Cysts (Epidermal, Dermoid, Trichilemmal)
Epidermal cysts are the most common type of cutaneous cyst and can occur anywhere on the body as a single, firm nodule. Trichilemmal (pilar) cysts, the next most common, occur more often in females and usually on the scalp. When ruptured, these cysts have a characteristic strong odor. Dermoid cysts are present at birth and may result from epithelium trapped during midline closure in fetal development. Dermoid cysts are most often found in the midline of the face (e.g., on the nose or forehead) and also are common on the lateral eyebrow. The walls of all these cysts consist of a layer of epidermis oriented with the basal layer superficial and the more mature layers deep (i.e., with the epidermis growing into the center of the cyst). The desquamated cells (keratin) collect in the center and form the creamy substance of the cyst. Histologic examination
is needed to differentiate the different types. Surgeons often refer to cutaneous cysts as sebaceous cysts because they appear to contain sebum; however, this is a misnomer because the substance is actually keratin. Cysts usually are asymptomatic and ignored until they rupture and cause local inflammation. The area becomes infected and an abscess forms. Incision and drainage is recommended for an acutely infected cyst. After resolution of the abscess, the cyst wall must be excised or the cyst will recur. Similarly, when excising an unruptured cyst, care must be taken to remove the entire wall to prevent recurrence.
Nevi (Acquired, Congenital) Acquired melanocytic nevi are classified as junctional, compound, or dermal, depending on the location of the nevus cells. This classification does not represent different types of nevi but rather different stages in the maturation of nevi. Initially, nevus cells accumulate in the epidermis (junctional), migrate partially into the dermis (compound), and finally rest completely in the dermis (dermal). Eventually most lesions undergo involution. Congenital nevi are much rarer, occurring in only 1 percent of neonates. These lesions are larger and oftentimes contain hair. Histologically they appear similar to acquired nevi. Congenital giant lesions (giant hairy nevus) most often occur in a bathing trunk distribution or on the chest and back. These lesions are cosmetically unpleasant. Additionally, they may develop malignant melanoma in 1–5 percent of the cases. Excision of the nevus is the treatment of choice, but often the lesion is so large that closure of thewound with autologous skin grafts is not possible because of the lack of adequate donor sites. Serial excisions over several years with either primary closure or skin grafting and tissue expansion of the normal surrounding skin are the present modes of therapy.
Soft-Tissue Tumors (Acrochordons, Dermatofibromas, Lipomas) Acrochordons (skin tags) are fleshy, pedunculated masses located on the axillae, trunk, and eyelids. They are composed of hyperplastic epidermis over a fibrous connective tissue stalk. These lesions are usually small and are always benign. Dermatofibromas are usually solitary nodules measuring approximately 1–2 cm in diameter. They are found primarily on the legs and sides of the trunk. The lesions are composed of whorls of connective tissue containing fibroblasts. The mass is not encapsulated and vascularization is variable. Dermatofibromas can be diagnosed by clinical examination. When lesions enlarge to 2–3 cm, excisional biopsy is recommended to assess for malignancy. Lipomas are the most common subcutaneous neoplasm. They are found mostly on the trunk but may appear anywhere. They may sometimes grow to a large size. Microscopic examination reveals a lobulated tumor containing normal fat cells. Excision is performed for diagnosis and to restore