Aspiration pneumonia is caused by a direct chemical insult due to the entry of a foreign substance, solid or liquid, into the respiratory tract.
Aspiration may be clinically silent, or it may present with dyspnoea, cough or fever. The clinical and radiographic features depend on the aspirated volume, pH and chronicity 2.
According to time of onset it may be divided into two groups:
- acute aspiration pneumonitis
chronic aspiration pneumonia: recurrent aspiration pneumonia
- mixed anaerobic aerodigestive tract organisms are the underlying causative agent 4
The clinical and radiological manifestations are protean, varying from asymptomatic focal inflammatory reaction with few or no radiological abnormalities to severe life-threatening disease.
- alcohol intoxication
- general anaesthesia
- loss of consciousness
- structural abnormalities of the pharynx and oesophagus
- neuromuscular disorders
- swallowing disorders
- laparoscopic gastric banding
A chest x-ray may demonstrate airspace opacification in a lobar or segmental distribution. There may be a gravity dependent predilection.
The posterior segment of the upper lobes and the superior segment of the lower lobes are most commonly involved lung sites when aspiration occurs in a recumbent patient. In an erect patient, aspiration is more likely to involve bilateral basal segments, right middle lobe and lingula 2.
Aspirated low-density organic material such as mineral oil in the tracheobronchial tree or alveolar spaces cannot be diagnosed on plain radiographs, but they can be demonstrated on CT scans.
Opaque aspirates are also well demonstrated on CT scans.
Treatment and prognosis
The major complication associated with aspiration is pulmonary infection:
Other causes of airspace opacity need to be considered 3:
- 1. Franquet T, Giménez A, Rosón N et-al. Aspiration diseases: findings, pitfalls, and differential diagnosis. Radiographics. 20 (3): 673-85. Radiographics (full text) - Pubmed citation
- 2. Kim M, Lee KY, Lee KW et-al. MDCT evaluation of foreign bodies and liquid aspiration pneumonia in adults. AJR Am J Roentgenol. 2008;190 (4): 907-15. doi:10.2214/AJR.07.2766 - Pubmed citation
- 3. Pediatric Radiology (Rotations in Radiology). Oxford University Press. ISBN:0199755329. Read it at Google Books - Find it at Amazon
- 4. Brant WE, Helms C. Fundamentals of Diagnostic Radiology. Lippincott Williams & Wilkins. (2012) ISBN:1608319113. Read it at Google Books - Find it at Amazon