Chiari’s Network (CN) is a fairly rare defect that was first described by Hans Chiari  in 1897. In fetal life, the Eustachian valve, which normally regresses at 9–15 weeks of gestation, is located in the superior portion of the right sinus venosus and directs blood from the inferior vena cava toward the foramen ovale. Incomplete regression causes a persistent or prominent Eustachian valve. It can be determined by the presence of a thin ridge that arises from the anterior rim of the inferior vena cava orifice . If the Eustachian valve remnants involve a membrane of fine fenestrated fibers that is located in the right atrium, it is called CN [1,3,4,5].
CN is usually an incidental finding with no further clinical consequences. Usually it has no clinical significance. Nevertheless, a number of cases have been described with clinical pathology believed to be associated with the presence of CN [6,7,8,9]. It has been reported that it can cause thromboembolism, infective endocarditis, and dysrhythmias, and that it represents a physical barrier to invasive procedures . In light of this information, we aimed to study the prevalence of CN and whether it is associated with other congenital defects among our pediatric cardiology outpatient department records.
Material and Method
All patients who underwent cardiac examination and transthoracic echocardiography (TTE) at the pediatric cardiology outpatient department of our institution between April 2013 and April 2014 were included in the study. Routine M-mode, 2-D, and Doppler studies were applied. All co-existent lesions were recorded. Ratio between heights of early and late diastolic flow velocity peaks (E/A) were <1 in tricuspid and mitral valves considered as right and left ventricular diastolic dysfunctions respectively. CN was diagnosed by TTE, defined as a remnant originating close to the Eustachian or Thebesian valve at the orifice of the inferior vena cava or the coronary sinus and demonstrating attachments to the upper wall of the right atrium or the interatrial septum (Fig 1, Fig 2, Fig 3). All patients were studied regarding the coexistence of other congenital anomalies with CN.
Of 2232 studied patients, CN was detected in 76 patients (3.41%). The male/female ratio among patients with CN was 43/34. The co-lesions associated with CN and age distribution of these patients are listed in Tables 1 and 2 respectively. Atrial septal defect and patent foramen ovale (ASD/PFO) was the most common congenital defect seen with CN (55.3%). It was found most frequently during the first month. Of the total studied population, 267 patients (12%) demonstrated atrial septal aneurysm (ASA) whereas 7 patients (9.6%) had CN. The characteristics of the CN patients with peripheral pulmonary stenosis (PPS) are listed in Table 3. The age distribution of all ASA patients is shown in Table 4. The co-lesions with ASA are summarized in Table 5. PFO was the most common defect observed with ASA. Of patients with CN, a total of 11 patients (14.5%) (10 of them 1-8 days old and one patient 17 days old), and 3 patients (3.9%) all 1-12 days old, demonstrated a ratio between heights of early and late diastolic flow velocity peaks (E/A) less than 1 over the tricuspid and mitral valves, respectively. This was true for only the tricuspid valve of 29 out of 267 patients with ASA (11%) (90% 1-30 days old). The latter findings indicate that further studies are necessary to rule out the possible coexistence of any ventricular diastolic dysfunction among pediatric patients, especially the neonates with CN and ASA.
Developmentally, the embryological remnants of the right venous valve evolve into the valve of the inferior vena cava (Eustachian valve) and the valve of the coronary sinus (Thebesian valve) and Chiari Network (CN) [11,12].
Echocardiography is an excellent tool for the diagnosis of these structures, including CN. In transthoracic and transesophageal echocardiography, CN presents as a highly mobile, highly reflectant echo target in several locations in the right atrium . CN is believed to be of little clinical consequence. However, in previous reports it has been shown that it is not always a benign structure . This structure, particularly in the context of fever, congestive heart failure, pulmonary infiltrates, or a history of intravenous drug abuse, could be mistaken for evidence of active infection or disruption of normal right-sided structures, possibly requiring urgent cardiac surgery . It may cause persistence of a patent foramen ovale and formation of an atrial septal aneurysm and may facilitate paradoxical embolism . It may be associated with thrombi formation, and part of the strands may be embolized [16,17]. Infective endocarditis has been reported in association with the CN [18,19]. It also may cause abnormal atrial depolarization favoring supraventricular dysrhythmia . Catheters , guidewires , and pacemaker leads  may become entrapped within the network during invasive procedures. CN has also been demonstrated in association with neurofibromatosis , Behçet syndrome , platypnea–orthodeoxia , and migraine  and therefore it is not always a benign structure .
In the current study, the prevalence of CN in the pediatric cardiology outpatient department of our hospital was 3.4%, which is compatible with other published reports. Previous studies have reported the prevalence to be approximately 2% ; 4.6% as a postmortem finding ; and 2% as screened by TTE. These studies report no significant difference regarding age and gender .
CN may be associated with an increased prevalence of other congenital anomalies including a PFO and ASA [31, 15]. The etiology is not well known, but coexistence with other congenital heart disease is well documented [2,3]. Schneider et al.  demonstrated the presence of a PFO in 83% of patients with CN as compared to 28% in control patients among 1436 adult patients evaluated by TEE. The current study showed that ASD and PFO were the most common (55.3%) accompanying findings among individuals with CN. Additionally CN was found frequently among patients with ASA. It has been reported that ASA was found in 24% of patients with CN diagnosed by TEE . We observed ASA in about 9.2% of our patients and it occurred most frequently during the first month of life. Ninety-five percent of our patients with ASA were associated with PFO. In a study evaluating patients with embolic stroke, of those with a PFO and ASA, a significant number (6/32) showed coexistence with CN . ASA has been attributed to a congenital connective tissue defect, leading over time to degeneration and weakening of the interatrial septum with subsequent aneurysm formation.
PPS in our series was also associated with CN (13.2%), mostly (80%) among patients less than 2 months old. It may produce continuous or systolic murmur, clinically, that could be confused with bruit de Roger of a ventricular septal defect  and characterized by multiple distributed narrowed ostia of the branch pulmonary arteries. It is frequently associated with Alagille and Williams syndromes and can result in pulmonary flow disparity and right ventricular hypertension . In clinical practice, various symptoms can be observed depending on the severity of stenosis and coexisting cardiac and pulmonary disorders. Some cases may mimic pulmonary embolism, leading to misdiagnosis. We detected tricuspid E/A<1 in 11 (14.5%) and also E/A<1 for mitral and tricuspid valves in 3 (3.9%) of our patients with CN, whereas 29 indivuduals out of 267 (11%) tiwh ASA showed E/A<1 in tricuspid valve. We were unable to find any information about coexistence of CN or ASA with E/A<1 in tricuspid valve in the pediatric age group.
CN, not always an innocent abnormality, is an uncommon and incidental finding that should be recognized appropriately. Proper documentation of CN is critical regarding possible future complications.
The authors declare that they have no competing interests.
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