Answer: Hamartomatous polyp with prolapse

Histology: This is a transmural proliferation of epithelium associated with dissecting mucin, which raised the possibility of an invasive mucinous carcinoma. However, there is no epithelium floating within the mucin, the epithelium within the lesion lacks cytologic atypia, and some of the epithelium within the lesion carries its lamina propria with it into the muscularis propria. At the top of the lesion, facing the lumen, one can appreciate branching smooth muscle typical of a hamartomatous (Peutz Jegher) polyp. These polyps frequently demonstrate prolapse, which can be transmural as in this case.

Discussion: As indicated above, mucinous adenocarcinoma is excluded by the absence of cytologic atypia, absence of an adenomatous precursor lesion, and absence of epithelium floating centrally within the mucin pools. The lining cells do not demonstrate low grade dysplasia as would be seen in adenoma with similar prolapse. The absence of endometrial stroma, as well as the gender of the patient, excludes endometriosis.