Proliferating trichilemmal cyst

Last revised by Henry Knipe on 10 Aug 2023

Proliferating trichilemmal cysts, sometimes known as proliferating trichilemmal tumors, are dermal or subcutaneous tumors with squamoid cytologic features and trichilemmal-type keratinization, which usually arise in the scalp.

A variety of names have been used for this pathology, including proliferating epidermoid cyst, pilar tumor of the scalp, proliferating epidermoid cyst, giant hair matrix tumor, hydatidiform keratinous cyst, trichochlamydocarcinoma, and invasive hair matrix tumor 1.

Proliferating trichilemmal cysts have female predominance 3,4.

Some cases have a syndromic association:

Proliferating trichilemmal cysts present as lobulated masses within the scalp. They vary considerably in size from a few millimeters to large masses many centimeters in diameter. Occasionally clinical presentation will be with superimposed infection or malignant transformation, although both of these complications are uncommon 3

Although they are mostly benign, there are also local invasive and malignant types 2. The latter show extensive epithelial proliferation, variable cytologic atypia and mitotic activity.

Proliferating trichilemmal cysts usually are located within the scalp and appear as multiple complex subcutaneous solid or cystic masses. The cystic components contain high-density proteinaceous material which sometimes layers dependently 3. Ring-like patterns of mineralization are also encountered 3

Proliferating trichilemmal cysts were first described by Edward Wilson Jones, an English dermatopathologist, in 1966 2

In some situations, consider an epidermal inclusion cyst.

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Cases and figures

  • Figure 1: histology
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  • Case 1
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  • Case 2
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  • Case 3
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  • Case 4
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