We aim to follow the CARE guidelines for cases reports. A 34-year-old man was admitted to the hospital with chest tightness and a cough that had been present for 6 days. He described having dyspnea that was gradually worsening. His other complaints included bloating, acid reflux, and heartburn. His blood pressure was 139/97 mm Hg, his heart rate was 85 beats/min, and his oxygen saturation was 98% with supplemental oxygen. His Holter monitoring showed sporadic atrial premature beats, sustained ST-T changes, and an abnormal Q wave of the posterior wall. Laboratory investigations demonstrated an elevated white blood cell count of 13.90 x 109/L, a D-dimer level of 5100 ng/mL, and an N-telencephalon sodium peptide precursor (B-type natriuretic peptide) level of 843.20 pg/mL; however, the level of troponin-T was normal. The patient's medical history and physical examination showed no significant abnormalities. An echocardiogram revealed a substantial amount of pericardial effusion and a 7.9 x 2.3 cm2 heterogeneous hypoechoic mass located in the left visceral pericardium. The mass was found to have a broad base and to be adjacent to the left ventricle and atrium ( Figure 1A ).
CMRI and CT examinations were requested for the further diagnosis and assessment of the relationship between the tumor and its adjacent structures. Both of these imaging studies noted a large mass situated superior and inferior to the left side of the heart and adhering to the left ventricular free wall. The tumor completely covered the left atrium, superiorly extended between the ascending aorta and the superior vena cava, and partly encased the pulmonary artery trunk and the left pulmonary artery. In addition, CMRI showed that the irregular soft-tissue mass was asymmetrically hypointense on T1-weighted images and heterogeneously hyperintense on T2-weighted images and fat suppression images ( Figures 1B-F ). The first-pass perfusion images showed that there was no enhancement during the early phase; however, during the balance phase, the lesion appeared slight enhancement. Delayed enhancement images showed that part of the tumor presented mild to moderate patchy enhancement ( Figures 1G-I ). There were large pericardial effusions and bilateral pleural effusions, primarily on the right side. The CT imaging showed that the pericardium was invaded by a cystic solid lesion, and it presented local, unevenly thickened, and nodular changes. After the injection of contrast medium, the solid composition and septa of the tumor were slightly enhanced ( Figure 2 ). CT scans of the head, chest, abdomen, and pelvis were negative, with no evidence of metastasis. Pericardial drainage under ultrasound guidance was performed before CT examination to relieve the patient's chest tightness symptoms, and examination of the bloody pericardial fluid found a few short spindle-shaped cells with dyskaryosis.
The patient subsequently underwent a CT guided percutaneous needle puncture biopsy in the CT room. Histopathological examination of the tissue samples showed spindle cell tumors with a typical structure of hematoxylin-eosin staining arranged in vague fascicles or sheets, which was most compatible with a diagnosis of monophasic SS ( Figures 3A, B ). Immune and molecular pathology results were as follows: AE1/AE3(CK) (individual +), EMA (+), Nestin (+), SMA (weak +), CD 34 (-); CD56(56C04)*(+), SYN (-), INI-1*(+), and CD99 (+). Fluorescence in situ hybridization (FISH) testing was positive as an SS18 (SYT) break-apart probe found that the SS18 gene was broken, thereby further supporting the diagnosis of PSS ( Figure 3C ).
Given that the tumor has invaded the major vascular structures and could not be completely excised, the patient was not considered for surgical treatment. He elected to receive a doxorubicin-ifosfamide chemotherapy regimen in the oncology department. After six cycles of chemotherapy, the tumor had significantly shrunk, which was very well observed via CT imaging ( Figure 4A ). The patient then received one radiation treatment and was discharged home. Four months later, the patient came to the hospital for follow-up examination. CT images showed tumor relapse in the contralateral pericardial cavity. The tumor was located adjacent to the right atrium and the right ventricular junction, but there were no signs of recurrence at the site where the primary tumor had been located ( Figure 4B ). The patient underwent eight cycles of gemcitabine-based combination chemotherapy with acceptable tolerance. There was a slight reduction in tumor size ( Figure 4C ), but the second round of chemotherapy did not seem to be as effective as the first, possibly due to the change in the chemotherapy regimen. Unfortunately, the patient died 17 months after receiving his diagnosis and initiating chemotherapy.
(B) Enhanced CT image of the coronal reconstruction showing the tumor circumscribing the ascending aorta, the superior vena cava, and the pulmonary artery.