First report of an aneurysmal bone cyst presenting as subungual mass.

Painful subungual tumor masses in the toes usually emerge as glomus tumors or subungual exostoses. We present a patient with an aneurysmal bone cyst located subungually in whom the diagnosis was delayed due to inadequate diagnostic procedures, which led to marked destruction of the distal phalanx of the great toe of the right foot. After biopsy, the distal phalanx could not be preserved due to critical soft tissue involvement and the size of the process. Thus, we describe this rare entity to encourage clinicians to establish the diagnosis by biopsy of a tissue swelling of unclear origin and duration that does not resolve after a short time. Imaging examinations are useful in demonstrating periosteal involvement and extension of the lesion and can be helpful in the diagnostic algorithm. An interdisciplinary approach is a top priority to ensure optimal treatment.