Invasive carcinoma is present in 30 to 40 percent of rectal villous adenomas. Approximately 10 percent of biopsy-negative villous adenomas contain invasive cancer, even if those with induration, ulceration, and other signs of malignancy are excluded. If a potentially malignant adenoma is misdiagnosed as a benign lesion, a suboptimal resection may be performed for a potentially curable lesion. Several small studies have reported that endorectal ultrasound (ERUS) examination can identify focal carcinomas that are missed by biopsy of adenomas. The generalizability of these studies is limited by number and selection of participants and by the variability in the utility of ERUS, depending on the operator. Worrell and colleagues reviewed published studies since 1986 to assess the potential role of ERUS in improving diagnostic accuracy for patients with biopsy-negative rectal adenomas.
Their initial search of an electronic database identified 47 articles, but only five studies required complete excision of the lesion and comparison of the ERUS and histopathologic diagnosis. Histopathologic examination of the excised lesions identified focal invasive carcinoma in 62 (24 percent) of the 258 biopsy-negative specimens. Fifty (81 percent) of these lesions were diagnosed correctly by ERUS examination before excision. Conversely, ERUS incorrectly identified 12 percent of benign rectal adenomas as malignant. The authors estimate that these results are equivalent to requiring five patients with biopsy-negative adenomas to be examined by ERUS to prevent missing one case of invasive carcinoma. Conversely, one case would be incorrectly diagnosed for every 11 patients examined with ERUS.
The authors conclude that use of ERUS and directed biopsy of rectal adenomas could reduce the rate of misdiagnosis of malignant lesions from 24 percent to 5 percent. They recommend the routine use of adjunctive ERUS in the evaluation of all rectal villous adenomas, especially those with increased clinical suspicion of malignancy.