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1
Department of Radiology, Thomas Jefferson University Hospital, 111 S. 11th
St., Ste. 3390 Gibbon, Philadelphia, PA 19107.
2
Department of Radiology, Yale University School of Medicine, 333 Cedar St.,
New Haven, CT 06520.
3
Department of Radiology, Medical College of Georgia, 1120 15th St., Augusta,
GA 30912.
4
Department of Infectious Disease, Medical College of Pennsylvania, 3300 Henry
Ave., Philadelphia, PA 19129.
Received April 22, 1999;
accepted after revision May 12, 2000.
Presented at the annual meeting of the American Roentgen Ray Society, San
Francisco, April-May 1998.
Abstract
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MATERIALS AND METHODS. Eighty-one patients with community-acquired pneumococcal pneumonia and positive findings on admission chest radiographs were selected from a group of 105 patients with positive findings for Streptococcus pneumoniae from sputum or blood cultures. Patients less than 16 years old and those with nosocomial pneumonia, aspiration pneumonia, or coexistent lung disease were excluded. The dominant pattern was classified as lobar or lobular bronchopneumonia by two radiologists who were unaware of results from blood cultures and HIV testing.
RESULTS. Forty-three females and 38 males, with a mean age of 48 years (age range, 16-92 years), required admission for pneumococcal pneumonia. Fifty-nine (73%) of the 81 patients were bacteremic and 20 (25%) of the 81 patients were HIV-positive, including 14 patients (17%) who were both bacteremic and HIV-positive. Among all the patients, focal lobar consolidation was the most common pattern, observed in 48%. Multifocal lobar consolidation was the next most frequent pattern, occurring in 33%. Multifocal and focal bronchopneumonia patterns were seen in 16% and 2% of the patients, respectively. Overall, multifocal consolidation occurred in 49%. The dominant radiographic pattern and incidence of multicentric disease were not affected by HIV seropositivity (p = 0.61) or bacteremia (p = 0.17).
CONCLUSION. Lobar consolidation, involving single or multiple lobes, is the most common radiographic pattern of community-acquired pneumococcal pneumonia in patients requiring hospitalization. The pattern of consolidation is not influenced by bacteremia or HIV status.
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In addition to localized lobar consolidation, studies addressing the radiographic appearance of pneumococcal pneumonia in hospitalized or immunosuppressed patients frequently report atypical appearances, including bronchopneumonic or interstitial patterns [3,4,5].
We have observed a number of cases of multifocal pneumonia with striking lobar patterns that were later diagnosed as pneumococcal pneumonia in which HIV test results were positive. It was unclear to us if this variant pattern of pneumonia reflected HIV seropositivity or if it was a manifestation of disease severity leading to hospitalization. Although the previously mentioned literature has described the appearance of pneumococcal pneumonia in HIV-positive and hospitalized patients, we are not aware of a study directly comparing HIV-positive and HIV-negative patients who have pneumococcal pneumonia [4,5,6].
Our purpose was to determine if the dominant chest radiographic pattern of pneumococcal pneumonia in hospitalized patients was influenced by HIV status or general disease severity. We chose bacteremia as an indicator of severity.
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The dominant pattern seen on admission chest radiographs was classified as lobar or lobular bronchopneumonia by the consensus interpretation of two radiologists. According to classic radiologic descriptions, a lobar pattern of consolidation was considered present in the setting of homogeneous confluent air-space density, with or without associated findings of air bronchograms or the presence of acinar shadows [7, 8] (Fig. 1). The lobular or bronchopneumonia pattern was considered present when consolidation was heterogeneous, nonconfluent, and with prominent peribronchial thickening. [7, 8] (Fig. 2). Regardless of the size of the consolidation, any heterogeneity was classified as bronchopneumonic unless limited to the advancing edge of the infiltrate. The frequency of multilobar consolidation was also recorded. The reviewers were unaware of the clinical results of blood cultures and HIV testing.
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By consensus, lobar consolidation was present in 66 (81%) of the 81 patients. Lobular or bronchopneumonic consolidation was present in 15 (19%) of the 81 patients. Initial disagreement regarding the dominant pattern occurred in four cases, three of which were ultimately classified as lobar and one as bronchopneumonic. In the three cases of lobar consolidation, heterogeneity was limited to the periphery.
Focal lobar consolidation was the most common pattern, identified in 39 patients (48%), followed by multifocal lobar consolidation in 27 (33%), multifocal bronchopneumonia 13 (16%), and focal bronchopneumonia in two (2%) (Figs. 1, 3, and 4 and Table 1).
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The dominant radiographic pattern and the incidence of multicentric disease
were not affected by HIV seropositivity or bacteremia. Using the
Kruskal-Wallis test for a three-group comparison, we found no significance
(p = 0.61) between the incidence of focal or multifocal lobar
consolidation and bronchopneumonia with HIV seropositivity. Similarly, no
significance (p = 0.17) was found between focal or multifocal lobar
consolidation or bronchopneumonia patterns and positive results from blood
cultures. Power analysis revealed a power of 0.80 to detect differences of 35%
between the groups (
= 0.05, two-tailed).
Pleural effusions were noted in 12 patients, including 10 HIV-negative and two HIV-positive patients. Neither cavitation nor abscess formation was detected on any of the admission radiographs. Follow-up radiographs were not assessed.
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Despite significant limitations, the radiographic pattern approach to the diagnosis of pneumonia remains important. This may especially be true in the HIV-positive patient presenting with acute symptoms indicative of pneumonia. Treatment regimens differ significantly among pneumonias because of routine bacterial causes, Pneumocystis carinii, and other atypical organisms. Improvement in chest radiographic abnormalities during the course of treatment and adequate clinical response may be sufficient to prevent further diagnostic evaluation in most patients.
Familiarity with the common and uncommon radiographic appearances of pneumococcal pneumonia in the AIDS population is extremely important. According to the 1993 revised AIDS case definition by the Centers for Disease Control and Prevention [10], recurrent bacterial pneumonia is considered an AIDS-defining illness in the setting of positive HIV serology. Of the bacterial pneumonias in AIDS, S. pneumoniae is the most common, occurring five to 18 times more frequently than in the population at large [11,12,13]. The literature suggests a declining incidence of pneumocystis pneumonia, replaced by a rising incidence of bacterial pneumonia. In a prospective study of 1130 patients with HIV infection, Hirschtick et al. [11] found bacterial pneumonia to be the most common cause of pulmonary infection. This trend likely reflects the B-cell and neutrophilic dysfunction that are now recognized to occur in the early and advanced immunosuppressive stages of AIDS. Defects in B-cell or humoral immunity are primarily responsible for the increased rate of infection with encapsulated bacteria. Furthermore, there is an apparent tendency toward frequent complications, including abscess formation, empyemas, and bronchiectasis [14,15,16].
In agreement with early literature on the radiographic appearance of pneumococcal pneumonia, we were able to show that the focal lobar pattern of consolidation is the most common pattern of streptococcal pneumonia in all patients examined—regardless of HIV status or associated bacteremia. Multifocal lobar type consolidation, observed in one third of our patients, was the next most frequent variant pattern, also occurring independently of HIV status or bacteremic state. Together, multifocal lobar or bronchopneumonic patterns accounted for nearly half of all cases and were apparently unrelated to HIV status or bacteremic state. The high incidence of multifocal consolidation in our study may be related to the severity of illness leading to hospitalization in our patient population. Prior studies have reported a high incidence of morbidity and mortality in patients with bacteremia, contributing to our decision to use bacteremia as an indicator of severity [17,18,19]. A limitation of our series is that an outpatient population, presumedly those with less severe disease, was not studied. We also did not have results of HIV serology for most patients; thus, we potentially included some HIV-positive patients in the group with negative serologic findings. Because the study was not performed prospectively and patients were not enrolled into the study, this was unavoidable.
We did not attempt to include the interstitial pattern as a descriptor for the radiographic findings of pneumococcal pneumonia. There is significant overlap in the imaging features of the bronchopneumonias and interstitial pneumonias, largely related to a prominent component of peribronchial thickening occurring in both. It is unclear whether prior studies reporting interstitial patterns in streptococcal pneumonia reliably distinguished true interstitial abnormality from bronchopneumonia.
Underlying lung disease can alter the appearance of usual radiographic patterns, often contributing to heterogeneity. For this reason, we excluded patients with known pulmonary disorders, but we likely retained some patients with unsuspected disease including those with emphysema. These patients might have increased the number of patients classified as having bronchopneumonia. Differentiation may have been facilitated with CT. Although radiographic—CT correlation would have been optimal, CT is infrequently performed in the initial treatment of pneumonia. Because evaluation of the chest radiograph remains integral to patient workup, our reliance on descriptions of radiography of the chest for classification of radiographic abnormalities remains important.
Focal or multifocal lobar consolidation is the most common pattern of pneumococcal pneumonia in patients requiring hospitalization regardless of HIV status or bacteremic state.
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