Pathology of Basaloid Follicular Hamartoma

Dr Sampurna Roy MD                   2023

Basaloid follicular hamartoma (BFH) is a benign adnexal tumour characterized by superficial dermal proliferation of thin basaloid cords in a fibrous stroma.

These lesions are regarded as malformation of hair follicle.

Basaloid follicular hamartoma may be congenital or acquired.

The congenital form can be further divided into the generalized and unilateral type.

The acquired form may present as localized and solitary lesions.

Congenital, generalized Basaloid follicular hamartoma (BFH) is associated with systemic diseases such as alopecia, cystic fibrosis, hypohidrosis, and myasthenia gravis.

Sporadic cases present as unilateral or localized lesions.

These lesions are usually located on the scalp, face and rarely on the chest, back and extremities.

Clinically, basaloid follicular hamartoma presents as a brown or skin coloured papule or plaque.

BFH is linked to a mutation in the patched (PTCH) gene on chromosome band 9q23.

Immunohistochemistry: The lesion shows CD34-positive, mildly cellular myxoid stroma with many CK20-positive Merkel cells scattered within the basaloid cellular strands, which exhibited BCL-2 positivity only within the outermost cells bordering the stroma.

These immunohistochemical features are the opposite of those displayed by basal cell carcinomas, which require more aggressive surgical management.

Differential diagnosis :  Besides basal cell carcinomas, the differential diagnosis of basaloid follicular hamartoma includes, Tumour of the Follicular Infundibulum ; Poroma , and trabecular (Merkel cell) carcinoma.

Dermatopathology Quiz Case