ARTICLE
Desmoplastic trichoepithelioma was first described
as a distinct clinicopathological entity in 1976 by Brownstein and Shapiro
[1]. The same condition has also been designated as sclerosing epithelial
hamartoma in 1977 by MacDonald et al. [2]. This lesion
has been previously reported under other names, most often as solitary
trichoepithelioma [3, 4].
Clinical features of desmoplastic trichoepithelioma are solitary, hard,
annular lesions on the face of a female [5]. Histologically,
it has three characteristic findings: narrow strands of basaloid cells,
keratinous cysts, and desmoplastic stroma [4].
Desmoplastic trichoepithelioma is associated with nevus cell nevus or
ossification in approximately 10% and 6% of cases, respectively [5-8].
Here, we report two cases of desmolastic trichoepithelioma, one associated
with a compound nevus and the other with ossification.
Case reports
Case 1: A 54-year-old woman with a brownish nodule on her face was first
examined in April of 1999. She had been aware of the pigmented macule
on her cheek for 10 years, and the lesion recently increased in size and
became elevated. On examination, she had an 8 x 7 x 2 mm, brownish, firm
nodule in the center of her left cheek (Fig.
1). The lesion had a delled center and elevated borders. The initial
diagnosis was basal cell carcinoma, and the lesion was excised. Histological
findings revealed a well-demarcated, but not encapsulated, solitary tumor
asymmetrically situated in the entire dermis. In the center of the specimen,
the basaloid cells were arranged in narrow strands, with one to three
rows of the cells (Fig. 2a).
The stroma consisted of collagen and there was no cleft between the nests
of tumor cells and the stroma. Palisading was not observed. Multiple keratinous
cysts were also present. In the peripheral area of the tumor the nevus
cell nests were intermingled with the strands of the basaloid cells (Fig.
2b). The nevus cells were also present in the dermoepidermal junction.
The diagnosis based on these findings was desmoplastic trichoepithelioma
developed in the lesion of compound nevus. There was no recurrence 2 years
after the operation.
Case 2: A 44-year-old man presented with a 3-year history of a nodular
lesion on his cheek. On examination, he had a solitary, skin-colored,
firm nodule, 6 mm in diameter, with a central depression and raised borders
at the center of his right cheek (Fig.
3). The clinical diagnosis was desmoplastic trichoepithelioma and
the lesion was excised. Histological examination revealed a symmetrical,
well-demarcated tumor situated in the entire dermis (Fig.
4a). The tumor consisted of basaloid cells arranged in narrow strands,
with one to three rows of cells. The stroma was a homogeneous eosinophilic
stained collagen and it surrounded the strands of basaloid cells. Horn
cysts were also present. At the base of the lesion, there was a circular
bone structure (Fig. 4b).
Adjacent to the bone, a foreign-body giant-cell reaction and calcification
were present. Based on these histological findings, the diagnosis of desmoplastic
trichoepithelioma associated with ossification was made. The patient was
tumor-free for 1 year and 9 months after the operation.
Discussion
Brownstein and Starink reported that among 76 cases of desmoplastic
trichoepithelioma, 10 (13%) contained nests of nevocytes in the cutis
[6]. Takei et al. reported that approximately one in every ten
cases of desmoplastic trichoepithelioma has nevus cells [7].
The association of these two conditions was considered to be either coincidental
[9] or related [6, 8, 10]. The relatively high percentage of association
suggests that there might be some relation between these two conditions
[6, 8].
Brownstein and Starink stated that the association of desmoplastic trichoepithelioma
with intradermal nevus might represent an example of epithelial induction
by melanocytic nevi [6]. Rhabari and Mehregan considered that this association
was supporting evidence for the idea that the nevus cell nevi were complex
neoplasms consisting of nevus cells together with the new formation of
connective tissues and various types of epithelial elements [10]. Keen
suggested that the local paracrine effect of cytokines or growth factors
secreted by the nevus cells accounts for epithelial proliferation [11].
In case 1, a pigmented macule existed for ten years and it became elevated
and enlarged only recently. This clinical course suggests that the original
lesion might be a pigmented nevus and desmoplastic trichoepithelioma developed
later on the site of the nevus cell nevus. The histological findings also
support this hypothesis, that is, the components of desmoplastic trichoepithelioma
are situated in the center of the tumor and the nests of nevus cells are
distributed in the peripheral area. Nevus cells may have induced the proliferation
of desmoplastic trichoepithelioma.
Desmoplastic trichoepithelioma occurring simultaneously
in the same lesion with ossification has seldom been reported. In their
original reports, Brownstein and Shapiro found only three cases (6%) of
desmoplastic trichoepithelioma which was associated with ossification
in their series of 50 cases of the disease [5]. However, there has been
no individual case report with a detailed description of the lesion. The
pathophysiological mechanism of this association remains unclear.
In three cases reported by Brownstein and Shapiro and in our case 2,
bone formation occurred in the same area of the foreign-body granuloma
and calcification. Knox examined ossification in melanocytic nevi and
proposed that foreign-body giant-cell reactions occurred as a result of
follicular damage, and then ossification occurred as a phenomenon secondary
to these reactions [12]. We also consider that the mechanism of ossification
in desmoplastic trichoepithelioma is related to foreign-body granuloma
caused by the rupture of horn cysts because of their being located on
the same site.
Calcification was observed in 68% of desmoplastic trichoepithelioma
cases almost invariably near ruptured or apparently intact horn cysts
[5]. In case 2, calcification was observed adjacent to the foreign-body
reaction and bone formation. Foreign-body reactions might affect certain
aspects of the microenvironment, such as pH, calcium phosphorus and citrate
ion concentrations, oxygen tension and enzymes, causing calcium deposition
[13]. Oikarinen et al. suggested that fibroblasts may have the
ability to differentiate into osteoblastic cells [14]. In desmoplastic
trichoepithelioma, it is possible that osteoblasts that were formed from
fibroblasts may produce osteoids and then calcium deposition occurs in
the collagen matrix, resulting in metaplastic bone formation.
Article accepted on 2/8/01
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