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Pathology of Trichilemmoma  

Dr Sampurna Roy MD 




Syn: Tricholemmoma.

Trichilemmoma arises from the outer root sheath of the hair follicle (mainly of the bulb region).

May be associated with Cowden's syndrome.

[ Cowden's syndrome (multiple hamartoma syndrome) is an autosomal dominant disease  characterized by multiple cutaneous hamartoma (trichilemmoma, fibroma, verrucous lesions), visceral hamartoma (hyperplastic gastric polyp) or visceral carcinoma (breast carcinoma). ]

Clinical presentation : Solitary or multiple papules in adults ; dome shaped, flesh coloured lesions usually less than 5mm in diameter.

Sites :  Face, nose, eyelids, lips and oral cavity.

Microscopic features :

Symmetrical  tumour ; 

Well- circumscribed margin resting on PAS-positive thickened  basement membrane ; 

Composed of glycogenated clear epithelial cells with peripheral palisading in deeper parts ;

Cells are PAS- diastase positive ;

Some lesions contain eosinophilic "intermediate cells" (some times known as follicular poroma) ; 

Architectural patterns ranges from follicle like, vertically orientated, bulbous, lobular, verrucous or poroma- like ; 

There is broad connection with overlying surface epithelium ;

Some cases display connection with individual hair follicle ;

Epidermal changes resembling verruca vulgaris present in some cases (focal koilocytosis and prominent hyaline granules).

Diagnostic feature of trichilemmoma:  Evidence of outer root sheath differentiation characterized by:

1. Bland epithelial cells showing peripheral palisading ;

2. Clear cytoplasm ;

3. Prominent intercellular borders ;

4. Thickened and eosinophilic, PAS- positive basement membrane.

These changes are usually noted at the base or at the lateral margin of the lesion.

Immunohistochemistry: CD34 and cytokeratins: Positive


Differential diagnosis:

Trichilemmal Carcinoma ; Basal cell carcinoma ; squamous cell carcinoma,

Hidradenoma;  pilar tumour and other adnexal tumours showing focal trichilemmal differentiation.

Clear cell poroma (contain duct lumina and there is no basement membrane  or peripheral palisading).

Related post: Desmoplastic Trichilemmoma


Further reading:

Phosphatase and tensin homolog immunohistochemical staining and clinical criteria for Cowden syndrome in patients with trichilemmoma or associated lesions.

Trichilemmoma arising in the nasal vestibule: report of three cases with special emphasis on the differential diagnosis.

Trichilemmomas show loss of PTEN in Cowden syndrome but only rarely in sporadic tumors.

Atypical clinical appearance and localization of trichilemmoma. a case report.

Detection of human papillomavirus infection in trichilemmomas and verrucae using in situ hybridization.

Trichilemmoma: an immunohistochemical study of cytokeratins.

Trichilemmoma of eyelid and eyebrow. A clinicopathologic study of 31 cases.

Tricholemmoma. A cutaneous hamartoma.

Trichilemmal tumor undergoing specific keratinization: "keratinizing trichilemmoma".




Dr Sampurna Roy  MD

Consultant  Histopathologist (Kolkata - India)









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