Thymoma Histopathology

Histopathology

Thymoma originates from the epithelial cell population in the thymus, and several microscopic subtypes are now recognized.There are three principal histological types of thymoma, depending on the appearance of the cells by microscopy:

• Type A if the epithelial cells have an oval or fusiform shape (less lymphocyte count);
• Type B if they have an epithelioid shape (Type B has three subtypes: B1 (lymphocyte-rich), B2 (cortical) and B3 (epithelial).);
• Type AB if the tumor contains a combination of both cell types.

Thymic cortical epithelial cells have abundant cytoplasm, vesicular nucleus with finely divided chromatin and small nucleoli and cytoplasmic filaments contact adjacent cells. Thymic medullary epithelial cells in contrast are spindle shaped with oval dense nucleus and scant cytoplasm thymoma if recapitulates cortical cell features more, is thought to be less benign.