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Trichoblastoma - Submitted on: Thursday May, 04, 2000
Contributed by:Artur Zembowicz, MD PhD.
Trichoblastoma (TB) was first described as a pathological entity by Headington, who noted that these "trichogenic adnexal tumors" show peculiar relationship between epithelial component and cellular stroma, reminiscent of mutual induction between epithelium and mesenchyme during hair development in embryogenesis.

Definition:
TB is a benign dermal basaloid epithelial and stromal neoplasm showing complex architectural relationship between the epithelium and the stroma reminiscent of germinal hair follicle.

Clinical Features:
TB can arise practically at any age, but are more common in adults. Women are equally often affected as men. The preferred anatomical sites are head and neck region, especially face and scalp. They are extremely rare on distal extremities. The majority of trichoblastomas are less then 2 cm in size with occasional examples of giant trichoblastomas sometimes reaching several centimeters. Giant trichoblastomas are also sometimes referred to as solitary or giant trichoepitheliomas have special predilection for the face and perianal area.

Histology:
Figures
(Click on an image for a larger view)
Figure 1. Trichoblastome. Low magnification view.
Figure 2. Trichoblastoma. High magnification view.
Figure 3. Trichoblastoma. High magnification view.
Trichoblastomas are well-circumscribed symmetrical dermal tumors, with no epidermal connection, and in their giant form, extend to subcutis. The epithelial component consists of proliferation of basaloid cells arranged in cords, strands and nests; with extensive anastomosing and mixing of patterns from one area to another (Figure 1).
The evidence of trichogenic differentiation is present in the form of abortive hair papillae formation (so called papillary mesenchymal bodies), consisting of an indentation of the stroma into nests of epithelial cells, reminiscent of the relationship between primitive hair papillae and hair bulbs. (Figures 2,3).
Peripheral pallasading of cells in larger nests is often present. Mitotic activity varies from tumor to tumor, but is always present and can be brisk. Apoptosis is rare. Sometimes, tumor nests are colonized by dendritic melanocytes and can be pigmented. Keratinization within the nests is rare. The stroma varies in cellularity. It is typically composed of plump stellate to fusiform spindle cells with eosinophilic cytoplasm. Sometimes clefting between epithelial nests and stroma, reminiscent of basal cell carcinoma is present, but stromal mucin is almost never found. The ratio between the epithelial component and the stroma varies. The tumors with predominance of the epithelial component are sometimes referred to as "trichoblastic trichoblastomas", whereas those with stromal predominance are often called trichoblastic fibromas.


Treatment:
Simple excision is curative. In the case of incompletely excised lesions, a re-excision with clean surgical margins should be recommended to prevent local recurrence.

Bibliography:
  • McKee, PH Pathology of the skin. (1996) Mosby-Wolfe. 11.25-11.28.
  • Weadon, D, Skin Pathology. (1998) Churchill Livingstone, 288-291.
     

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