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. This high magnification view of an atypical carcinoid of thymus shows a focus of necrosis as well as several mitotic figures.