Chiari network occurs due to incomplete resorption of right valve of sinus venosus. It is often noticed as fenestrated membranous structure or reticular network like structure in the valve of inferior vena cava and coronary sinus. The remnant of left venous valve is observed as trabeculae over the fossa ovalis. The incidence of Chiari network and the remnant of left venous valve were studied in 80 cadaveric hearts utilized for teaching the undergraduates. The right atrium was opened anterior to sulcus terminalis and the interior was examined for the presence of these embryological remnants. The incidence of Chiari network and left venous valve in the present study is 3.75% and 7.5%, respectively. Chiari network was observed as a fenestrated membranous structure in 2 specimens and a reticular network in 1 specimen, with variable extension to coronary sinus opening and right atrial wall. The remnant of left venous valve was observed as multiple fine strands in 3 specimens and trabecular structure in 3 specimens. These structures may create diagnostic confusion, difficulty in interventional procedures, and complications like thromboembolic events. Hence, the knowledge about the incidence, morphology, and clinical manifestations of these rare embryological remnants is mandatory.
In 1897, Hans Chiari described abnormal fibrous lace-like strands extending from the margin of the inferior vena cava or coronary sinus valves to the crista terminalis region. The network was termed after him. The Chiari network is derived from the incomplete resorption of right valve of sinus venosus [
The study or case report mentioned in most of the literature about these embryological remnants was based on echocardiographic findings. There is paucity of literature about the anatomical study of these structures. Although Chiari network was considered as a benign variant in the far past, the use of echocardiography allowed recognition of the network with its associated complications [
Hence, the aim of this study is to find the incidence of these rare embryological remnants with its morphology and possible associated clinical manifestations.
A total of 80 heart specimens collected for the purpose of teaching undergraduate students were utilized for this study. These specimens were collected irrespective of age, sex, and race from Department of Anatomy, Sree Gokulam Medical College, India, and Department of Anatomy, Oman Medical College (affiliated to West Virginia University), Oman. The specimens from Oman Medical College were provided by Department of Anatomy, West Virginia University, United States.
The heart was opened anterior to sulcus terminalis. The interior of right atrium was observed for the presence of Chiari network and remnant of left venous valve.
Out of 80 hearts studied, Chiari network was noticed in 3 specimens (3.75%) and remnants of left venous valve were noticed in 6 specimens (7.5%).
Out of those 3 specimens, Chiari network was observed as fenestrated membranous structure in 2 specimens (Figures
Features of Chiari network and associated left venous valve remnant.
Specimen number | Characteristic feature | Number of fenestrations | Primary attachment | Extent to | Feature of the associated left venous valve remnant |
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1 | Fenestrated membranous structure | 27 | Valve of inferior vena cava | Coronary sinus orifice | (Not associated) |
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2 | Fenestrated membranous structure | 10 | Valve of inferior vena cava | Right atrial wall | Membranous structure with single fenestration |
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3 | Reticular network of fine strands | — | Valve of inferior vena cava | Right atrial wall | Single strand over fossa ovalis |
Interior of right atrium showing Chiari network as a fenestrated membranous structure (
Dissection of right atrium showing Chiari network in the valve of inferior vena cava (
Right atrium dissection showing Chiari network as a reticular network of fine strands (
Out of 6 specimens with remnant of left venous valve, 2 were associated with Chiari network (Figures
Interior of right atrium (RA) showing the remnant of left venous valve (
Interior of right atrium (RA) showing the remnant of left venous valve (
During development of heart, when the right horn of sinus venosus is incorporated into the primitive atrium to form the smooth part of right atrium, its entrance, the sinoatrial orifice is guarded by two muscular folds, the right and left valve of sinus venosus.
The cranial portion of the right venous valve is indicated as crista terminalis and its caudal portion forms the valve of inferior vena cava (Eustachian’s valve) and valve of coronary sinus (Thebesian valves). The left venous valve blends with the right side of the interatrial septum [
During involution of these valves, the tissue undergoes fenestration so that a network may be formed from remnants that usually disappear. Incomplete resorption of right venous valve leads to Chiari network, which is described as a meshwork of thread-like strands connecting the edges of inferior vena cava and coronary sinus valves with crista terminalis [
If the left venous valve fuses with right aspect of interatrial septal complex incompletely; it remains free, leading to incomplete resorption by apoptosis. Thereby, the remnant of the left venous valve is found to be adherent to the superior portion of atrial septum or the fossa ovalis [
Its incidence varies from 1.5 to 3% [
The incidence of left venous valve was observed in 6 out of 80 specimens (7.5%) in the present study. To the best of our knowledge, apart from case reports [
Chiari network is characterized as reticular network of fine strands attached to right atrium [
This morphology is essential to identify the Chiari network in echocardiography. It is often observed as web-like structure with a variable number of thread-like components with characteristic whip-like motion within the right atrium moving with each contraction of the heart [
Regarding the morphology of left venous valve remnant, there is only one study that described it as a trabecular remnant over the fossa ovalis. In the present study, this remnant was noticed as fibrous strands in 3 specimens and as trabecular membranous structure in 3 specimens.
Since Chiari network is considered as a remnant of right venous valve, it often prefers the pattern of fetal circulation, thus directing the blood flow towards the foramen ovale. This favors the persistence of patent foramen ovale thus creating cyanosis [
Chiari network may create turbulent blood flow leading to thrombus formation. The fibers of the network are sometimes torn during life and may break free. The fenestrated types may rarely remove emboli from the circulation, but this is purely by chance, and further emboli are likely to reach the lung [
Cardiac catheter can be entrapped by strands of Chiari network during an attempt to close the atrial septal defect [
In spite of its benign nature, Chiari network can be associated with infective endocarditis [
Chiari network can be more accurately diagnosed by transoesophageal echocardiography than the transthoracic echocardiography [
The difficulty encountered during cardiac catheterization had been reported in 3 cases. In spite of its rarity, the knowledge of left venous valve remnant is mandatory for the successful device closure of atrial septal defect [
The incidence of Chiari network and left venous valve in the present study is 3.75% and 7.5%, respectively. Chiari network was observed as a fenestrated membranous structure in 2 specimens and a reticular network in 1 specimen, with variable extension to coronary sinus opening and right atrial wall. The remnant of left venous valve was observed as multiple fine strands in 3 specimens and trabecular structure in 3 specimens.
In spite of their rarity and being considered as benign, both Chiari network and remnant of left venous valve should be no longer considered as always-harmless structures. Therefore, the knowledge about their morphology and clinical manifestations is mandatory for the clinicians to reach for correct diagnosis, to achieve success in interventional procedures, and to anticipate the possible complications, so that surgical or medical management can be done at a right time.
The authors declare that there is no conflict of interests regarding publication of this paper.
The authors would like to acknowledge the support exerted by Dr. M. L. Ajmani, Professor and Head, Department of Human structure and Neurobiology, Oman Medical College (OMC), Oman, and Dr. K. Chandrakumari, Professor and Head, Department of Anatomy, Sree Gokulum Medical College & Research Foundation, Trivandrum (SGMC&RF), India. The authors submit their sincere thanks to the Head and all the faculty of Department of Anatomy, West Virginia University, United States, for providing the specimens. The authors extend their gratitude to Dr. Saleh Al Khusaiby, Dean, Dr. Thomas Heming, Vice Dean, Dr. Mubarak Pasha, Deputy Dean of OMC, and Dr. K. K. Manojan, Director of SGMC&RF, for their constant support for smooth conduct of this study. The authors also thank the faculty and technicians of OMC & SGMC&RF for their help to complete this study.