Primary leiomyosarcoma arising adjacent to a femoral stem following total hip arthroplasty: a case report with radiologic and histopathological correlation.

Periprosthetic sarcomas associated with total hip arthroplasty (THA) are exceedingly rare, and most reported cases represent undifferentiated pleomorphic sarcoma or osteosarcoma. Primary leiomyosarcoma of bone is also an uncommon malignancy, accounting for less than 1% of primary malignant bone tumors. The occurrence of primary leiomyosarcoma adjacent to an orthopedic implant is therefore exceptionally rare. A 69-year-old woman presented with progressive left thigh pain 13 years after THA. Radiographs demonstrated osteolysis and cortical thinning at the distal femoral stem. Computed tomography (CT) and magnetic resonance imaging (MRI) revealed an intramedullary lesion with cortical thinning and contrast enhancement. 18F-fluorodeoxyglucose positron emission tomography-CT showed increased uptake at the lesion (SUV max, 11.9), without evidence of other primary tumors. The differential diagnoses included implant-related osteolysis, infection, metastatic tumor, and primary bone tumor. An open biopsy was performed, and a diagnosis of pleomorphic sarcoma was made. Wide resection with proximal femoral replacement was performed. Histopathological examination established the diagnosis of primary leiomyosarcoma of bone. Prominent lymphocytic infiltration and immunohistochemical findings, including p53 overexpression and partial loss of Rb expression, within the tumor, raise the possibility of chronic inflammation and associated molecular alterations as theoretical contributing factors to tumorigenesis. Periprosthetic sarcomas can mimic more common postoperative complications, making diagnosis challenging. Delayed diagnosis may adversely affect prognosis. This case highlights the importance of considering malignancy in atypical periprosthetic lesions and underscores the role of multimodality imaging and biopsy in achieving an accurate diagnosis.