Atypical Carcinoid of Thymus : Histologic Features
The microscopic features of atypical carcinoid are similar to those of typical carcinoids. In addition, necrosis and/or increased mitotic activity (2-10 or more mitoses/HPF) are present by definition. Nuclear pleomorphism, diffuse sheet-like areas, and calcification are more commonly seen than typical carcinoids. Even small punctate areas of necrosis are enough to justify the designation of atypical carcinoid.