Morphologic and clinico-pathologic features of thymus tumours.

A total of 37 thymic tumours was studied out of which 29 proved to be of epithelial origin. Thymomas may be accompanied by a minimal, marked or an overwhelming lymphoid reaction, pointing to the degree of the cellular defensive mechanism. According to the findings, two main types of thymoma with minimal lymphoid reaction (light and dark cell types) can be distinguished. All the 7 light cell thymomas with minimal lymphoid reaction proved to be malignant in their clinical course. Thymomas of light cell origin with marked lymphoid reaction may be clinically benign or malignant. Thymomas with overwhelming lymphoid reaction were clinically benign. The clinical behavior of the dark cell thymomas was benign. The dark cell thymomas could be divided into subgroups with solid, lacunar and spindle cell forms. Three non-Hodgkin type thymic lymphomas were observed. The T cell origin of one of these tumours was demonstrated immunologically. All the five cases of Hodgkin type thymic lymphoma were morphologically identical to the modular sclerotic form of lymphogranulomatosis.