Chapter 133. Malformations of The Heart and Great Vessels - Review of Medical Embryology Book

ANOMALIES OF THE INTERVENTRICULAR SEPTUM: common; isolated ventricular defects are detected in about 10 to 12/10,000 infants between birth and the age of 5 years

High membranous type: most common. Incomplete closure of the interventricular foramen and failure of the membranous septum to develop due to failure of extensions of subendocardial tissue to grow from the right side of the fused endocardial cushions and fuse with the aorticopulmonary septum and muscular part of the interventricular septum
Low, muscular type: less common; seen anywhere in the muscle portion of the septum (single or multiple). Probably a result of excessive resorption of myocardial tissue during the formation of the muscular part of the septum
Single ventricle (absence of interventricular septum): very rare; results in a 3-chamber heart (cortriloculare biatriatum)

Persistent truncus arteriosus: failure of the aorticopulmonary septum to develop and divide the truncus into an aorta and pulmonary trunk. Also may see defective fusion of the bulbar ridges. Most commonly see one vessel giving rise to an aorta pulmonary trunk, but other variations are possible
Aorticopulmonary septal defect (or fistula): very rare; consists of a round or oval opening between the aorta and pulmonary arterial trunk near the aortic valv Due to localized defect in the aorticopulmonary septum
Unequal division of the truncus arteriosus: unequal partitioning of the truncus above the valves, resulting in one great artery being large and the other small or stenoti The aorticopulmonary septum may not be aligned with the interventricular septum, and one sees ventricular septal defects. The larger of the 2 vessels usually overrides the septal defect

Typically, the aorta lies anterior to the pulmonary trunk and arises from the right ventricle, and the pulmonary trunk arises from the left ventricle
For survival, there is an associated septal defect or patent ductus arteriosus to allow for interchange between pulmonary and systemic blood
Its possible cause: during partitioning of the bulbus cordis and truncus arteriosus, the aorticopulmonary septum fails to follow a spiral course

The straight septum results from failure of the conus arteriosus or pulmonary infundibulum to develop during incorporation of the bulbus into the ventricles

PULMONARY VALVE STENOSIS: the pulmonary valve cusps are fused together to form a narrow central opening

Infundibular pulmonary stenosis: one sees an underdeveloped infundibulum in the right ventricle
The degree of right ventricular hypertrophy depends on the degree of obstruction of the blood flow through the pulmonary trunk