Fetal Echocardiography: Normal Variants and Artifacts
Four Chamber View
· Echogenic masses within ventricles- In the region of the papillary muscles!chordae tendineae small echogenic masses may be seen in the left (up to 20%) or right ventricle (up to 2%) in normal fetuses.
· Echogenic mass at edge of myocardium- A small mass, which may at times be very bright and mimic calcification, may be seen at the periphery of ventricular myocardium. This represents artifact and is demonstrated when the imaging plane includes the anterior end of a rib or edge of the sternum.
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· Prominent Eustachian valve/Chiari's network- These remnants of embryonic valves of the sinus venosus may appear as bright linear structures within the right atrium, and should not be confused with a pathologic process. Chiari’s network is sometimes seen as several thin echogenic strands within the right atrium; this is usually of no clinical significance, although associated fetal arrythmias have been observed.
· Pseudo-VSD- The membranous part of the ventricular septum may occasionally be devoid of echoes mimicking a VSD. This artifact typically occurs when the septum is parallel to the ultrasonic beam; scanning in alternative planes may clarify the situation.
· Psudothickening of tricuspid valve- The parietal band, which represents a band of muscle placed between the tricuspid and pulmonary valves, can be confused with a thickened tricuspid valve.
· Psudo- ASD- The coronary sinus can be identified in the normal fetus. The sinus may become prominent in some forms of anomalous pulmonary venous drainage. The opening of the coronary sinus may be mistaken for lower ASD. Scanning in different anatomical planes should clarify the position.
· Psudopericardial effusion- The peripheral part of the myocardium, which may appear as a hypoechoic rim, may simulate pericardial fluid. A tiny amount of pericardial fluid is normally present and has no pathologic significance.
Aortic and Pulmonary Outflow Tracts
· Psudocoarcatation- Aortic isthmus narrowing is a normal feature in utero because there is relatively little blood flow through this segment of the aorta. It can be distinguished from coarctation because of the lack of other recognized features, e.g. the left ventricle is normal in size, not small.
· Psudo-overriding of aorta- An overriding aorta occurs when the aortic root is displaced anteriorly so that it arises astride the ventricular septum. There is usually an associated VSD. An overriding aorta can occasionally be simulated. This is an artifact due to a combination of effects. While true overriding is present on several views, pseudo-overriding is usually seen in one plane only.
· Dilated proximal PA- Slight dilatation of the proximal PA distal to the PV is normally seen and should not be confused with poststenotic dilatation of pulmonary stenosis. True poststenotic dilatation may be confirmed by pulsed or color flow Doppler, which will demonstrate a stenotic jet phenomenon.
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