Ultrastructural Characteristics of Trichilemmal Cysts: Report of Two Cases

The study examined two trichilemmal cysts on the scalps of Japanese women using electron microscopy. The cysts displayed a unique keratinization pattern, characterized by an abrupt transition from nucleate to anucleate cells, small keratohyaline granules, and increasing tonofibrils. Unlike typical soft or hard keratinization, trichilemmal keratinization was observed, which is usually found in trichilemmal sacs and outer root sheaths of hair follicles. The findings suggested that trichilemmal cysts might originate from the proliferation of the outer root sheath in the follicular isthmus of anagen hairs.