Chest

X-Ray

Cardiothoracic Ratio (Adults - PA View)

< 0.5

Normal Value

Measured as Maximal cardiac width ÷ Thoracic width (inner rib to inner rib at diaphragm level). CTR > 0.5 = cardiomegaly. Most reliable on PA films.

Cardiothoracic Ratio (Adults - AP View)

Often > 0.5 (not reliable)

Normal Value

AP view exaggerates heart size due to magnification and shorter source-to-image distance. Portable ICU films often misleading.

Cardiothoracic Ratio (Pediatrics - PA View)

< 0.6 in infants (<1 yr)

Normal Value

Higher normal cutoff in children due to relatively larger thymus and smaller thoracic cage.

Cardiothoracic Ratio (Pediatrics - AP View)

Often > 0.6

Normal Value

Even less reliable because both thymus and AP magnification contribute to apparent cardiomegaly.

Trachea AP Diameter

1.5 – 2.5 cm

Normal Value

Measured at thoracic inlet (C6–T1). Narrowing → tracheal stenosis; widening → tracheomalacia. Deviation suggests thyroid mass, mediastinal mass, or tension pneumothorax.

Diaphragmatic Contour

Smooth, dome-shaped

Normal Value

Right hemidiaphragm usually 1–2 cm higher than left (due to liver). Flattening → COPD/hyperinflation. Elevated → subphrenic pathology or diaphragmatic paralysis.

Costophrenic Angles

Sharp & acute

Normal Value

Blunting suggests pleural effusion or chronic pleural thickening. Best seen on erect PA film.

Hilar Structures

Left hilum slightly higher

Normal Value

Normally pulmonary arteries dominate. Enlargement suggests pulmonary hypertension, sarcoidosis, or lymphoma.

Mediastinal Width

< 8 cm (at aortic arch on PA view)

Normal Value

Widening (>8 cm) suggests mediastinal mass, aortic aneurysm, or trauma (mediastinal hematoma).

Lung Fields

Clear, equal translucency

Normal Value

Check for asymmetry, opacities, consolidation, nodules. Hyperlucency suggests emphysema or pneumothorax.

Ribs & Bony Thorax

Normal cortical outline, alignment

Normal Value

Look for fractures, lytic/sclerotic lesions → trauma, metastases, metabolic bone disease.

Measurement	Normal Value	Comments
Cardiothoracic Ratio (Adults - PA View)	< 0.5	Measured as Maximal cardiac width ÷ Thoracic width (inner rib to inner rib at diaphragm level). CTR > 0.5 = cardiomegaly. Most reliable on PA films.
Cardiothoracic Ratio (Adults - AP View)	Often > 0.5 (not reliable)	AP view exaggerates heart size due to magnification and shorter source-to-image distance. Portable ICU films often misleading.
Cardiothoracic Ratio (Pediatrics - PA View)	< 0.6 in infants (<1 yr)	Higher normal cutoff in children due to relatively larger thymus and smaller thoracic cage.
Cardiothoracic Ratio (Pediatrics - AP View)	Often > 0.6	Even less reliable because both thymus and AP magnification contribute to apparent cardiomegaly.
Trachea AP Diameter	1.5 – 2.5 cm	Measured at thoracic inlet (C6–T1). Narrowing → tracheal stenosis; widening → tracheomalacia. Deviation suggests thyroid mass, mediastinal mass, or tension pneumothorax.
Diaphragmatic Contour	Smooth, dome-shaped	Right hemidiaphragm usually 1–2 cm higher than left (due to liver). Flattening → COPD/hyperinflation. Elevated → subphrenic pathology or diaphragmatic paralysis.
Costophrenic Angles	Sharp & acute	Blunting suggests pleural effusion or chronic pleural thickening. Best seen on erect PA film.
Hilar Structures	Left hilum slightly higher	Normally pulmonary arteries dominate. Enlargement suggests pulmonary hypertension, sarcoidosis, or lymphoma.
Mediastinal Width	< 8 cm (at aortic arch on PA view)	Widening (>8 cm) suggests mediastinal mass, aortic aneurysm, or trauma (mediastinal hematoma).
Lung Fields	Clear, equal translucency	Check for asymmetry, opacities, consolidation, nodules. Hyperlucency suggests emphysema or pneumothorax.
Ribs & Bony Thorax	Normal cortical outline, alignment	Look for fractures, lytic/sclerotic lesions → trauma, metastases, metabolic bone disease.