Anatomical Check List of Fetal Four Chamber View
· What is the cardiac situs?Normally the cardiac apex lies on the same side as the left sided gastric bubble. The right ventricle lies closer to the anterior chest wall than the left. Situs abnormalities are associated with asplenia, polysplenia and complex CHD.
· Is the heart normal in size?- The heart occupies approximately one third of the fetal thorax. Standard ratios of external biventricular diameter compared with chest circumference, as obtained by real time and M mode sonography, are available. These ratios may be helpful in predicting cardiomegaly and pulmonary hypoplasia.
· Are the two ventricles of approximately equal size?- The two ventricles and atria are of approximately equal size. The muscle mass is also of similar size with the same degree of contractility. The ventricular septum is approximately the same thickness as the ventricular wall.
· Is the septum intact?- The flap of foramen ovale should lie in the left atrium. The septum needs careful evaluation as small to moderate VSDs can easily be missed on routine scanning. The use of color flow mapping may allow more accurate diagnosis of VSDs to be made.
· What is the position of AV valves?- Of the two AV valves, the tricuspid lies slightly nearer the apex of the heart. The AV valves meet the atrial and ventricular septa to form an offset cross appearance.
· Is the endocardium normal? -The moderater band should be visible near the tip of the right ventricle. The valve of the IVC (eustachian valve) may be seen within the right atrium. In endocardial fibroelastosis, sonography reveals a dilated, poorly contracting heart with diffusely echogenic endocardium.
· Is the myocardium normal? - Cardiomyopathies detected in utero are congestive in type, with a dilated, poorly contracting ventricle and AV valve regurgitation associated with hydrops. Hypertrophic cardiomyopathy has been recognized in association with Noonan’s syndrome or poor diabetic control in the third trimester. Rhabdomyoma/rhabdomyosarcoma may cause focal intramural echogenicity.
· Is the pericardium normal? - A small amount of pericardial fluid is a normal finding but a larger pericardial effusion may be a manifestation of a systemic disorder such as fetal hydrops.
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