Respiratory epithelial adenomatoid hamartoma: diagnostic pitfalls with emphasis on differential diagnosis.

In the upper aerodigestive tract, respiratory epithelial adenomatoid hamartoma (REAH) is described as a polypoid proliferation of glands lined by ciliated respiratory epithelium that seem to invaginate downward into the submucosa while maintaining direct continuity with the surface mucosa. The lesion can be confused with a variety of benign and malignant entities, including inflammatory polyp, inverted schneiderian papilloma, and low-grade sinonasal adenocarcinoma. In reviewing the historical, clinical, gross, and histopathologic features of REAH and its subtypes, we elucidate how the distinction of REAH with florid mucinous metaplasia from low-grade adenocarcinoma can be challenging particularly in the setting of small biopsy samples. Diagnostic criteria are reviewed with emphasis on key distinguishing characteristics. The significance of this distinction is paramount in preventing unwarranted surgery and untoward consequences for the patient.