Colonic Tubulovillous Adenoma With High-Grade Dysplasia and Pseudoinvasion: A Diagnostic Pitfall

Abstract

Introduction: interpretation of histopathologic features of resected colonic polyps is critical to subsequent management. We are a presenting a case of colonic villous adenoma with pseudoinvasion /misplacement of epithelium (PEM) into the stalk mimicking invasive carcinoma. Such phenomenon can be unfamiliar to the gastroenterologist. Case: 56 y/o male, h/o diabetes and hypertension, referred for colon cancer screening. Patient has been asymptomatic. His physical examination was unremarkable. Colonoscopy revealed 1.5 cm polyp with short stalk polyp at the splenic flexure (figure 1), which was removed wit hot snare. Pathology was consistent with tubulovillous adenoma with focal high grade dysplasia and pseudoinvasion involving the cauterized margin, with misplaced epithelium, and rounded, displaced glands surrounded by lamina propria (Figure 1).Figure: MUCOSA WITH RELATED MUSCULARIS MUCOSA. THE MUCOSA IS HERNIATING INTO THE SUBMUCOSA PSEUDOINVASION LOW POWER VIEW.Discussion: Colon cancer is the second leading cause of cancer-related deaths in the United States (when men and women are combined). It is established that removing precancerous adenomas not only reduce the risk of colorectal cancer but also significantly reduce the deaths from the disease. The histopathological features of resected polyps impact on subsequent management. In this case, there was high grade dysplasia, and the adenomatous epithelium appeared misplaced into the stalk and as such mimicking invasive carcinoma (pseuodinvasion). There are no definite endoscopic or clinical features to differentiate between the two lesions, and diagnosis depends solely on pathologic findings. In pseudoinvasion, the displaced glands are cytologically similar to the overlying adenoma and are rounded, often admixed with nonadenomatous glands, and surrounded by normal lamina propria, and often hemosiderin is seen in lamina propria. These features are in contrast with those of an invasive mucinous carcinoma. Additional histological scrutiny along with histochemical staining was necessary to exclude invasive cancer. Pseud invasion may be the result of repeated twisting of the stalk causing hemorrhage and this facilitates the prolapse of non-malignant adenomatous epithelium through the muscularis mucosa. Conclusion: There is difficulty inherent in distinguishing between pseudoinvasion and invasive carcinoma. Awareness and recognition of pseudo-carcinomatous invasion in adenomatous polyps and its distinction from invasive cancer is critical for both subsequent treatment and appropriate reporting.