全髋關節置換術（THA）是骨關節炎的常見治療方法，也用於其他情況，如因髖關節發育不良引起的繼發性關節炎。各種THA類型可能由於金屬屑的不良反應而并發骨溶解和炎性假腫瘤。罕見情況下，THA與惡性腫瘤有關，但其因果關系尚不明確。在本案例報告中，我們描述了一名患有髖關節發育不良的女性患者。她曾接受左側金屬-聚乙烯全髖關節置換術、THA髂臼修復手術以及左膝全關節置換術。此外，她還有脂質代謝異常和眼部毛細血管擴張、貧血、脫層疝和胸膜炎的病史。在先前因胸膜炎住院期間檢測到與THA有關的腫瘤（疑似假腫瘤）。她因左下肢腫脹、疲勞和淤血而住院。臨床檢查顯示貧血、血小板減少和疑似假腫瘤增長。在6周內，她出現口腔黏膜出血、咳血、黑便、嚴重血小板減少無反應、D二聚體和C-反應蛋白水平升高、劇烈疼痛、骨溶解增加以及THA周圍骨折。懷疑有感染或惡性腫瘤，但兩次穿刺活檢結果顯示炎性假腫瘤。鑑于她的貧血和血小板減少被認為是疑似假腫瘤內的炎症過程引起的，她的疑似假腫瘤和所有THA組件被手術切除。然而，她出現嚴重的肺泡出血和低氧血症，在手術后2周去世。對手術和解剖樣本的組織病理學分析顯示高度惡性血管肉瘤。盡管有報告單個與THA相關的惡性腫瘤病例，但文獻中缺乏明確的THA與增加的癌症風險之間的關聯。大多數假腫瘤是非惡性的。本報告中患者的病例展示了THA相關假腫瘤和罕見的血管肉瘤鑒別診斷的挑戰。非典型的快速腫瘤生長、嚴重骨溶解和整體健康下降提示存在惡性疾病。© 2023 Skants，Rönty，Komulainen，Keski-Keturi，Huotari，Alander-Pekkarinen，Sihvo，Laitinen和Linko。

Total hip arthroplasty (THA) is a common treatment for osteoarthritis and is also performed for other conditions, such as secondary arthritis due to developmental dysplasia of the hip. Various THA types may be complicated by osteolysis and an inflammatory pseudotumor due to an adverse reaction to metal debris. Rarely, THA has been associated with malignant tumors, but their causality remains unclear. In this case report, we describe a female patient with developmental dysplasia of the hip. She had undergone left metal-on-polyethylene THA, acetabular revision of the THA, and left total knee arthroplasty. In addition, she had a history of dyslipidemia and telangiectasia of the eyes, anemia, hiatal hernia, and pleuritis. A THA-associated mass (suspected to be a pseudotumor) had been detected during a previous hospital admission due to pleuritis. She was hospitalized due to swelling in her left lower limb, fatigue, and bruises. A clinical examination revealed anemia, thrombocytopenia, and growth of the suspected pseudotumor. Within 6 weeks, she presented with bleeding of the oral mucosa, hemoptysis, melena, severe thrombocytopenia that did not respond to treatment, elevated D-dimer and C-reactive protein levels, severe pain, increased osteolysis, and fractures around the THA. Infection or malignancy was suspected, but two trocar biopsies suggested an inflammatory pseudotumor. Since her anemia and thrombocytopenia were considered to have been caused by an inflammatory process within the suspected pseudotumor, her suspected pseudotumor and all THA components were surgically removed. However, she developed severe alveolar hemorrhaging and hypoxia and died 2 weeks after her surgery. Histopathological analysis of her surgical and autopsy samples revealed highly malignant angiosarcoma. Although individual cases of malignancies associated with THA have been reported, the literature lacks a clear association between THA and increased cancer risk. Most pseudotumors are non-malignant. The patient's case presented in this report exemplifies the challenges to the differential diagnosis of a THA-associated pseudotumor and rare angiosarcoma. Atypically rapid tumor growth, severe osteolysis, and deterioration in the general wellbeing suggest a malignant disease.© 2023 Skants, Rönty, Komulainen, Keski-Keturi, Huotari, Alander-Pekkarinen, Sihvo, Laitinen and Linko.