Chest X-ray continues to have an important and integral role in diagnosis of both congenital heart diseases (CHD) and acquired heart diseases (AHD). Its role may have declined over the past two decades because of many factors. These factors include advent of echocardiography, less of late diagnosis, thereby decline of classical X-ray appearances and appearance of newer imaging tools. Still it has a pride of place in clinical cardiology, both in adults and children.
In children with suspected heart lesions, usually X-ray chest frontal view is taken; which is most often a PA view. The usual X-ray source – plate distance in adults is 180 cms, but is shorter in infants and young children. In small infants often what we obtain is an AP view. Lateral view could be useful as well as oblique view, but to a limited extent. Barium study is more or less extinct except in suspected vascular ring, vascular sling or situs problems. Fluoroscopy can be useful in assessing prosthetic valve function.
X-rays are often taken in three situations
a. Diagnostic issues in both CHD and Acquired HD.
b. Pre operative and post operative evaluation.
c. Periodic evaluation of already diagnosed heart disease.
It is to be noted that normal chest x-ray need not rule out structural cardiac problem and conversely a normal heart can have an apparently abnormal cardiac shadow. Still, a well taken chest x-ray is an important clinical tool for Pediatrician, Pediatric Cardiologist, Radiologist and Family physician.
X-rays are routinely taken using a non portable machine. Portable x-rays are AP and have other inherent limitations, including creating an impression of cardiomegaly.
Currently digital x-rays are becoming popular in bigger centers and labs. It can be of indirect digital format or direct digital format. Direct format are film less. Digital radiographs have the advantages of ability for storage, archival, transmission, less of radiation and less of time consumption.
Normal Chest X-ray
It is preferably taken PA. Child is in upright position. The exposure time currently is less than 100 m seconds, reducing motion blurring. It is ideally taken during inspiration and the diaphragm must be at the level of 9th rib or so. Normally right cardiac border consists of right atrium and superior vena cava and occasionally ascending aorta. Left heart border consists of aortic knuckle, pulmonary. Artery segment, left atrial appendage (concavity) and left ventricle. Lung zones are divided into three horizontal are as– medial, intermediate and lateral. In the vertical axis, it is divided into upper zone and lower zone as far as the vascularity is concerned, especially venous vascularity.
Whenever an X-ray chest is assessed one must note the age of child, date of X-ray and position (marker – right or left).
How to read X-ray chest in cardiology?
We expect the heart shadow to be on the left side. But dextrocardia can occur as evidenced by occupation of major cardiac shadow on the right hemithorax with apex pointing to right. There can be a midline heart also (Mesocardia). Dextrocardia has to be differentiated from dextroposition, where the heart is on the right due to abnormal thoracic structures or changes eg: diaphragmatic hernia; agenesis of lung; collapse or fibrosis of lung.
In the presence of true dextrocardia one should make out situs – whether liver is on the right and stomach shadow is on left or vice versa – situs solitus and in versus. In dextrocardia with situs inversus, CHD is present in 5%; in situs solitus with dextrocardia it is 90% and in Levocardia with situs in versus CHD occurs in 100%.
Assessment is generally subjective. However Cardio Thoracic Ratio (CTR) can be measured by measuring maximum internal thoracic diameter at the level of diaphragm and measuring cardiac diameter which is maximum and dividing the latter by former.
Normal CTR in adult is 45% (mean).
Cardiomegaly in adult is CTR > 50%
In new born is CTR > 57%
Infant is CTR > 55%
A small heart (microcardia) can rarely occur when CTR is less than 40%. It occurs in Addison’s disease, anorexia nervosa, severe PEM and in COPD.
Contour of heart shadow usually gives information regarding ventricular hypertrophy / enlargement.
Mild right ventricular enlargement does not cause cardiomegaly. Modest or marked enlargement causes cardiomegaly with rotated apex which is elevated from diaphragm which gives rise to an upturned apex. An upturned apex without cardiac enlargement occurs in right ventricular hypertrophy.
RV Apex - No cardiomegaly
Tetralogy of Fallot
- Cardiomegaly d- TGA.
DORV. VSD. PAH
VSD . PAH
Left ventricle (LV) is border forming on the left side and hence can be evidently enlarged easily. The apex is shifted down and laterally and even can be below diaphragm. There will be rounding off the apex and elongation of long axis of LV. In DCM heart can be enlarged and can be globular. In LV aneurism, there could be a bulge on left heart border. Cardiomegaly with LV apex occurs in large PDA, VSD, AR, MR and DCM.
Right atrial enlargement is relatively rare in children. It forms a prominent convexity on the right side which is lower and more lateral. It can be seen as a large diffuse bulge on right side. In adults right atrial enlargement is said to be present if distance from midline to right heart border is > 5.5 cms. In young children it is > 4 cms. RA enlargement can occur in Ebstein, RV EMF and Tricuspid Atresia.
Left atrial enlargement in frontal view can manifest in many ways.
a. Prominent LA appendage on left border (normally this area is concave).
b. Elevation of left bronchus (well appreciated in well penetrated or digital X-ray)
c. Widening of carinal angle
d. Shadow on shadow (double shadow) appearance.
E. Great Vessels
Ascending aorta can be border forming on the right side and aortic knuckle is the upper most part of left heart border. Arching – left or right can be made out by ipsilateral indentation of trachea. Dilated aortic shadow can occur in AS, AR, Hypertension, Coarctation of Aorta and aneurism of Aorta. Bicuspid Aortic valve with no AS can also make Aorta prominent.
Main pulmonary artery (MPA) and its branches can be assessed. MPA divides into right and left and the left PA is a continuation of MPA. RPA shortly divides into 2 branches at right hilum – a smaller ascending pulmonary artery and a larger descending pulmonary artery (RDPA). In adults both LPA and descending RPA are between 9-15 mm in size near the hilum. Pa s are dilated in PS, PAH, Idiopathic Dilatation, Absent Pulmonary Valve syndrome and in Eisenmenger syndrome.
F. Pulmonary vascularity
Abnormal pulmonary vascularity can be generally divided into four types.
3. Pulmonary venous hypertension
4. Pulmonary Edema
a. Pulmonary oligemia
Vascular shadows are reduced. They are not seen even in the intermediate Lung zones. MPA, LPA and Right descending PA (RDPA) are all small. (Normally RDPA is of the same size as Rt Lower lobe bronchus). Oligemia occurs in TOF, severe PAH, critical PS with reversal of shunt etc.
b. Pulmonary plethora
Vascular shadows are numerous. They are seen in the lateral one third of lung fields. MPA, LPA and RDPA are large. End on vessels are more in number (> 5 in number per both lungs). The end on vessel diameter is more than that of accompanying bronchus. There will be left atrial or right atrial enlargement usually.
Plethora occurs in L ® R shunts, Admixture lesions and d-TGA without PS. To have plethora L ® R should be at least 1.5:1.
Occasionally there can be unilateral plethora as in BT shunt, unilateral MAPCA. Asymmetry in lung vascularity can also occur in Glenn surgery and PA branch stenosis.
c. Pulmonary venous hypertension (PVH):
Normally upper lobe veins are less prominent than lower lobe veins. In PVH there is equalization of the vascularity. When pulmonary venous pressure is > 12 mm Hg, upper lobe veins are equal in size to lower lobe veins. When it is > 15 mm Hg, Kerley B lines (Lateral, septal lines) and Kerley A lines (longer, linear lines reaching hilum) are present with occasional pleural effusion. When the pressure is > 25 mm Hg, frank alveolar edema occurs.
d. Pulmonary edema
Occurs when Pulmonary Venous pressure exceeds 25-28 mmHg. There is alveolar edema, reaching to hilum and a typical ‘bat Wing’ appearance.
PVH and Edema occur in mitral valve disease, obstructed TAPVC, HLHS, DCM etc.
i. Cephalization - in PVH
ii. Centralization (Pruning) - in severe PVOD (Pulmonary vascular
iii. Lateralization - Unilateral pulmonary embolism
iv. Localization - in pulmonary AV Fistula
v. Collateralization - in TOG etc.
G. Other Abnormalities
They include cervical rib, rib notching (3 rd to 8th ribs), ductal calcium, mitral and aortic valve calcium, calcification of Aorta, LV aneurism and pericardium, associated pneumonia, collapse and bronhiectasis.
1. New born X-ray
The x-ray is of lesser value as there is not enough time to develop classical radiological features like figure of 8 appearance etc. Lungs appear blackish and oligemic in newborn. One major use of a X-ray is to help differentiate a cardiac pathology from respiratory pathology in a new born with respiratory distress. It is always useful in cardiac malpositions in the new born.
Thymic shadow in infancy can cause diagnostic confusion. It can mimic cardiomegaly, tumor of mediastinum and even TAPVC.
STANDARD FORMAT FOR X-RAY CHEST READING
1. Chest X-ray Frontal / PA / AP
*2. Levocardia / Dextrocardia / Mesocardia with situs
3. Cardiomegaly – mild / moderate / Marked / CT Ratio
4. LV Contour / RV contour / can’t say
5. LA enlargement / RA enlargement. / Bi atrial
6. Aorta / Pulmonary Artery and Branches
7. Pulmonary vascularity / categorization
8. Others – Lungs. Ribs. Thymus etc.
9. Classic descriptions if any eg: Figure of 8; Egg on side.
* in infants
* Professor of Pediatric Cardiology, Department of Pediatrics, Government Medical College, Thiruvananthapuram
** Associate Professor of Pediatrics, Moulana Azad Medical College. New Delhi
*** Professor and HOD, Department of Pediatrics, Government Medical College , Thiruvananthapuram