Inverted follicular keratosis
IFK; inverted seborrhoeic keratosis; basaloid follicular keratosis
Inverted follicular keratosis is a benign follicular epithelial tumour that presents as a solitary, slow-growing, flesh-coloured to lightly pigmented papule, usually on the face of middle-aged and older adults. It is a well-recognised clinical and histological mimic of basal cell carcinoma, cutaneous squamous cell carcinoma and pigmented lesions. Most cases are diagnosed only after excision because of clinical uncertainty. Treatment is complete surgical excision with histology — recurrence is rare after complete removal.
Clinical features
- Solitary, dome-shaped or polypoid, skin-coloured to pink papule or thin nodule, 3–10 mm.
- Distribution — face (particularly upper lip, cheek, eyelid), occasionally scalp or neck.
- Slow growth over months to years; occasional ulceration or crusting.
- Median age 50–70; slight male predominance.
- Usually asymptomatic.
Dermoscopy
- Non-specific — keratin-filled crater, white-yellow structureless areas, fine peripheral vessels, occasional pigmentation.
- Considerable overlap with non-pigmented BCC, KA and SCC — dermoscopy cannot exclude malignancy in most cases.
Histology
- Endophytic ("inverted") lobular proliferation of squamoid and basaloid keratinocytes arising from a follicular infundibulum.
- Squamous eddies (whorls of squamous cells) within the lobules — a characteristic feature.
- Mitotic figures present but no atypia.
- Differential on histology — irritated seborrhoeic keratosis (overlapping morphology, often considered the same entity), trichilemmoma (PTEN-related when multiple), BCC (peripheral palisading, mucinous stroma).
Management
- Complete surgical excision is the default — diagnostic uncertainty and the impossibility of reliable clinical distinction from BCC/SCC makes this the safer pathway.
- Confirmed IFK on histology — no further treatment; recurrence after complete excision is rare.
- Incompletely excised IFK with diagnostic uncertainty — discuss at MDT and consider re-excision particularly on cosmetic sites.
- Multiple IFKs are rare and not an established marker of Cowden syndrome; the validated cutaneous marker of Cowden / PHTS is multiple trichilemmomas — see Cowden / PHTS.
References
- Helwig EB. Inverted follicular keratosis. Seminar on the skin; AFIP 1955 (original description).
- Mehregan AH. Inverted follicular keratosis is a distinct follicular tumor. Am J Dermatopathol; 1983.
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