52 year-old male presenting with progressively worsening shortness of breath and irregular heart beat.

Figure 1: Axial HASTE image demonstrates cardiomegaly, right ventricular hypertrophy, and a large ventricular septal defect (arrow).

Figure 2: Axial HASTE image demonstrates the aortic root overriding the interventricular septum (arrow). There are also bilateral pleural effusions and right lung base atelectasis.

Figures 3 and 4: Coronal HASTE images confirm that the aortic root is overriding the interventricular septum.

Figure 5: Sagittal MPR image demonstrates a stenotic pulmonic infundibulum (arrow) measuring approximately 1.5 cm.

Tetralogy of Fallot.

Tetralogy of Fallot (TOF), the most common type of cyanotic congenital heart disease, accounts for approximately 5.5-6% of cases of congenital heart disease. The characteristic features of TOF are:

• Right ventricular (RV) outflow obstruction (infundibular, valvar, supravalvar or a combination.
• RV hypertrophy
• Overriding aorta
• Ventricular Septal Defect (VSD)

These anomalies are the consequence of a primary developmental defect where there is a misalignment of the muscular infundibular outlet septum with superior and leftward displacement of the parietal band (crista supraventricularis). This displacement is responsible for narrowing of the RV outflow tract and leads to underdeveloped pulmonary arteries and pulmonary valves and to the overriding aorta. Additional associated anomalies include a right aortic arch (25%), abnormal origin and course of the coronary arteries, patent ductus arteriosis (PDA), aortic root dilation, and aortopulmonary collaterals. Chromosomal anomalies, in particular deletions of chromosome 22, have been identified in some patients with classic TOF and TOF with pulmonary atresia.

The clinical presentation depends on the severity of two anatomic features in a given patient: the pulmonary stenosis and the ventricular septal defect (VSD). Severe pulmonary stenosis results in right to left shunting through the VSD. The volume of the shunt determines the degree of cyanosis. When there is minimal obstruction to flow through the right ventricular outflow tract, shunting will be predominately left to right, with little if any hypoxemia. Typically patients develop cyanosis within the first few years of life. Symptoms generally progress secondary to hypertrophy of the infundibular septum. The rare patient may remain marginally and imperceptibly cyanotic or acyanotic and asymptomatic into adult life, as demonstrated by our patient.

Echocardiography remains the principal initial diagnostic tool in patients with TOF. However MR imaging has been shown to provide additional information on anatomy and function in TOF and also assist in preoperative planning. Sagittal and coronal MR images display the size and overriding position of the aorta and the narrowing of the RV outflow tract. Transverse and oblique images can demonstrate the VSD and the location of the pulmonary outflow and arterial stenoses. Coronary artery anomalies are also well visualized using MR imaging.

Surgical correction of TOF is done early in infancy and includes relieving the pulmonic stenosis and closing the VSD. After repair, however, patients are not free from residual sequelae and MRI allows for a comprehensive analysis of the postoperative anatomy and function in a TOF patient. In the follow-up of patients who have undergone repair of TOF the following information needs to assessed:

1. Residual anatomical problems including VSD, pulmonary stenosis, RV outflow aneurysm.
2. Extent of pulmonary stenosis (residual or recurrent)
3. Amount of pulmonary regurgitation
4. Systolic and diastolic biventricular size and function.

Both intracardiac and large vessel anatomy may be depicted clearly with electocardiogram (ECG) gated spin-echo and gradient-echo MR images. Transaxial, coronal, sagittal, and oblique views are generally applied to access RV hypertrophy, RV outflow tract stenosis, and pulmonary artery anatomy and size may be assessed. Gadolinium-enhanced imaging is sometimes also helpful.

References:

1. Higgins CB and A De Roos. Cardiovascular MRI & MRA. Philadelphia: Lippincott Williams & Wilkins, 2003.
2. Rebergen SA and A De Roos. Congenital Heart Disease: Evaluation of Anatomy and Function by MRI. Herz. 2000; 25(4): 365-383.
3. Roest AAW and A De Roos. Evaluation of Congenital Heart Disease by Magnetic Resonance Imaging. European Radiology. 2000; 10: 2-6.
4. Helbing WA and A De Roos. Clinical Applications of Cardiac Magnetic Resonance Imaging After Repair of Tetralogy of Fallot. Pediatric Cardiology. 2000; 21: 70-79.