7/21/2019 Derm 35

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Benign tumors and cysts of the epidermis

The abrupt keratinization of pilar cysts resemblesthat of the outer root sheath (the trichilemma).

Proliferating pilar cystKey features

 • Rolls and scrolls • May form small new cysts within the confines of

the mother cyst  • Trichilemmal keratinization

As the epithelium proliferates, the wall buckles in-ward, rolling on itself and producing a trabecularor scroll-like appearance (“rolls and scrolls”).

A diagnosis of trichilemmal carcinoma should besuspected in tumors with a location other thanscalp, recent rapid growth, size greater than 5 cm,infiltrative growth, significant cytologic atypia,and mitotic activity.

b

Figure 2-34 Pilar cyst

a

a

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Figure 2-35 Proliferating pilar cyst

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