In the United States, rectal cancer is diagnosed in approximately 40,000 individuals annually.1 Although definitions vary, locally advanced rectal cancer generally refers to patients with T3/T4 disease and/or positive lymph nodes.2 In patients with locally advanced rectal cancer, treatment with surgery alone results in substantial risk of local recurrence; therefore, multimodality therapy is recommended.
Common clinical symptoms of rectal cancer include a change in stool caliber, hematochezia, rectal pain, tenesmus, or obstructive symptoms (abdominal pain, nausea/vomiting, obstipation). The presence of specific symptoms may aid in diagnosis: tenesmus is generally associated with bulky or fixed tumors, while pain with defecation suggests involvement of the distal one-third of the rectum. On history, full evaluation of rectal function, urinary function, and sexual function is crucial, not only for diagnosis but also to predict the extent of tumor involvement and to plan operative therapy. On physical examination, digital rectal examination is used to assess the position of the tumor (relative to the anorectal ring) and fixation to the anal sphincters, the levators, and the bony pelvis. Digital rectal examination can also assess the degree of obstruction for distal tumors. Female genital tract involvement can be evaluated by completing a rectovaginal examination.
Following history and physical examination, a colonoscopy is generally indicated to further workup symptoms suspicious for rectal cancer. Colonoscopy is the gold standard for diagnosis of rectal cancer because it allows for tissue diagnosis of the primary lesion, evaluation of the remainder of the colon for synchronous tumors (the incidence of synchronous tumors is approximately 4%), and removal of any polyps.3 In addition to full colonoscopy, rigid sigmoidoscopy can be used to determine the position of the tumor within the rectum (anterior, posterior, left, or right) and the distance between the distal tumor margin and the anal verge. Following tissue diagnosis, patients require staging for locoregional and metastatic disease.
The goals of locoregional staging for rectal cancer are to determine the optimal surgical approach and to determine whether neoadjuvant therapy is required. Locoregional staging utilizes imaging to assess for the depth of tumor invasion, the presence of lymph node involvement, invasion into adjacent organs, and to determine the circumferential radial margin (CRM). Although some information can be gained from computerized tomography (CT) scan, magnetic resonance imaging (MRI) and transrectal ultrasound (TRUS) are the most helpful imaging modalities for locoregional staging of rectal cancer. All patients with locally advanced rectal cancer should undergo staging with CT scan of the chest, abdomen, and pelvis along with evaluation of the rectal tumor with either MRI or TRUS.
Compared to MRI and TRUS, CT scan has decreased sensitivity and specificity for identifying T-stage, N-stage, and CRM for rectal cancer.4 CT scan can, however, be useful in predicting adjacent organ involvement and in identifying tumor-related complications of rectal ...