Laboratory Studies
Relevant laboratory studies include the following:
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A CBC with differential may reveal a leukocytosis and a left shift.
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Collect sputum for Gram staining, culturing, and sensitivity testing.
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If tuberculosis is suspected, acid-fast bacilli testing should be obtained.
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In the presence of fever, obtaining a blood culture may be appropriate.
Additional potentially useful tests include the following:
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Pulse oximetry to assess oxygenation
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ABG or VBG analysis to assess respiratory adequacy
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Transtracheal aspiration for culturing (if sputum findings are nondiagnostic)
Imaging Studies
Perform chest radiography to diagnose and differentiate pneumonia, pulmonary abscess, and empyema. Distinction of these conditions is important because lung abscesses and pneumonia require medical treatment, while empyema frequently requires definitive surgical therapy. Several radiographs are shown below.
A 54-year-old patient developed cough with foul-smelling sputum production. A chest radiograph shows lung abscess in the left lower lobe, superior segment.
A 42-year-old man developed fever and production of foul-smelling sputum. He had a history of heavy alcohol use, and poor dentition was obvious on physical examination. Chest radiograph shows lung abscess in the posterior segment of the right upper lobe.
Chest radiograph of a patient who had foul-smelling and bad-tasting sputum, an almost diagnostic feature of anaerobic lung abscess.
On the chest radiograph, a lung abscess appears as a solitary cavitary area with an air-fluid level, which typically is present in a dependent portion of the lung. A surrounding patchy area of infiltrate aids in differentiating a pulmonary abscess from a cavitary lung cancer.
On the chest radiograph, findings that suggest empyema, as opposed to lung abscess, include extension of the air-fluid level to the chest wall, extension of the air-fluid level across fissure lines, and a tapering border of the air-fluid collection.
The costophrenic angle should be closely inspected on the chest radiograph to assess the presence of fluid that suggests effusion or empyema.
On the chest radiograph obtained of the patient in an upright position, blunting of the costophrenic angle occurs when approximately 200 mL of fluid accumulates.
A lateral chest decubitus radiograph, obtained with the patient on his or her side, reveals whether the pleural fluid is mobile and forms layers or whether it is loculated.
To better assess any abnormal lung findings found on a chest radiograph, CT of the chest or ultrasonography is usually necessary. Ultrasonography is useful for needle-guided aspiration and drainage of a potential pleural effusion or empyema. When ultrasonography is not used to guide needle aspiration, the failure rate is 12-15%. Color Doppler ultrasonography can also assist in differentiating empyema from peripheral air-fluid pulmonary abscess. Chen et al reported in a retrospective study that identification of color Doppler ultrasonography vessel signals in pericavitary consolidation was useful and specific for identifying lung abscesses, with sensitivity of 94% and specificity of 100%. [17]
CT of the chest can assess for pneumonia, lung abscess, tumor, pleural effusions and septations, other pleural diseases, or pleural thickening. CT of the chest has shown increased sensitivity for detection of pulmonary infections compared to chest radiograph, especially for immunocompromised individuals. Chest CT may be considered when the index of suspicion for significant pulmonary infection is high despite a negative radiograph findings. [5]
Many clinicians recommend limiting the use of CT in children to reduce radiation exposure. Jaffe et al studied the utility of routine CT scanning in children and concluded that, while CTs detected more parenchymal abnormalities, the additional information did not alter management and it did not predict clinical outcome in patients who were being treated with chest tube drainage and fibrinolytics. [18] The British Thoracic Society guidelines conclude that chest CT has no role in the routine identification of pleural collections in children. [19]
A lung abscess in an adult is shown in the image below.
A 42-year-old man developed fever and production of foul-smelling sputum. He had a history of heavy alcohol use, and poor dentition was obvious on physical examination. Lung abscess in the posterior segment of the right upper lobe was demonstrated on chest radiograph. CT scan shows a thin-walled cavity with surrounding consolidation.
Procedures
If a pleural effusion is present, a diagnostic thoracentesis may be performed and analyzed for pH, lactate dehydrogenase, glucose levels, specific gravity, and cell count with differential. Pleural fluid may also be sent for Gram stain, culture, and sensitivity. Acid-fast bacillus testing may also be considered.
The fluid may be sent for cytology if cancer is suspected.
The following findings are suggestive of an empyema or parapneumonic effusion that will likely need a chest tube or pigtail catheter for complete resolution:
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Grossly purulent pleural fluid
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pH level less than 7.2
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WBC count greater than 50,000 cells/µL (or polymorphonuclear leukocyte count of 1,000 IU/dL)
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Glucose level less than 60 mg/dL
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Lactate dehydrogenase level greater than 1,000 IU/mL
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Positive pleural fluid culture
There is increasing evidence that tumor necrosis factor (TNF)–alpha may be used to help determine whether a pleural effusion is a complicated parapneumonic effusion or an empyema. [20, 21, 22]
Histologic Findings
In acute lung abscess, there are necrotic tissue mixed with necrotic granulocytes and bacteria in the central parts. Around this area there are preserved neutrophilic granulocytes with dilated blood vessels and inflammatory edema. In chronic lung abscess, puss is present with or without bacteria. Around the abscess is a pyogenic membrane and around the pyogenic membrane are lymphocytes, plasma cells, and histiocytes in connective tissue. [4]
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Histology of a lung abscess shows dense inflammatory reaction (low power).
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A thick-walled lung abscess.
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Pneumococcal pneumonia complicated by lung necrosis and abscess formation.
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A lateral chest radiograph shows air-fluid level characteristic of lung abscess.
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A 54-year-old patient developed cough with foul-smelling sputum production. A chest radiograph shows lung abscess in the left lower lobe, superior segment.
-
A 42-year-old man developed fever and production of foul-smelling sputum. He had a history of heavy alcohol use, and poor dentition was obvious on physical examination. Chest radiograph shows lung abscess in the posterior segment of the right upper lobe.
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A 42-year-old man developed fever and production of foul-smelling sputum. He had a history of heavy alcohol use, and poor dentition was obvious on physical examination. Lung abscess in the posterior segment of the right upper lobe was demonstrated on chest radiograph. CT scan shows a thin-walled cavity with surrounding consolidation.
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Chest radiograph of a patient who had foul-smelling and bad-tasting sputum, an almost diagnostic feature of anaerobic lung abscess.
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Histology of a lung abscess shows dense inflammatory reaction (high power).
