The natural history of trichilemmal cysts.

The histological features of 149 trichilemmal cysts removed from sixty-five patients are reviewed and related to the clinical findings. These cysts, which may be solitary or multiple, gradually increase in size and number, and may produce daughter cysts by budding. When a breach occurs in the wall, inflammatory cells pour in but do not replace the cyst wall. This event may be followed by healing from the margins of the breach, by marsupialization to the overlying epidermis and thus natural resolution, or by proliferation to produce a pseudo-epitheliomatous change which can be confused with a well differentiated squamous cell carcinoma.