Subungual exostoses are benign osteocartilaginous tumours that occur beneath the nail bed.
These lesions are most commonly found in children and young adolescents 1-2.
Although they can be found beneath any nail, they most commonly affect the big (first) toe 1-2. In the majority of cases patients are able to give a history of trauma or infection to the affected toe 3. Presentation is usually with pain and swelling. There may be ulceration of the overlying nail 3.
Subungual exostoses probably result from metaplasia in mechanical irritations or diseases of the nailbed although the precise aetiology is unknown 2. The lesion is composed of mature fibrocartilagnious tissue and bone and resembles callus1,3.
These lesions are osseous although in some cases they can grow very rapidly and mimic a sarcoma 3. They are almost invariably connected to the underlying bone. Although usually appear as well circumscribed bone, they lack a clear continuity of both the medullary cavity and cortex, which helps to distinguish them from osteochondromas.
Treatment and prognosis
These lesions are benign. Resection of the exostosis and curettage of the underlying bone is curative 1.
On radiographs consider
- osteochondroma: cortex and medullary cavity continuous with lesion
- Nora's lesion (BPOP)
- subungual osteogenic melanoma
The differential diagnosis for bone tumours is dependent on the age of the patient, with a very different set of differentials for the paediatric patient.
- bone-forming tumours
- cartilage-forming tumours
- chondromyxoid fibroma
- fibrous bone lesions
- bone marrow tumours
- other bone tumours or tumour-like lesions
- aneurysmal bone cyst
- benign fibrous histiocytoma
- giant cell tumour of bone
- Gorham massive osteolysis
- haemophilic pseudotumour
- intradiploic epidermoid cyst
- intraosseous lipoma
- musculoskeletal angiosarcoma
- musculoskeletal haemangiopericytoma
- primary intraosseous haemangioma
- simple bone cyst
- impending fracture risk
- 1. Braun-Falco O. Dermatology. Springer Verlag. (2000) ISBN:3540594523. Read it at Google Books - Find it at Amazon
- 2. Campanelli A, Borradori L. Images in clinical medicine. Subungual exostosis. N. Engl. J. Med. 2008;359 (25): e31. doi:10.1056/NEJMicm074461 - Pubmed citation
- 3. Unni KK, Inwards CY, Research MF. Dahlin's bone tumors, general aspects and data on 10,165 cases. Lippincott Williams & Wilkins. (2009) ISBN:0781762421. Read it at Google Books - Find it at Amazon