Paradoxical Embolism Through Patent Foramen Ovale: A Case Report of Thrombus in Transit

Introduction

The presence of entrapped thrombus within a patent foramen ovale (PFO) is a rare and potentially life-threatening condition. A PFO is an embryological remnant that persists in approximately 25% of the adult population [1]. Although most individuals remain asymptomatic, PFO can become clinically significant in the presence of venous thromboembolism or elevated right atrial pressure, allowing embolic material to travel through an intracardiac defect into systemic circulation – a paradoxical embolus, resulting in systemic thromboembolic events [1,2]. Diagnosis is often incidental during echocardiographic evaluation, but in patients with unexplained systemic embolism or cryptogenic stroke, targeted assessment is warranted. Management can include medical therapy, percutaneous device closure, or surgical repair [1]. We herein describe a patient with extensive bilateral pulmonary embolism with paradoxical cerebral thromboembolism due to thrombus-in-transit via a PFO. This case highlights the importance of prompt recognition of concomitant venous and systemic thromboembolic phenomena, as well as the need for timely intervention, to mitigate the risks of catastrophic embolic events.

Case Report

A 41-year-old woman was brought to the Emergency Department following a syncopal episode resulting in a head injury, with brief expressive aphasia noted on waking. This occurred on the background of elective varicose vein stripping 2 weeks earlier. She was noted to have hypoxia on room air (SaO2 86% on room air, improving with supplemental oxygen) and tachycardia (sinus rhythm 110 bpm), but her blood pressure was normal (112/87 mmHg). Cardiopulmonary and neurological examinations were unremarkable, although the right calf was notably tender and swollen, compared with the left.

Her relevant past medical history included obesity (body mass index 35.9 kg/m2) and previous superficial venous thrombosis involving the right greater saphenous vein, extending to the saphenofemoral junction, 12 months earlier. She was treated with rivaroxaban, but she had discontinued it herself, believing it was no longer required. She had no known hypercoagulable disorders, was a non-smoker, consumed minimal alcohol, and was taking no regular medications.

Electrocardiogram on admission revealed sinus tachycardia, with isolated T-wave inversion in lead III. Computed tomography pulmonary angiography performed urgently revealed a saddle embolus extending into bilateral lobar, segmental and subsegmental pulmonary branches, with features of right ventricular (RV) strain (Figure 1). Therapeutic enoxaparin was commenced for management of pulmonary embolism. Due to the head injury, a non-contrast head computed tomography (CT) was performed, revealing patchy bifrontal cerebral contusions without significant regional mass effect. CT cerebral angiogram was normal. A subsequent brain magnetic resonance imaging (MRI) scan performed for further review of cerebral contusions, revealed multiple small areas of infarction within the left insular, superior and middle temporal gyri, with petechial haemorrhagic transformation (Figure 2). Enoxaparin was withheld due to concerns regarding the risk of worsening intracerebral hemorrhage.

Further investigation with lower extremity vascular ultrasound showed extensive deep vein thrombosis involving the right popliteal, peroneal, soleal and medial gastrocnemius veins. A transthoracic echocardiogram identified a large (approximately 4 cm) highly mobile mass prolapsing through the mitral valve into the left ventricle (LV). The left atrium appeared normal in size. There was also moderately elevated pulmonary artery systolic pressure (53 mmHg), and evidence of RV dilatation with impaired RV contraction. Given the context of extensive PE, the left-sided mass was thought most likely to represent a thrombus-in-transit through a PFO.

The anticoagulation strategy was changed to intravenous unfractionated heparin due to its immediate reversibility. Following a multidisciplinary discussion, the patient was referred for urgent cardiac surgery as an alternative to systemic thrombolysis, given recent head trauma and evidence of embolic stroke with associated hemorrhagic changes. Intraoperative transoesophageal echocardiography confirmed a large thrombus traversing the PFO (Figures 3, 4). The patient subsequently underwent emergent pulmonary embolectomy, atrial thrombectomy, and PFO closure. Cardiopulmonary bypass was established, and following cardioplegic arrest of the heart, the thrombus was carefully extracted from the right atrium, visibly emerging through the PFO. This confirms its role as a pathway for paradoxical embolization. Additional thrombi were extracted from incisions made in the main pulmonary artery and bilateral pulmonary branches, resulting in a marked improvement in the patient’s pulmonary pressures. Histopathological analysis confirmed the extracted material to be of blood clot. The patient’s condition was stable following the operation, and unfractionated heparin infusion was recommenced. Postoperative transthoracic echocardiogram confirmed normalization of pulmonary artery systolic pressure, reduction in RV cavity size, improved RV contraction, and no residual cardiac thrombus or interatrial shunt. The patient recovered well and was discharged home on postoperative day 8 with oral apixaban 5 mg twice daily.

At the 6-week outpatient follow-up, she remained well with no residual cardiac or neurological sequelae. Three months follow-up Doppler ultrasound showed partial resolution of the lower leg deep vein thrombosis, and ventilation/perfusion scanning showed resolution of pulmonary embolism. The patient was continued on lifelong anticoagulation therapy, with regular cardiology and hematology follow-ups for monitoring anticoagulation efficacy and potential complications, alongside counseling on medication adherence and lifestyle modifications to prevent recurrent thromboembolic events.

Discussion

This case highlights the need to consider thrombus-in-transit across a PFO in patients presenting with simultaneous pulmonary and systemic emboli, particularly after recent surgery. In our patient, paradoxical embolism occurred secondary to elevated right atrial pressure resulting from extensive PE, causing right-to-left intracardiac shunting through the patent PFO. Entrapped thrombus within a PFO is a rare and potentially life-threatening condition. A systematic review by Kalangos et al identified 174 patients with such presentation over a 44-year period, reporting an overall mortality rate of 18%, with 66% of these deaths occurring within 24 h [3].

Therapeutic management of such cases requires a delicate balance between thrombus resolution and prevention of embolic complications. Treatment options include systemic anticoagulation, thrombolysis, and cardiac thrombectomy combined with PFO closure [3,4]. Given the scarcity of reported cases, consensus treatment guidelines have yet to be established. A review by Seo et al found that surgery lowers the incidence of post-treatment embolic events and 60-day mortality, compared with conservative treatment [4]. There have been conflicting reports regarding the effectiveness of thrombolytic therapy. One systematic review found that thrombolytic therapy used in patients with trapped thrombus within a PFO was linked to higher mortality rates [4], whereas a 34-year review by Rose et al found lower mortality with thrombolysis, compared with surgery [5]. Nonetheless, due to its theoretically greater risk of causing clot fragmentation, thrombolysis remains the preferred treatment approach for patients who have greater hemodynamic compromise, which may have contributed to the differences in reported mortality. In the present case, we decided against proceeding with thrombolysis, due to the heightened risk of hemorrhagic transformation following the recent cardioembolic stroke and head injury.

Percutaneous catheter-directed therapies, which aim to deliver thrombolysis or perform mechanical clot extraction have emerged as a minimally invasive alternative for managing massive pulmonary embolism, especially for patients with high surgical risk. Kaymaz et al provide insights into the efficacy and safety of catheter-directed therapies, underscoring their role as effective alternatives in selected clinical settings [6]. However, they were not considered appropriate for this case due to the presence of a large, highly mobile intracardiac thrombus in our patient.

Similar cases in the literature further highlight the variability in clinical presentation and management of thrombus-in-transit. One young woman with bilateral pulmonary embolism and a thrombus traversing a PFO underwent thrombolysis after spontaneous thrombus disappearance during transoesophageal echocardiography; she recovered well, although delayed imaging revealed carotid artery thrombosis [7]. Conversely, another elderly woman with pulmonary embolism and stroke symptoms, deemed unfit for surgery, was successfully managed conservatively with unfractionated heparin [8]. Compared with these cases, our decision for urgent surgical intervention was driven by the thrombus size, mobility, and contraindications for thrombolysis. Collectively, these examples reinforce the need for a tailored approach guided by multidisciplinary collaboration.

Conclusions

This case underscores the importance of early diagnosis in patients with paradoxical embolism through PFO. It also highlights the value of timely, team-based decision-making to significantly improve patient outcomes and help minimise the serious morbidity and mortality associated with this condition. Further research and clinical experience are needed to guide best practice and develop clear, management guidelines.