Anatomic variants of the remnants of the right valve of the sinus venosus in adults are common and usually observed on cardiac imaging studies. Because the anatomy and function of these vestiges are not well known, errors may occur in the differential diagnosis and treatment of patients with unclear images in the right atrium. Clinical implications may arise from (1) differential diagnosis with some diseases, especially when the remnants act as sites of attachment for masses; (2) the need for invasive treatment if the anatomic variant displays obstructive behavior; (3) the association between remnants and patent foramen ovale; and (4) secondary complications related to these structures in invasive procedures. Thus, the aim of this review is to provide cardiologists and radiologists specializing in cardiac imaging techniques with the basic anatomic information and clinical implications required to understand morphologic variants of right sinus venosus valve vestiges in adults.
Highlights
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Definition and embryology of remnants of the right valve of the sinus venosus.
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Differential diagnosis of the right valve of sinus venosus remnants by imaging techniques.
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Clinical implications of persistence of remnants of right valve of sinus venosus in adults.
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Invasive procedures in relation with remnants of right valve of sinus venosus.
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Embryology of Remnants of the Right Sinus Venosus Valve
In the fifth week of cardiogenesis, embryonic venous drainage reaches the primitive right atrium through the sinus venosus. Both cavities are connected through the sinoatrial orifice, which is flanked by two valvular folds: the right and left venous valves. These venous valves encircle the orifice, project into the atrial cavity, and are dorsocranially fused, forming a ridge known as the septum spurium ( Figure 1 A).
Between the 6 th and 8 th weeks of embryologic development, the larger right valve of the sinus venosus grows to reach two thirds of the atrium, dividing the right cavity into two chambers. The right valve of the sinus venosus extends from the lateral margin of the superior vena cava to the orifices of the inferior vena cava (IVC) and coronary sinus (CS). At this stage of embryologic development, the right venous valve functions to direct oxygenated venous return from the IVC via the foramen ovale (FO) to the left side of the heart throughout fetal development ( Figure 1 B).
From the 9 th to 15 th weeks, the smaller left venous valve and septum spurium fuse with the developing interatrial septum and form part of the septum secundum. Furthermore, the right sinus venosus valve atrophies and mostly involutes; the cranial part remains as the crista terminalis, and the caudal part fuses with the septum between the orifices of the IVC and CS. Remnants of the inferior part of the right valve are the Eustachian valve (EV) adjacent to IVC, and the Thebesian valve (ThV) at the orifice of the CS ( Figure 1 C).
Embryology of Remnants of the Right Sinus Venosus Valve
In the fifth week of cardiogenesis, embryonic venous drainage reaches the primitive right atrium through the sinus venosus. Both cavities are connected through the sinoatrial orifice, which is flanked by two valvular folds: the right and left venous valves. These venous valves encircle the orifice, project into the atrial cavity, and are dorsocranially fused, forming a ridge known as the septum spurium ( Figure 1 A).
Between the 6 th and 8 th weeks of embryologic development, the larger right valve of the sinus venosus grows to reach two thirds of the atrium, dividing the right cavity into two chambers. The right valve of the sinus venosus extends from the lateral margin of the superior vena cava to the orifices of the inferior vena cava (IVC) and coronary sinus (CS). At this stage of embryologic development, the right venous valve functions to direct oxygenated venous return from the IVC via the foramen ovale (FO) to the left side of the heart throughout fetal development ( Figure 1 B).
From the 9 th to 15 th weeks, the smaller left venous valve and septum spurium fuse with the developing interatrial septum and form part of the septum secundum. Furthermore, the right sinus venosus valve atrophies and mostly involutes; the cranial part remains as the crista terminalis, and the caudal part fuses with the septum between the orifices of the IVC and CS. Remnants of the inferior part of the right valve are the Eustachian valve (EV) adjacent to IVC, and the Thebesian valve (ThV) at the orifice of the CS ( Figure 1 C).
Definitions and Prevalence of Remnants of the Right Sinus Venosus Valve
Persistence of the right valve of the sinus venosus to varying degrees represents a spectrum of anatomic variants, not easily distinguishable by imaging techniques, ranging from cor triatriatum dexter (CTD) to EV and ThV ( Tables 1 and 2 ; Figures 2 and 3 ).
| Anatomic structure | Cor triatriatum dexter | CN | EV | ThV |
|---|---|---|---|---|
| Definition and embryology | Persistence of the right valve of sinus venosus which divides the right atrium into two chambers, producing flow obstruction | Incomplete resorption of the right sinus valve and the septum spurium, forming a reticulated network of fibres | Caudal remnant of the right sinus valve located in the orifice of IVC | Caudal remnant of the right sinus valve located in the orifice of CS |
| First described | Carl von Rokitansky (1875) | Hans Chiari (1897) | Bartolomeo Eustachius (1563) | Adam Christian Thebesius (1708) |
| Prevalence | <0.025% of all congenital heart diseases | 2%–15% with current imaging techniques and autopsy studies | >50% with current imaging techniques and autopsy studies Prominent EV: 13% of patients with cryptogenic stroke | 65%–90% with current imaging techniques and autopsy studies |
| Morphology | Large fenestrated membrane separating the right atrium into two cavities | Thin web-like structure with whip movement | Variable:
| Variable:
|
| Insertion | Crista terminalis | Variable:
| In the margin of IVC orifice | Usually in the inferior or posterior margin of the CS orifice |
| Size | — | >1.0 cm (mean length, ∼3.0 cm) | 1.0 ± 0.4 cm (TEE in bicaval view) Prominent EV: mean, >1.0 cm | 0.5 cm (range, 0.1–1.2 cm) |
| Cor triatriatum dexter | CN | EV | ThV | |
|---|---|---|---|---|
| Differential diagnosis by imaging techniques | Large leaflike linear structure
| Free-floating web-like structure
| Leaflike linear structure
| Leaflike linear structure
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| Planes ∗ | ||||
| TTE |
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| TEE |
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| CMR/CT |
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| Usefulness in diagnosis | ||||
| TTE | +++ | ++ | ++ | − |
| TEE | +++ | +++ | +++ | + |
| CMR | ++ | + | +++ | + |
| CT | ++ | − | +++ | + |
∗ Best planes to establish the diagnosis of the different right valve of sinus venosus remnants, on the basis of standardized planes of imaging technique guidelines.
CTD
CTD is a very rare malformation in which a large membrane divides the right atrium into two chambers: the proximal chamber usually receives blood from the superior vena cava and IVC, while the distal chamber contains the tricuspid valve and the right atrial appendage ( Figure 2 A). However, four types of CTD have been reported depending on the relative position of the IVC, superior vena cava, and CS in relation to the septum. Gharagozloo et al . proposed that the obstructing membrane originates from the crista terminalis and should be distinguished from the more commonly observed prominent EV. Although some authors consider CTD present only if there is venous flow obstruction and cyanosis, the presence of any degree of obstruction is mandatory to differentiate between this entity and prominent EV ( Figure 4 ; Videos 1 and 2 ; available at www.onlinejase.com ). The prevalence of CTD is not well known given the rarity of this anomaly, as it represents only approximately 0.025% of cases of all congenital heart diseases reported in the medical literature. Symptoms depend on the degree of obstruction produced by the membrane, which is usually fenestrated, and interatrial septum status. When septation is mild, this lesion is often asymptomatic and may be detected incidentally during routine echocardiography or in postmortem studies. Cyanosis may be frequent because of shunting of inferior caval blood into the left atrium through a patent FO (PFO), an atrial septal defect (ASD), or other congenital malformations. However, although this situation is often well tolerated into adult life, it may only occasionally result in severe hypoxemia in infancy. More severe septation can cause right-sided heart failure and elevated central venous pressures secondary to obstruction of the flow. In addition, CTD may be associated with other right congenital heart lesions, such as pulmonary valve stenosis or atresia, hypoplastic right ventricle, or tricuspid valve stenosis or atresia. Hemodynamic status seems to play an important part in the persistence of the right sinus venosus valve and the development of the right side of the heart. It has been speculated that underdevelopment of the right side of the heart may be related to the decreased blood flow due to the persistent right sinus venosus valve.
