Trichoblastoma is a small benign hair follicle tumour originating from follicular germinative cells. It is thought to be a variant of trichoepithelioma. It typically presents as a solitary mass of small skin-coloured to brown or blue-black papules or nodules, usually 1-2 cm in diameter. They most commonly occur on the face and scalp of adults around 40-50 years of age.
The main difference between trichoblastomas and trichoepitheliomas is the depth at which they arise in the dermis. Trichoblastomas are found in the deep dermis and subcutaneous tissue, whereas trichoepitheliomas are more superficial.
A small biopsy (when a tiny piece of skin is removed under local anaesthetic) is the only definitive diagnosis for trichoblastoma. The histology of trichoblastoma will differentiate it from other skin tumours that have similar clinical presentations, these include trichoepithelioma and basal cell carcinoma.
Trichoblastomas may occur with pre-existing sebaceous naevus or may occasionally co-exist with basal cell carcinoma, hence it is important to establish correct diagnosis. Some trichoblastoma may also transform into the malignant counterpart trichoblastic carcinoma, which can be locally aggressive and have the potential to spread and metastasize.
Trichoblastoma is a benign follicular tumour that requires no treatment. However, because of its association with basal cell carcinoma and the chance that it may transform into trichoblastic carcinoma, additional biopsy or complete surgical excision or Mohs micrographic surgery should be considered if there is uncertainty about the diagnosis.
Occasionally true trichoblastomas may be excised for cosmetic reasons or if they occur in functionally sensitive areas. Treatment options include curettage and electrodesiccation or surgical excision.
