Periungual fibroma (Koenen tumour)
Koenen tumour; ungual fibroma; subungual fibroma
Periungual fibroma (Koenen tumour) is a benign fibrous tumour of the proximal or lateral nail fold, presenting as a firm, smooth, skin-coloured papule emerging from beneath the cuticle. A solitary lesion may follow trauma, but multiple periungual fibromas are a major diagnostic criterion of tuberous sclerosis complex (TSC) — appearing in approximately 50% of TSC patients by adulthood, particularly on the toes. Discovery of multiple Koenen tumours mandates a full TSC clinical assessment, including dermatological, neurological, ophthalmological and renal evaluation.
Clinical features
- Firm, smooth, skin-coloured to pink, dome-shaped or finger-like papule, 2–10 mm, emerging from the proximal or lateral nail fold.
- Often forms a longitudinal groove in the nail plate as it grows.
- Toenails more commonly affected than fingernails.
- Solitary lesions occur sporadically, often following trauma.
- Multiple lesions, particularly in childhood/adolescence, are highly suggestive of TSC.
- Other TSC skin features may coexist — facial angiofibromas, hypomelanotic macules (ash-leaf), shagreen patch.
Histology
- Polypoid dermal lesion with overlying acanthotic epidermis.
- Dense vertically oriented collagen with scattered stellate / spindled fibroblasts and small vessels — overlap with acquired digital fibrokeratoma histology.
- Distinction from acquired digital fibrokeratoma is largely clinical (single vs multiple, TSC features).
TSC evaluation
- Multiple periungual fibromas — refer for full TSC clinical assessment.
- 2021 (Northrup 2021) TSC consensus diagnostic criteria — definite TSC requires either:
- Two major features, OR
- One major + ≥ 2 minor features, OR
- Pathogenic TSC1 or TSC2 germline variant.
- Major skin features include facial angiofibromas (≥ 3), hypomelanotic macules (≥ 3, ≥ 5 mm), shagreen patch, ungual fibromas (≥ 2).
- Systemic surveillance — brain (subependymal giant-cell astrocytoma, tubers), retinal hamartomas, cardiac rhabdomyomas (in infancy), renal angiomyolipomas, lung LAM in women.
Management
- Surgical excision under digital block for symptomatic, cosmetically problematic or rapidly growing lesions.
- Recurrence is common — re-excision may be required.
- Topical/oral mTOR inhibitors (sirolimus, everolimus) reduce TSC-related skin lesion burden — coordinate with TSC clinic.
- Multidisciplinary management for confirmed TSC.
References
- Northrup H et al. Tuberous sclerosis complex diagnostic criteria update — 2012 International TSC Consensus Conference. Pediatr Neurol; 2013.
- Aldrich CS et al. Periungual fibromas of tuberous sclerosis complex. Pediatr Dermatol; 2010.
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