**Background:** Heterotopic gastric mucosa (HGM) in the rectum is a very uncommon finding, more typically found in the esophagus, small intestine, or with Meckel's diverticulum. A 2017 systematic review by Iacopini et al identified 78 total cases (34 pediatric) since the first pediatric case in 1939, with a median age at diagnosis of 22 years and 63% male predominance. HGM in the rectum is typically found 5–8 cm from the anal verge and most commonly presents with hematochezia, though symptoms can include anal pain, tenesmus, burning, pruritis ani, and abdominal discomfort. Pediatric patients are more likely to have HGM-related complications such as ulcers, fistulas, or bowel perforation. The pathogenesis remains unclear, thought to be either congenital (heteroplasia) or acquired (metaplasia from epithelial repair). Histopathological examination most commonly demonstrates oxyntic-type gastric mucosa.
**Methods:** This is a single case report of an 8-year-old male with a history of constipation, eosinophilic esophagitis (EoE), and failure to thrive who presented with worsening intermittent hematochezia initially attributed to constipation. He was initially treated with ranitidine, omeprazole, polyethylene glycol, and a high-fiber diet with resolution of hematochezia. EoE was diagnosed at age 6 via upper endoscopy. The family elected to stop PPI and initiated a diet elimination intervention excluding gluten, dairy, soy, egg, nuts, and fish/shellfish. Hematochezia recurred with mucous-filled stools. Differential diagnosis included constipation, fissures, infectious colitis, Meckel's diverticulum, vascular ectasias, bleeding disorder, rectal ulcers, polyps, and IBD. Stool samples were negative for microorganisms, and calprotectin was normal. Due to worsening symptoms (blood dripping down the leg after bowel movements), repeat esophagogastroduodenoscopy and colonoscopy were performed.
**Key Results:** Colonoscopy revealed grossly normal mucosa of the terminal ileum and entire colon except for edema and erythema of the rectum (5 cm from the anal verge) without ulceration or nodularity. Histology demonstrated heterotopic gastric oxyntic (fundic) mucosa in continuation with colonic and rectal mucosa. There was no evidence of granulomas, cryptitis, microorganisms, dysplasia, or malignancy. No eosinophils were present in the mucosa. The HGM sample tested negative for Helicobacter pylori by Warthin Starry special stain and immunohistochemical staining. A subsequent Meckel scan with technetium-99m (with H2 blocker priming) did not show abnormal radiopharmaceutical uptake in the descending colon, rectum, or other parts of the gastrointestinal tract. The patient was restarted on PPI, with the family considering treatment options.
**Clinical Implications:** This case highlights that HGM in the rectum can mimic inflammatory bowel disease and may be difficult to differentiate without histological evaluation. A recent retrospective case-control study found the prevalence of IBD among pediatric EoE patients to be significantly higher than in the general population (2.2% compared to 0.4%), which prompted the colonoscopy leading to diagnosis. Importantly, a negative Meckel scan does not exclude small foci of HGM — in 9 pediatric cases of HGM, only 3 had positive scans with uptake in the rectum. PPIs or H2 receptor antagonists can provide temporary symptom control, but surgical excision (for larger lesions, median size 25 mm) or endoscopic removal (median size 20 mm) has been reported in 60 cases with no symptom recurrence during follow-up (median 22 months, range 2–84 months). At least 4 pediatric cases have been treated with endoscopic mucosal resection without complications. While no pediatric cases of malignancy have been reported, there are 3 adult cases of rectal HGM with metaplasia, and malignant transformation has been documented in other organs. Endoscopic surveillance may be needed if the lesion is not resected.