Trichilemmoma (Surgical-Pathology.com ; Histopathology-India.net)

[ 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 : Image Link1; Image Link2 ; Image Link3 ; Image Link4.

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 & 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 & other adnexal tumours showing focal trichilemmal differentiation. Clear cell poroma (contain duct lumina and there is no basement membrane or peripheral palisading).

Image Link: TRICHILEMMOMA(Dr Weems)CLICK

DESMOPLASTIC TRICHILEMMOMA:

Desmoplastic trichilemmoma, is a pseudomalignant variant of trichilemmoma.

Clinical presentation: Occurs in men after the fifth decade of life and presents as a small solitary nodule on the face. It is frequently misdiagnosed clinically as a basal cell carcinoma or a papilloma.

Microscopic features:

Variant of trichilemmoma: Characterized by extensive sclerotic stromal component together with complex strands of clear epithelial cell in the periphery ; Desmoplastic changes are present in the deep and central portion of the lesion ; Stroma is also present in the centre of epithelial nodules ; Eosinophilic, amorphous alcian blue and PAS-diastase positive material is present (basement membrane material) ; CD34 positive cells are identified ; Stroma contains vimentin positive cells.

Differential diagnosis:

Inverted seborrheic keratosis ; Spindle cell squamous cell carcinoma and desmoplastic basal cell carcinoma ( spindle cell component in desmoplastic trichilemmoma merge with surrounding stroma, resembling infiltrating carcinoma).