Epithelial misplacement in the gastrointestinal tract: a diagnostic pitfall revisited in a patient with peutz jegher’s syndrome

Abstract

Epithelial misplacement or ‘pseudoinvasion' is a known phenomenon occurring in the gastrointestinal tract that may potentially result in the misdiagnosis of a malignancy, particularly to the uninitiated. Recent papers indicated that similar diagnostic dilemmas occur in the breast and thyroid tissues, usually following a biopsy procedure. In the gastrointestinal tract, the epithelial displacement is thought to result from herniation of the mucosa through defects of the muscularis mucosae and propria secondary to trauma from medical procedures or due to the inherent peristaltic action. We detail an instance where epithelial misplacement in a hamar-tomatous polyp in the ileum affecting a 17-year-old Malay man with Peutz-Jeghers syndrome raised the concern for malignancy. The patient had undergone a subtotal colectomy with extended ileal resection following intussusception. The resected specimen revealed multiple hamartomatous polyps in the small bowel and caecum. On histology, one polyp disclosed the presence of mucosa and mucinous pools in the adipose tissue of the serosal layer which abut the peritoneal surface, mimicking an adenocarcinoma with mucinous features. The criteria and immunohistochemical stains acting as adjuncts for separating ‘pseudoinvasion' occurring in the various types of gastrointestinal polyp including those with dys-plasia from an adenocarcinoma are presented.