DESMOPLASTIC TRICHOEPITHELIOMA
Overview image.
Microcysts sharing the dermis with thin strands of basaloid epithelium
that are associated with a distinctive pattern
of collagen are the characteristic features of desmoplastic trichoepitheliomas.
These don't look anything like the more common trichoepithelioma that is
characterized by foreshortened follicular differentiation with a
primordial epithelial component and dedicated fibroblastic stroma.
Many of these can be classified as follicular hamartomas with mantle structure
dominance. Others may be low grade follicular neoplasms with the capacity
to infiltrate locally. Foci of follicular differentiation
within basal carcinomas may resemble desmoplastic trichoepithelioma.
Microcysts and small strands of epithelium can be found in some basal cell
carcinomas, microcystic adnexal carcinomas and syringomas. Small biopsies,
particularly shave biopsies, having features of desmoplastic trichoepithelioma
should be interpreted with caution.
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Desmoplastic trichoepitheliomas are:
Found mostly in adults but can be seen in children
Supposed to be benign, but long term followup studies are lacking
Sometimes associated with nevocellular nevi
Sometimes associated with overt follicular
malformations
Microcysts in desmoplastic trichoepitheliomas:
May be a dominant feature
Are lined by squamous epithelium that has an inconspicuous or absent
stratum granulosum (note in all views of microcysts)
Resemble cysts of follicular mantle derivation
May be located anywhere in the reticular dermis
May appear to be empty but usually contain
variable amounts of laminated keratin which may be calcified (rarely
ossified). There may be destruction of the lining epithelium leaving foci
of calcium or bone in the dermis and/or a granulomatous response.
May have follicular components in the wall
Strands of basaloid epithelium in desmoplastic trichoepitheliomas:
May be the dominant element (caution!
often indicative of basal cell carcinoma)
May resemble the mantle structure formed by some
normal follicles
Usually are thin (note this in most of the photomicrographs referenced
for other purposes)
May be found in a perineural distribution
(caution! can also be seen in basal cell carcinomas)
Are often 'wrapped' by collagen in a distinctive
pattern
May be associated with ductal structures (caution!
this is a feature of microcystic adnexal carcinomas)
May contain sebaceous elements
May be connected to some of the microcysts forming comma
or tadpole shaped structures resembling syringoma
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