ARTICLE
In 1979, Brownstein [1] reported 19 cases of
cutaneous horns showing trichilemmal keratinization and named this type
of tumor trichilemmal horn. Trichilemmal horns are thought to originate
from cells of the outer root sheath of the hair follicle [2, 3]. However,
there have been few reports of trichilemmal horns appearing on burn scar
tissue, as normally the hair follicles are no longer present. Here we
report a case of a trichilemmal horn appearing on burn scar tissue.
Case report
A 53-year-old Japanese woman had an asymptomatic tumor on burn scar
tissue on her left arm. The tumor slowly grew until it measured 12 x 18
mm in diameter and protruded 3 mm above the skin surface. The top of the
tumor was keratotic (Fig.
1). The lesion was removed under local anesthesia and examined using
conventional light microscopy, immunohistochemistry, and electron microscopy.
In H-E stainings, U-shaped epidermal proliferation with chromophoric hyperkeratosis
was observed (Fig. 2A).
The epidermis beneath the horny layer consisted mostly of large, pale-stained
cells containing a small number of keratohyaline granules (Fig.
2B). PAS staining revealed a modest increase in PAS-positive substances
in the keratinizing cells, apparently due to increased intracellular glycogen,
and the basement membrane was also positive stained. The tumor showed
negative staining with anti human papilloma virus immune serum.
Immunostainings for 34betaB4 (against CK1), DE-K10 (against CK10), AE1
(against CK10, 14-16, and 19), E3 (against CK17), and involucrin (polyclonal)
were positive in the tumoral epithelial cells. Immunostainings for LL002
(against CK14) and b170 (against CK19) were negative in the tumor. With
electron microscopy, an uneven and coarsely interdigited outline was observed
along the border between the cornified cells and the keratinizing cells.
The electron microscopy also showed a small number of lamellar granules
in the keratinizing cells in the upper layer of stratum spinosum, and
the cells containing these lamellar granules were connected by desmosomes.
The nuclei of the keratinizing cells were shrunken and degenerated with
dense chromatin concentrated along the inner nuclear membrane and small
dense particles aggregated in the karyoplasma.
Discussion
Trichilemmal horns show a pattern of keratinization similar to that
of trichilemmal keratinization in the hair follicle [1-3], and for this
reason they are thought to originate from cells of the outer root sheath
of the hair follicle. In examination of 19 trichilemmal horns, Brownstein
observed that, in 5 lesions, there were structures in the superficial
corium, usually multiple (or multilobular), that resembled miniature trichilemmal
cysts. Based on this observation, he considered the origin of this type
of lesion to be associated with trichilemmal cysts [1]. The findings of
our immunohistochemical study are consistent with the assumption that
trichilemmal horns originate from cells of the outer root sheath of the
hair follicle. Generally, staining for cytokeratin 17 is positive in the
lower part of the infundibulum of the outer root sheath. In addition,
the expression of cytokeratin 17 is also observed in tumor cells, which
may indicate that trichilemmal horns originate from cells belonging to
the lower part of the infundibulum of the outer root sheath.
Nishiyama et al. [4] observed two cases of trichilemmal horn
on the face and concluded that the properties of immunohistochemical staining
indicated a tumor origin in the lower part of the infundibulum of the
hair follicle. In our case, immunohistochemical and electron microscopical
observations were both consistent with a tumor origin in the hair sheath
cells. However, the tumor occurred on burn scar tissue in the absence
of hair follicles. To explain in this we inferred that the tumor originated
from cells of the hair follicle remaining in the epidermis of the burn
scar tissue.
In an electron microscopic study of trichilemmal horns, Kimura [5] observed
intranuclear dense particles in the upper part of the epithelium and concluded
that some of the trichilemmal horns were derived from viral warts. Although
intranuclear particles were observed in our case, the absence of positive
staining with anti human papilloma virus immune serum did not support
Kimura's conclusion.
Article accepted on 21/6/01
REFERENCES
1. Brownstein MH. Trichilemmal horn: cutaneous horn showing trichilemmal
keratinization. Br J Dermatol 1979; 100: 303-9.
2. Headington JT. Tumors of the hair follicle. A review. Am
J Pathol 1976; 85: 480-514.
3. Morioka S, et al. Biology and disease of the hair.
University of Tokyo Press, Tokyo 1976; 377-96.
4. Nishiyama Y, Ohnishi T, Watanabe S, Takahashi H. Two cases
of trichilemmal horn with immunohistochemical study of keratin expression.
Jpn J Clin Dermatol 1996; 50: 549-52 (in Japanese).
5. Kimura S. Trichilemmal keratosis (horn): a light and electron
microscopic study. J Cutan Pathol 1983; 10: 59-68.
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