Lymphocyte-Rich Spindle-Cell Thymoma (WHO Type AB), [Pathology] Atlas of Lymphocyte-Rich Spindle-Cell Thymoma (WHO Type AB), Atlas of Lymphocyte-Rich Spindle-Cell Thymoma, Atlas of Mediastinal Pathology
Fig. 2.47 Gross appearance of lymphocyte-rich spindle-cell thymoma
(WHO type AB) shows a well-circumscribed and encapsulated mass
with a tan-white lobulated cut surface
Fig. 2.48 Lymphocyte-rich spindle-cell thymoma (WHO type AB) is
characterized by areas displaying conventional spindle-cell thymoma
(WHO type A, lower half) that is poor in lymphocytes admixed with
areas that contain abundant lymphocytes (type B-like areas, top right
and left). Although in the original defi nition of the WHO this tumor was
supposed to contain an admixture of type A and type B cells
(i.e., spindle/oval cells and round/epithelioid cells), in reality this is a
misconception because the shape of the cells is the same
in both the lymphocyte-poor and the lymphocyte-rich areas
Fig. 2.49 Higher magnification from preceding field (type AB thymoma)
showing (a) lymphocyte-poor spindle-cell thymoma component
(WHO type A) with oval to spindle nuclei without any discernible
cytoplasm and dispersed chromatin with inconspicuous nucleoli and (b)
lymphocyte-rich component (B-like component) showing an
abundance of scattered small lymphocytes admixed with oval to spindle
nuclei without any discernible cytoplasm and dispersed chromatin with
inconspicuous nucleoli (i.e., the thymic epithelial cells are the same in
both components, and there are no type B cells)
Fig. 2.50 Lymphocyte-rich spindle-cell thymoma (WHO type AB)
can sometimes be exclusively composed of sheets of lymphocytes
admixed with small spindly epithelial cells without more overt
lymphocyte-poor spindle-cell areas. These tumors can be
easily mistaken for the WHO B1 type of thymoma
Fig. 2.51 Higher magnification of the preceding fi eld in WHO type
AB thymoma shows the proliferating epithelial cells to be of spindlecell type,
with oval nuclei showing dispersed chromatin and absent or
inconspicuous nucleoli and no discernible cytoplasm. Notice the
abundance of small lymphocytes admixed with the spindle-cell population
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