[Abstract] Objective To investigate the imaging manifestations of Legionella pneumonia and its diagnostic imaging value, and to improve the understanding of this disease. Methods The clinical and serial imaging data of 35 cases of Legionella pneumonia diagnosed by clinical synthesis were reviewed and analyzed, and their imaging features were summarized. Results The main imaging manifestations of Legionella pneumonia were: 31 cases of polymorphic lesions; 25 cases of multilobar multisegmental lesions; 10 cases of pleural effusion; 6 cases of lung abscess; 21 cases of inconsistency between clinical symptoms and imaging manifestations; 30 cases of slow absorption of imaging changes (time greater than 2 weeks); 28 cases with fibrous cords, reticular shadow or honeycomb shadow. Thus, the signs of Legionella pneumonia were mainly characterized by polymorphic lesions, multilobar multisegmental lesions, and fibrosis with fibrous cords, reticular shadows, or honeycomb shadows; and its dynamic imaging was mainly characterized by slow absorption of imaging changes and inconsistency between imaging changes and clinical symptoms. Conclusion Although the imaging manifestations of Legionella pneumonia are complex, they have certain characteristics, and the combination of history, physical signs and laboratory tests can suggest the diagnosis. Lei Zhidan, Department of Radiology, Henan Provincial People’s Hospital
[Keywords] Legionella pneumonia; radiography; tomography, X-ray computer
Legionella pneumonia (LP) is a serious lung infection caused by Legionella pneumonia, with a mortality rate of up to 45% in those without effective treatment [1], and serologic tests require more than 2 weeks of disease to meet diagnostic criteria. Therefore, practical methods for early diagnosis and treatment are needed. Although LP has been reported in the domestic and foreign literature through different ways [2-7], the comprehensive diagnosis of the disease by analyzing the imaging features of LP and combining clinical and laboratory tests has been less reported in recent years [8]. We collected 35 cases of LP with comprehensive clinical diagnosis and complete imaging and clinical data in the past 15 years from July 1991 to July 2006 in our hospital for analysis and discussion of their imaging features, aiming to improve the understanding of this disease and thus to diagnose it timely and accurately.
1 Data and methods
1.1 General data All 35 LP cases were diagnosed according to the comprehensive diagnosis based on the diagnostic criteria established by the editorial board of the Chinese Journal of Tuberculosis and Respiratory [9], including 20 males and 15 females, aged 25-75 years, with an average age of 53 years. Symptoms: 35 cases had fever, cough and sputum, body temperature 38-40.2°C, with shortness of breath in 23 cases, chest pain in 8 cases, malaise in 6 cases, dizziness and headache in 2 cases, nausea and vomiting in 4 cases, and hemoptysis in 2 cases. Signs: wet lung in 31 cases, pleural fluid sign in 10 cases, Velcro in 23 cases, cyanosis in 8 cases. Laboratory tests: total leukocyte count and classification were elevated in 27 cases, and blood sedimentation was increased in 18 cases. Serological examination: 35 cases had antibody titers of 1:320 or higher, and all of them reached the diagnostic standard on the 14th to 35th day of the disease course. The antibody titers of 7 cases decreased to normal on the 10th day after drug administration, and the antibody titers of 19 cases decreased to normal in 10 to 21 days. Treatment and regression: 18 cases in this group had been treated with a variety of antibiotics that were ineffective, and then switched to erythromycin drugs, and their conditions improved significantly, and they were finally discharged from the hospital cured; 10 cases were cured 10-70 days after the application of erythromycin drugs with clear diagnosis; 3 of the 7 cases of severe LP were cured, 3 cases became chronic pneumonia, and 1 patient died.
1.2 Examination methods All 35 LP cases had serial imaging data, among which 35 cases had 3-5 chest radiographs, 21 cases had 1-2 CT examinations, and 10 patients also had HRCT examinations. CT scans were performed with Shimadzu/S4500 CT and GE/Light Speed Plus 4 multi-layer spiral CT machines. The layer thickness of plain CT was 10 mm, the layer pitch was 10 mm, the matrix was 512×512, and the range was from the entrance of the thorax to the base of the lung, and the lung window and mediastinal window were observed; while the layer thickness of spiral CT was 7.5 mm, the pitch factor was 1.5:1, the reconstruction interval was 5 mm, and the matrix and range were the same as those of plain CT. 10mm, bone algorithm image reconstruction, from the level of the aortic arch to the diaphragm, and observed with a lung window.
1.3 Analysis method Two radiologists who were unaware of the results and experienced in the field analyzed the serial imaging data of 35 LP cases, recorded the imaging signs, and summarized their imaging features. These imaging features were then synthesized and analyzed by a radiologist together with a respiratory physician to discuss the clinical value of LP imaging diagnosis.
2 Results
2.1 Major imaging morphological changes of LP (Table 1) (1) Thirty-one of the 35 LP cases showed coexistence of multiple morphological lesions (Figure 1), including central lobular nodules, alveolar nodules, whole lobular shadows (patchy shadows), lamellar shadows, large lamellar shadows, cavities, striae, reticular shadows, foveal shadows, pleural effusion and pericardial effusion, and other two or more of the above-mentioned lesions. (2) The lesions in 25 LP cases showed a multilobar multisegmental distribution (Figure 2), of which 18 cases were more diffusely distributed lesions in both lungs, 5 cases were intrapulmonary shadows in both or three lobes of the right lung, and 2 cases had lesions in both the upper and lower lobes of the left lung. (3) There were 28 cases of fibrous streaks, reticular shadows or foveal shadows, including 21 cases of all three kinds of shadows and 5 cases of LP with fibrous streak presentation only. (4) There were 6 cases of lung abscess, 4 cases of single cavity and 2 cases of multiple cavities. (5) There were 10 cases of pleural effusion, 6 cases of right-sided effusion and 4 cases of left-sided effusion, and 5 of the 10 cases were encapsulated effusion, and the amount of effusion was generally small to moderate, and there was no one case of large amount of effusion. (6) There was one case of pericardial effusion, which was a small amount of effusion.
Table 1 Morphological characteristics and distribution of 35 cases of LP imaging (cases)
Subgroup Left lung Right lung Both lungs Total
Polymorphic lesion 7 11 13 31
Multi-lobe multisegmental distribution 5 9 11 25
Interstitial fibrosis 6 10 12 28
Lung abscess 1 3 2 6
Pleural effusion D D D D 10
Pericardial effusion D D D D 1
2.2 Characteristics of dynamic changes in imaging of LP (Table 2) (1) Clinical symptoms and imaging were inconsistent in 21 cases, which showed that: (1) lung shadowing was later than clinical symptoms for 5-7 days in 17 cases, i.e., symptoms were obvious but lung shadowing was light or no shadowing was shown; (2) imaging abnormalities continued to progress after clinical treatment in 12 cases (Figure 3), which showed the expansion of the lesion and the increase of the degree of fibrosis; (3) 9 cases of LP had clinical symptoms that basically disappeared and imaging abnormalities continued to progress; (4) the lung abnormalities were not consistent with clinical symptoms, which showed the increase of the extent of the lesion and the increase of the degree of fibrosis; and (5) the lung abnormalities were not consistent with clinical symptoms. The clinical symptoms of LP had basically disappeared while the imaging lesions still existed. (2) The imaging changes were slowly absorbed in 30 cases, and the time of their complete absorption was greater than 2 weeks or more, and the longest disease duration was 75 days in the cured patients. (3) Three of the seven patients with severe LP were prolonged and formed chronic pneumonia, two of which were reviewed up to 6 months (Figure 4), and the other one was reviewed up to 8 months; in the three cases of chronic pneumonia, symptoms and imaging changes persisted, although they were better than in the acute phase. (4) All 10 LP cases healed from 10 to 70 days after the application of erythromycin-based drugs with a clear diagnosis, and 5 of these patients had milder imaging changes and complete absorption of the lesions within 2 weeks.
Table 2 Dynamic changes of imaging in 35 cases of LP
Subgroup Number of cases
Inconsistency between symptoms and imaging 21
Shadows later than symptoms 5 to 7 days 17
Symptoms improve imaging continues to progress 12
Symptoms disappear while imaging lesions remain 9
Slow absorption of imaging changes 30
Chronic pneumonia 3
Complete absorption of lesions within 2 weeks 5
3 Discussion
3.1 Diagnostic criteria of LP
LP is a community-acquired or nosocomial infectious bacterial pneumonia caused by gram-negative bacilli, which occurs in pregnant women, the elderly, and immunocompromised populations, and is characterized by pulmonary infection and multisystem damage, with a clinically critical, complex, and nonspecific presentation [1-7]. Clinically, it is mainly based on the criteria established by the editorial board of the Chinese Journal of Tuberculosis and Respiratory Medicine in 1992 [9], which are: (1) Clinical manifestations: fever, chills, cough, chest pain and other symptoms of respiratory tract infection. (2) X-ray chest film with inflammatory shadows. (3) Respiratory secretions, sputum, blood or pleural fluid with Legionella growth in activated charcoal yeast infusion agar medium (BCYE) or other special medium culture. (4) Positive direct fluorescence assay (DFA) of respiratory secretions. (5) Blood indirect fluorescence assay (IFA): 4-fold or more increase in antibody titers before and after 2 tests, up to 1:128 or more; blood test tube agglutination test (TAT): 4-fold or more increase in antibody titers before and after 2 tests, up to 1:160 or more; blood microagglutination test (MAA): 4-fold or more increase in antibody titers before and after 2 tests, up to 1:64 or more. Anyone with 1 or 2 items and any one of 3, 4 or 5 items at the same time is diagnosed with Legionella pneumonia.
3.2 Inadequacy of laboratory methods for detection of Legionella
Although laboratory methods play a crucial role in the diagnosis of LP, there are some shortcomings in its diagnosis, treatment and prognosis assessment. Mainly: (1) Positive culture is the gold standard for clear diagnosis, but culture of Legionella is expensive, time-consuming and laborious, and the positive rate is low, and the requirements for laboratory technicians are high, so it is difficult to promote in the clinic. (2) Urinary antigen test and DFA method are also laboratory methods for early diagnosis of Legionella pneumonia, but at present, the lack of ideal kits for the former and the low sensitivity of the latter are not conducive to early diagnosis. (3) The detection of Legionella-specific antibody titers (indirect fluorescence method, etc.) is still the main method for clinical diagnosis of Legionella pneumonia, but a significant increase in serum antibodies usually takes 2-6 weeks, and its sensitivity can be reduced due to early anti-inflammatory treatment, low immunity of the body, and low detection of antibody species, and the positive rate of serum Legionella antibodies in patients with fever of other etiologies can also be increased [4]. (4) Although PCR can be used for early detection of Legionella to determine the diagnosis [5. 6], it is more expensive and not easily carried out in primary hospitals, and it cannot correctly assess the extent, severity, and prognosis of pulmonary and systemic lesions. Therefore, the diagnosis, treatment and prognosis of LP must be evaluated in combination with clinical, laboratory tests and imaging data.
3.3 Imaging manifestations and diagnostic value of LP
3.3.1 Imaging morphological features and dynamic changes of LP Because of the above deficiencies in the early laboratory methods of lesions and the non-specificity of clinical symptoms and signs, if its imaging performance has some characteristics, it will provide important values for the early clinical diagnosis and treatment. Although the domestic literature reports on the imaging manifestations of LP are considered non-specific [1. 2. 3. 8.], the author found that there are certain characteristics through the study of 35 cases of LP series diagnosed by clinical comprehensive diagnosis in our hospital in the past 15 years. The imaging features mainly lie in the morphology and distribution of lesions in the lungs and the dynamic process of lesion changes are significantly different from other types of pneumonia. Among the 35 cases in this group, there were 31 cases of polymorphic lesions, 25 cases of multilobar multisegmental lesions, 10 cases of pleural effusion, 6 cases of lung abscess, and 28 cases of fibrous cords, reticular shadows or honeycomb shadows. Thus, the morphological characteristics of LP in the lung are often characterized by the coexistence of multiple morphological shadows, and its distribution is characterized by multilobar multisegmental distribution, and the lesion areas are often combined with interstitial fibrosis of the lung, and cavities and pleural effusions are also more common. 21 of the 35 cases had inconsistent clinical symptoms and imaging manifestations, i.e., the lung shadows were later than clinical symptoms for 5-7 days in 17 cases, and the symptoms improved after clinical treatment while the imaging abnormalities continued. In 12 cases, the symptoms improved after clinical treatment while the imaging abnormalities continued to progress, and in 9 cases, the symptoms of LP disappeared while the imaging lesions persisted. This suggests that the dynamic imaging changes in LP are generally later than the changes in clinical symptoms, and the imaging abnormalities may continue to exist or even worsen when the clinical symptoms improve or disappear, which is consistent with the literature [1. 10]. In our group, the absorption period of imaging changes was greater than 2 weeks in 30 cases and up to 75 days in the longest case, and three LP patients developed prolonged chronic pneumonia. This further suggests that the majority of LP imaging abnormalities are absorbed more slowly and can leave fibrotic lesions of varying degrees. The above presentation demonstrates that the imaging changes of LP are mainly characterized by polymorphic lesions, multilobar and multisegmental divisions, often combined with interstitial fibrosis of the lung, slow absorption, inconsistent imaging abnormalities with clinical symptoms, and lesions that are not easily and completely absorbed. Thus, in combination with laboratory tests, clinical symptoms and signs, and treatment, imaging is feasible for the diagnosis of LP, and may even lead to an early and correct diagnosis of the disease.
3.3.2 Assessment of imaging changes on the treatment and prognosis of LP Among the 35 cases of LP in this group, the absorption time of imaging abnormalities was greater than 2 weeks in 21 cases. Analysis of their imaging characteristics was mainly due to the following reasons: (1) the lesions were more widely distributed, with a multi-lobed, multi-segmental distribution
(1) The distribution of the lesions was widespread, with multi-lobe and multi-segmental distribution, and even diffuse distribution. (2) The fibrosis is more severe, often in the form of lattice-like and honeycomb changes, and the distribution of such lesions is more extensive. (3) There are more types of lesion morphology, and solid shadows are often accompanied by fibrosis, cavities and even pleural effusion. In contrast, the imaging changes in the 5 patients with lesion absorption within 2 weeks were milder, i.e., the distribution of shadows was more limited (single lobe or lung segment), the morphology was more homogeneous (1 to 2 morphologies), and the interstitium was only thickened or had only mild fibrosis. Therefore, although the imaging changes of LP do not coincide with the clinical manifestations in time, their extent, morphology and degree of fibrosis reflect the severity, prognosis and regression of their lesions to a certain extent, especially the degree of fibrosis has a greater impact on the latter two. Therefore, the analysis and study of the imaging performance characteristics of LP can not only provide timely and accurate diagnosis, but also have great significance in guiding the selection of treatment plan and duration of treatment.
3.4 Differential diagnosis of LP
LP needs to be differentiated from other diseases that show a wide distribution of polymorphic changes on imaging and combined with interstitial fibrosis. The most common ones are idiopathic interstitial pneumonia, pneumonic lung cancer and viral pneumonia. Most interstitial pneumonias have no fever and the acute phase of ground glass and solid shadows are effective with hormonal therapy, and distension of the bronchi is more common [11]. Pneumonia-type lung cancer usually has no febrile symptoms, and the lesion area can be seen as “dead branch sign”, mass shadow, or even lymphatic metastasis [12]. Viral pneumonia is also often combined with fibrosis, but most of the symptoms of viral pneumonia are mild, and most of the early imaging is not abnormal or only shows non-segmental ground glass shadows, and the total leukocyte count and classification count are usually not increased in laboratory tests.
In summary, the imaging manifestations of LP are complex, but compared with other types of pneumonia and other diseases with similar imaging manifestations, LP has relatively characteristic features, and the combination of history, physical signs and laboratory tests can suggest the diagnosis. It can provide reference value for clinical diagnosis and treatment.
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