Introduction
Aspiration is defined as entry of a foreign substance, solid or liquid, into the respiratory tract or inhalation of fumes and vapors. Aspiration pneumonia is an infectious process caused by aspirated oropharyngeal flora. Aspiration pneumonitis, which is caused by a direct chemical insult due to the aspirated material, is technically a different entity, but is often referred to as aspiration pneumonia. (See the images below.)
Aspiration pneumonia. A 29-year-old man with history of cerebral palsy and seizure disorder was brought to the emergency department because he had decreased responsiveness for 3 days. The patient was in respiratory distress on arrival and was immediately intubated. His vital signs were as follows: temperature, 92.9°F; blood pressure, 85 mm Hg/23 mm Hg, respirations, 25 per minute; and heart rate, 89 per minute. Chest radiograph revealed an endotracheal tube far above the carina, bilateral opacities, and a well-defined right upper lobe consolidation.
Aspiration pneumonia. CT scan through the lower-lobe bronchi demonstrates a metallic object in the left lower-lobe bronchus. The patient had aspirated a filling, which had fallen out of one of his teeth. The patient underwent bronchoscopy, and the foreign body was removed. The patient was treated with antibiotics for the pneumonia, which eventually resolved. Incidentally, a small pleural effusion on the right side was due to minimal congestive heart failure (CHF).
The clinical history is important in diagnosing aspiration pneumonia. The nature of the aspirated material, the quantity of aspirated material, and the time course of the event influence the size and distribution of the lung parenchymal abnormality. The most common predisposing factors for aspiration in adults are alcoholism, stroke and other neuromuscular disorders, seizures, and loss of consciousness.
Preferred examination
Chest radiography is readily available and inexpensive and is by far the most commonly used imaging test to evaluate aspiration pneumonia.1,2,3,4 Traditionally, posteroanterior (PA) and lateral chest radiographs have been recommended for imaging aspiration pneumonia and its complications. However, because many patients are not able to cooperate for PA and lateral imaging, anteroposterior (AP) portable images have been more commonly used for diagnosis.
Computed tomography (CT) scanning is the best method for diagnosing aspiration pneumonia, an abscess, or an empyema. CT scanning precisely delineates the location of the lobar or segmental opacity. A foreign body in the tracheobronchial tree and associated atelectasis or consolidation can be defined with relative ease on CT scans. Aspiration of specific material such as fat or contrast material can sometimes be determined by measuring the tissue attenuation on CT scans. Esophageal abnormalities may also be seen on CT images without the need for contrast material. Necrosis, cavity formation, and empyema are all complications of aspiration pneumonia that are seen better and earlier with CT scanning than with plain radiography.
The patient's swallowing mechanism can be studied by using fluoroscopy with a contrast agent. This is a real-time evaluation of the swallowing process that is often performed in conjunction with speech therapy.
Magnetic resonance imaging (MRI) is more sensitive than plain radiography. To date, no large study has been performed to compare MRI with CT scanning for the evaluation of aspiration.
Limitations of techniques
Radiography remains the most practical first-line imaging study for patients with suspected aspiration pneumonia. Chest radiographs usually adequately demonstrate lung consolidation, atelectasis, and abscess formation. However, CT scanning is more sensitive and specific than radiography.5,6
Many factors affect the appearance on initial studies, including the patient's hydration status, his or her ability to mount an adequate inflammatory response, and the nature and amount of aspirate. Days may pass before aspiration is visible on imaging studies.
More on Aspiration Pneumonia Imaging |
 Overview: Aspiration Pneumonia Imaging |
| Imaging: Aspiration Pneumonia Imaging |
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References
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Further Reading
Keywords
aspiration pneumonia, chemical insult, bacterial infection, fume inhalation, vapor inhalation, aspirated foreign material
