The World Health Organization histological classification of tumours of the upper respiratory tract and ear. A commentary on the second edition.

The second edition of Histological Typing of Tumours of the Upper Respiratory Tract and Ear, in the World Health Organization series International Histological Classification of Tumours, provides a comprehensive classification of tumors and tumor-like lesions occurring in (1) the nasal cavity and paranasal sinuses; (2) the nasopharynx; (3) the larynx, hypopharynx, and trachea; (4) the external ear; and (5) the middle and inner ear. The classification includes several newly recognized entities and many that were omitted from the first edition on account of their rarity. The terminology and definitions of several tumor types have been revised in the light of experience gained during the past 12 years. This article discusses the revised classification with special reference to some of the major changes in the listings, terminology, and definitions.