Proliferating trichilemmal cyst: an ultrastructural study.

A 73-year-old woman had a walnut-sized tumor in the occipital region for 10 years. The growth consisted of multiple small and large cystic epithelial masses. The cyst wall exhibited trichilemmal keratinization. Numerous squamous eddies as well as many glycogen-rich cells were present in the cyst wall. Some small round keratohyalin granules were observed in the cells below the horny layer. The desmosomes and masses of lipid droplets were seen in the horny layer. The findings described above are similar to those observed in the follicular isthmus and the follicular infundibulum. Other interesting findings include the presence of intranuclear inclusions of tonofilament-like material and/or keratohyalin-like granules within the cells near the mid-layer of the cyst wall.