Pilar or Trichilemmal cysts are common dermal cysts. They occur in less than 10% of the population. Of all skin cysts, Pilar cysts are the most common cysts, mostly affect the skin of the scalp. Trichilemmal cysts never give rise to malignant lesions. They are usually sporadic. The cysts contain keratin and are outlined by stratified squamous epithelium similar to what we see in the outer(external) root sheath of the hair follicle. Proliferating trichilemmal cysts are the tumor form of pilar cysts, and it would appear in less than 3% of all cases of pilar cysts, and it might ulcerate and may be locally aggressive.
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