Huge Chiari Network in the Right Atrium Diagnosed as Thrombosis - Case Report and a Brief Review.

The Chiari network is a common benign finding usually found incidentally in the right atrium (RA). This lesion frequently coexists with patent foramen ovale (PFO). Although the Chiari network is diagnosed easily and has no clinical importance, sometimes, the accurate diagnosis becomes hard and the lesion itself, or with PFO, can lead to clinical events. Accordingly, cardiologists should consider the Chiari network and its differential diagnosis in the evaluation of RA masses. Copyright:

INTRODUCTION

The Chiari network and the eustachian valve are usually found in the right atrium (RA) through echocardiography and cardiac magnetic resonance (CMR) imaging as accidental findings.[1] The Chiari network is a congenital remnant of inferior vena cava (IVC) orifice in the RA and the Thebesian valve in the orifice of the coronary sinus.[2] The Chiari network is a mobile and network-like mass that is seen in about 3% of the normal adult population.[34] Although the Chiari network is assumed as a benign finding, it may cause infective endocarditis, arrhythmias, and catheter entrapment when undertaking right heart catheterization or other procedures where catheter should be placed in the RA (such as catheter ablation of the accessory pathway, etc.) or the right ventricle (such as implantable cardioverter-defibrillator implantation).[56] Furthermore, it is a known nidus of thrombosis formation which may cause cerebrovascular accident (CVA) in the case of patent foramen ovale (PFO) existence by paradoxical emboli migrating from RA to the left atrium (LA) and systemic circulation.[6] The Chiari network frequently coexists with a PFO (in about 80% of cases) and an atrial septal aneurysm (in about 20% of cases). However, it is not necessary to prescribe prophylactic anticoagulant or antiplatelet for CVA prevention in a patient who had not any history of CVA or transient ischemic attack (TIA) even if a large PFO exists.[789] Some experts believe the Chiari network acts as a filter for thrombosis entrapment and prevents pulmonary and systemic embolization in some cases rather than a site for thrombus formation.[1]

CASE REPORT

A 53-year-old man without a remarkable past medical history was a candidate for nasal septoplasty. He had a sinus rhythm without any abnormalities. For preoperation workups, he underwent transthoracic echocardiography which demonstrated a suspicious mass in the RA [Figure 1 and Videos 1 and 2] and evidence of a PFO due to transseptal bubble passage from the RA to the LA after injection of 10 cc agitated saline as a contrast agent [Figure 2 and Video 3]. Since the patient was considered to have RA thrombosis, 20 mg of rivaroxaban was prescribed. For more evaluation, he underwent transesophageal echocardiography (TEE) which showed a large (about 8 cm length), thick, hypermobile, and filamentous-like mass in the RA. The mass was attached to the anterior of the IVC-RA junction and the inferior part of interatrial septum (IAS) which looped around the RA and protruded to the RV during diastole. These findings were mostly compatible with the existence of the Chiari network, but the clot formation should be considered too. Another important finding was a large PFO (width = 4 mm and length = 15 mm) with a left-to-right shunt. The other findings included a redundant IAS, mild tricuspid, pulmonary and mitral regurgitation, normal pulmonary arterial pressure (23 mmHg), normal IVC size with good collapse, normal RV and LV size and function, and normal biatrial size. The patient had not had any CVAs (neither CVA nor TIA) or venous thromboembolism (VTE) and did not have any signs of endocarditis; however, due to TEE suggestion, the patient was scheduled for performing CMR. The CMR finding was inconclusive and the existence of a clot could not be ruled out [Figure 3]. The patient continued rivaroxaban consumption, and after a month, he came for follow-up echocardiography which revealed no change in the mass' feature in comparison to the previous echocardiography [Video 4], thus, the anticoagulation therapy was discontinued. At 6-month follow-up, the patient remained asymptomatic and we did not detect any advancement in echocardiography.

Figure 1

Huge Chiari network in the right atrium in transthoracic echocardiography apical 4-chamber view

Figure 2

Transseptal bubble passage after agitated saline injection

Figure 3

Cardiac magnetic resonance study for right atrium mass evaluation

Management of the Chiari network and patent foramen ovale coexistence in asymptomatic and symptomatic patients

A prophylactic anticoagulant or an antiplatelet is not indicated in patients who did not have a history of TIA or CVA. However, it is a well-recognized issue that an aneurysmal IAS increases the risk of paradoxical embolism from a PFO. Hence, in the case of VTE in a patient who already has had a PFO and aneurysmal IAS, there would be a significant risk for left circulation embolism. Since a small deep-vein thrombosis may cause a catastrophic CVA, physicians must be cautious for VTE detection in such high-risk patients. In the left circulation thromboembolism such as CVA and TIA, if a patient has a PFO, it must be classified as a PFO-related embolism instead of a cryptogenic embolism. However, together with the treatment, other causes of embolisms such as atrial fibrillation (AF) rhythm should be evaluated. The novel criteria of risk of Paradoxical Embolism (RoPE score) could determine whether a PFO has played a role in CVA. Treatment methods of PFO-related CVA are controversial. Some guidelines advise using antiplatelet agents for secondary prevention, but the newer approaches mostly insist on the superiority of oral anticoagulants. Considering secondary prevention, PFO closure has not been well-established as an absolute effective procedure, but it must be considered in high-risk patients. In addition, a PFO closure might prevent AF rhythm from happening which is another cause of the left circulatory embolism.[789]

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The authors declare that all appropriate patient consent forms are obtained. The patient agreed to publish his images and his clinical information without mentioning his name.

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Conflicts of interest

There are no conflicts of interest.