A practical approach to the chest x-ray of a child with known or suspected congenital heart disease

T he definitive diagnosis of congenital heart disease (CHD) is made on echocardiography or cardiac catherisation. Today, in most centres these procedures are performed by specialist cardiologists.The plain chest X-ray is still valuable and is used to assess some specific criteria. With a logical approach and some understanding of CHD, the radiologist can greatly assist the clinician in the workup and follow-up of patients with CHD. Making a definitive diagnosis of a specific cardiac anomaly from a chest X-ray is unwise. The patient with CHD can usually, but not invariably, be placed into one of the broad categories listed in the table overleaf. The following are the most important features to note on a plain chest X-ray of a patient with known or suspected CHD: • The size and shape of the heart VDahya MBBCh

• The state of the pulmonary vasculature • The position and shape of the aortic arch • The cardiac and visceral situs • Skeletal abnormalities • Evidence of cardiac failure • Evidence of infection The size and shape of the heart It is generally accepted that the normal cardiothoracic ratio (CTR) between nought and two years of age is 60% and that over the age of four years it should be 50%. It stands to reason that the CTR between the ages of two and four is between 50% and 60%. An enlarged heart may be the only sign of CHD early on, highlighting the importance of measuring the CTR accurately (see Figure 1). vessels. These characteristic shapes occur only in the minority of examples of each anomaly. The snowman appearance of TAPVD can easily be caused by the thymic shadow of the young child. Also, with early surgery, these characteristic shapes are now rarely seen.

The state of the pulmonary vasculature
The assessment of the pulmonary vasculature is extremely important, but unfortunately remains quite subjective and requires good quality radiographs for the observer to be confident. The radiologist needs to decide if the lungs are oligaemic (decreased pulmonary blood flow) or plethoric (increased pulmonary blood flow). One easy method of noting plethora is to obliterate the medial two-thirds of each lung; if vessels are easily noted in the outer third, there is likely to be increased pulmonary blood flow (see Figure 3a).An additional finding commonly noted in patients with increased pulmonary blood flow is diffuse hyperinflation of the lungs with sloping of and flattening of the hemidiaphragms, anterior bowing of the chest wall and widening of the intercostal spaces (see Figure 3b). The state of the pulmonary vasculature in conjunction with the colour of the patient, Le. cyanotic or acyanotic (which is usually noted on the request form), forms the basis of our classification in the

Position of the aortic arch
The importance of assessing the position of the aortic arch lies in its association with specific cardiac anomalies as well as the planning of shunt procedures. A right-sided aortic arch is found in 25% of Tetralogy of Fallot, 25% of DORV (double-outlet right ventricle), 35% of truncus arteriosis and 12,5% of single-ventricle anomalies.
The position of the arch is often not easy to assess in the young child. One useful hint is to note the position of the trachea, which is normally slightly deviated to the right in the child. If the trachea is central or displaced to the left, one should suspect a right-sided aortic arch (see Figure 4).
An important observation is that the shape of the aortic arch is often abnormal in coarctation.

Cardiac and visceral situs
The incidence of CHD is high in patients with dextrocardia and normally sited abdominal viscera. The incidence of CHD in patients with true situs inversus (heart and abdominal viscera on reversed side) is much lower and, in fact, is almost the same as that for the normal population (see Figure 5).

Skeletal abnormalities
A most important observation to be made is to assess for evidence of previous surgery. A sternotomy usually means that the cardiac defect has been corrected. A thoracotomy is usually done for one of the following procedures: pulmonary artery banding, Blallock/modified Blallock shunt (see Figure 6), closure of a PDA or repair of a coarctation of the aorta.  Notching of the ribs can be noted in the older child (usually after the age of 10 years) with coarctation of the aorta. This can also be a feature of the child with a long-standing Blallock shunt.
One should always remember that the cardiac lesion may be part of a syndrome or a complex of anomalies. An example of a complex of anomalies is the VACTREL (vertebral, anorectal, cardiac, tracheal, renal, oesophageal, limb) association. Common syndromes include Down's syndrome (trisomy 21), which is associated with endocardial cushion defects, VSDs and Tetralogy of Fallot, and Turner's syndrome, which is associated with aortic coarctation.

Evidence of cardiac failure
The features of cardiac failure on the chest X-ray should be actively sought. These features include upper-lobe blood diversion, peri-hilar haze, pleural effusions and septal lines (see Figure 7). In children, Kerley A lines are often more prominent than Kerley B lines, unlike the situation in adults.
The importance of cardiac failure lies in the fact that it has some prognostic value. For example, a lone ASD or a VSD with a shunt less than 2: 1 (pulmonary to systemic flow) is unlikely to cause cardiac failure early on, whereas a larger left to right shunt having a worse prognosis will cause cardiac failure sooner.