Spontaneous pathology of the thymus in aging Wistar (Cpb:WU) rats.

Spontaneous thymic lesions were investigated in Wistar (Cpb:WU) rats. Thymic tumors were not uncommon and most showed medullary differentiation. Thymic involution was investigated in a limited group of animals in which the survival rate for males and females was similar. The histological pattern of thymic involution differed between sexes. Severe thymic involution occurred more frequently in males than in females and at an earlier age.