Findings: Axial ECG-gated T1-weighted MR images at the level of the great vessels demonstrate a right aortic arch. Coronal T1-weighted image demonstrates hyposplasia of the pulmonary infundibulum. Axial gradient-recalled-echo MR images through the heart reveal right ventricular hypertrophy (rvh) and a high membranous ventricular septal defect.
Diagnosis: Tetralogy of fallot
Tetralogy of Fallot (TOF) is a congenital heart defect which is classically understood to involve four anatomical abnormalities of the heart (although only three of them are always present). It is the most common cyanotic heart defect and the most common cause of blue baby syndrome. TOF is usually a right-to-left shunt, in which higher resistance to right ventricular outflow results in more severe cyanosis symptoms.
In the United States, the prevalence of TOF is 3.9 per 10,000 live births and accounts for 7-10% of congenital heart diseases. It was described in 1672 by Niels Stensen, in 1773 by Edward Sandifort, and in 1888 by the French physician Étienne-Louis Arthur Fallot, after whom it is named.
Discussion: Tetralogy of Fallot is characterized by a combination of (a) infundibular pulmonic hypoplasia, (b) ventricular septal defect, (c) right ventricular hypertrophy, (d) and (d) overriding of the aortic root above the ventricular septal defect. The pulmonic infundibular stenosis and overriding of the aorta facilitate shunting of deoxygenated blood from the right ventricle to the aorta, thereby producing cyanosis. Approximately one-forth of patients with tetralogy of Fallot also have a right aortic arch (below), usually with mirror image branching.
In fact, the plain film findings of right aortic arch with decreased pulmonary vasculature should strongly suggest the diagnosis. cardiomegaly usually is not present in these patients.
In planing surgery for tetralogy of Fallot, it is important to assess the degree of hyposplasia of the pulmonary arteries and the development of collateral vessels from the systemic to pulmonary arteries. Surgical correction varies from palliative shunt procedures (Blalock-Taussig) to complete repair of the infundibular outflow obstruction and patching of the ventricular septal defect (Lillehei procedure).
From Aunt Minnie’s Pearls:
- Infundibular stenosis + ventricular septal defect + overriding aorta + right ventricular hypertrophy = tetralogy of Fallot.
- Right arch + decreased pulmonary flow + no cardiomegaly on plain films = think tetralogy of Fallot