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 arising from the hair follicle outer root sheath, characterized histologically by squamoid cytologic features and trichilemmal keratinization. Trichilemmal cysts are a common cutaneous cyst of the skull. These tumors are solitary in 30% of cases and multiple in 70%. The trichilemmal cysts may transform into proliferating trichilemmal cysts or proliferating trichilemmal tumors.
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 in 2% may occur transformation of trichilemmal cysts into proliferating trichilemmal cysts, which even biologically benign, may be locally aggressive. Rarely malignant transformation may occur and very uncommonly distant metastases. A lesion > 5 cm in size, evidence of infiltration, and recent growth are suspicious in this regard.
Q: What is the clinical presentation of the trichilemmal cysts and proliferating trichilemmal cysts?
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A: Trichilemmal cysts and proliferating trichilemmal cysts are more common in middle-aged women, usually asymptomatic, and may manifest as nodules or masses within areas of dense hair follicle concentrations. About 90% occur on the scalp, with 10% occurring on the back. They reach sizes of 2 to 10 cm in diameter but may extend to 25 cm. Alopecia and ulceration on the local of the tumor may occur. Occasionally clinical presentation will be with superimposed infection or rupture. Malignant transformation is very uncommon. The more aggressive behavior is more common in tumors located out of the scalp, tumors larger than 5 cm, with necrosis, atypia, and mitotic activity. Some cases of proliferating trichilemmal cysts may be associated with Cowden syndrome.
Q: When are imaging studies useful for the diagnosis of trichilemmal cysts/proliferating trichilemmal cysts?
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A: The diagnosis of trichilemmal cysts and proliferating trichilemmal cysts are on clinical signs and symptoms. Ultrasonography, CT, and MRI are imaging tests useful for evaluating the extent of the lesion and verifying the differential diagnosis. Trichilemmal cysts and proliferating trichilemmal cysts are solitary or multiple subcutaneous nodules usually located within the scalp. CT is the best tool to investigate bony erosion, whereas MRI is useful to assess soft-tissue infiltration.
Q: How is the treatment of trichilemmal cysts/proliferating trichilemmal cysts?
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A: Trichilemmal cysts/proliferating trichilemmal cysts are incidental subcutaneous nodules finding on routine brain imaging, and when asymptomatic, usually are of no medical concern, but it may need surveillance. Surgical removal may be indicated due to general discomfort, for cosmetics reasons, or to prevent the possibility of malignant transformation. Proliferating trichilemmal cysts with cytological atypia may recur and need various surgical excisions, and in rare select cases of malignant transformation, radiation therapy, and chemotherapy.
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