Abstract
The morphology of the thymus at post mortem may be misleading. Acute illness and stress lead to lymphophagocytosis and outflow of of lymphocytes (thymocytes) resulting in lymphodepletion of cortex obscuring cortico-medullary differentiation, shrinkage of the whole organ and often a relative increase in central medullary epithelium and Hassall bodies (H.B.) (involution). Longstanding debilitating disease and/or drug therapy will lead to similar changes, but in addition, possible disappearance through attrition of differentiated central epithelium and H.B. (hyperinvolution), morphologically resembling the thymus found in Severe Combined Immunodeficiency Disease (SCID). The thymus in adenosine deaminase (ADA) deficient SCID is of the hyperinvoluted type, rather than the embryonal non-differentiated type found in ADA positive cases.
The morphological interpretation of the thymus does not permit firm conclusions relating to function. Small size, weight and diminished lymphocyte content are of little value. Size of the “corpus thymicum” and size and number of blood vessels may simply indicate hyper-involution. Distinguishing hyper-involution from non-differentiation at an embryonal level may only be possible with serial sectioning and close scrutiny of the whole of the epithelial structure.
Firm conclusions of the functional competence of the thymus can only be drawn after taking into account morphology, clinical course and in-vitro assessment of thymic epithelial function.
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Huber, J., Gelfand, E. & Visser, H. 160: Pathology of Thymus Insufficiency. Pediatr Res 10, 897 (1976). https://doi.org/10.1203/00006450-197610000-00151
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DOI: https://doi.org/10.1203/00006450-197610000-00151