Abstract/Description
INTRODUCTION: Chiari networks are reticulated networks of fibers that result from incomplete reabsorption of the right valve of the sinus venosus. While the true clinical significance of these is currently unknown, there are associations with dysrhythmias, paradoxical emboli, and thrombi formation. Here, we describe a large, incidentally found Chiari network which encompasses most of the right atrium.
CASE: A 42-year-old female with a past medical history of obesity (BMI 58) and well-controlled asthma presented to the emergency department in respiratory distress with hypercapnia and hypoxemia. Computed tomography (CT) with angiography of the chest was performed and did not show a pulmonary embolism, but an abnormal filling defect was seen in the right atrium. She was intubated due to worsening respiratory failure and admitted to the intensive care unit. While undergoing empiric treatment for asthma exacerbation, a transthoracic echocardiogram was performed and demonstrated an enlarged right atrium with a mobile structure that was absent on previous echocardiograms. The patient was liberated from the ventilator and transferred out of the intensive care unit. A cardiac magnetic resonance imaging (cMRI) scan was done and showed evidence of a dense filamentous mass in the right atrium consistent with a Chiari network. Unfortunately, she was not able to tolerate the contrast portion of the cMRI to better visualize the findings. She was discharged from the hospital with plans for routine follow up.
DISCUSSION: The Chiari Network, first described by Austrian pathologist Hans Chiari in 1897, is a mesh of thread-like strands which results from the failure of reabsorption of the sinus venosus. Developmentally, the right valve of the sinus venosus evolves into the Eustachian valve (valve of the inferior vena cava) and Thebesian valve (valve of the coronary sinus) and as these valves involute, the tissue undergoes fenestration which can leave a network of the remnants. Usually, they are first diagnosed by echocardiography, where the network presents as a mobile, highly reflective echotexture within the right atrium. On CT, Chiari networks may be visualized as a lace-like filling defect in the right atrium, however there is often diagnostic uncertainty due to heterogeneity of contrast enhancement in the right atrium as seen in our case. This is likely due to the atypical size and density of our patient’s Chiari network compared to the more usual, lace-like appearance. MRI is quickly becoming a complimentary method of differentiating types of right atrial pathologies. Typically, the Chiari network is discovered incidentally and itself does not pose major clinical significance aside from diagnostic challenges on imaging studies where misdiagnosis as thrombus, tumor, or vegetation can occur. The Chiari network has small associations with patent foramen ovales, thromboembolism formation, infective endocarditis, and supraventricular tachycardia. Rarely, the Chiari network can protrude into the right ventricle and cause clinically significant tricuspid regurgitation.
CONCLUSION: The Chiari network is an uncommon anatomical variant which should be recognized appropriately to prevent misdiagnosis. Diagnosis is most often made by echocardiography; however cardiac MRI can also be useful if there is uncertainty. While the Chiari network has no inherent clinical significance, clinicians must be aware of the associations with thromboembolism, infective endocarditis, and tachydysrhythmias.
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A Diagnostic Dilemma Due to a Large Chiari Network
INTRODUCTION: Chiari networks are reticulated networks of fibers that result from incomplete reabsorption of the right valve of the sinus venosus. While the true clinical significance of these is currently unknown, there are associations with dysrhythmias, paradoxical emboli, and thrombi formation. Here, we describe a large, incidentally found Chiari network which encompasses most of the right atrium.
CASE: A 42-year-old female with a past medical history of obesity (BMI 58) and well-controlled asthma presented to the emergency department in respiratory distress with hypercapnia and hypoxemia. Computed tomography (CT) with angiography of the chest was performed and did not show a pulmonary embolism, but an abnormal filling defect was seen in the right atrium. She was intubated due to worsening respiratory failure and admitted to the intensive care unit. While undergoing empiric treatment for asthma exacerbation, a transthoracic echocardiogram was performed and demonstrated an enlarged right atrium with a mobile structure that was absent on previous echocardiograms. The patient was liberated from the ventilator and transferred out of the intensive care unit. A cardiac magnetic resonance imaging (cMRI) scan was done and showed evidence of a dense filamentous mass in the right atrium consistent with a Chiari network. Unfortunately, she was not able to tolerate the contrast portion of the cMRI to better visualize the findings. She was discharged from the hospital with plans for routine follow up.
DISCUSSION: The Chiari Network, first described by Austrian pathologist Hans Chiari in 1897, is a mesh of thread-like strands which results from the failure of reabsorption of the sinus venosus. Developmentally, the right valve of the sinus venosus evolves into the Eustachian valve (valve of the inferior vena cava) and Thebesian valve (valve of the coronary sinus) and as these valves involute, the tissue undergoes fenestration which can leave a network of the remnants. Usually, they are first diagnosed by echocardiography, where the network presents as a mobile, highly reflective echotexture within the right atrium. On CT, Chiari networks may be visualized as a lace-like filling defect in the right atrium, however there is often diagnostic uncertainty due to heterogeneity of contrast enhancement in the right atrium as seen in our case. This is likely due to the atypical size and density of our patient’s Chiari network compared to the more usual, lace-like appearance. MRI is quickly becoming a complimentary method of differentiating types of right atrial pathologies. Typically, the Chiari network is discovered incidentally and itself does not pose major clinical significance aside from diagnostic challenges on imaging studies where misdiagnosis as thrombus, tumor, or vegetation can occur. The Chiari network has small associations with patent foramen ovales, thromboembolism formation, infective endocarditis, and supraventricular tachycardia. Rarely, the Chiari network can protrude into the right ventricle and cause clinically significant tricuspid regurgitation.
CONCLUSION: The Chiari network is an uncommon anatomical variant which should be recognized appropriately to prevent misdiagnosis. Diagnosis is most often made by echocardiography; however cardiac MRI can also be useful if there is uncertainty. While the Chiari network has no inherent clinical significance, clinicians must be aware of the associations with thromboembolism, infective endocarditis, and tachydysrhythmias.