Confusion over a rectal biopsy sample

Correct answer: a.

Discussion

There was some confusion over the biopsy samples taken from this lesion because the H&E stain shows gastric mucosa. Indeed, there was a suggestion that biopsy samples taken from the stomach and rectum had been mixed up; however, this was not the case. In fact, the patient has a patch of ectopic gastric mucosa in the rectum!

Endoscopists are used to finding ectopic gastric mucosa in the high oesophagus; although this is the first time that I have seen ectopic gastric mucosa in the rectum, the condition was first described in 1939.¹ Most case reports of ectopic gastric mucosa in the rectum have been in children presenting with rectal bleeding. Marines et al. reviewed the first 12 published cases in 1988 and concluded that in all cases the ectopic tissue was located within 10 cm of the anus.² There have also been case series of gastric mucosa arising within the anus.³

It has been proposed that the reason for heterotopic gastric mucosa is abnormal differentiation of the endoderm.⁴ However, the finding of more than one type of gastric mucosa (cardiac, fundic, antral, pyloric or associated with heterotopic pancreatic tissue) suggests that the condition is due to a developmental ‘accident’. Another indication that the condition is caused by neural-crest-derived cells going astray, is that the condition is commonly associated with a rectal duplication cysts.⁵

Naturally, the condition will only require treatment if there is ulceration when either acid-reducing therapy^6,7 or surgery is indicated. Gastric cancer arising from heterotopic gastric mucosa in the oesophagus is well described, but I have not found a single case report of gastric cancer arising in the rectum.