Right atrial thrombus-in-transit initially suspected as myxoma in a patient with acute pulmonary embolism: A case report

Abstract

A 60-year-old man presented with sudden syncope, chest pain, and dyspnea. Transthoracic echocardiography at a local hospital suggested a right atrial myxoma, and he was referred for emergency treatment. On admission, markedly elevated D-dimer and cardiac troponin I levels were accompanied by severe hypoxemia. Intraoperative transesophageal echocardiography showed a large, highly mobile, cord-like right atrial mass without a definite pedicle. Because of the patient’s critical condition, emergency surgical thrombectomy and pulmonary embolectomy under cardiopulmonary bypass were undertaken, revealing right atrial thrombus-in-transit with partial incarceration through the foramen ovale into the left atrium and extensive pulmonary emboli. Histopathological examination confirmed thrombus, and postoperative ultrasonography demonstrated deep venous thrombosis in the right lower extremity. The patient recovered well with anticoagulation. This case highlights that right atrial thrombus-in-transit may mimic myxoma on echocardiography and should be strongly suspected when a right atrial mass is accompanied by severe hypoxemia and other findings suggestive of acute pulmonary embolism.

Introduction

Mobile thrombotic material in the right heart is uncommon but clinically important because it may indicate active embolic transit and impending hemodynamic compromise. ¹ In practice, diagnostic difficulty arises when an intracardiac mass has imaging features that overlap with those of a tumor, particularly myxoma.^{2 –6} We describe a patient in whom an apparently tumorous right atrial lesion was ultimately shown to be thrombus associated with pulmonary embolism. The case underscores the importance of interpreting echocardiographic findings in the context of the patient’s acute physiological instability.

Case presentation

A 60-year-old man was transferred to The First Affiliated Hospital of Wannan Medical University (Yijishan Hospital), Wuhu, Anhui, China, in November 2019, from Guangde County Hospital because of sudden syncope with chest pain and chest tightness for more than 3 days. Transthoracic echocardiography performed at the referring hospital demonstrated an abnormal hyperechoic mass in the right atrium, and right atrial myxoma was initially suspected. He was transferred to our institution on the same day for further management and was admitted at 11:38 on November 15, 2019, with a provisional diagnosis of atrial mass. The patient had no known history of major cardiovascular disease or other significant comorbidities. No documented preoperative history of lower-extremity swelling or pain, prolonged immobilization, long-distance travel, or prior venous thromboembolism was present. The reporting of this study conforms to CARE guidelines. ⁷

On admission, his heart rate was 93 beats/min, respiratory rate was 18 breaths/min, and blood pressure was 142/90 mmHg. Laboratory investigations showed a markedly elevated D-dimer level of 39.63 μg/mL and a cardiac troponin I level of 1.82 ng/mL. Arterial blood gas analysis demonstrated severe hypoxemia, with a partial pressure of oxygen of 59 mmHg, a base excess of −3.7 mmol/L, and a lactate level of 1.7 mmol/L.

After induction of anesthesia, transesophageal echocardiography revealed a large, mobile, cord-like mass in the right atrium that partially prolapsed into the right ventricle during the cardiac cycle (Figure 1 and Supplemental Video 1). No definite pedicle arising from the interatrial septum or atrial wall was identified, making a neoplastic diagnosis less convincing. Because the patient’s oxygen saturation dropped abruptly and remained around 50% despite ventilation with 100% oxygen, only an emergency echocardiographic assessment could be completed. No contrast echocardiography or contrast Doppler study was performed, and additional imaging studies, including computed tomography pulmonary angiography and cardiac magnetic resonance imaging, were considered unsafe and unlikely to change the immediate need for intervention. Emergency surgery was therefore undertaken without delay. The operation started at 14:06 on November 15, 2019.

Figure 1.

Transesophageal echocardiography. (a) A mobile echogenic mass is visible in the right atrium (red arrow). (b) The mass appears elongated and highly mobile during the cardiac cycle (red dotted line).

A median sternotomy was performed, and cardiopulmonary bypass was established through the ascending aorta and the superior and inferior venae cavae. After the right atrium was opened, two long, cord-like thrombi were identified within the right atrial cavity; when placed together, the total length of the extracted thrombotic material was approximately 30 cm (Figure 2(a)). Part of the thrombotic material was found to be incarcerated through the foramen ovale into the left atrium. The atrial septum was opened to allow full exploration of the left atrium, where no free thrombus was found, and the incarcerated thrombotic material was removed. Further exploration along the thrombotic tract revealed residual thrombus attached to the subtricuspid valvular apparatus.

Figure 2.

Intraoperative findings. (a) Two long cord-like thrombi removed from the right atrium. (b) Large amounts of thrombotic material extracted from the main and bilateral pulmonary arteries.

The operative findings indicated that the mass was thrombotic rather than neoplastic. Because the extent and configuration of the lesion suggested associated pulmonary embolism, the main pulmonary artery and left pulmonary artery were opened, revealing a large amount of thrombotic material within the arterial lumen (Figure 2(b)). Repeated thrombectomy and irrigation were performed. The right pulmonary artery was then exposed posterior to the superior vena cava and opened, and additional thrombotic material was removed. After careful extraction, no obvious residual thrombus was identified in the distal pulmonary arterial branches on direct inspection. The operation ended at 18:00 on November 15, 2019.

The total cardiopulmonary bypass time was 103 min, and the aortic cross-clamp time was 53 min. Histopathological examination confirmed thrombotic material without evidence of myxoma (Figure 3). The patient required ventilatory support for 13 h postoperatively and remained in the intensive care unit for 2 days. He was transferred to the ICU on the day of surgery, returned to the general ward on November 18, 2019, and was discharged on November 27, 2019. During postoperative intensive care, lower-extremity vascular ultrasonography performed on November 16, 2019 demonstrated right lower-extremity deep venous thrombosis, involving the mid superficial femoral vein, popliteal vein, posterior tibial vein, and intramuscular veins, as well as bilateral great saphenous vein dilatation/varicosity-related changes. Anticoagulation with warfarin was initiated after surgery. Computed tomography pulmonary angiography performed 11 days postoperatively showed satisfactory clearance of the pulmonary arterial thrombi (Figure 4 and Supplemental Video 2). No inferior vena cava filter was placed, because current guideline-based recommendations generally reserve filter placement for selected patients with venous thromboembolism, particularly when anticoagulation is contraindicated or recurrent embolization occurs despite adequate therapy.^8,9 In the present patient, the early postoperative phase after cardiac surgery did not preclude anticoagulation; there was no contraindication to anticoagulation, and there was no clear indication mandating filter placement. High-resolution chest computed tomography obtained 2 years later demonstrated no residual thrombus in the pulmonary arteries (Supplemental Video 3). The key chronological events of the patient’s presentation, treatment, and follow-up are summarized in Table 1.

Figure 3.

Histopathological examination showing thrombotic material without evidence of myxoma. (A, B) Representative hematoxylin and eosin-stained sections showing thrombotic material without histopathological evidence of myxoma. Original magnification ×100.

Figure 4.

Postoperative computed tomography pulmonary angiography obtained 11 days after surgery showing satisfactory clearance of pulmonary arterial thrombi. All patient-identifying information has been removed from the image.

Table 1.

Clinical timeline.

Time	Clinical events
>3 days before admission	Sudden syncope accompanied by chest pain and chest tightness
Same day as transfer	The patient first presented to Guangde County Hospital, where transthoracic echocardiography suggested a right atrial mass and right atrial myxoma was initially suspected
November 15, 2019, 11:38	Admitted to The First Affiliated Hospital of Wannan Medical University (Yijishan Hospital), Wuhu, Anhui, China
November 15, 2019, after admission	Laboratory tests showed markedly elevated D-dimer and cardiac troponin I levels; arterial blood gas analysis demonstrated severe hypoxemia
November 15, 2019, after induction of anesthesia	Transesophageal echocardiography revealed a large, highly mobile, cord-like right atrial mass without a definite pedicle
November 15, 2019, 14:06	Emergency surgical thrombectomy and pulmonary embolectomy under cardiopulmonary bypass were started
November 15, 2019, intraoperatively	Right atrial thrombus-in-transit with partial incarceration through the foramen ovale into the left atrium and extensive pulmonary emboli were identified and removed
November 15, 2019, 18:00	Surgery was completed, and the patient was transferred to the ICU postoperatively
November 16, 2019	Lower-extremity vascular ultrasonography demonstrated right lower-extremity deep venous thrombosis
November 18, 2019	Returned to the general ward
November 26, 2019	Computed tomography pulmonary angiography showed satisfactory clearance of the pulmonary arterial thrombi
November 27, 2019	Discharged in stable condition with anticoagulation therapy
2 years after surgery	High-resolution chest computed tomography showed no residual pulmonary arterial thrombus

Discussion

The main diagnostic challenge in this case was distinguishing thrombus from myxoma before surgery. Although myxomas most often arise from the interatrial septum and are typically attached by a pedicle, thrombi may appear elongated, serpiginous, or extremely mobile, especially when they represent embolic material passing through the right heart.^{2 –6} In the referring hospital, the initial suspicion of myxoma was based on the presence of a right atrial intracavitary mass on transthoracic echocardiography under emergency conditions, without complete characterization of its attachment and dynamic morphology. However, after transfer to our institution, intraoperative transesophageal echocardiography demonstrated a large, highly mobile, cord-like mass without a definite pedicle arising from the interatrial septum or atrial wall. Together with the acute presentation, severe hypoxemia, markedly elevated D-dimer level, and the eventual intraoperative finding of extensive pulmonary emboli, these features strongly favored thrombus-in-transit rather than a benign primary cardiac tumor.

Another important issue was whether additional imaging should have been pursued before intervention. In stable patients, multimodality imaging can improve tissue characterization and assist differential diagnosis.^2,3 In the present patient, however, oxygen saturation deteriorated abruptly, and even after induction of anesthesia, it remained around 50% despite ventilation with 100% oxygen. Under these circumstances, only an emergency echocardiographic assessment could be completed. No contrast echocardiography or contrast Doppler study was performed, and further imaging studies such as computed tomography pulmonary angiography or cardiac magnetic resonance imaging were considered unsafe and unlikely to alter the urgent need for surgery. Therefore, transesophageal echocardiography, together with the overall clinical picture, provided sufficient justification for immediate operative treatment.^10,11

Management of right-sided intracardiac thrombus must be individualized according to thrombus mobility, embolic burden, hemodynamic status, contraindications to thrombolysis, and available expertise.^11,12 In the present case, surgery was chosen because the patient had thrombus-in-transit with severe physiological compromise, reflected by severe refractory hypoxemia, markedly elevated D-dimer and cardiac troponin I levels, and extensive pulmonary arterial obstruction confirmed intraoperatively. The indication for surgery was therefore not merely the presence of a right atrial mass, but the combination of a highly mobile intracardiac thrombus, critical gas-exchange impairment, and a substantial risk of further embolization and sudden deterioration. Surgery also permitted direct clearance of thrombotic material, relief of foramen ovale involvement, and pathological confirmation of the diagnosis.

The postoperative findings further strengthened the mechanistic interpretation of the case. Although no documented preoperative symptoms such as lower-extremity swelling or pain were present, postoperative lower-extremity vascular ultrasonography performed on November 16, 2019 demonstrated right lower-extremity deep venous thrombosis involving the mid superficial femoral vein, popliteal vein, posterior tibial vein, and intramuscular veins. These findings strongly supported the conclusion that the right atrial lesion represented thrombus-in-transit rather than a primary cardiac mass.^1,13 The histopathological findings were also consistent with thrombotic material and, when interpreted together with the intraoperative findings and clinical presentation, further supported the diagnosis of thrombus-in-transit rather than myxoma. Taken together, venous thrombosis, migration through the right heart, and pulmonary arterial obstruction provided a coherent explanation for both the intraoperative findings and the patient’s presentation.

In summary, a right atrial mass should not be assumed to be myxoma solely on the basis of echocardiographic appearance. When such a lesion is seen in a patient with syncope, severe hypoxemia, and evidence suggestive of acute pulmonary embolism, right atrial thrombus-in-transit should be strongly considered.^1,13 In these high-risk circumstances, prompt emergency surgical thrombectomy and pulmonary embolectomy under cardiopulmonary bypass may be both diagnostically decisive and therapeutically lifesaving.^8,9

Supplemental Material