TRICHILEMMAL CYST
TRICHILEMMAL CYST ICD-10: L72.100
• A trichilemmal cyst is the second most common type of cutaneous cyst and is seen most often in middle age, more frequently in females. It is often familial and occurs frequently as multiple lesions.
• These are smooth, firm, dome-shaped, 0.5- to 5-cm nodules or tumors; they lack the central punctum seen in epidermoid cysts. They are not connected to the epidermis.
• More than 90% occur on the scalp, and the overlying scalp hair is usually normal but may be thinned if the cyst is large (Fig. 9-32).
• The cyst wall is usually thick, and the cyst can be removed intact. The wall is a stratified squamous epithelium with a palisaded outer layer resembling that of the outer root sheath of hair follicles. The inner layer is corrugated without a granular layer.
• The cyst contains keratin—very dense, homogeneous; it is often calcified, with cholesterol clefts. If cyst ruptures, it may be inflamed and very painful.
• Synonym: Pilar cyst.
FIGURE 9-32 • Trichilemmal cyst A firm, dome-shaped nodule on the scalp. Pressure by the cyst has caused atrophy of hair bulbs, and it thus appears without hairs.