Nasal polyps update. Histopathology.

Sinonasal polyps are benign mucosal swellings that occur in four different histological patterns. The most common type is the edematous, eosinophilic (so-called "allergic") nasal polyp, which constitutes 85-90% of nasal polyps. The edematous polyp is morphologically characterized by edema, goblet cell hyperplasia of the epithelium, thickening of the basement membrane, and of numerous leukocytes, predominantly eosinophils. The second histological type is a fibroinflammatory polyp characterized by chronic inflammation and metaplastic changes of the overlying epithelium. Another rare variant presents with pronounced hyperplasia of seromucinous glands, but otherwise shows many similarities with the edematous type of polyp. The fourth type is very rare and is a polyp with atypical stroma. This latter polyp calls for awareness and careful histological examination to avoid misdiagnosis of a neoplasm.