Colorectal villous adenoma: transrectal US in screening for invasive malignancy.

Exclusion of focal infiltrating malignancy in colorectal villous adenoma is a prerequisite when nonsurgical treatment is considered. In a study of 81 patients with endoscopically identified colorectal villous adenoma screened for malignancy with transrectal ultrasonography (US), 15 patients were excluded because of incomplete follow-up. Twelve carcinomas were present, confirmed with either histopathologic examination after surgical resection (n = 9) or biopsies during laser treatment (n = 3). Nine of them were detected with transrectal US on the basis of disruption of the anatomic wall layers (sensitivity, 75%). In 46 of the 54 adenomas transrectal US helped confirm the benign nature of the lesion (specificity, 85%). Seven of the eight false-positive cases happened to be previously treated with surgery or coagulation. Treatment-associated inflammatory changes in the wall layers seemed responsible for this misinterpretation. Because of the high predictive value for a negative result (benign adenoma, 94%), transrectal US is recommended for the evaluation of villous adenomas to detect malignancy, especially when nonsurgical treatment is considered. Transrectal US should be performed before diagnostic polypectomy.