Chronic Expanding Hematoma Presenting 15 Years After Metal-on-Metal Total Hip Arthroplasty With Multiple Recurrences: A Case Report.

Chronic expanding hematoma (CEH) is an uncommon clinicopathologic entity characterized by a slowly enlarging, encapsulated hematoma that can mimic neoplasms or infection. CEH is typically associated with prior trauma or surgery and may present months to years after the inciting event. Computed tomography and magnetic resonance imaging can help define the lesion, but findings are often nonspecific; histopathologic examination is required for definitive diagnosis. Complete surgical excision, including the pseudocapsule, is generally recommended to minimize recurrence. We report a 67-year-old Hispanic male who developed progressive left hip pain and a large periprosthetic soft-tissue mass 15 years after metal-on-metal total hip arthroplasty. Repeated aspirations and cultures were negative; serum metal ion levels remained within a low range; and histopathology demonstrated an organizing hematoma without adverse local tissue reactions or malignancy. The lesion recurred multiple times, ultimately requiring repeated surgical interventions. This case highlights CEH as a rare cause of late-onset periprosthetic mass and pain after hip arthroplasty and underscores the importance of considering CEH in the differential diagnosis of late-onset periprosthetic masses when infection, adverse local tissue reactions, and malignancy have been excluded.