& Subungual Tumours
- A subungual exostosis (Dupuytren's exostosis) is a BENIGN osteocartilaginous outgrowth - trabecular bone capped by FIBROCARTILAGE - that arises from the DORSAL or dorsomedial aspect of the DISTAL PHALANX, most commonly of the GREAT TOE, typically in adolescents and young adults, and a history of preceding TRAUMA is often present.
- It is histologically and radiologically DISTINCT from a true (hyaline-cartilage-capped) OSTEOCHONDROMA: a subungual exostosis has a FIBROCARTILAGE cap and does NOT show continuity of its cortex and medulla with the underlying bone (unlike an osteochondroma), and it arises from the surface of the distal phalanx rather than the metaphysis of a long bone.
- It PRESENTS as a firm subungual or periungual nodule that ELEVATES and DEFORMS the nail (onycholysis/nail-plate elevation), is often painful (especially with footwear pressure), and may ulcerate or bleed; the diagnosis is suggested clinically and confirmed on a plain RADIOGRAPH showing the bony outgrowth projecting from the distal phalanx.
- It must be considered within the broader differential of SUBUNGUAL TUMOURS, which includes benign solid lesions (glomus tumour - classically severe pain/cold sensitivity, subungual exostosis, soft-tissue chondroma, keratoacanthoma, haemangioma/pyogenic granuloma), benign cysts (epidermal/mucoid), and MALIGNANT tumours - squamous cell carcinoma and, crucially, subungual MELANOMA - so imaging (radiograph, and ultrasound/MRI for soft-tissue lesions) and a low threshold for biopsy are used to differentiate them.
- The MUST-NOT-MISS diagnosis is subungual MELANOMA: any persistent pigmented subungual lesion, a longitudinal melanonychia with Hutchinson's sign (pigment spread to the nail fold), or an atypical/non-healing subungual lesion must prompt suspicion and biopsy, because mis-diagnosing a melanoma as a benign subungual lesion is a catastrophic error - so a subungual mass is not assumed benign without appropriate assessment.
- TREATMENT of a symptomatic subungual exostosis is MARGINAL EXCISION - removing the exostosis with its fibrocartilage cap down to its base on the distal phalanx (often with partial nail-plate removal for access) - and the key principle is COMPLETE excision, because an incompletely excised lesion (cartilage cap left behind) RECURS; histology should confirm the benign diagnosis.
- “Subungual exostosis (Dupuytren) = BENIGN FIBROCARTILAGE-capped bony outgrowth from the DORSAL DISTAL PHALANX, usually the great toe, in adolescents/young adults (often post-trauma) - elevates/deforms the nail.
- “Distinct from a true osteochondroma (fibrocartilage not hyaline cap; NO medullary continuity). Radiograph shows the outgrowth.
- “Part of the SUBUNGUAL TUMOUR differential (glomus, osteochondroma, pyogenic granuloma) - MUST EXCLUDE subungual MELANOMA/SCC. Treat by COMPLETE marginal excision (recurs if cartilage cap left).
A fibrocartilage-capped bony outgrowth from the dorsal distal phalanx (usually the great toe) that elevates/deforms the nail - confirmed on radiograph. Treat by complete marginal excision.
Any subungual mass sits in a differential that includes subungual MELANOMA and SCC - a pigmented/ atypical/non-healing lesion must prompt biopsy.
The Lesion, Its Differential & Treatment
A subungual exostosis (Dupuytren's exostosis) is a benign osteocartilaginous outgrowth - trabecular bone capped by fibrocartilage - arising from the dorsal/dorsomedial distal phalanx, most often the great toe, in adolescents/young adults, often after trauma. It is distinct from a true osteochondroma (fibrocartilage rather than hyaline cap; no continuity with the medullary canal). It presents as a firm subungual nodule that elevates and deforms the nail, is often painful and may ulcerate, and is confirmed on a plain radiograph. Crucially it sits within the subungual tumour differential - glomus tumour (severe pain/cold sensitivity), osteochondroma, soft-tissue chondroma, pyogenic granuloma, and the must-not-miss subungual MELANOMA and squamous cell carcinoma - so a subungual mass is not assumed benign. Treatment is complete marginal excision (with the cartilage cap); incomplete excision recurs.
| Lesion | Clue | Note |
|---|---|---|
| Subungual exostosis | Bony outgrowth on radiograph; nail elevation; great toe | Benign; fibrocartilage cap; marginal excision |
| Glomus tumour | Severe pinpoint pain, cold sensitivity, blue-red nail-bed spot | Benign; MRI; excision |
| Osteochondroma | Bony outgrowth with medullary continuity | Benign; differs from exostosis (hyaline cap, continuity) |
| Pyogenic granuloma / keratoacanthoma | Friable, bleeding/rapid lesion | Benign but mimics malignancy |
| Subungual MELANOMA / SCC | Pigment, Hutchinson's sign, non-healing/atypical lesion | MALIGNANT - must not miss; biopsy |
Diagnosis, Excision & Exclusion of Malignancy
- Diagnose: clinical (firm subungual nodule deforming the nail, often great toe, often post-trauma) plus a plain radiograph showing the bony outgrowth from the distal phalanx; ultrasound/MRI help for soft-tissue subungual lesions.
- Exclude malignancy: a subungual mass is part of a differential that includes melanoma and SCC - a pigmented, atypical, ulcerated or non-healing lesion (especially with Hutchinson's sign) needs BIOPSY.
- Treat by complete marginal excision: remove the exostosis with its fibrocartilage cap down to its base (with partial nail-plate removal for access); send for histology.
- Avoid recurrence: incomplete excision (cartilage cap left) is the main cause of recurrence - excise completely.
- Manage the nail: preserve/repair the nail bed where possible to minimise nail deformity."
The crucial safety principle for any subungual lesion is to exclude malignancy - above all subungual MELANOMA - before treating it as a benign subungual exostosis. While the subungual exostosis is a common, benign, fibrocartilage-capped bony outgrowth of the distal phalanx that is confirmed on radiograph and cured by complete marginal excision, the subungual space also harbours dangerous tumours, and a pigmented subungual lesion, a longitudinal melanonychia with Hutchinson's sign (pigment spreading to the nail fold), or an atypical, ulcerated or non-healing subungual lesion must raise suspicion of melanoma or squamous cell carcinoma and prompt biopsy. Equally, when excising a subungual exostosis, removing the lesion completely with its cartilage cap is what prevents recurrence, and the specimen should always go for histology to confirm the benign diagnosis.
Evidence & Key Studies
Subungual tumours: clinicopathologic correlation with US and MR imaging (differential)
- Subungual tumours include benign solid lesions (glomus tumour, subungual exostosis, soft-tissue chondroma, keratoacanthoma, haemangioma), benign cystic lesions, and malignant tumours (squamous cell carcinoma, malignant melanoma).
- Imaging is important because of the small size, nonspecific clinical manifestations and functional significance of these lesions; ultrasound and MRI help characterise and differentiate them.
- Accurate diagnosis requires correlation of imaging with clinical and pathological findings.
Differential diagnosis of bony surface (periosteal) lesions including subungual exostosis
- Reactive/benign surface bone lesions - including subungual exostosis, bizarre parosteal osteochondromatous proliferation (Nora's lesion) and florid reactive periostitis - show imaging/histological overlap with each other and with malignant surface tumours (periosteal/parosteal osteosarcoma).
- It is important to recognise the benign entities so they are not mistaken for an aggressive neoplasm.
- A correct diagnosis (and benign vs malignant distinction) guides appropriate, conservative management.
According to PubMed, the differential of subungual tumours (including the subungual exostosis among benign solid lesions, alongside the malignant squamous cell carcinoma and melanoma) and the role of imaging in differentiating them come from the cited Baek review; the imaging/histological overlap of benign surface bone lesions (subungual exostosis, Nora's lesion, reactive periostitis) with malignant surface tumours, and the importance of not mistaking benign lesions for aggressive neoplasms, from the cited Soni review. The subungual exostosis being a benign fibrocartilage-capped outgrowth of the distal phalanx (usually the great toe, often post-trauma), its distinction from a true osteochondroma, the nail deformity, the must-not-miss melanoma, and complete marginal excision are standard, well-established teaching. (See also our Subungual Melanoma and Glomus Tumour topics.)
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
“A teenager has a painful firm lump under the great toenail that is lifting the nail. What is the likely diagnosis and how do you approach it?”
Mnemonics & Memory Aids
NAIL
Hook:NAIL: Nodule deforms nail, Adolescent/post-trauma fibrocartilage cap, Image + exclude malignancy, Lesion excised completely.
Subungual exostosis
- Benign osteocartilaginous outgrowth, fibrocartilage cap
- Dorsal/dorsomedial distal phalanx, usually great toe; adolescents/young adults (often post-trauma)
- Elevates/deforms the nail; painful; confirm on radiograph
Vs true osteochondroma
- Subungual exostosis: fibrocartilage cap, NO medullary continuity, surface of distal phalanx
- Osteochondroma: hyaline cap, cortical/medullary continuity, long-bone metaphysis
- Distinct entities
Subungual tumour differential
- Benign: glomus tumour (severe pain/cold), exostosis, chondroma, pyogenic granuloma, keratoacanthoma
- Malignant (must not miss): subungual MELANOMA, squamous cell carcinoma
- Pigmented/atypical/non-healing/Hutchinson's sign -> biopsy
Treatment
- Complete marginal excision (with fibrocartilage cap) - send histology
- Incomplete excision -> recurrence
- Preserve/repair the nail bed where possible