Dermal thymus. A light microscopic and immunohistochemical study.

Two rare cases of distinctive thymic remnants occurring in the skin are described. The lesions were present at birth, and involved the side of the neck. One child had a complete cleft lip and palate. The other had multiple congenital anomalies consistent with a rare syndrome entitled branchio-oculo-facial syndrome. Microscopically, lobular foci were present in the dermis and consistent with both prethymic and thymic remnants. Immunohistochemical studies using antibodies to T cells and B cells showed a distribution similar to that seen in normal thymus. Dermal thymus appears to be a distinct entity and may be associated with other faciobranchial defects.