CASE REPORT Eur J Anat, 15 (2): 107-110 (2011) The Chiari network: an anatomical variation or a risk factor? Case report Elena Félix-Dominguez, Blanca Mompeó-Corredera Departamento de Morfología, Facultad de Ciencias de la Salud, Universidad de Las Palmas de Gran Canaria, Spain SUMMARY described in the 19th century, becoming important after the introduction of We report an association between a Chiari Echocardiography. Its morphology has been network and an abnormally long coronary studied by echography and it plays a role in sinus. The network, at the Eustachian valve differential diagnosis with some right heart and a morphologically similar network in the pathologies (Goedde et al., 1990; Patane et Thebesian valve, was also associated with a al., 2009). permeable foramen ovale. We review the embryological basis, associated anomalies, The variation is usually discovered during pathological conditions and clinical rele- diagnostic imaging studies, necropsies, and vance. surgical procedures (Loukas et al., 2010). Although it has often been considered clin- ically insignificant, it has been associated with Key words: Chiari network – Embryological some pathologies (Loukas et al., 2010), such as heart development – Vena cava valve – Coro- a patent foramen ovale, atrial septal nary sinus valve aneurysms, and paradoxical embolisms. It has also been described as associated with papil- lary fibroelastomas (Wasdahl et al., 1992), INTRODUCTION arrhythmias, and the development of tumours In human anatomy the concept of normali- (Stanley, 2001). ty includes a range of common morphologies, Some of these associations may be a conse- while less frequent morphologies considered quence of the behavior of the net itself, like normal are described as variations. the net prolapsed in the tricuspid valve orifice The Chiari network is a fenestrated struc- during the diastole period. Other associations ture consisting of strands originating from can be explained through the study of embry- the cava inferior valve in the right atrium of ological heart development. the heart. It is considered to be an anatomi- In this report, we describe the association of cal variation, with an incidence of about 1- a Chiari net associated with other embryolog- 3% in the general population and was ical heart anomalies. Correspondence to: Blanca Mompeó Corredera. Depto. de Morfología, ULPGC, Dr. Pasteur s/n, 35016 Submitted: January 31, 2011 Las Palmas, Spain. Phone: 928453414, 928451436, 928459694; Fax: 928453420. Accepted: April 25, 2011 E-mail: [email protected] 107 Elena Félix-Dominguez, Blanca Mompeó-Corredera CASE REPORT The histological study revealed that the network was mainly composed of fibrous tis- We observed the presence of a Chiari net- sue and some muscle cells (Fig. 5). work in a heart extracted from a male cadaver in the dissection room of our Medical School. The heart was 165 mm in length and 287 g DISCUSSION in weight. Its cavities displayed the following features: The Chiari network is a congenital remnant The interatrial septum showed a permeable of the right valve of the venous sinus and it is foramen ovale (Fig. 1). considered to be an anatomical variation, The inferior vena cava opening into the which overall presents few clinical manifesta- atrium was 26.5 mm in diameter and 80 mm tions. However, this network has been associ- in length. ated with other defects in embryological heart The network in the inferior cava opening, development (Schneider et al., 1995), with exhibited an almost semicircular shape with a alterations in cardiac rhythm (Hajime et al., base of 60 mm, representing about 75% of the 1992; Doig et al., 1995), and with other heart total length of the opening, and it has a max- pathologies (Benbow et al., 1987; Wasdahl et imum width of 35 mm from its adherent bor- al., 1992; Loukas et al., 2010). der to the free border. A festooned veil spread Many of the pathological associations with out from the adherent border. This veil was the Chiari network may be consequence of the formed by a superposition by several arches up behaviour of the network itself. The network to the free border (Fig. 2). could act as a natural filter at the inferior vena The coronary sinus was 80 mm in length cava for the formation or trapping of thrombi between its orifice in the right atrium and the (Benbow et al., 1987) and it may be a place Vieussens valve, which separate the coronary where certain processes such as endocarditis sinus from the great cardiac vein. The left part and tumours can develop. In some cases, net- of the coronary sinus was 15 mm wide and the works of large dimensions may occupy other right part 20 mm wide. The coronary sinus heart cavities (Cooke et al., 1999), or may be a atrial opening was 14.7 mm in diameter and risk factor in radiofrequency ablation proce- 46 mm in length (Fig. 3). dures in patients with arrhythmias. As a con- The net in the coronary sinus valve was sequence, the Chiari network may predispose inserted in the more external part of the orifice to wire entrapment (Shimoike et al., 2001). and covered 50% of the sinus orifice. It was 23 Other associations of the Chiari network mm in length at its adherent border and 15 can be explained in terms of the processes mm at its maximum width (Fig. 4). The net- involved in the embryological heart develop- work’s morphology was similar to that of the ment and the relationship between the venous inferior vena cava. sinus and the development of the cardiac con- Fig. 1. In the opened right atrium a patent foramen ovale is shown Fig. 2. Diaphragmatic surface of the heart and opened right atri- on the atrial septum. um. The veil structure of the Chari network is shown. 108 The Chiari network: an anatomical variation or a risk factor? Case report duction system. During embryological devel- opment, the right horn of the venous sinus increases to the detriment of the left horn, and before its incorporation in the right atrium the venous sinus opens into the right atrium; the sinus atrial-orifice is formed and is guard- ed by right and left venous valves. These valves fuse rostrally as the septum spurium. At the inferior end, the two valves fuse with the dorsal endocardial cushion of the atrium. The embryological development of the right sinus valve forms the crista terminalis, the intervenous tubercle, the valves of the coro- nary sinus, and a large part of the inferior cava valve. The sinus septum, whose origin is located in the region where the right and left horn meet, takes part in the subdivision of the right Fig. 3. Diaphragmatic surface of the heart. The coronary sinus is opened. It is possible to observe the differences between the right sinus valve into the Eustachian and Thebesian and the left part of the coronary sinus. valve. The Eustachian valve is formed by the superior portion of the right sinus valve, and its left end by a small fold that spreads from the sinus septum. The Thebesian valve is formed by the inferior portion of the right sinus valve. The left sinus valve fuses with the right part of the interatrial septum, and at the same time the left horn of the sinus venous forms the coronary sinus. The heart studied showed at least two structural modifications, a consequence of defects in heart development; a) a patent fora- men ovale and b) an abnormally long atrial coronary sinus opening. In the reported case, the heart showed a patent foramen ovale. The recognition and treatment of a permeable foramen ovale has Fig. 4. Diaphragmatic surface of the heart. The coronary sinus lies attracted interest due to the importance and in the atrioventricular groove. A network is shown in its opening frequency of paradoxical embolism (Price et into the right atrium. al., 2004) and a causal relationship between a patent foramen ovale and atrial septal aneurysm and neurologic ischemic events has been considered in patients younger than 55 years old. A patent foramen ovale has also been related with decompression sickness in divers and astronauts, and with migraine headaches (Kerut et al., 2001; Holmes et al., 2004). The incidence of a patent foramen ovale in autopsy patients in the general popu- lation is 27.3% with no sex differences (Hagen et al., 1984). The association between Chiari network and a patent foramen ovale is 83% (Schneider et al., 1995). During the embryological development the cava valve directs the blood towards the inter- Fig. 5. Van Gienson staining of the Chiari network. Connective atrial foramen. The high incidence of associa- tissue in red, muscle cells in yellow. x 160. tion between the Chiari network and a persist- 109 Elena Félix-Dominguez, Blanca Mompeó-Corredera ent foramen ovale can be attributed to the 2. The network may be associated with a per- defect in the regression of the right venous meable foramen ovale and its complica- valve. In this case, the valve, which had not tions, such as a paradoxical embolus or regressed, may have created abnormalities in atrial septal defects. intraatrial circulation, causing difficulties in 3. The Chiari network can be associated with the closing of the foramen (Schuchlenz et al., alterations in heart rhythm. 2004). The presence of a Chiari network should alert about the presence of a patent foramen ovale. REFERENCES The heart studied showed an 80 mm- BEMBOW EW, LOVE EM, LOVE HG, MCCALLUM PK (1987). length sinus coronary, which is considered Massive right atrial thrombus associated with Chiari normal. However, its morphology was not network and a Hickman catheter. Am J Clin Pathol, 88: 234-238. tubular but resembled a wind sock with an COOKE JC, GELMAN JS, HARPER RW (1999).