Benign Epithelial Cysts
Following the epithelial hyperplasias in frequency are the benign epithelial cysts. The most common of these are the epidermal inclusion cysts (Figure 4), which develop from epidermal cells trapped within the hair follicle, allowing desquamated keratin to accumulate beneath the cutaneous surface. The lesions are smooth and round, with a central pore that represents the pre-existing pilar duct. Previously, these were often diagnosed as “sebaceous cysts,” but they contain keratin, not sebaceous material. Intense localized inflammation may occur due to spontaneous rupture of the cyst wall, or due to a secondary infection. Although the best treatment is complete excision with removal of the intact cyst wall, small cysts can be marsupialized, in which the anterior cyst wall is excised. With this option, it is also helpful to lightly cauterize the posterior wall of the cyst with an Optemp cautery to further reduce the chance of recurrence of the cyst.
These tiny epidermal inclusion cysts are often observed in clusters and may involve large areas of the face (Figure 5). They may arise de novo or develop after skin trauma, or during the resolution phase of a bullous epidermal disease process. Although common in newborn infants, milia usually resolve spontaneously. If milia persist, they may be marsupialized with a small blade or needle. Topical retinoic acid cream has been used successfully to treat multiple, confluent milia.
Pilar or Trichilemmal Cyst
These are clinically identical to epidermal inclusion cysts; however, they arise in skin with a high density of hair follicles and therefore are very common on the scalp. Periocular pilar cysts are often located within the eyebrows. These cysts are filled with desquamated epithelium, and calcification is observed in about 25% of histopathologic specimens.
These lesions (Figure 6) characteristically present with a waxy, nodular appearance with central umbilication. They arise from skin infection by a virus of the same name. This virus may also cause an associated chronic follicular conjunctivitis, due to an immune response to viral particles shedding onto the conjunctiva. Molluscum contagiosum nodules are common on the eyelid skin and lid margins of children. The lesions may be particularly large and disseminated in patients with acquired immunodeficiency syndrome (AIDS). If Molluscum lesions do not involute spontaneously, treatment options may include excision, curettage, or cautious cryotherapy. These should be performed carefully to limit injury to eyelash follicles or the lid margin, and to avoid hypopigmentation of the skin.