Aortic hypoplasia is a common observation in many congenital heart diseases especially acyanotic CHD. It is important to know the adequacy of systemic blood flow , in left-sided embryonic flow defects like , co- arctation of aorta, interrupted aortic arch, shone’s complex etc .
The hypoplasia is thought to be due to two mechnaisms
1. Low flow state in utero( fetal heart) and the resultant hypoplasia.
2.Ductal tissue migration into adjacent arch which leads to friendly arch contraction ! when the PDA gets closed
in the immediate new born period .
When do you suspect aortic hypoplasia ?
There is no strict definition available.But the Becker’s data base provides a working rule.
Hypoplasia is diagnosed when ,
Isthmus is , < 40 % of diameter of ascending aorta
Proximal transverse arch is , < 60 % diameter of ascending aorta
Distal transverse aortic arch is , < 50% of diameter of ascending aorta
Why ascending aorta is taken as reference ?
It is least likely to affected by the shrinking ductal tissue . Descending aorta can be a reference but it is at a remote location and difficult to image .