๐ ็ธฝ็ฎ้ ๏ฝ ๐ ่ฑๆๅๆ๏ผๆฌ็ฏ๏ผ ๏ฝ ๐ ๅฎๆด็ฟป่ญฏ ๏ฝ โญ ็ฒพ่ฏ็ญ่จ
Trichilemmal cyst
Trichilemmal cyst
The outer root sheath of the hair follicle at the level of the follicular isthmus is recapitulated in the wall of trichilemmal (pilar) cysts.1โ3 It has been suggested that these cysts should be renamed as isthmic-catagen cysts. Their origin is unknown, but it has been suggested that they are produced by budding off from the external root sheath as a genetically determined structural aberration. Familial occurrence is seen in 75% of patients, in a pattern suggesting autosomal dominant inheritance.4
Clinical features Trichilemmal cysts are found on the scalp in 90% of cases; they are solitary in 30% and multiple in 70% (Fig. 34.18).4 Unusual sites such as the pulp of
1688 Cutaneous cysts
Fig. 34.18 Trichilemmal cyst: note the characteristic dome-shaped swelling on the scalp, a typical site. By courtesy of A. du Vivier, MD, Kingโs College Hospital, London, UK.
Fig. 34.20 Trichilemmal cyst: this shows the typical macroscopic appearance of cheesy lamellated contents.