Massive pseudotumor of unknown etiology in a cemented metal-on-polyethylene total hip arthroplasty: a case report.

Background: The formation of destructive pseudotumors is a well-documented, albeit rare, complication of total hip arthroplasties. They tend to be progressive and, if left untreated, can result in extensive periprosthetic bony destruction. The current case presents a large benign mass consistent with a pseudotumor on both imaging and intraoperative findings but histologic findings demonstrating chronic hematoma. Case Description: An 86-year-old female with a metal-on-polyethylene total hip presented with a massive pseudotumor accompanied by extensive bony lysis. Due to pain and chronic anemia, a palliative debulking procedure was undertaken as a palliative measure. At one year follow-up, the patient reported significant pain relief and was able to ambulate safely with gait aids. Her hemoglobin stabilized post-operatively and ongoing transfusions were not required. Final pathology was not supportive of particle disease despite this being the leading diagnosis. Microscopic sections showed tissue mostly composed of fibrin and blood with multiple foci of calcification and reactive papillary endothelial hyperplasia which can be seen in chronic hematomas. Conclusions: This case presents the diagnostic dilemma of a large benign mass consistent with a pseudotumor on both imaging and intraoperative findings but histologic findings consistent with a chronic hematoma. It highlights the importance of close follow-up and early intervention when periprosthetic osteolysis is detected.