A subungual exostosis is a benign bone tumor that arises from bone beneath a nail.


Features of a subungual exostosis:

(1) The lesion consists of benign bone and cartilage.

(2) It presents as a slowly-growing hard nodule underneath the nail.

(3) It is more common on a toe but can affect a finger.

(4) It may be described as tender or painful.

(5) The nail may be displaced and deformed but remains intact.


An X-ray or MRI shows that an exophytic bone lesion is continuous with the cortex and medullary space of the underlying distal phalangeal bone.


Differential diagnosis:

(1) acral lentiginous melanoma

(2) glomus tumor

(3) pyogenic granuloma

(4) wart (verruca vulgaris)

(5) other bone tumor

(6) squamous cell carcinoma


Examination of the resected lesion will show benign bone and cartilage.


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