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What is a trichilemmal cyst?

A trichilemmal cyst (or pilar cyst) is a common cyst that forms from a hair follicle, most often on the scalp, and is smooth, mobile, and filled with keratin, a protein component found in hair, nails, and skin.

A trichilemmal cyst, also known as a pilar cyst, is a keratin-filled cyst that originates from the outer hair root sheath. Keratin is the protein that makes up hair and nails. Trichilemmal cysts are most commonly found on the scalp and are usually diagnosed in middle-aged females. They often run in the family, as they have an autosomal dominant pattern of inheritance (i.e. the tendency of the cysts can be passed on by a parent to their child of either sex, and the child has a 1 in 2 likelihood of inheriting it).


Clinical features of a trichilemmal cyst

Trichilemmal cysts may look similar to epidermoid cysts and are often incorrectly termed sebaceous cysts. Trichilemmal cysts present as one or more firm, mobile, subcutaneous nodules measuring 0.5 to 5 cm in diameter. There is no central punctum, unlike an epidermoid cyst. A trichilemmal cyst can be painful if inflamed. 90% of trichilemmal cysts are found on the scalp and less frequently the scrotum.


• Central punctum is absent


• Origin is outer root sheath


• Cyst wall is thick and not prone to rupture


• Histology: granular layer is absent


Treatment

It is not necessary to remove trichilemmal cysts if they are not causing symptoms. However, incision and drainage under local anesthesia provides comfort and elective excision before rupture prevents scarring.

Pilar cyst
Pilar cyst

Surgical treatment involves one of the following methods:


• Removal of the cyst without cutting into it and leaving surrounding skin intact


• Incision followed by expression of contents and removal of cyst wall – this is often best achieved with a surgical punch with the cyst expressed through the hole


Acute inflammation after rupture is often misdiagnosed as a bacterial infection. Antibiotics are of little value unless an actual infection is present.


Citation: Kapadia, A. (2014, June 1). Trichilemmal Cyst. DermNet. Retrieved July 26, 2023, from https://dermnetnz.org/topics/trichilemmal-cyst

Condition photos reproduced with permission from: https://dermnetnz.org/





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