What is the definition or description of: inverting papillomas?

Inverted papilloma: Inverted papilloma is a tumor that displays papillary growth, except instead of growing out of a surface, it grows into a surface. They can occur in the bladder and sinuses - rare in both locations.

Rare nasal polyp: Inverting or inverted papilloma is a nasal and sinus mucosal membrane benign neoplasm(tumor) that looks like a polyp, when it presents in the nose. However, it typically occurs on one side of the nose and sinuses. It has the potential to contain focal malignancy in about 5-15 % of cases and needs careful evaluation and surgical treatment to remove it. Long term follow-up is mandatory.