Case report and diagnostic implications of misdiagnosis of pericardial myxoid liposarcoma by multimodal imaging.

Myxoid liposarcoma (MLPS) typically occurs in the extremities. Pericardial involvement is exceptionally rare and usually indicates metastatic disease. Because of their non-specific imaging features, such lesions are often mistaken for benign tumors, leading to diagnostic errors. This report describes the case of a 69-year-old woman who presented with chest tightness and had a history of gluteal MLPS. Multimodal imaging (CT, ultrasound, MRI) revealed a pericardial mass. Although features such as well-circumscribed margins and delayed contrast filling suggested a benign-appearing lesion rather than enabling a definitive diagnosis, the clinical history of the patient strongly favored metastatic MLPS. Imaging alone could not provide a definitive diagnosis, highlighting the challenge posed by overlapping features between benign and malignant cardiac masses. The final diagnosis relied on histopathology and molecular testing. Postoperative immunohistochemistry revealed a spindle cell tumor with myxoid stroma (S-100 negative, MDM2 weakly positive). Molecular pathology confirmed the diagnosis by detecting the FUS-DDIT3 fusion gene, establishing metastatic MLPS. This case underscores the critical limitations of imaging in reaching a definitive diagnosis and emphasizes that accurate classification necessitates integration with histopathological and molecular analyses. An optimized diagnostic strategy should incorporate a comprehensive review of clinical history-especially any prior sarcoma-maintain heightened vigilance for overlapping imaging features of rare sarcomas in atypical locations, and include molecular pathology to effectively prevent misdiagnosis.