Sebaceous glands within the thymus: report of three cases

Sebaceous glands in the thymus were discovered in three patients--two with myasthenia gravis and the other, who was operated on because of aortic valvular disease--with an unsuspected thymoma. Sebaceous glands not associated with hair follicles occur in diverse sites, the majority of which are in the head and neck or anogenital regions. Although most of these sites arise from the ectoderm, sebaceous glands have been reported in a thyroglossal duct, the larynx, and the esophagus, which are entodermal structures. Thus, precedents for ectodermally derived sebaceous glands in endodermal sites exist, but sebaceous glands have not previously been reported in the thymus. The authors speculate that their occurrence in the thymus may be related to the reported ectodermal contribution to the developing thymus by the epibranchial placode or cervical sinus.