case_images: PMC10436479_01
case_images: (A) Echocardiography. (B) MRI fat suppression image, short axial position of the left ventricle. (C) Half-Fourier single-shot turbo spin-echo MRI coronal image showing the tumor-encased superior vena cava, ascending aorta, and pulmonary trunk (black arrows). (D) MRI cine sequence, four-chamber position. (E) MRI T2-weighted image, short axial position. (F) MRI T1-weighted image, short axial position. (G-I) MRI delayed enhancement, four-chamber position, two-chamber position, and short axial position. There is an inhomogeneous, enhancing intrapericardial mass surrounded by fluid, with no intracavitary or endoluminal invasion.
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case_images: The mass was found to have a broad base and to be adjacent to the left ventricle and atrium ( Figure 1A ). 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 ).
case_images: (A) Mildly enhanced axial CT image showing the large heterogenous left pericardial mass. There was a slight pericardial effusion. (B) Enhanced CT image of the coronal reconstruction showing the tumor circumscribing the ascending aorta, the superior vena cava, and the pulmonary artery. (C) CT image of the sagittal reconstruction showing the mass invading the pericardium, which presented uneven thickening andnodular changes.
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case_images: After the injection of contrast medium, the solid composition and septa of the tumor were slightly enhanced ( Figure 2 ).
case_images: (A, B) Histopathological examination of the tumor tissue samples showing the fascicles of the spindle cells, (C) Fluorescence in situ hybridization demonstrating a separated red and green signal pattern indicative of an SS18 (SYT) gene rearrangement.
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case_images: 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 ). 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 ).
case_images: (A) CT enhanced image after six cycles of chemotherapy showing that the tumor has significantly regressed (white short arrow).
  (B) CT enhanced image tumor recrudescence in the contralateral pericardial cavity (white long arrow). (C) CT enhanced image showing a slight reduction in the size of the primary and secondary tumors. This image was acquired after the recurrent tumor was treated with eight cycles of chemotherapy.
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case_images: After six cycles of chemotherapy, the tumor had significantly shrunk, which was very well observed via CT imaging ( Figure 4A ). 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 ). 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.