Distinguishing Inverted Sinonasal Papilloma and Respiratory Epithelial Adenomatoid Hamartoma: A Single Institution Case Series.

Inverted sinonasal papilloma (ISP) and respiratory epithelial adenomatoid hamartoma (REAH) are sinonasal lesions with overlapping clinical, radiographic, and histologic features, making accurate diagnosis challenging. ISP is a benign but aggressive tumor with a propensity for local destruction, recurrence, and malignant transformation, whereas REAH is a hamartomatous lesion often arising in the olfactory cleft. We present four patients with lesions initially suspected to be ISP based on intraoperative frozen section but ultimately diagnosed as REAH on permanent pathology. All patients had polypoid sinonasal masses, frequently involving or adjacent to the olfactory cleft. Intraoperative frozen sections were often inconclusive or favored ISP, reflecting the difficulty of distinguishing these entities. Histologic analysis revealed that epithelial thickness served as a key morphologic feature differentiating ISP from REAH, with REAH exhibiting ciliated glandular proliferation and ISP characterized by hyperplastic epithelium with features of columnar and squamous differentiation. These patients underscore the diagnostic pitfalls of small biopsies and frozen sections, and highlight the importance of permanent specimens and collaboration with experienced pathologists. Accurate differentiation is critical, as management strategies differ substantially: ISP requires aggressive resection and long-term surveillance, while REAH may be treated with limited excision and minimal follow-up.