Trichilemmal cyst

Their origin is currently unknown, but they may be produced by budding from the external root sheath as a genetically determined structural aberration.

They arise preferentially in areas of high hair follicle concentrations, so 90% of cases occur on the scalp.

[10] Histologically, they are lined by stratified squamous epithelium that lacks a granular cell layer and are filled with compact "wet" keratin.

The tumor is clinically benign, although it may display nuclear atypia, dyskeratotic cells, and mitotic figures.

This method is best performed on cysts larger than a pea that have formed a thick enough wall to be easily identified after the sac is emptied.

Relative incidence of cutaneous cysts: Trichilemmal cyst is labeled near top.
Histopathology of a trichilemmal cyst, from internal (top) to external (bottom): [ 9 ]
- Solid eosinophilic-staining keratin .
- Swollen pale keratinocytes , which increase in height closer to the interior.
- Small, cuboidal, dark-staining basal epithelial cells in a palisade arrangement, with no distinct intercellular bridging.
- Fibrous capsule .
There is no granular cell layer (in contrast to an epidermoid cyst ).