Differential diagnosis for a small cardiothoracic ratio

A small cardiothoracic ratio (CTR) is defined as <42%/0.42 when assessed on a PA chest radiograph, and is often called small heart syndrome. A pathologically-small heart is also known as microcardia. 

It can be due to/associated with a number of entities:

• adrenal insufficiency, e.g. Addison disease

• heart transplant

• cachectic state 

  • advanced age

  • malnutrition

  • bulimia nervosa

  • anorexia nervosa

  • advanced malignancy

• asthmatic paroxysm with emphysema

• constrictive pericarditis

• myalgic encephalomyelitis/chronic fatigue syndrome​ (ME/CFS) ³

• physiological factors: e.g. Valsalva maneuver