Preoperative evaluation of the rectal cancer patient provides data for individualizing management. Rectal cancer staging involves complete colonoscopy with biopsy, CEA level, CT scan with contrast of the abdomen and pelvis, CT scan of the chest, and MRI of the pelvis using a rectal cancer MRI protocol.
Pre-treatment staging of rectal cancer differs from colon cancer due to the need for local T-stage and N-stage evaluation of the primary tumor, which determines whether the case should undergo neoadjuvant therapy or may be amenable to local excision. Thus, in addition to CT scanning, rectal cancers should have a pelvic MRI using a rectal cancer protocol. One of the most common mistakes in the management of rectal cancer is the failure to recognize that the tumor is in the rectum, which may occur because flexible endoscopy frequently overestimates the distance from the anal verge to the tumor. Thus surgeons should have a low threshold for performing rigid proctoscopy and/or pelvic MRI to confirm tumor location whenever a tumor is characterized as "rectosigmoid" or "sigmoid" on colonoscopy.
MRI with rectal cancer protocol has largely replaced endorectal ultrasound (ERUS) for local staging of rectal cancers because it gives better anatomic guidance for surgery and is less operator-dependent (Figure 1.1). Cancer Care Ontario created an MRI protocol and synoptic MRI report for rectal cancer which greatly improved the quality and consistency of rectal cancer MRI in Ontario. This also has been widely used in the USA. More recently, the American Society of Abdominal Radiology (SAR) has created a rectal cancer MRI synoptic report based on the Ontario report. This has been adopted by the National Accreditation Program for Rectal Cancer as the recommended synoptic MRI report, and it can be accessed through their website.
Management of rectal cancer is different from management of colon cancer because of confinement of the pelvic organs within a fixed small space and proximity of the rectum to the anal sphincter. This results in a technically challenging surgical dissection and potential risk for anorectal and genitourinary dysfunction. Preservation of the anal sphincter with avoidance of a permanent colostomy is an important consideration for the patient and surgeon. Preoperative evaluation is required to assess suitability for more or less radical therapy.
The patient’s symptoms and physical examination can provide important information about tumor stage, and supplement the imaging and other tests that are obtained. For example, a rectal mass encroaching on the lumen may cause symptoms of decreased stool caliber, bleeding, tenesmus, and incomplete rectal evacuation. A mass invading the anal sphincter may cause significant pain. Severe symptoms and risk for complete obstruction may be an indication for diverting colostomy prior to neoadjuvant therapy. Clinical assessment of pre-treatment continence is also important. Patients with incontinence will usually do poorly with a low colorectal anastomosis. Formal evaluation with manometry may be indicated in equivocal cases.
Digital rectal examination allows the surgeon to evaluate the tumor’s distance from the levator muscles and anal sphincter. The distance of the lesion from the upper sphincter is best assessed with digital rectal examination, but this distance should also be recorded after rigid proctoscopy, flexible endoscopy, and sagittal magnetic resonance imaging (MRI) measurement. The relationship of the distal edge of the lesion can also be assessed as above or below the peritoneal reflection as estimated by visualization of the tumor’s association with the middle rectal valve and confirmed by sagittal MRI.
The tumor may be superficial with mobility from the rectal wall, freely mobile, but involving the entire depth of the rectal wall, or deeply penetrating outside the rectal wall with tethering or fixation to an anterior organ, lateral pelvic side wall, or anal sphincter. Mobility suggests a more straightforward resection, while tethering and fixation raise concern for resectability and the potential that a multivisceral resection would be required. Modern rectal cancer MRI has greatly improved the predictability of what type surgery will be required, by accurately demonstrating whether there is invasion of the sphincter, levator muscle, and/or other pelvic organs and structures.
Depth of invasion and lymph node involvement are determinants for the recommendation of neoadjuvant therapy and are best assessed using MRI. ERUS may be used in some centers to evaluate superficial lesions being considered for local excision or may be used if the patient is not a candidate for MRI. CT imaging is used to assess paraaortic lymph nodes and distant metastases that lie outside of the imaging field of the pelvic MRI.
It is essential to assess the circumferential resection margin (CRM), which is the distance between the tumor and the closest predicted radial resection margin as estimated by the circumferential mesorectal fascia. The current standard for assessing CRM is MRI. MR CRM assessment has less accuracy for lesions anteriorly located and at the anorectal junction where there is paucity of mesorectal fat. At these locations, ERUS may complement MR assessment of CRM.
Lesions not invading the anal sphincter can be considered for sphincter preserving surgery if adequate anal sphincter function is noted from the patient’s history and sufficient anal sphincter tone is noted on digital examination.
The diagnosis of invasive adenocarcinoma is confirmed by endoscopy and biopsy. At endoscopy, the lesion is assessed for distance from the anal verge, size, percent circumference of the lumen occupied by the lesion, quadrant(s) location, and whether the lesion is polypoid or ulcerated. Examination of the colon should be performed for detection of synchronous colon neoplasms. Synchronous colon adenomatous polyps may occur in 20% to 33% of patients, and synchronous colon cancers are found in 4% to 8% of patients with rectal cancer. Cancers can be tattooed to mark their location in the event of complete clinical response to neoadjuvant chemotherapy and radiation. If a colonoscopy cannot be completed up to the cecum due to obstruction or angulation then attempt should be made prior to surgery and usually after neoadjuvant therapy to complete evaluation or within three months post-operatively.
Histologic characteristics on biopsy associated with higher potential for lymph node metastasis and worse prognosis include poor differentiation and lymphovascular invasion. These histologic characteristics are contraindications for local excision of superficial lesions. Biopsies from high-risk individuals (e.g., family history of colorectal/endometrial cancer, multiple colorectal tumors, younger age) should be routinely assessed for microsatellite instability. If found, the patient should appropriately be referred to a genetic counselor to exclude the possibility of a hereditary disorder. Many centers routinely test all tumors for microsatellite instability as it has implications for postoperative adjuvant therapy recommendations prior to the planned operation and liberally refer patients for genetic counseling.
Serum carcinoembryonic antigen (CEA) level should be preoperatively measured to compare the level with serial measurements after cancer treatment. Serial CEA measurement is used with CT imaging for surveillance.
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