B64-13 Know Normal: Chiari Network Masquerading as Right Heart Thrombus

Introduction Right atrial thrombus is a rare but potentially fatal finding often associated with pulmonary embolism. Its presence may prompt urgent thrombolytic therapy or surgical intervention, both of which carry significant bleeding risk. However, certain benign intracardiac structures can mimic thrombi on imaging, leading to diagnostic uncertainty. One such variant, the Chiari network, is a filamentous embryologic remnant found in up to 4% of the population. Although typically asymptomatic, it can appear as a filling defect on imaging, particularly on computed tomographic angiography (CTA), and be mistaken for a thrombus. Differentiating this normal variant from true pathology is critical to prevent unnecessary and potentially harmful interventions. Case A 66-year-old woman with a history of congestive heart failure, diabetes mellitus, metastatic breast cancer, cerebrovascular accident, deep vein thrombosis, chronic thrombocytopenia, and tobacco use presented with progressive dyspnea and lower extremity edema. CTA of the chest revealed a right pulmonary artery embolism and a non-enhancing filling defect in the right ventricle concerning for a thrombus. Transthoracic echocardiography showed severely reduced left ventricular systolic function (EF 10-15%) and identified a prominent Chiari network in the right atrium, with no thrombus visualized (Image 1). The previously noted filling defect was attributed to the normal moderator band. The patient received anticoagulation for pulmonary embolism but was spared thrombolytic therapy after re-evaluation of imaging findings. She improved clinically with oxygen and diuresis and was discharged on apixaban with outpatient cardiology follow-up. Discussion This case illustrates a potentially dangerous mimic of right atrial thrombus. The Chiari network, a benign embryologic remnant of the sinus venosus valve, can present as a mobile intracardiac structure on imaging and be misinterpreted as a thrombus, tumor, or vegetation. Echocardiography, particularly transesophageal imaging, is the diagnostic modality of choice for distinguishing these entities. Accurate recognition of a Chiari network can prevent unnecessary thrombolytic therapy, surgical intervention, or prolonged hospitalization. Clinicians should maintain awareness of this normal variant when interpreting cardiac imaging, particularly in patients with concomitant pulmonary embolism or intracardiac filling defect This abstract is funded by: None