Rectal Cancer


Rectal Cancer

  1. Anatomic Considerations
    • rectal cancer is considered separately from colon cancer because of its anatomic location
    • because the rectum resides in the narrow bony pelvis, wide excision of the cancer and surrounding structures is impossible
    • the proximity of the rectum to the anal sphincter mechanism, autonomic nerves, and urogenital organs makes surgical access difficult
    • the retroperitoneal location and distance from the small bowel makes radiation treatment feasible

  2. Surgical Anatomy
    1. Pelvic Anatomy
      1. Male and Female Pelvic Organs

        2. Female and Male Pelvises
      2. Pelvic Floor

        3. Pelvic Floor Anatomy
    2. Rectum
      • lacks taeniae, appendices epiploicae, haustra, or a well-defined mesentery
      • in women, the anterior rectum abuts the cervix and vagina
      • in men, the anterior rectum is in proximity to the bladder, seminal vesicles, and prostate
      • has an intraperitoneal and extraperitoneal component, separated by the peritoneal reflection
      • has 3 lateral curves, the valves (folds) of Houston

      1. Borders
        1. Lower Border
          • dentate line

        2. Upper Border
          • anatomic definition: where the taeniae coalesce to become a continuous layer of longitudinal smooth muscle
          • radiographic definition: sacral promontory
          • endoscopic definition: 15 cm from the anal verge
          • surgical definition: below the peritoneal reflection

        Anatomy of the Rectum and Anus
    3. Mesorectum
      • not a true mesentery (no peritoneum, doesn’t suspend the rectum)
      • consists of fat and areolar tissue that surrounds the rectum
      • contained within the mesorectal fascia
      • more prominent posteriorly and laterally than anteriorly
      • contains the blood supply and lymphatic drainage of the rectum, making it a critical structure during rectal cancer surgery

      MRI - Mesorectum
    4. Rectal Fascia
      1. Mesorectal (Perirectal) Fascia
        • surrounds the rectum and mesorectum
        • condenses to form the lateral ligaments of the rectum
        • surgical dissection for rectal cancer should not violate this layer

        MRI - Mesorectal Fascia
      2. Presacral Fascia
        • covers the sacrum and coccyx
        • the presacral venous plexus and presacral nerves lie below this layer
        • surgical dissection needs to stay anterior to this layer because tearing the presacral veins can lead to massive hemorrhage (the veins retract into the bone making suture ligation or cauterization impossible)

        Presacral Fascia and Presacral Venous Plexus
      3. Waldeyer’s Fascia
        • originates from the presacral fascia and fuses with the mesorectal fascia
        • this layer will have to be divided to get adequate mobilization for low rectal cancers
        • this fascia should be sharply divided, because blunt dissection risks injuring the presacral fascia and the underlying presacral veins

        Waldeyer's Fascia
      4. Denonvilliers’ Fascia
        • separates the bladder, seminal vesicles, and prostate from the rectum in men, and the vagina from the rectum in women
        • macroscopically this is not a visible layer

        Denonvilliers' Fascia
    5. Blood Supply and Lymphatic Drainage
      1. Arterial Blood Supply
        • enters the rectum posteriorly
        • upper rectum is supplied by the superior rectal artery from the IMA
        • middle rectum is supplied by the middle rectal artery from the internal iliac artery
        • lower rectum is supplied by the inferior rectal artery from the internal iliac or pudendal artery

      2. Venous Drainage
        • follows the arteries

      3. Lymphatic Drainage
        • drainage is cephalad and lateral, but not caudal
        • upper two-thirds of the rectum follows the superior rectal vessels to the IMA and paraaortic nodes
        • the lower third of the rectum drains cephalad as well as lateral to the internal iliac nodes

        Rectal Blood Supply and Lymphatic Drainage
    6. Pelvic Nerves

      7. Pelvic Nerves
  3. Pretreatment Staging Evaluation
    • choice of appropriate therapy for rectal cancer requires accurate preoperative staging
    • patient should be questioned carefully about any functional impairment of continence
    • accurate determination of the depth of invasion and the presence or absence of lymph node metastases are important in the selection of appropriate therapy (± neoadjuvant treatment, local versus radical excision)

    1. Digital Rectal Exam and Rigid Proctoscopy
      • must be performed by the operating surgeon
      • provides critical information about the distance of the cancer from the anal verge, mobility, and position in relation to the anal ring
      • an accurate evaluation may need to be done in the OR

    2. CEA Level
      • has value in pretreatment staging and patient follow-up
      • patients with a preop CEA > 5 ng/ml have a worse prognosis, stage for stage, than those with lower levels
      • elevated levels that do not normalize following resection is suggestive of unresected disease, and additional work-up is required (PET scan)
      • rising levels in posttreatment follow-up require evaluation

    3. CT Scan
      • chest, abdomen, and pelvis to assess for metastatic disease
      • ineffective in visualizing the layers of the rectal wall and so is not effective in evaluating the extent of rectal wall invasion by an early rectal cancer
      • 40% to 50% accurate in determining the presence of lymph node metastases

    4. MRI
      • highly accurate in assessing lymph node status
      • cannot reliably distinguish between T1 and T2 tumors
      • also allows for evaluation of the mesorectal fascia (circumferential margin)
      • involvement of adjacent organs can also be assessed

      Suspicious Nodes - MRI
      Suspicious Nodes

    5. Endorectal Ultrasound (EUS)
      • has largely been replaced by pelvic MRI
      • not very good at assessing local invasion in bulky tumors
      • poor at assessing the radial margin for posterior or posterolateral tumors
      • if local excision is being considered, EUS is the best tool for distinguishing between T1 and T2 tumors

      T-stages - Endorectal Ultrasound
      (Left) T1 - muscularis propria intact.   (Middle) T2 - muscularis propria involved.   (Right) T3 - into the perirectal fat.

  4. Resection Margins
    1. Proximal Margin
      • should be at least 5 cm to remove draining lymphatics

    2. Distal margin
      • a positive distal margin is associated with a 40% local recurrence rate and a decreased 5-year survival rate
      • however, a long distal margin will decrease the rate of sphincter preservation in mid-to-low cancers
      • most surgeons will accept a 1 to 2 cm grossly negative margin as an acceptable compromise between oncologic safety and sphincter preservation
      • if a 1 to 2 cm margin cannot be obtained, then the operation must be converted to an abdominoperineal resection, which extends the distal margin to the anal verge

    3. Radial Margins
      • the circumferential radial margin (CRM) is as important as the distal margin
      • a histologic CRM of > 1 mm is required
      • a positive CRM is an independent predictor of local recurrence and decreased survival

      Circumferential Radial Margin
  5. Total Mesorectal Excision (TME)
    • requires sharp dissection in the plane between the presacral fascia and the perirectal fascia (‘holy’ plane)
    • ensures removal of tumor cells that have invaded downward into the mesorectum
    • dissection in the proper plane is the way to achieve a negative CRM
    • TME is associated with fewer local recurrences and improved survival
    • TME is also associated with less postop urinary and sexual dysfunction due to better autonomic nerve preservation
    • for low rectal cancers, the TME should be carried down to the pelvic floor (levators)
    • for higher rectal cancers, the TME should be carried 5 cm past the primary tumor

    Total Mesorectal Excision
  6. Regional Lymph Node Dissection
    1. Standard Technique
      • in most situations, the superior rectal artery is ligated just distal to the takeoff of the left colic from the IMA (low tie technique) – this minimizes injury to the superior hypogastric plexus, which in turn minimizes post op bladder and sexual dysfunction
      • the low tie approach also results in better blood flow to the anastomosis by preserving the left colic
      • if there is nodal involvement at the root of the IMA, then the IMA can be ligated flush to the aorta (high tie technique)
      • the high tie technique may also be necessary to facilitate a tension-free anastomosis deep in the pelvis
      • ligation of the superior rectal artery allows access to the ‘holy plane’ for TME

    2. Extended (Lateral) Lymphadenectomy
      • involves resection of nodes along the internal iliac artery
      • although commonly performed in Japan, it has not been adopted in western countries
      • one possible indication is persistently enlarged internal iliac nodes after neoadjuvant therapy

  7. Neoadjuvant Chemoradiation
    1. Benefits
      • historically, rectal cancer has a high local recurrence rate (30%)
      • this may be related to tumor-related factors (challenging anatomic location) and surgery-related factors (extent of lymphadenectomy, positive distal or radial margin)
      • symptoms are disabling and may include pelvic pain, ulcerating perineal wounds, ureteral obstruction, leg swelling, fistulas, and pelvic sepsis
      • if there is no disseminated disease, treatment of local recurrence may consist of pelvic exenteration or sacrectomy
      • using the technique of total mesorectum excision, as well as neoadjuvant chemoradiation, the local recurrence rate can be reduced below 10%
      • additional benefits of neoadjuvant therapy include improved sphincter preservation rates and a lower rate of anastomotic stenoses
      • 20% of patients may have a complete tumor response

    2. Indications
      • clinical T3 or T4 tumors
      • clinical node-positive tumors
      • distal early stage (T2N0) tumors if tumor regression will permit a sphincter-sparing procedure
      • preoperative imaging suggests invasion of the mesorectal fascia or a threatened radial margin

      1. Preoperative Radiation
        • has several theoretical advantages over postoperative radiation:
          • more effective against a well-oxygenated tumor with a good blood supply
          • small bowel complications are less common before the development of pelvic adhesions
        • disadvantages include delay of surgery, poor healing
        • high doses must be used (50 Gy)
        • dose administered over 5 to 6 weeks, with another 3 to 4 weeks before surgery

      2. Preoperative Chemotherapy
        • functions as a radiosensitizer
        • infusional 5-FU or oral capecitabine are equivalent in terms of radiosensitization

  8. Surgical Therapy
    1. Local Excision
      • appropriate for T1 tumors (invades submucosa but not the muscularis propria, T1N0)
      • T2 tumors have a high rate of local recurrence and nodal metastases, and so should only be considered for local excision if they are a prohibitive risk for laparotomy, refuse a laparotomy, or have extensive metastatic disease

      1. Criteria for Local Excision
        • T0 or T1
        • < 3 cm in diameter
        • involves < 30% of the bowel lumen circumference
        • mobile, nonfixed
        • well-differentiated histology
        • no lymphovascular or perineural invasion
        • no clinical or radiographic evidence of positive nodes
        • able to get negative margins

      2. Transanal Excision
        • tumors should be within 8 cm of the anal verge because of limited exposure
        • electrocautery is used to excise the tumor with a 1 cm margin
        • depth of the excision is into the perirectal fat
        • defect may be closed with an absorbable suture or left open
        • local excision does not remove lymph nodes, so pathological staging is limited
        • cure rate for appropriately chosen lesions is 84%

        Transanal Excision - Rectal Cancer
      3. Transanal Endoscopic Microsurgery
        • used for cancers located more proximally in the rectosigmoid
        • offers improved visualization, exposure, and access compared to transanal excision
        • also associated with lower rates of positive margins and local recurrence
        • requires specialized training and instruments, and is not routinely available
        • technically demanding

        Transanal Endoscopic Excision - Rectal Cancer
    2. Anterior Resection
      • used for patients with T2 or greater cancers of the middle and upper rectum
      • patients must have adequate anorectal sphincter function preoperatively
      • may be done open, laparoscopically, or robotically
      • splenic flexure will require mobilization to make a tension-free anastomosis deep in the pelvis
      • a protective loop ileostomy is indicated if the patient has received neoadjuvant chemoradiation, has a very low or coloanal anastomosis, has a positive intraoperative leak test, or is on immunosuppressive drugs

      1. Low Anterior Resection
        • 2 cm distal margin is appropriate
        • radial margin is as important as the distal margin
        • entire mesorectum should be excised
        • during the posterior dissection, must avoid injury to the presacral venous plexus
        • laterally, the nervi erigentes must be preserved along the pelvic sidewall
        • anteriorly, the bladder must be protected, as well as the vagina in women and the prostate and seminal vesicles in males
        • functional results may be poor secondary to loss of rectal capacity
        • anastomotic leaks occur in 5% to 10% of cases

        EEA Stapled Anastomosis
        The EEA stapler makes low pelvic anastomoses possible

      2. Coloanal Anastomosis
        • ultimate anterior resection
        • functional results are often poor with a straight coloanal anastomosis
        • creation of a colopouch J-pouch reservoir or side-to-end reservoir has been proposed as a method to improve functional results

        Coloanal Reconstructions
    3. Abdominal Perineal Resection
      • indicated for patients with low rectal cancers involving the sphincter muscles, or if the tumor is too close to the sphincters for an adequate margin to be obtained
      • additional indications include involvement of the rectovaginal septum in women and poor preoperative continence
      • anteriorly, in men, must avoid injury to the urethra during the perineal dissection
      • perineal wound complications are high, especially if the patient has been radiated – closure with a muscle or myocutaneous flap may be necessary

      Perineal Portion of an Abdominoperineal Resection
      Perineal Portion of an Abdominoperineal Resection







References

  1. Cameron, 11th ed., pgs 218 – 224, 236 – 241
  2. Sabiston, 20th ed., pgs 1377 – 1381
  3. UpToDate. Rectal Cancer: Surgical Principles. Ronald Bleday, MD, David Shibata, MD. Jan 16, 2020. Pgs 1- 35.
  4. UpToDate. Rectal Cancer: Surgical Techniques. Ronald Bleday, MD, David Shibata, MD. Oct 07, 2019. Pgs 1- 18.
  5. UpToDate. Overview of the Management of Rectal Adenocarcinoma. David P. Ryan, MD, Miguel A. Rodriguez-Bigas, MD. Feb 27, 2020. Pgs 1- 31.