The os styloideum is an uncommon accessory ossicle located at the dorsum of the wrist, which may present with symptoms similar to those of a ganglion cyst. The presumed etiology of the os styloideum is congenital non-fusion of cartilaginous components about the carpals. Various imaging modalities, including ultrasonography, can be used to differentiate this entity from various other sources of painful dorsal-sided wrist nodules. A 13-year-old female presented with dorsal wrist pain and focal swelling. She reported that the symptoms began two months prior to the initial evaluation. A clinical diagnosis of a ganglion cyst was made. The initial radiographic examination was interpreted as negative. Sonographic examination revealed the presence of an accessory ossicle consistent with an os styloideum, which was later confirmed on the initial radiographic study. The patient elected for a trial of conservative treatment, which included activity modification and functional taping. This resulted in moderate, but not complete, reduction in pain and improvement in function. The clinical presentation of a painful dorsal nodule about the wrist should prompt the consideration of an os styloideum. This case demonstrates the use of diagnostic ultrasound as a modality for evaluating and confirming the diagnosis of an os styloideum.
Keywords: diagnostic musculoskeletal ultrasound; musculoskeletal radiology; os styloideum; pediatric sports medicine; wrist.
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