Adenoma, Hamartoma, or Something Else? Unique Diagnostic Challenges in Mixed Epithelial-Mesenchymal Lesions of the Gastrointestinal Tract

Abstract Introduction/Objective Mixed epithelial-mesenchymal lesions (MEMLs) are well-known in the gynecologic tract and, to a lesser extent, in the lungs and kidneys. However, the literature is mostly lacking in the GI tract. These cases pose significant diagnostic challenge when encountered upon, as there are many pitfalls and gray areas exist in characterization. Amongst other entities, hamartomas can account for a portion of these cases. Herein, we present a unique case of MEML identified in duodenum, which was reported as a hamartoma. Methods/Case Report A 59-year-old male presented with persistent upper GI bleeding requiring multiple transfusions. Initial upper GI endoscopy revealed an oozing ulcer as part of a 30 mm polyp in the second portion of duodenum opposite to ampulla. Epinephrine was injected for homeostasis. After repeat endoscopy failed to completely resect the lesion, the patient underwent exploratory laparotomy with resection of the 2nd portion of duodenum. The sections showed a submucosal proliferation of epithelial and mesenchymal elements. The epithelial component consisted of bland-appearing foveolar type mucinous glands, partly showing cystic dilation, while the mesenchymal component consisted of lymphovascular and neural structures as well as a population of small round cells that showed patchy SMA immunolabeling and low Ki67 proliferation index. The case was reported as hamartoma, however, a Brunner’s gland cyst and pericytic tumors (i.e. glomus tumor) were also considered. While the histologic features did not suggest malignancy, the patient had been followed-up closely for 6 months. Recurrence or malignant transformation was not reported. Results (if a Case Study enter NA) NA Conclusion MEMLs in the GI tract are always challenging to diagnose due to their rarity, unknown etiology and natural history, and lack of established risk factors. Furthermore, mesenchymal component is often difficult to characterize due to multiple differentiations and patchy/unrevealing immunohistochemistry. We report this unique case to enhance the awareness and recognition of MEMLS in the GI tract.