Back issues No.4 - 2009 / Correspondence  

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Trichilemmal Keratosis Manifesting as a Cutaneous Horn
Feng-Ling Lin, Che-Hao Hsu
Dermatol Sinica 27: 254-256, 2009

A 45-year-old man presented with an
asymptomatic, slowly growing, keratotic
nodule on his left fl ank for one year. Physical
examination revealed a pea-sized, horn-like
plaque protruding from a brownish nodule
(Fig. 1 A, B). The tumor had been present for
years as a cyst-like lesion before, but the tumor
ruptured 1 year before this consultation.
Later, a horn-like structure developed on the
center of it. The lesion was excised en bloc
under the impression of keratoacanthoma.
Sections showed a cup-shaped epidermal
proliferation with overlying compact hyperkeratosis
and focal parakeratosis (Fig 2).
The epithelium invaginates into dermis and
form connecting lobules. Palisading basal
cells were seen at the peripheral of the lobules
(Fig. 3). The epithelium were composed
of pale keratinocytes that transform into a
keratinized layer without a granular layer
formation (Fig. 4). There is a clear distinction
between trichilemmal keratinization and
epidermoid keratinization of the perilesional
skin. Vascular dilatation and chronic infl ammatory
cell infi ltrations are noted in the dermis.
The CD34 staining in this case shows
positive in the peripheral cells of the lesion
(Fig. 5).

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