Type B1 Thymoma (Lymphocyte-rich) : Microscopic

Comments:
Type B1 thymomas resemble normal non-involuted thymus and show a predominance of cortical areas composed mostly of densely-packed non-neoplastic immature T-cells and scattered pale areas of medullary differentiation. One such medullary focus is shown here.

The paler medullary areas are less cellular and contain few or no immature T-cells but have increased numbers of B cells and mature T-cells, and may have myoid cells and Hassall corpuscles.