Radiography
A 53-year-old patient with severe Legionella pneumonia. Chest radiograph shows dense consolidation in both lower lobes.
A 40-year-old patient with Chlamydia pneumonia. Chest radiograph shows multifocal, patchy consolidation in the right upper, middle, and lower lobes.
A 38-year-old patient with Mycoplasma pneumonia. Chest radiograph shows a vague, ill-defined opacity in the left lower lobe.
Findings
Legionella pneumonia
Legionella species are implicated in 2-15% of CAP cases.
These organisms usually cause a patchy, localized infiltrate in the lower lobes. Associated hilar adenopathy may be present. Pleural effusion is seen in up to 30% of cases. In rare instances, Legionella infection is associated with cavitation and a masslike appearance.
Radiologic resolution of Legionella pneumonia may take 6-12 months. Permanent residual fibrosis is observed in as many as 25% of patients. An early progression of infiltrates can occur despite clinical improvement.
Mycoplasma pneumonia
M pneumoniae is implicated in 2-30% of all cases of CAP. Mycoplasma pneumonia is usually mild and results in a rapid resolution of any radiologic findings. However, it tends to be more severe in patients with sickle cell anemia. Radiographic resolution in 40% of patients occurs in 4 weeks, and 80% of cases resolve by 8 weeks. Residual radiographic abnormalities are uncommon.
The infiltrates in Mycoplasma pneumonia can be unilateral, multilobar, or bilateral. In about 20% of patients, pleural effusion or hilar adenopathy may be present.
Chlamydia pneumonia
The infiltrates may be subsegmental or more extensive in elderly patients; pleural effusions are rarely seen. Chest radiographs show 50% resolution in 4 weeks. In 20% of cases, resolution takes longer than 9 weeks.
Degree of Confidence
Radiologic findings alone are not reliable in differentiating pneumonia into typical or atypical forms. Therefore, the radiographic findings described above should be used along with clinical and laboratory data to narrow the possibilities.
Structural lung disease with abnormal lung parenchyma affects the pattern of infiltrates. In cases of severe emphysematous lung disease, clinicians may tend to underestimate the presence of infiltrates on chest radiographs.
Computed Tomography
Chest computed tomography scan in the same patient as in Multimedia Image 3 shows the ill-defined, airspace infiltrate in the left lower lobe better than Image 3 does.
Chest computed tomography scan in a 45-year-old patient with Chlamydia pneumonia shows a right upper-lobe infiltrate.
Image in a 66-year-old patient with Legionella pneumonia. Chest computed tomography scan shows dense alveolar consolidations in both lower lobes.
Although this patient smokes, this lesion most likely has an inflammatory etiology, given the clinical symptoms and a recent, normal CT scan. Appropriate management includes repeat CT scanning in 3 months if the lesion persists or enlarges despite clinical improvement.
Findings
CT scans are increasingly being used in clinical practice. Various authors have questioned CT scanning's usefulness in evaluating consolidations, suggesting that the value of CT in the diagnosis of pneumonia is limited to specific cases involving (1) an indistinct, abnormal opacity on chest radiographs; (2) patchy, ground-glass, linear, or reticular opacities on chest radiographs; (3) possible pleural effusion; and (4) neutropenia and fever of unknown origin (for which ultra–thin-section CT scanning may be helpful).
High-resolution CT findings in CAP
Tanaka et al compared high-resolution CT (HRCT) scan findings in CAP with pathologic findings and evaluated the role of HRCT scanning in differentiating between bacterial and atypical pneumonias in 32 patients with CAP (18 with bacterial pneumonia, 14 with atypical pneumonia).14
Bacterial pneumonia often resulted in airspace consolidation with a segmental distribution (72%) that typically occurred toward the middle and outer zones of the lungs. Atypical pneumonias included Mycoplasma and Chlamydia pneumonias, as well as influenza viral pneumonia. These conditions frequently caused a centrilobular shadow (64%), an acinar shadow (71%), and/or airspace consolidation (57%) and ground-glass attenuation (86%) with a lobular distribution. The lesions were often distributed to the inner, middle, and outer layers of the lung (86%).
Legionella pneumonia
Mild Legionella pneumonia may manifest with bilateral involvement of the lung parenchyma. Multiple segments are affected, and peripheral lung consolidation with ground-glass opacity and pleural effusion may be seen. With more severe infection, lung cavitation and bulging of the fissure have been reported. Residual lung parenchymal scarring can be found, even after the acute infection resolves.15
Mycoplasma pneumonia
Reittner et al examined 28 patients, identifying ground-glass attenuation in 24 (86%) and airspace consolidation in 22 (79%). In 13 of the latter 22 patients (59%), the areas of consolidation had a lobular distribution. Nodules were more common on HRCT scans (89%) than on radiographic images (50%), and in 24 of 28 patients (86%), the nodules had a predominantly centrilobular distribution on CT scans. Thickening of bronchovascular markings were more often found with CT scanning (82%) than with radiography (18%).16
Degree of Confidence
Coinfection with several organisms is not uncommon. Underlying parenchymal lung abnormalities usually predispose patients to pneumonia. Therefore, in patients with pneumonia, the overall clinical and radiologic picture must be considered in place of an independent, dichotomous view.
Ultrasonography
Findings
The literature suggests that ultrasonography can help in differentiating between consolidation and effusion. Consolidated lung tissue may appear as hypoechoic areas with blurred margins. The texture varies with the amount of aeration, being more heterogeneous with aeration and more homogeneous with dense consolidation. The literature also reports that sonography may aid in the diagnosis of empyema and abscesses. However, the current authors believe that in clinical practice, sonography's usefulness is limited to the identification and quantification of parapneumonic effusions. Once found, the area where an effusion occurs can be marked for subsequent diagnostic or therapeutic thoracentesis.
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Further Reading
Keywords
walking pneumonia, atypical pneumonia, Legionella pneumonia, Chlamydia pneumonia, Mycoplasma pneumonia, Mycobacterium tuberculosis, community-acquired pneumonia, CAP, Legionnaires disease, Legionnaire's disease, Legionnaires' disease, Legionella pneumophila, Legionella micdadei, Mycoplasma hominis, Ureaplasma urealyticum, Chlamydia psittaci, Chlamydia trachomatis, Chlamydia pneumoniae, TWAR agent
