Pancreatic Heterotopia Presenting as a Mimic of Fistulizing Crohn's Disease: Expanding the Differential Diagnosis of Inflammatory Bowel Disease.

Pancreatic heterotopia (PH) involves pancreatic tissue located outside its typical anatomical position, lacking vascular or ductal communication with the pancreas. Despite frequently having acini with the capacity to produce digestive enzymes, PH is usually asymptomatic. When symptoms do occur, they typically present in middle to late adulthood and include abdominal pain, nausea, and diarrhea. This clinical presentation is similar to that of Crohn's disease, an autoimmune inflammatory bowel disease (IBD). The presentation of symptomatic PH varies depending on the location of the ectopic pancreatic tissue and its microanatomical constituents, including exocrine and endocrine tissue as well as a duct system. We present a case of a patient who came to medical attention with abdominal pain and was found on colonoscopy to have a non-obstructing stricture of the transverse colon without an associated mass. Biopsies of the area revealed chronic active colitis, leading to a diagnosis of Crohn's disease. Her gastroenterological symptoms remained stable for several years while receiving infliximab infusions until she presented to the emergency department with severe abdominal pain, diarrhea, and sepsis, meeting the criteria for systemic inflammatory response syndrome. Imaging studies revealed a fistula between the previous colonic stricture and the jejunum, again attributed to Crohn's disease. She underwent surgery to remove the fistula between the small and large bowels. Unexpectedly, the resection specimen showed a mass insinuated between the loops of the large intestine, which histological review revealed to be ectopic pancreatic tissue. Following the resection of the ectopic pancreatic tissue, her symptoms resolved without the need for further treatment. In retrospect, the ectopic pancreatic tissue, which contained acini with digestive enzymes, ducts, and islets, may have also caused seemingly unrelated pathology in the patient. Symptomatic PH should be recognized as a pathology that can mimic IBD, prompting reconsideration of the diagnosis in cases of refractory disease while on biologics.