You are in: eMedicine Specialties > Radiology > CARDIAC Tetralogy of FallotArticle Last Updated: Aug 21, 2007AUTHOR AND EDITOR INFORMATIONSection 1 of 11
  Author: S Bruce Greenberg, MD, Professor of Radiology, University of Arkansas for Medical Sciences; Consulting Staff, Department of Radiology, Arkansas Children's Hospital S Bruce Greenberg is a member of the following medical societies: Radiological Society of North America Editors: Justin D Pearlman, MD, PhD, ME, MA, Director of Dartmouth Advanced Imaging Center, Professor of Medicine, Professor of Radiology, Adjunct Professor, Thayer Bioengineering and Computer Science, Dartmouth-Hitchcock Medical Center; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; Robert M Steiner, MD, Professor of Radiology, Temple University School of Medicine, Clinical Professor of Radiology, Medical School of the University of Pennsylvania; Consulting Radiologist, Temple University Hospital, Temple University Children's Medical Center; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Eugene C Lin, MD, Consulting Staff, Department of Radiology, Virginia Mason Medical Center Author and Editor Disclosure Synonyms and related keywords: cyanotic congenital heart disease, right ventricular outflow tract obstruction, malalignment ventricular septal defect, overriding aorta, right ventricular hypertrophy INTRODUCTIONSection 2 of 11
  BackgroundTetralogy of Fallot is the most common type of cyanotic congenital heart disease. It consists of a right ventricular outflow tract obstruction, a malalignment ventricular septal defect, an overriding aorta, and right ventricular hypertrophy. Patient Education: For excellent patient education resources, visit eMedicine's Heart Center. Also, see eMedicine's patient education article Tetralogy of Fallot. PathophysiologyAnterior and superior displacement of the crista supraventricularis causes narrowing of the developing right ventricular outflow tract. A ventricular septal defect and an overriding aorta are the consequences of the septal displacement. The large ventricular septal defect equalizes the right and left ventricular pressures, resulting in persistent right ventricular hypertrophy. Right-to-left shunting varies with the degree of pulmonary outflow tract obstruction, but it is progressive. FrequencyUnited StatesCongenital heart disease is present in 1% of neonates. Of these neonates, tetralogy of Fallot is the most common cause of cyanotic congenital heart disease and is responsible for as many as 10% of all cases of congenital heart disease. Mortality/MorbidityThe mortality rates for patients who are untreated for tetralogy of Fallot are progressive with the patient's age. Mortality Rates for Untreated Tetralogy of Fallot
Surgical treatment has greatly improved the prognosis of tetralogy of Fallot because of the introduction of palliative shunts and corrective surgery. Morbidity is a consequence of hypoxia and right-to-left shunting. Chronic hypoxia that is caused by such shunting is associated with decreased neurologic function. Episodes of acute hypoxia from infundibular spasm are life threatening. Polycythemia that is associated with chronic hypoxia causes hypercoagulability and thrombosis. Right-to-left shunting that bypasses the filtering of the pulmonary capillaries is associated with a higher incidence of systemic infection such as a brain abscess. SexTetralogy of Fallot has a slight male predominance. AgeTetralogy of Fallot usually becomes clinically apparent in infants. AnatomyTetralogy of Fallot includes the following:
Infundibular stenosis Infundibular stenosis is the classic form of right ventricular outflow tract obstruction; however, 75% of affected children have a combination of infundibular and pulmonary valve stenosis. Pulmonary artery supravalvular stenosis and branch pulmonary artery hypoplasia or atresia are frequently associated with tetralogy of Fallot; they are a consequence of decreased pulmonary flow during development. A branch pulmonary artery, usually the left, can originate from a patent ductus arteriosus. The branch pulmonary arteries may be nonconfluent or completely absent The size and number of the branch pulmonary arteries are critical to management of tetralogy of Fallot. Children with hypoplastic pulmonary arteries, particularly those with associated pulmonary artery atresia, are not candidates for immediate corrective surgery. As Kirklin and Barratt-Boyes reported, the McGoon ratio, which is the result of the combined branch pulmonary arterial diameters divided by the descending aorta diameter, and the Nakata index, which is the combined cross-sectional area of the branch pulmonary arteries per square meter, are used to determine if the branch pulmonary arteries are large enough to permit corrective surgery.1 Children with small McGoon ratios are poor candidates for complete surgical repair because of the inability of the small pulmonary arteries to adequately handle the increased blood flow after complete repair. Typically, a systemic-pulmonary artery shunt is placed in children with small pulmonary arteries until the arteries grow to a sufficient size to allow corrective surgery. The branch pulmonary arteries can be completely separate from each other or nonconfluent. Children with nonconfluent branch pulmonary arteries require bilateral palliative shunts. Children in whom a pulmonary artery is absent are not candidates for conventional systemic-pulmonary artery shunt placement or corrective surgery. Unifocalization, or the creation of a neopulmonary artery from large systemic collateral vessels, can be performed in children without branch pulmonary arteries. Vascular anomalies A right-sided aortic arch is present in 25% of children with tetralogy of Fallot. Of these children, 90% have mirror-image branching, and 10% have an aberrant left subclavian artery. Among children with combined congenital heart disease and a mirror-image, right-sided aortic arch, 90% have tetralogy of Fallot. Of the children with congenital heart disease and an aberrant left subclavian artery, 71% have tetralogy of Fallot. Coronary arterial anomalies are common when a single right or left coronary artery is present, as is the case in 4% of children. The anterior descending artery and prominent conal branches may originate from the right coronary artery. The relationship of these vessels to the infundibulum influences surgical management. Postoperative complications Common postoperative complications include residual pulmonary outflow tract stenosis, branch pulmonary arterial stenosis or occlusion, and shunt stenosis or occlusion. Pulmonary regurgitation is almost universal in corrected tetralogy of Fallot and results in right ventriculomegaly. Long-term pulmonary regurgitation reduces cardiac function. Clinical DetailsInfants may initially be acyanotic and typically have progressive cyanosis in their first months of life. In fact, the ventricular septal defect may act as a left-to-right shunt with pulmonary overcirculation. However, the right ventricular tract stenosis is progressive and leads to the progressive cyanosis that is usually identified when the neonate is several weeks old. Those with severe right ventricular outflow tract obstruction present earlier. The pulmonary infundibulum is prone to spasm, which causes acute episodes of cyanosis, referred to as "tet spells." Activity stimulates these episodes, and squatting may relieve them. In children with a right-sided aortic arch, the large ascending aorta causes tracheal compression that can result in feeding or respiratory difficulty. Polycythemia that is associated with cyanosis may lead to pulmonary thrombosis or cerebral thrombosis. Preferred ExaminationEchocardiographic findings are diagnostic for tetralogy of Fallot in infants and young children, and echocardiography may be the only examination required before surgery. Conventional radiography, magnetic resonance imaging (MRI), and angiography are also helpful for complete preoperative evaluation. Angiography has been used for preoperative evaluation of the coronary arteries and peripheral pulmonary circulation; however, intracardiac catheterization may stimulate pulmonary outflow tract spasm. Noninvasive peripheral pulmonary arterial evaluation is possible with MRI. In the postoperative evaluation, echocardiography and MRI are preferred. The choice of imaging examinations depends on their availability and clinical preference. Limitations of TechniquesEchocardiographic findings are diagnostic of intracardiac abnormalities, but echocardiography is limited in the evaluation of the peripheral pulmonary arteries and collateral flow. If the confluence or presence of the branch pulmonary arteries is in doubt after echocardiography, perform MRI or angiography. DIFFERENTIALSSection 3 of 11
Pulmonic Stenosis Pulmonic Valvular Stenosis Tricuspid Atresia Truncus Arteriosus Other Problems to Be ConsideredDouble-outlet right ventricle
RADIOGRAPHSection 4 of 11
FindingsOn radiographs, the cardiac silhouette in patients with tetralogy of Fallot is normal in size; however, right ventricular hypertrophy can elevate the left ventricle. Combined with a small or absent main pulmonary artery segment, the heart can have the classic boot-shaped appearance (see Image 1). Most children with tetralogy of Fallot do not have boot-shaped heart (see Image 2). Typically, the appearance of the vascularity of the pulmonary artery is reduced, but it can also be normal. Decreased pulmonary vascularity is frequently difficult for the general radiologist to appreciate. Large collaterals may give the appearance of normal vascularity. The enlarged aorta in children with a right-sided arch can cause airway compression that can be identified on the chest radiograph (see Image 3). A right-sided arch is present in 25% of children with tetralogy of Fallot, and it can be identified by means of direct visualization, with displacement of the trachea to the left or with increased opacity of the spinal pedicles on the ipsilateral side of the aortic arch. The position of the aortic arch influences surgical planning because Blalock-Taussig shunts are more easily placed on the contralateral side of the aortic arch. Modified Blalock-Taussig shunts can be placed bilaterally. Degree of ConfidenceConfidence in conventional chest radiographic findings increases with the radiologist's reading experience. The use of echocardiography has reduced the importance of chest radiography in the initial diagnosis of congenital heart disease. Echocardiography should be used to confirm radiographic findings that are suggestive of tetralogy of Fallot. False Positives/NegativesThe boot-shaped heart is overlabeled in neonates, who normally have right ventricular hypertrophy. If the chest radiograph shows lordosis, a normal heart may appear boot shaped. A right-sided aortic arch in a child with congenital heart disease is most commonly associated with tetralogy of Fallot. Children with a large right-sided aortic arch may have a double aortic arch or an aberrant left subclavian artery without congenital heart disease. Other forms of cyanotic heart disease that are associated with a right-sided aortic arch are usually hypervascular and associated with cardiomegaly (eg, truncus arteriosus, transposition of the great arteries). Although cyanosis and a right-sided aortic arch are associated with tetralogy of Fallot, the presence of cardiomegaly and increased pulmonary vascularity make an admixture lesion the more likely diagnosis. Transposition of the great vessels or truncus arteriosus is associated with increased pulmonary vascularity, cardiomegaly, and cyanosis, as well as a right-sided arch. Approximately one third of children with truncus arteriosus have a right-sided aortic arch. Only 5% of children with transposition of the great vessels have a right-sided aortic arch, but this is a more common form of congenital heart disease than truncus arteriosus. CT SCANSection 5 of 11
FindingsComputed tomography (CT) scanning has an infrequent role in the evaluation of tetralogy of Fallot. This modality is useful for the evaluation of surgical complications such as infection or pseudoaneurysm formation. Helical CT scanning can be used to identify airway compression that is caused by a large ascending aorta that is associated with tetralogy of Fallot. MRISection 6 of 11
FindingsSpin-echo MRI can be used to identify the morphologic abnormalities of tetralogy of Fallot (see Image 4), which are as follows: right ventricular outflow tract obstruction, ventricular septal defect, right ventricular hypertrophy, and an overriding aorta. The confluence, presence, and size of the branch pulmonary arteries can be identified (see Image 5). MRI measurements of the size of the pulmonary and branch pulmonary arteries are as accurate as angiographic measurements, and they can be used to calculate the McGoon ratio and the Nakata index (see Anatomy, Branch pulmonary arteries). Postoperative evaluation of pulmonary artery stenoses is better with MRI than with echocardiography. Cine imaging can be used to identify pulmonary stenosis or regurgitation, which is depicted as flow voids. Right ventricular enlargement is best quantified with MRI. Flow-analysis quantification of pulmonary regurgitation is unique to MRI. Although gradients can be measured with echocardiography, only MR flow analysis enables the accurate cross-sectional measurement of flow. Degree of ConfidenceExperienced operators are required for a high-quality MRI evaluation. If properly performed, MRI can replace preoperative angiography, which is more invasive. False Positives/NegativesOblique imaging with thin sections may be necessary to verify pulmonary arterial confluence and identify hypoplastic pulmonary arteries in neonates and infants. Flow analysis of pulmonary regurgitation is susceptible to aliasing if the velocity encoding is too low. ULTRASOUNDSection 7 of 11
FindingsEchocardiography is the primary imaging method for examining a child in whom tetralogy of Fallot is suspected. Intracardiac anomalies, including pulmonary infundibular and valvular stenosis and the position of the aortic root overriding the ventricular septal defect, are identified with 2-dimensional echocardiography. The origins of the coronary arteries can also be identified. Doppler ultrasonographic examination of the pulmonary outflow tract can be used to measure the velocity gradient in the right ventricular outflow tract and to differentiate severe stenosis from atresia. Continuity of the branch pulmonary artery with the main pulmonary artery can be identified, and the size of the branch pulmonary arteries can be measured. The initial placement of palliative shunts is likely in children who have small branch pulmonary arteries in order to allow the pulmonary arteries to grow before corrective surgery. The full length of the shunts may not be visible; however, Doppler ultrasonography can be used to verify shunt patency, even when the entire length of the shunt cannot be imaged. Degree of ConfidenceIntracardiac and central pulmonary artery abnormalities are identified in the presurgical patient with a high degree of confidence. Ultrasonographic windows in the older child and young adult limit the usefulness of echocardiography in postoperative follow-up imaging. Postoperative fibrosis in the mediastinum also reduces the effectiveness of echocardiography. False Positives/NegativesThe pulmonary arteries and systemic-pulmonary arterial shunts are difficult to evaluate after surgery in children. Pulmonary regurgitation, a common complication of corrective surgery, is better evaluated with MRI. ANGIOGRAPHYSection 8 of 11
FindingsAngiography is the traditional criterion standard and best modality for the evaluation of the pulmonary and coronary arterial morphology, as well as the morphology of the systemic collateral arteries. The branch pulmonary arteries have a characteristic seagull appearance (see Image 6). Pulmonary arterial measurements for the calculation of the McGoon ratio and Nakata index are critical to surgical planning. An aortic root injection is used to evaluate the position and number of coronary arteries. Degree of ConfidenceCatheter studies remain the criterion standard for blood pressure measurements and morphologic imaging of the coronary and branch pulmonary arteries. Noninvasive techniques are preferred when they are available so that vascular access for potential future interventional procedures is preserved. False Positives/NegativesUnlike inherently tomographic studies such as echocardiography, MRI, and CT scanning, angiography may be limited by overlapping structures that may obscure other structures, despite the use of multiple planes. INTERVENTIONSection 9 of 11
Palliative and corrective surgery is the primary treatment for tetralogy of Fallot. Interventional procedures have a supportive role. Balloon angioplasty that is performed to enlarge the pulmonary outflow tract can sufficiently improve the pulmonary circulation and allow surgery to be delayed until the infant grows large enough to improve the surgical risk. In the treatment of postoperative pulmonary arterial stenosis treatment in children, balloon angioplasty and stent placement are becoming increasingly important. In select patients, embolization of the systemic collateral arteries helps to improve pulmonary arterial flow and development. MULTIMEDIASection 10 of 11
REFERENCESSection 11 of 11
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