Hair follicle nevus
It is hypothesized that the lesions occur as a result of somatic point mutations. While hair follicle nevi are commonly congenital, they can be less frequently acquired, presenting in adults. Isolated reports note possible links to epidermal nevus-like lesions and frontonasal dysplasia. Moreover, a single case of hair follicle nevus has been described in association with ipsilateral leptomeningeal angiomatosis of the brain and congenital alopecia.
Given the rarity of this skin condition, its distribution and prevalence among different races and ethnicities is unknown.
L73.9 – Follicular disorder, unspecified
239127008 – Hair follicle nevus
Differential Diagnosis & Pitfalls
- Accessory tragus – Commonly found on the anterior ear or preauricular skin.
- Trichofolliculoma – A central vellus hair may be seen clinically. Histopathologically, these lesions have a central invagination from which the hair follicles radiate.
- Acrochordon – Lack clustering of vellus hairs seen in hair follicle nevi.
- Adnexal polyp of neonatal skin – A pedunculated polyp that is present at birth and spontaneously separates within the first few days of life. The areola is a common site.
- Nevus sebaceus – These lesions are initially macular and hairless and progress to become more raised and verrucous at puberty. They are typically found on the scalp.
- Trichodiscomas and fibrofolliculomas – Small, dome-shaped papules that are not typically seen in the pediatric population. Occur in the setting of Birt-Hogg-Dubé syndrome.
- Epidermoid cyst – A firm nodule that often has a dilated punctum.
- Intradermal nevus – Not associated with a clustering of vellus hairs that is characteristic of hair follicle nevi.
- Basal cell carcinoma – Pearly papule with raised rolled borders and occasional central ulceration.
- Dilated pore of Winer – Presents as a solitary enlarged pore filled with keratin.
- Pilar sheath acanthoma – Presents as a papule or nodule with a central opening.
- Thyroglossal duct cyst – Presents as a midline neck mass that elevates with protrusion of the tongue and with swallowing.
- Branchial cleft cyst – A skin-colored nodule or cyst, usually on the inferior and lateral neck.