Overview
Definition:
Intersphincteric resection (ISR) is a surgical technique for managing low rectal cancers located within the anal canal or very close to the anal verge, aiming to preserve anal sphincter function
It involves the resection of the tumor along with a segment of the bowel wall extending from the mesorectum down through the intersphincteric plane, allowing for a more distal anastomosis than traditional low anterior resections, while potentially avoiding a permanent colostomy.
Epidemiology:
Low rectal cancers (distal to 5 cm from the anal verge) constitute a significant proportion of all rectal cancers
The incidence of rectal cancer varies globally, with increasing rates in some regions
Factors such as age, diet, lifestyle, and genetic predisposition influence its occurrence
ISR is considered for a select group of patients with these distal tumors where sphincter preservation is feasible.
Clinical Significance:
ISR represents a paradigm shift in the surgical management of low rectal cancers, offering a chance for functional anal preservation in patients who might otherwise require an abdominoperineal resection (APR) and a permanent stoma
Successful ISR can significantly improve a patient's quality of life by avoiding permanent diversion
However, it requires meticulous surgical technique and careful patient selection to achieve oncological safety and acceptable functional outcomes.
Indications
Surgical Indications:
ISR is primarily indicated for histologically confirmed adenocarcinoma of the rectum located within 1-2 cm of the dentate line or within the anal canal, where a sufficient distal margin can be achieved with sphincter preservation
Ideal candidates have T1 or T2 tumors with no evidence of lymph node involvement or distant metastasis (M0 disease)
The tumor should be mobile, without extensive local invasion into surrounding structures
A multidisciplinary team (MDT) approach is crucial for patient selection.
Contraindications:
Absolute contraindications include extensive local invasion (T3/T4 tumors with fixation to surrounding structures), significant lymph node metastasis, distant metastases, inflammatory bowel disease, significant comorbidities precluding major surgery, and poor anal sphincter function prior to surgery
Relative contraindications may include very low tumors requiring unrealistic distal margins or patient preference for a stoma if functional outcomes are predicted to be poor.
Patient Selection:
Careful assessment of tumor stage, location, and relationship to the sphincter complex is paramount
Endoscopic ultrasound (EUS) and MRI are essential for local staging
The patient's overall health status, desire for stoma avoidance, and ability to tolerate potential functional deficits (e.g., fecal incontinence) must be considered
Preoperative chemoradiotherapy may be considered for locally advanced tumors to downstage and improve resectability, but this can impact sphincter function.
Preoperative Preparation
Diagnostic Workup:
Comprehensive staging including colonoscopy, biopsy, serum carcinoembryonic antigen (CEA), CT chest/abdomen/pelvis for distant metastasis, and pelvic MRI or EUS for local staging
Rectal MRI is crucial for assessing tumor depth, circumferential resection margin (CRM), and lymph node involvement.
Neoadjuvant Therapy:
Depending on the stage, neoadjuvant chemoradiotherapy may be administered to downstage the tumor, improve resectability, and increase the likelihood of sphincter preservation
This is typically followed by a rest period before surgery.
Bowel Preparation:
Standard mechanical bowel preparation with oral laxatives and antibiotics is performed 24-48 hours prior to surgery
Intravenous prophylactic antibiotics are administered preoperatively.
Anesthesia Considerations:
General anesthesia with epidural analgesia is often preferred for perioperative pain control
Careful intraoperative monitoring of hemodynamics and fluid balance is essential.
Procedure Steps
Surgical Approach:
ISR can be performed through various approaches, including abdominosacral (using both abdominal and perineal dissection), transanal total mesorectal excision (TaTME), or laparoscopic/robotic-assisted abdominal dissection combined with perineal excision
The choice depends on surgeon expertise, tumor characteristics, and institutional preference.
Abdominal Phase:
Mobilization of the mesorectum and sigmoid colon
High ligation of the inferior mesenteric artery
Division of the rectum at an appropriate level above the tumor, ensuring adequate proximal margins
Care is taken to identify and preserve the autonomic nerves of the pelvis.
Perineal Phase:
Perineal dissection begins at the anus and proceeds upwards, dividing the internal and external anal sphincters anteriorly and laterally, along the plane between the levator ani muscles and the rectum
The dissection enters the intersphincteric space, allowing removal of the specimen en bloc with the mesorectum.
Anastomosis:
The specimen is delivered through the perineal wound
A coloanal anastomosis is then fashioned, typically using a stapling device or hand-sewn technique, ensuring adequate tension-free closure and a secure suture line
The integrity of the anastomosis is checked with air insufflation or intraoperative endoscopy.
Diversion Stoma:
A temporary diverting loop ileostomy or colostomy is usually created to protect the coloanal anastomosis from fecal spillage, reducing the risk of anastomotic leak and allowing for early mobilization
This stoma is typically closed 6-8 weeks postoperatively.
Postoperative Care
Monitoring:
Close monitoring of vital signs, urine output, and abdominal distension
Regular assessment of the stoma (if present) and perineal wound
Monitoring for signs of anastomotic leak, bleeding, or infection.
Pain Management:
Aggressive pain control using patient-controlled analgesia (PCA) or epidural analgesia, transitioning to oral analgesics as tolerated
Perineal wound care and sitz baths are important for comfort and healing.
Nutritional Support:
Early enteral feeding is encouraged once bowel function returns
Intravenous fluids are administered as needed
Nutritional assessment and support may be required for patients with significant weight loss or comorbidities.
Mobilization:
Early ambulation is crucial to prevent deep vein thrombosis, pulmonary complications, and promote bowel function
Gradual increase in activity as tolerated.
Stoma Care And Reversal:
Patients are educated on stoma management
Once the anastomosis has healed (usually confirmed by endoscopy and/or contrast study), the diverting stoma is reversed surgically, typically 6-8 weeks after the initial resection.
Complications
Early Complications:
Anastomotic leak is a major concern, potentially leading to sepsis, abscess formation, or rectovaginal/rectourethral fistula
Pelvic sepsis, wound infection, perineal wound dehiscence, and bleeding are also risks
Urinary retention and ileus are common.
Late Complications:
Fecal incontinence (ranging from minor urgency to severe soiling), anal stricture, bowel obstruction due to adhesions, sexual dysfunction, and chronic perineal pain
Recurrence of rectal cancer is a significant long-term concern.
Prevention Strategies:
Meticulous surgical technique, precise dissection within the mesorectum, secure anastomosis, and diversion stoma are key for preventing anastomotic complications
Adherence to neoadjuvant protocols, judicious use of intraoperative imaging, and good postoperative care also play vital roles
Careful patient selection minimizes risks related to functional outcomes.
Prognosis
Factors Affecting Prognosis:
The primary prognostic factors are the pathological stage of the tumor (T and N stage), the adequacy of the circumferential resection margin (CRM), the presence of lymph node metastases, and the achievement of a complete total mesorectal excision (TME)
Patient factors like age and comorbidities also influence outcomes.
Outcomes:
When performed in carefully selected patients with early-stage tumors by experienced surgeons, ISR can achieve oncological outcomes comparable to APR, with significant functional benefits
However, the rate of fecal incontinence and other functional deficits can still be considerable
Long-term survival depends heavily on the stage of disease.
Follow Up:
Regular follow-up is essential, including physical examination, CEA monitoring, and imaging (CT scans) to detect recurrence or metastases
Endoscopic surveillance of the anastomosis and distal rectum is also performed
Follow-up schedules are typically similar to those for other rectal cancer resections, with increased attention to functional outcomes.
Key Points
Exam Focus:
Understand the indications for ISR versus APR/LAR
Differentiate between intersphincteric and supralevator dissections
Recognize the role of neoadjuvant therapy and its impact on sphincter function
Know the common complications and their management
Importance of CRM and TME in oncological outcomes.
Clinical Pearls:
MDT discussion is crucial for optimal patient selection
Meticulous dissection within the defined planes is key to achieving safe oncological margins
A temporary stoma is almost always necessary for protection
Functional outcomes should be discussed thoroughly with the patient preoperatively.
Common Mistakes:
Operating on unsuitable tumor types (e.g., locally advanced fixed tumors)
Inadequate mesorectal excision
Compromising CRM to achieve anastomosis
Failure to adequately counsel patients on potential functional deficits
Delaying stoma reversal without proper assessment.