[Thymus hyperplasia: classification, problems of patho- and morphogenesis, importance in human pathology]

Thymus hyperplasia may be congenital (thymomegaly) and acquired (acquired thymomegaly, "tumour-like" hyperplasia, lymphofollicular hyperplasia). Congenital thymomegaly is represented by variants with hypo- and hyperfunction of an adequately formed thymus and results from the congenital neuro-endocrine disturbances. Thymomegaly with a thymus hypofunction is a marker of the immunodeficiency. Acquired thymomegaly is also represented by two variants with hypo- and hyper-function of the thymus and is in fact a "phenocopy" of the congenital one. "Tumor-like" thymus hyperplasia is a rare form of its pathology with a thymic weight reaching 800 g thus resulting in a syndrome of the mediastinum organs compression. Lymphofollicular thymus hyperplasia can not be always considered to be a thymus pathology but it is characteristic of autoimmune and infectious-allergic diseases with lymphoid follicles localizing in the hyperplastic intralobular perivascular spaces. Thymus parenchyma changes depend on the main disease and play a main role in the development of thymus dysfunction, for example, in the autoimmune diseases. Formation of lymphoid follicles in the dilated perivascular spaces is a non-specific process.