Pilar cyst = كيسة الشعر |
Trichilemmal Cyst (Pilar
Cyst)
Trichilemmal cysts are keratin-filled, epithelial-lined cysts usually on the scalp that arise from the outer root sheath of the hair follicle. EPIDEMIOLOGY Trichilemmal cysts can be found in 5 percent to 10 percent of the population, most commonly in middle-aged women. Pilar cysts arise from the epithelium located between the orifice of the sebaceous gland and the arrector pili muscle. This squamous epithelium undergoes rapid keratinization resulting in a cyst wall without a granular layer.
CLINICAL FEATURES Pilar cysts are mobile, firm, well-circumscribed nodules located overwhelmingly in the scalp . These lesions can also be found on the face, head, and neck. Most patients have more than one lesion, with 10 percent of people having more than 10 lesions. Rapid growth is abnormal and can be a sign of infection or malignant transformation.
COMPLICATIONS Although these lesions largely remain asymptomatic, rupture and infection can occur. Proliferating trichilemmal tumors are a variant of this benign lesion and are commonly found on the scalp of elderly women. This lesion can destroy adjacent lesions and ulcerate, mimicking skin cancer. Malignant degeneration of pilar cysts into malignant proliferating trichilemmal cysts can occasionally occur.
PATHOLOGY The hallmark finding of these cysts is the absence of a granular layer within the cyst wall . The cyst content is usually eosinophilic keratin, but basophilic areas of calcification may occur in the lumen of these lesions. If lobules of squamous epithelium are seen in the walls of the lesion, it is most likely a proliferating trichilemmal cyst. Invasion of the cyst lining into the surrounding tumor indicates malignancy.
DIFFERENTIAL DIAGNOSIS See Differential Diagnosis under Epidermoid Cyst.
TREATMENT The treatment is the same as with epidermoid cysts. Because the cyst wall of these tumors is clinically more firm than that of epidermoid cysts, it is possible to extract the lesion through a small incision made with a dermal punch trephine.
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