[New aspects in the genesis of inverted papillomas].

In the last 15 years papers dealing with the inverting papilloma (IP) of the nose and the paranasal sinuses mainly described the clinical appearance and behaviour and/or discussed treatment modalities. Little is known about the aetiology of the IP. Comparisons between the histological appearance of the IP and the different stages of the embryonic development of Schneider's membrane, i.e. the lamina mucosa nasi derived from the ectoderm, show strikingly similar growth patterns. The main task of Schneider's membrane is to actively form the inner nose and the paranasal sinuses during development of the foetus. Hence, it employs the system of "asymmetric dichotomy" when growing into the embryonic tissue of the viscerocranium. As the IP originates exclusively in the area equivalent to Schneider's membrane and moreover presents some unique features which are histologically and morphologically identical with this membrane, the author believes that the embryonic determination to build up the sinuses and the meatus of the nose is responsible for the histological appearance of the inverting papilloma.