Rectal gastric heterotopia with fundic gland polyps, mimicking a high-risk primary anorectal neoplasm: histological evidence of the effects of gastric acid-suppressing medication in a rectal ‘outlet patch’

Gastric heterotopia can occur in any part of the gastrointestinal tract but is rare in the rectum. This case of rectal gastric heterotopia is novel as the heterotopic mucosa contained fundic gland polyps, and there were histological changes in the gastric glands characteristic of proton pump inhibitor-related changes. These changes included apocrine-like luminal cytoplasmic protrusions in cystically dilated oxyntic gland parietal cells. These are well described in the native stomachs of PPI treated patients, but this is the first report of these changes in heterotopic gastric mucosa to our knowledge. The lesion was removed via transanal endoscopic operation (TEO) without prior biopsy due to its unusual irregular nodular appearance mimicking a high-risk rectal neoplasm.