Q: What are the general considerations of trichilemmal cysts (pilar cysts) and proliferating trichilemmal cysts?
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A: Trichilemmal cysts (non-proliferating trichilemmal cysts), also known as pilar cysts, are dermal or subcutaneous solid-cystic lesions squamoid cytologic features and trichilemmal-type keratinization. These cysts usually arise in the scalp in 90% of the time and can also affect the face, eyes, nose, lips, trunk, back, buttocks, mons púbis, vulva, and extremities. Trichilemmal cysts are a common cutaneous cyst of the skull. These tumors are solitary in 30% of cases and multiple in 70%, which may be inherited in an autosomal dominant manner or be sporadic. The trichilemmal cysts may transform into proliferating trichilemmal cysts or proliferating trichilemmal tumors.
Q: What percentage of the population is affected by trichilemmal cysts/proliferating trichilemmal cysts?
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A: The trichilemmal cysts/proliferating trichilemmal cysts affect 5% to 10% of the population.
Q: What gender and which age group predominates the trichilemmal cysts/proliferating trichilemmal cysts?
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A: Trichilemmal cysts and proliferating trichilemmal cysts are more common in middle-aged women than in men.
Q: Trichilemmal cysts/proliferating trichilemmal cysts are benign or malignant lesions?
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A: The vast majority of trichilemmal cysts are benign. Although 2% may occur transformation of trichilemmal cysts into proliferating trichilemmal cysts, which are biologically benign, gradually enlarging lesions, that may ulcerate and be locally aggressive. Superimposed infection is a complication. Rarely malignant transformation may occur and very uncommonly distant metástases. A lesion > 5 cm in size, evidence of infiltration, and recent growth are suspicious in this regard.
Q: What are the macroscopical appearances of trichilemmal cysts and proliferating trichilemmal cysts?
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A: Macroscopically, the lesions are multinodular. On the cut surface, the cysts are filled with keratin and calcification. The lesions range in size from a few millimeters to large masses, many centimeters in diameter.
Q: What are the microscopical characteristics of trichilemmal cysts and proliferating trichilemmal cysts?
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A: Microscopically, it is a solid-cystic, well-defined mass, affecting the dermis and the subcutaneous cellular tissue. It presents trichilemmal and squamous keratinization. Epithelial invagination into the cystic lumen may be present. Calcification and cholesterol crystals may be abundant. Epithelial cells vary from monotonous without atypia (trichilemmal cysts) to pleomorphic epithelial proliferation, with variable cytologic atypia, mitotic activity, and necrosis (proliferating trichilemmal tumors). Areas with atypia may be indistinguishable from squamous cell carcinoma. Ghosts, apocrine, and spindle cells can also be present.