Epidermoid bone inclusion cysts are pathological structures bordered by a layer of stratified squamous epithelium containing keratin debris. They are also called epidermal bone cysts. Intraosseous epidermoid cysts are rare entities; these lesions may occur as a result of trauma (puncture wound or pressure erosion).
They appear to be well defined, translucent lytic lesions with sclerotic margins on imaging studies. The most frequent sites affected are: the distal phalanx and the calvaria - intradiploic, but a few cases of larger bone involvement have been reported. The imagistic differential diagnosis of this lesion includes intraosseous extension of a glomus tumor, enchondroma, osteoid osteoma, acral metastases, some primary vascular bone tumors, giant cell reparative granuloma, subungual nodular melanoma or other lytic non-neoplastic lesions such as osteomyelitis. We present the case of a 70-year-old man experiencing anxiety and pain due to distal phalanx expansion of the IV digit, following hand trauma. An X-ray was performed, showing a radiotransparent lesion located in the distal phalanx. An intramedullary inclusion cyst must be taken into account as a clinical differential diagnosis. Due to the extensive destruction of the distal phalanx, amputation was necessary. Gross examination of the surgical specimen revealed a cystic lesion that contained whitish, creamy material with extensive necrotic areas. Microscopic examination revealed a ruptured intraosseous epidermoid inclusion cyst, which was successfully excised.
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