Trichilemmal carcinoma was originally
described by Headington as a "histologically invasive, cytologically atypical
clear cell neoplasm of adnexal keratinocytes which is in continuity with the
epidermis and / or follicular epithelium."
The outer root sheath consists of cells with clear vacuolated cytoplasm due to presence of abundant glycogen.
The trichilemmal carcinoma is a malignant tumour of the outer hair sheath.
Clinically, the tumour presents as a pale tan or reddish papule, indurated plaque or nodule.
The tumour size is usually between 0.4 and 2.0 cms.
Sites: The usual sites include scalp, face, trunk, upper extremities.
Despite an aggressive growth it has an indolent clinical course.
No cases with recurrence or metastasis have been reported in the literature.
Benign tumours like
hidradenoma lack the infiltrative
growth pattern and cytological atypia.
The latter, usually arises in a preexisting trichilemmal cyst and has metastatic potential.
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