Histological Signs of the Thymic Enlargement

Currently, the mortality rate in pediatric population resulted from such diseases as respiratory distress syndrome, pneumonia and infections is extremely high. It cannot be ruled out that this is due to impaired functioning of the children's immune system. The thymus gland appears to be the central organ of immunopoiesis in children, that is why pediatricians pay special attention to thymic hyperplasia. To date, there is no consensus on the nature and clinical significance of the thymic enlargement.

The aim of research was to study morphometric parameters of the thymus gland in children of the first year of life having thymic enlargement.

Material and methods. To analyze the incidence of thymic enlargement in deceased children, the authors selected 764 autopsy protocols of children for the period from 2012 to 2017; of these, 117 were children who died in their first year of life. Autopsies were performed in Saratov Centralized Pediatric Prosectorium. The thymic enlargement in deceased children of the first year of life was detected in 34% (40 cases). Autopsy material of 32 children was selected (15 cases with and 17 cases without the thymic enlargement) for histological examination. The thymic index was calculated to specify correlation between the thymus mass and the age and body weight of a child. Morphometric studies were performed using an mVizo-103 microvisor.

Results. As demonstrated, infectious diseases are a risk factor for the formation of thymomegaly in  children of the first year of life. A morphological study detected that the thymic enlargement occurred  mainly due to the enlargement of the cortical layer with the reduction of the lobule area. The lobule area in the studied group of children reduced by 15%, and the number of lobes bordering in the field of view increased by 50%, respectively to the similar parameters in children of the comparison group.

Conclusion. Thus, infectious pathologies appear to be the most common cause of death in children with the thymic enlargement. The study results support the fact that histological signs of thymomegaly are the increased number of bordering thymic lobes in the field of view and the increased number of immature thymocytes.

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