Nasal polyp with bizarre stromal cells mimicking malignancy: a diagnostic pitfall

Bizarre stromal cells in sinonasal polyps represent a rare reactive phenomenon that may closely mimic malignancy and lead to diagnostic pitfalls. We report the case of an 18-year-old male presenting with progressive unilateral nasal obstruction and a history of prior endoscopic sinus surgeries. Imaging revealed a large polypoid lesion occupying the left maxillary sinus and extending into the nasopharynx. Histopathological examination demonstrated an edematous, inflamed stroma with prominent vascular proliferation and scattered markedly atypical stromal cells showing pleomorphic, hyperchromatic to vesicular nuclei, prominent nucleoli, multinucleation, and focal rhabdoid-like features. Mitotic figures were absent. Immunohistochemically, the atypical cells were positive for vimentin and desmin, with focal pancytokeratin expression and a low Ki-67 proliferation index. Complete excision was performed, and no recurrence was observed at 5 years. Recognition of this benign reactive process, particularly in limited specimens, is essential to avoid misdiagnosis as malignancy and prevent unnecessary aggressive treatment.