ABSTRACT
Subungual exostosis is a bony benign tumor with fibrous cartilaginous cap arising from the distal phalanx and affecting toenails more often than fingernails. The most common symptom is a painful mass emerging from the nail bed with cosmetic deformity of the nail plate (onycholysis, bulging). Dermoscopy reveals vascular ectasia (neoangiogenesis) as the most common finding, followed by hyperkeratosis of the nail bed and ulceration. A collarette may be present. The hard character of the mass helps to distinguish it from an ungual fibrokeratoma and superficial acral fibromyxoma. X-ray is diagnostic showing an exophytic lesion on the distal phalangeal bone ( Figures 20.1–20.3 ).
