Endorectal ultrasound for preoperative staging
Evaluation of the anus and rectum has traditionally been done through external examination, digital rectal examination, anoscopy, flexible or rigid proctosigmoidoscopy, and colonoscopy. Imaging techniques have included barium enema, CT scan, and MRI. With
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Introduction Evaluation of the anus and rectum has traditionally been done through external examination, digital rectal examination, anoscopy, flexible or rigid proctosigmoidoscopy, and colonoscopy. Imaging techniques have included barium enema, CT scan, and MRI. With the introduction of endoluminal ultrasonography, a greater degree of objectivity has been implemented in the evaluation of the anorectum. This is especially important in the evaluation and treatment of rectal cancer. Accurate preoperative staging guides decision for neoadjuvant therapy, sphincter sparing procedures, and local excision. Endorectal ultrasound (ERUS) and endoanal ultrasound (ERAS) are also used in the diagnosis of benign mucosal lesions, fistula in ano, fecal incontinence, anorectal abscesses, and extrarectal masses. This chapter will focus on the use of endoluminal ultrasound in the evaluation of low rectal cancer, with particular attention to decisions regarding intersphincteric resection of low rectal tumors.
Staging of rectal cancer Historically, rectal cancer was staged using the Dukes classification developed by Sir Cuthbert Dukes [1]. The classification was based on depth of invasion of the bowel wall and regional lymph node metastases. Stage A was defined as tumor confined to the bowel wall, stage B as tumor extending through the bowel wall and stage C as tumor metastatic to regional lymph nodes. A later modification included stage D, which denotes distant metastasis. In 1949, Kirklin et al. modified the Dukes classification to subdivide category B into B1 and B2, with depth of penetration to the muscularis propria as a reference [2]. Stage B1 was defined as penetration into, but not through, the muscularis propria. Stage B2 was defined by tumor penetration through the muscularis propria. Aster and Coller further refined the staging to C1, C2, and C3 to include node positivity [3].
The standard in the United States is the tumor, node, metastasis (TNM) staging system. Addition of the prefix “u” indicates staging that has been performed by ultrasound [4]. The American Joint Committee on Cancer (AJCC)-endorsed TNM staging for rectal cancer is shown below [5].
TNM staging system for rectal cancer [5] Primary tumor (T) Tx: No description of the tumor’s extent is possible because of incomplete information. Tis: The cancer is in the earliest stage (in situ). It invades only the mucosa. T1: The cancer has grown through the muscularis mucosa and extends into the submucosa. T2: The cancer has grown through the submucosa and extends into the muscularis propria. T3: The cancer has grown through the muscularis propria and into the outermost layers of the colon and rectum but not through them. It has not yet reached any nearby organs or tissues. T4a: The cancer has grown through the serosa. T4b: The cancer has grown through the wall of the colon or rectum and is attached to or invades into nearby tissues or organs.
Regional lymph nodes (N) Nx: No description of lymph node involvement is possible because of incomplete information. N0: No cancer in nearb
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