Thymic Hassall's bodies of children with congenital heart defects.

The development of the thymus and heart are closely related while in both, the neural crest cells play an important role. In our preliminary study, the thymic microscopic structures of the infant's thymuses with the congenital heart defects were observed. The study was conducted on 36 specimens of newborn thymuses removed due to surgery for cardiovascular malformations. Standard formalin-fixed paraffin-embedded tissue technique was used. Five-microm-thick sections were stained with hematoxylin and eosin and the microscopic examination was focused on the structure of Hassall's bodies. The Hassall's bodies showed considerable variations in size as well as in quantity. In most cases, the Hassall's bodies were large with the heterogeneous amorphous material enclosed in cystic dilatations. This type of Hassall's bodies is typical for adult thymuses. The most conspicuous changes (huge Hassall's bodies with the cystic dilatation filled up with cell detritus) were observed in patients with ventricular septal defect, atrioventricular septal defect and tetralogy of Fallot. Small-sized Hassall's bodies corresponding with infant age, were observed in cases with pulmonary valve atresia, atrial septal defect and in some cases of transposition of great arteries. We assume that the changes of microenvironment of the thymic medulla are associated with disrupted migration of the neural crest cells which are essential in the normogenesis of both heart and thymus (Tab. 1, Fig. 12, Ref. 33).