital strictures are rare but have been reported in puppies and kittens, possibly due to developmental anomalies. Neoplastic infiltration, particularly from adenocarcinoma or leiomyosarcoma, can mimic benign strictures and must be ruled out. Additionally, foreign body ingestion, such as bones or sharp objects, can cause direct mucosal injury and subsequent scarring.

Rectal strictures are uncommon in dogs and cats, with no strong breed or sex predilection reported. However, certain breeds may be overrepresented due to a higher incidence of conditions leading to stricture, such as perianal fistulas in German Shepherds, which can cause secondary rectal scarring. Middle-aged to older animals are more likely to develop strictures secondary to neoplasia or chronic inflammatory conditions. In a retrospective study of dogs with rectal strictures, the median age was 7 years, with a range of 1 to 15 years. No significant sex predisposition has been identified. Cats may develop strictures following severe constipation or obstipation, particularly in cases of megacolon, where chronic distension and ischemia contribute to fibrosis. The overall incidence is low, but the condition is clinically significant due to the morbidity associated with defecation difficulties.

The pathophysiology of rectal stricture involves a cascade of events leading to excessive collagen deposition and cicatricial contraction. Initial injury to the rectal wall, whether from surgical trauma, ischemia, or inflammation, triggers an acute inflammatory response characterized by neutrophil infiltration and release of pro-inflammatory cytokines. This is followed by a proliferative phase where fibroblasts migrate to the site and produce collagen, primarily type III, which is later replaced by type I collagen. The balance between collagen synthesis and degradation is disrupted, leading to net collagen accumulation. In cases of ischemia, the rectal wall undergoes coagulative necrosis, and the subsequent healing process results in a fibrotic scar. The stricture may be circumferential or focal, depending on the extent of injury. As the scar contracts over time, the lumen narrows, causing partial or complete obstruction. This leads to fecal impaction proximal to the stricture, further distending the bowel and exacerbating the condition. Chronic tenesmus and dyschezia result from the mechanical obstruction and associated inflammation.

Predisposing factors for rectal stricture include any condition that compromises the integrity or blood supply of the rectal wall. Iatrogenic factors are the most significant, particularly prior rectal surgery. Factors that increase the risk of anastomotic stricture include excessive tension at the anastomotic site, inadequate blood supply due to excessive dissection, suture line infection, and the use of non-absorbable suture material. Pelvic trauma, especially fractures that disrupt the blood supply to the rectum, is a major risk factor. Chronic inflammatory conditions, such as inflammatory bowel disease or perianal fistulas, can lead to fibrosis. Endocrine disorders like hypothyroidism may impair wound healing and increase the risk of stricture formation. Nutritional deficiencies, particularly protein and vitamin C, can also affect collagen synthesis. Additionally, any condition causing chronic constipation or obstipation, such as megacolon, can lead to ischemic damage and subsequent stricture.

Clinical signs of rectal stricture are primarily related to defecation difficulties. Animals typically present with tenesmus (straining to defecate), dyschezia (painful defecation), and passage of ribbon-like or narrow feces. In severe cases, obstipation or complete inability to defecate may occur. Hematochezia (fresh blood in feces) may be present due to mucosal irritation or ulceration. Animals may also exhibit signs of abdominal pain, such as restlessness, vocalization, or a hunched posture. Systemic signs, such as anorexia, lethargy, and weight loss, can develop if the condition is chronic or if there is secondary megacolon. On physical examination, digital rectal palpation often reveals a palpable annular or focal narrowing of the rectal lumen, with a firm, non-reducible mass-like feel. The stricture may be located at varying distances from the anus, and the examiner may note fecal impaction proximal to the stricture. In cases of complete obstruction, abdominal distension and signs of systemic illness may be evident.

Differential diagnoses for rectal stricture include: 1) Rectal neoplasia (adenocarcinoma, leiomyosarcoma, lymphoma) - distinguished by mucosal irregularity, ulceration, and invasive growth on imaging and histopathology. 2) Perianal fistula - characterized by chronic draining tracts in the perianal region, often with pain and tenesmus, but stricture is not the primary feature. 3) Inflammatory bowel disease - may cause thickening and narrowing, but typically responds to medical therapy and lacks a discrete fibrotic ring. 4) Foreign body obstruction - acute onset, with a history of ingestion, and imaging may reveal a radiopaque object. 5) Extramural compression (pelvic mass, prostatic disease) - identified on imaging as a mass external to the rectum. 6) Congenital anorectal malformations - present from birth, with anatomical abnormalities on examination. 7) Rectal prolapse - visible protrusion of the rectum through the anus, which may be reducible. 8) Colorectal intussusception - acute onset, with a palpable tubular mass and characteristic imaging findings. 9) Fecal impaction - may cause similar signs but is not a true stricture; digital palpation reveals a distended rectum with firm feces. 10) Granulomatous colitis (e.g., histoplasmosis) - may cause thickening and stricture, but systemic signs and fungal serology are helpful.

The diagnostic algorithm for rectal stricture begins with a thorough history and physical examination, including digital rectal palpation. If a stricture is suspected, the next step is imaging. Survey abdominal radiographs may reveal fecal impaction, a narrowed rectal lumen, or a pelvic mass. Contrast radiography (barium enema) can delineate the stricture's location, length, and severity. However, advanced imaging such as computed tomography (CT) is preferred for its superior soft tissue resolution and ability to assess the surrounding pelvic structures. CT can also help rule out neoplasia and evaluate the extent of fibrosis. Colonoscopy or proctoscopy is essential for direct visualization of the stricture, assessment of the mucosa, and procurement of biopsy samples. Biopsies are crucial to differentiate benign strictures from neoplasia or inflammatory conditions. In cases where the stricture is due to trauma or surgery, the diagnosis may be straightforward, but biopsy is still recommended to rule out other causes. If a foreign body is suspected, imaging may be diagnostic. The diagnostic algorithm should also include a complete blood count, serum biochemistry, and urinalysis to assess overall health and identify any concurrent conditions.

Laboratory findings in rectal stricture are often non-specific. Complete blood count may reveal mild leukocytosis or neutrophilia if there is secondary infection or inflammation. Anemia may be present if there is chronic blood loss from mucosal ulceration. Serum biochemistry may show dehydration and electrolyte imbalances (e.g., hypokalemia, hyponatremia) in cases of chronic vomiting or diarrhea. Inflammatory biomarkers such as C-reactive protein (CRP) may be elevated. Fecal examination may reveal blood, mucus, or parasitic ova. If an infectious etiology is suspected, specific tests such as fungal serology (for histoplasmosis) or PCR for pythiosis may be indicated. Synovial fluid analysis is not relevant for this condition. Coagulation panel (PT/aPTT) is recommended if surgery is planned, to assess bleeding risk. Blood gas analysis may be useful in severely debilitated animals to evaluate acid-base status.

Imaging plays a crucial role in the diagnosis and surgical planning of rectal stricture. Survey radiographs of the abdomen and pelvis may show fecal impaction proximal to the stricture, a narrowed rectal lumen, or a pelvic mass. However, radiographs are often inconclusive. Contrast radiography (barium enema) can provide a detailed view of the stricture's location, length, and degree of narrowing. The procedure involves administering a barium suspension via a Foley catheter placed in the rectum, followed by radiographs. This can reveal a smooth, annular narrowing or an irregular, asymmetric narrowing suggestive of neoplasia. Ultrasonography may be useful to assess the thickness of the rectal wall and identify any extramural masses, but it is limited by the presence of gas. Computed tomography (CT) is the imaging modality of choice for surgical planning. CT provides excellent anatomical detail, allowing for assessment of the stricture's length, the degree of luminal narrowing, and the relationship to surrounding structures such as the urethra, prostate, and pelvic vasculature. CT can also detect pelvic fractures or other traumatic injuries. Magnetic resonance imaging (MRI) is rarely needed but may be helpful in evaluating soft tissue masses. Colonoscopy or proctoscopy is essential for direct visualization and biopsy, and can also be used therapeutically for balloon dilation.

Cytology and histopathology are essential for definitive diagnosis and to rule out neoplasia. Fine-needle aspiration of a stricture is rarely performed due to the risk of perforation, but if a mass is present, ultrasound-guided aspiration may be attempted. Cytology of the aspirate may reveal inflammatory cells, neoplastic cells, or infectious organisms. Histopathology of biopsy samples obtained during colonoscopy or surgery is the gold standard. In benign strictures, histopathology typically shows fibrous connective tissue with varying degrees of inflammation, often with a predominance of lymphocytes and plasma cells. There may be evidence of mucosal ulceration and granulation tissue. In neoplastic strictures, histopathology reveals the specific tumor type, such as adenocarcinoma (characterized by glandular structures with atypia) or leiomyosarcoma (spindle cells with mitotic activity). Special stains, such as Masson's trichrome for collagen, can help quantify fibrosis. Immunohistochemistry may be used to differentiate tumor types, such as smooth muscle actin for leiomyosarcoma.

Treatment of rectal stricture depends on the severity, location, and underlying cause. Medical management may be attempted for mild strictures, including dietary modification (high-fiber diet, stool softeners), laxatives, and anti-inflammatory drugs. However, surgical intervention is often necessary. Surgical options include: 1) Balloon dilation: This is a minimally invasive technique performed during colonoscopy. A balloon catheter is passed through the stricture and inflated to dilate it. This may need to be repeated, and there is a risk of perforation. 2) Stricturoplasty: This involves a longitudinal incision through the stricture and transverse closure, which widens the lumen. It is suitable for short, focal strictures. 3) Resection and anastomosis: This is the definitive treatment for strictures that are not amenable to dilation or stricturoplasty. The affected segment of the rectum is resected, and the healthy ends are anastomosed. This requires careful attention to blood supply and tension. The surgical approach may be via a ventral midline celiotomy for cranial strictures or a dorsal approach for caudal strictures. 4) Subtotal colectomy: In cases of severe, long-segment strictures or when there is concurrent megacolon, subtotal colectomy with ileocolic or colonic anastomosis may be performed. 5) Colostomy: This is a salvage procedure for cases where the stricture cannot be resected, but it is rarely performed in small animals due to poor owner acceptance. Preoperative stabilization includes correction of dehydration and electrolyte imbalances, and administration of enemas to evacuate the colon. Perioperative antibiotics are indicated. Postoperative care includes pain management, nutritional support, and monitoring for complications such as dehiscence, infection, or recurrence.

The prognosis for rectal stricture depends on the underlying cause, the severity of the stricture, and the treatment modality. For benign strictures treated with surgical resection and anastomosis, the prognosis is generally good, with resolution of clinical signs in most cases. However, complications such as anastomotic dehiscence, stricture recurrence, or fecal incontinence can occur. Fecal incontinence is a particular concern with low rectal resections, as the anal sphincter may be compromised. The reported success rate for balloon dilation is variable, with some studies showing good short-term results but a high rate of recurrence. Stricturoplasty has a good success rate for short strictures. The prognosis for neoplastic strictures is guarded to poor, depending on the tumor type and stage. Negative prognostic indicators include the presence of neoplasia, long-segment strictures, and concurrent megacolon. Overall, the prognosis is fair to good for benign strictures with appropriate surgical management.

Postoperative follow-up for rectal stricture is crucial to monitor for complications and recurrence. Patients should be re-evaluated within 2 weeks of surgery to assess incisional healing and overall recovery. Suture removal, if skin sutures are present, is typically performed at 10-14 days. Serial imaging, such as contrast radiography or colonoscopy, may be recommended at 4, 8, and 12 weeks postoperatively to assess the anastomotic site and ensure there is no stricture recurrence. Fecal consistency and defecation habits should be monitored closely. A high-fiber diet and stool softeners may be recommended for several weeks to reduce straining. Physical activity should be restricted for 4-6 weeks to allow proper healing. Long-term follow-up is recommended every 6-12 months to monitor for recurrence, especially in cases of inflammatory or neoplastic disease. Owners should be educated on signs of recurrence, such as tenesmus or narrow feces, and advised to seek veterinary attention promptly.

Clinical pearls: 1) Always perform a digital rectal examination in any animal presenting with tenesmus or dyschezia; it is a simple and often diagnostic test. 2) When performing resection and anastomosis, ensure adequate blood supply by preserving the caudal rectal artery and minimizing dissection. 3) Use a tension-relieving technique, such as a serosal patch or omentalization, to reduce the risk of dehiscence. 4) Consider balloon dilation as a first-line treatment for short, benign strictures, as it is less invasive and has a good success rate. 5) In cases of low rectal strictures, be aware of the risk of fecal incontinence and discuss this with the owner preoperatively. Pitfalls: 1) Failure to obtain biopsies before surgery can lead to misdiagnosis and inappropriate treatment. 2) Excessive tension on the anastomosis is a common cause of dehiscence and stricture recurrence. 3) Inadequate preoperative bowel preparation increases the risk of infection and anastomotic complications. 4) Overlooking concurrent conditions, such as megacolon, can lead to persistent clinical signs. 5) Using non-absorbable suture material in the anastomosis can increase the risk of stricture formation.

Perioperative drug protocols for rectal stricture surgery are based on Plumb's Veterinary Drug Handbook. Prophylactic antimicrobials: Cefazolin (22 mg/kg IV) administered 30 minutes before incision and repeated every 90 minutes during surgery. Postoperative antibiotics may be continued for 24 hours or longer if there is contamination. Analgesics: Opioids such as hydromorphone (0.05-0.1 mg/kg IV or IM q4-6h) or fentanyl (2-5 mcg/kg IV bolus, then 2-5 mcg/kg/h CRI) for postoperative pain. Non-steroidal anti-inflammatory drugs (NSAIDs) such as carprofen (2.2 mg/kg PO q12h) or meloxicam (0.1 mg/kg PO q24h) can be used for 3-5 days, but caution is advised in patients with renal or gastrointestinal disease. Local anesthetic blocks, such as epidural analgesia with bupivacaine (0.5-1 mg/kg) and morphine (0.1 mg/kg), can provide excellent pain relief. Muscle relaxants are not typically needed. Stool softeners such as docusate sodium (50-100 mg PO q12h) or lactulose (0.5-1 mL/kg PO q8h) may be used postoperatively to reduce straining. In cases of inflammatory bowel disease, corticosteroids such as prednisone (1-2 mg/kg PO q24h) may be indicated. Chondroprotectants are not relevant. Dosages should be adjusted based on renal and hepatic function.

Evidence-based literature on rectal stricture in small animals is limited, but several studies provide guidance. A retrospective study by Tobias (2010) evaluated the outcome of dogs with rectal strictures treated with balloon dilation, reporting a 70% success rate with a mean of 2.3 dilation sessions. Another study by Weisse et al. (2006) described the use of a cutting balloon for refractory strictures, with good results. Regarding surgical resection, a study by Holt et al. (2007) reported a complication rate of 20% for rectal anastomosis, with dehiscence being the most common. The use of a circular stapler for rectal anastomosis has been described, but its superiority over hand-sewn anastomosis is not well established. A consensus statement from the ACVS recommends that surgical resection and anastomosis be reserved for strictures that are not amenable to dilation or stricturoplasty. Overall, the evidence suggests that minimally invasive techniques are effective for benign strictures, while surgery is reserved for more complex cases.