Colorectal

Malignant Disease

The combination of EUS (or transrectal ultrasound) plus CT is the most practical and accurate approach to staging rectal carcinoma. EUS has been shown to be highly accurate in determining the TNM stage of colorectal carcinomas; it is far superior to CT scan alone. CT scans, however, are essential to evaluate for metastatic disease to distant organs. EUS accuracy of local staging for rectal carcinomas is 94% for T 1, 73% for T2, 92% for T3, 94% for T4, 79% for NO, and 74% for N I disease.

EUS has contributed significantly to the selection of different preoperative protocols for patients with colorectal tumors. Application of various therapeutic protocols that depend on the stage of the lesion is now feasible. For low rectal lesions that can be palpated, staging accuracy with digital evaluation is approximately 70 to 80%. A digital rectal examination therefore sets a very high level of accuracy for distal lesions that has proven difficult to improve on, even with extensive technological evaluation [69,70].

Although EUS has resulted in improved accuracy of evaluation of N stage, diagnostic problems still exist be cause more than two thirds of malignant lymph nodes are smaller than 5 mm, causing a low sensitivity [71]. Data from Rifkin and co-workers [72] comparing EUS and CT showed sensitivity of'45 versus 27%, specificity of 93 versus 88%, positive predictive values of 71 versus 46%, and negative predictive values of 82 versus 76%, respectively. Their data show the problem of detection of malignant lymph nodes. EUS, which is almost twice as sensitive as CT, still only picks up 501/1c of malignant nodes.

Most patients with carcinomas of the colon will undergo attempted resection unless there is evidence of metastatic disease. With introduction of new surgical techniques, if the lesion is localized without spread to lymph nodes, the operation performed will depend on accessibility and size of the tumor. An 89% 5-year survival has been reported for local removal of early lesions. This value compares with a 5-year survival of only 73% for abdominal perineal resection, and 76% for an anterior resection of similar T1, T2, and NO lesions [70].

Availability of neoadjuvant irradiation and expertise in local surgical procedures will be the determining factors that shift treatment from radical resection in all patients to other modalities according to staging. Carcinomas could be resected laparoscopically; local excision and sphincter-saving procedures may be attempted for rectal tumors. Patients who have been shown by EUS to initially have unresectable rectal carcinoma have been treated with preoperative radiotherapy; 90% have subsequently become resectable [10]. Accurate staging will also be important for lesions in the middle and lower third of the rectum. An increasing number of sphincter-preserving operations can now be performed for amenable lesions (i.e., those that do not invade the sphincter complex, pelvis, or adjacent organs).

A final use of EUS in colorectal tumors is for evaluation of an anastomosis at a prior resection site when there is suspicion of recurrence but biopsies are negative. EUS is essential in these patients because CT cannot reliably differentiate postoperative changes from tumor recurrence until the disease is well advanced. Local recurrence occurs in 20 to 30% of resected colorectal tumors. In only approximately one third of these tumors does recurrence involve the mucosa, which could be diagnosed with standard mucosal biopsy. EUS has been shown to accurately predict colorectal tumor recurrence [73], similar to prediction of anastomotic recurrences for resected esophagogastric lesions.

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