Ultrasonic manifestations of diffuse pericardial mesothelioma masquerading as pericardial effusion: a case report.

Background: Primary pericardial mesothelioma (PPM) is an exceedingly rare, highly invasive cardiac neoplasm with insidious onset and non-specific clinical symptoms. Due to the lack of typical early manifestations and effective routine diagnostic methods, PPM is often misdiagnosed and missed, resulting in delayed treatment and poor prognosis. Case presentation: A 42-year-old male presented with 6 months of recurrent chest tightness and pain, worsening over 2 months, and two prior admissions for unexplained pericardial effusion. On admission, he had tachycardia, distant heart sounds, bilateral lower extremity edema, and a 3×2 cm hard, fixed left supraclavicular lymph node. Imaging confirmed pericardial effusion with abnormal pericardial lesions. Ultrasound-guided pericardiocentesis yielded only a small amount of red jelly-like material, with cytology suggesting epithelioid neoplastic cells. Supraclavicular lymph node biopsy confirmed metastatic malignant mesothelioma. Nivolumab immunotherapy showed no improvement. Pericardial tumor resection revealed diffuse, fish-flesh-like tumor invading the myocardium and great vessels. Final pathology confirmed epithelioid-type PPM. Conclusion: Patients with recurrent unexplained pericardial effusion and atypical sonographic features, such as flocculent echoes and irregular pericardial thickening, should raise suspicion for PPM. Early recognition of these signs and timely pathological confirmation are critical to avoid diagnostic delays and may improve outcomes.