On admission, transthoracic echocardiography found a 4.5-cm × 5-cm space-occupying lesion in the right atrial chamber (see Figure 1A ). Color Doppler showed no intralesional blood flow ( Figure 1B ), raising the suspicion of a thrombus or tumor.

During hospitalization, the laboratory results of the patient were as follows: cardiac troponin T (cTNT), 0.022 ng/ml; B-type natriuretic peptide (NT-proBNP), 3,022 pg/ml; creatine kinase (CK), 82 U/L; creatine kinase–myocardial band (CK-MB), 15 U/L; serum creatinine (SCr), 74 μmol/L; uric acid (UA), 433 μmol/L; Na⁺, 138 mmol/L; K⁺, 4.7 mmol/L;Ca²⁺, 2.14 mmol/L; fasting blood glucose (FBG), 5.5 mmol/L; HbA1c, 6.5%; hemoglobin (Hb), 125 g/L; red blood cell (RBC), 5.83 × 10⁹/L; D-dimer, 0.65 g/L; and erythrocyte sedimentation rate (ESR), 19 mm/h. The viral antibody screening and tumor markers were negative. Physical examination revealed no jugular vein distension. The thoracic cage was symmetrical, the intercostal spaces were normal, the bilateral respiratory movements were consistent, and tactile fremitus was symmetrical. The breath sounds in both lungs are clear, with a few fine moist rales in the lower lobes of both lungs. The precordial region had no prominence, the cardiac dullness border was not enlarged, heart rhythm was irregular, no murmur was heard at the apex of the heart, and no thrill was detected. No enlargement of the superficial lymph nodes was detected.

To further evaluate the mass, cardiac magnetic resonance imaging (MRI) (3.0T Ingenia, Philips, Best Netherlands) was performed. The imaging protocol included pre-contrast black blood turbo spin echo T1-weighted imaging (T1WI), T2-weighted imaging (T2WI), T2 fat saturation (short-tau inversion recovery, STIR), and retrospective ECG-triggered balanced turbo field echo (steady-state free precession, SSFP) sequences. The sequences were oriented on the short and long axes (two-, three-, and four-chamber views of the heart). MRI showed a roundish mass in the RA with clear margins and broad-based attachment to the anterior/posterior walls. Adjacent RA wall thickening and edema, as well as narrowing of the inferior vena cava (IVC) inlet, were observed ( Figures 1C–F ). The SSFP sequence showed that the mass protruded into the tricuspid orifice during atrial systole (causing secondary tricuspid regurgitation) and returned to the RA during diastole. First-pass perfusion demonstrated homogeneous progressive enhancement of the mass, while the late gadolinium enhancement (LGE) showed patchy irregular enhancement ( Figures 1G, H ). To better highlight the key features in the figures, arrows and brief descriptions have been added to indicate the location of the mass, wall thickening, and other important signs.

Surgery and pathology: The patient underwent open-chest surgery on September 5, 2023. Intraoperatively, the RA was of normal size, containing a 3.0-cm × 5.0-cm mass with a smooth contour, broad-based pedicle, and minimal mobility. The neoplasm infiltrated the anterior/posterior RA walls, the superior vena cava (SVC) orifice, and the interatrial sulcus, with marked fibroedematous thickening of the involved tissues. The boundary between the tumor and the right atrial appendage and SVC ostium was ill-defined. The sinoatrial (SA) nodal complex and the surrounding adipose tissue were fibrosed and invaded. The tricuspid annulus was of normal size with trace regurgitation.

Pathological examination showed a 6.0-cm × 6.0-cm × 2.5-cm mass from the RA, partially encapsulated, with a tan-red to tan-white, solid, soft, and lobulated cut surface. The margin of the mass had a relatively intact capsule with focal areas of infiltration into adjacent tissues. Microscopy revealed diffuse sheets of atypical lymphocytes with a high nuclear-to-cytoplasmic ratio, large-to-medium pleomorphic cells with round to irregular nuclei, open chromatin, prominent nucleoli, and frequent mitotic figures (up to 20/10 high-power fields) ( Figure 2A ). The cytoplasm was scant to moderate, eosinophilic, and indistinct at the borders. A fibroedematous background was present within the mass, scattered with small lymphocytes ( Figure 2B ). Immunohistochemical staining showed diffuse positivity for CD20 and CD79a and focal positivity for MUM1 (50%+), C-myc (40%+), and BCL-2 (90%). The Ki-67 proliferation index was approximately 90%. The T-cell markers (CD3 and CD5), germinal center-associated markers (CD10 and BCL-6), epithelial markers (CK and EMA), EBV (Epstein–Barr virus-encoded small RNA, EBER), and immature lymphoid markers (CD99 and CD34) were negative. Clonal gene rearrangement studies of the IGH, IGλ, and IGλ genes were performed with polymerase chain reaction (PCR).

During the re-examination 2 months after surgery, the patient was found to have cardiac enlargement and pericardial effusion, with no recurrence in the surgical area ( Figure 1I ). However, the patient’s cardiac function showed progressive deterioration.

Most reported cases of PCL show hypervascularity on first-pass perfusion imaging (5). However, in our case, the mass presented with homogeneous progressive enhancement, which is an atypical finding. This difference may be related to the microvascular structure and cellular composition of the tumor. The fibroedematous background observed in the pathological results may have affected the distribution and enhancement pattern of the contrast agent, resulting in this unique imaging feature. Further research on the correlation between pathology and imaging in PCL is needed to better understand such differences.

The initial misdiagnosis of this case as cardiac myxoma can be attributed to several factors. Firstly, echocardiography has limitations in accurately differentiating tumors with similar morphological features. The lack of blood flow signals in the mass on color Doppler was not specific enough to rule out myxoma, as some myxomas may also have sparse blood supply. Secondly, the lack of awareness of the imaging features of PCL among clinicians led to insufficient consideration of this rare disease. In addition, the relatively nonspecific symptoms of the patient also contributed to the difficulty of early diagnosis. This emphasizes the importance of comprehensive imaging evaluation, in particular MRI, in differentiating primary cardiac tumors.

The patient in this case died 8 months after surgery, despite initial symptom improvement. Surgical resection alone may not be sufficient for PCL, as it is a highly aggressive tumor. Chemotherapy is considered the cornerstone of treatment for PCL. The patient’s refusal of further chemotherapy likely had a significant negative impact on the prognosis. Studies have shown that combined chemotherapy regimens can improve the survival rate of patients with PCL. This case highlights the need for clinicians to fully communicate the importance of chemotherapy with patients and explore more effective treatment strategies, such as the combination of surgery, chemotherapy, and targeted therapy, to improve the prognosis of patients with PCL.

Cardiac myxoma, angiosarcoma, and malignant lymphoma are among the most common primary neoplasms of the heart in adults (6). The patient in this case was misdiagnosed as myxoma, the most common benign tumor of the atrium. The myxoma originated from the atrial septal fossa ovale with a pedicled, irregular shape, calcification, and bleeding. It showed high signal on T2WI, low perfusion on perfusion imaging, and obvious enhancement on LGE.

Angiosarcoma of the heart occurs mostly in the right atrium (>90%), with slightly high signal on T2WI, no enhancement in first-pass perfusion, but obvious enhancement in the delayed phase. Internal bleeding and necrosis of the mass can form polymorphic “cauliflora” changes, and “solar ray” manifestations can occur when the mass invades the pericardium (7).

As demonstrated in this case, MRI provides detailed information about the tumor’s location, size, relationship with adjacent structures, and tissue characteristics. The ability to show the invasion of the right atrial wall and IVC inlet, as well as the unique enhancement patterns, helps in the differentiation of PCL from other cardiac tumors, reducing the misdiagnosis rate. Moreover, MRI can guide the selection of biopsy sites, ensuring that representative tumor tissues are obtained for accurate pathological diagnosis. In the treatment planning stage (8), MRI can also be used to evaluate the response to chemotherapy (9), providing valuable information for adjustment of treatment strategies.