Chest imaging characteristics of mycoplasma pneumoniae pneumonia in children

Caiting Chu; Lei Xu; Chengjin Gao

doi:10.4103/RID.RID_3_22

REVIEW ARTICLE

Year : 2022 | Volume : 9 | Issue : 2 | Page : 58-61

Chest imaging characteristics of mycoplasma pneumoniae pneumonia in children

Caiting Chu¹, Lei Xu¹, Chengjin Gao²
¹ Department of Radiology, Xinhua Hospital Affiliated to Shanghai Jiao Tong, University School of Medicine, Shanghai, China
² Department of Emergency, Xinhua Hospital Affiliated to Shanghai Jiao Tong, University School of Medicine, Shanghai, China

Date of Submission	06-Jan-2022
Date of Acceptance	18-Jun-2022
Date of Web Publication	8-Nov-2022

Correspondence Address:
Chengjin Gao
Department of Emergency, Xinhua Hospital Affiliated to Shanghai Jiao Tong, University School of Medicine, Shanghai
China

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/RID.RID_3_22

Abstract

Mycoplasma pneumoniae pneumonia (MPP) is the most common type of childhood community-acquired pneumonia. MPP is generally mild and self-limiting, but a small percentage of patients still develop a refractory or severe clinical course. Imaging is an important tool for confirmed pneumonia, and it plays an important role in the diagnosis of MPP and assessment of the clinical course. However, imaging features of MPP reported in the literature vary in their patterns to distribution. A comprehensive and deep understanding of imaging findings of MPP in children is beneficial for an accurate diagnosis and guidance of its treatment.

Keywords: Children, imaging, Mycoplasma pneumoniae, pneumonia

How to cite this article:
Chu C, Xu L, Gao C. Chest imaging characteristics of mycoplasma pneumoniae pneumonia in children. Radiol Infect Dis 2022;9:58-61

How to cite this URL:
Chu C, Xu L, Gao C. Chest imaging characteristics of mycoplasma pneumoniae pneumonia in children. Radiol Infect Dis [serial online] 2022 [cited 2023 Mar 23];9:58-61. Available from: http://www.ridiseases.org/text.asp?2022/9/2/58/360505

Introduction

Mycoplasma pneumoniae is a common pathogen causing community-acquired pneumonia (CAP), and pneumonia caused by M. pneumoniae is responsible for 30% of pediatric CAP.^[1] M. pneumoniae pneumonia (MPP) mostly occurs in children aged 5–14 years and is more frequent in girls.^[2] Numerous studies have shown that M. pneumoniae primarily involves the lungs and presents with nonspecific symptoms of a fever and cough.^[3] M. pneumoniae occasionally involves extrapulmonary organs, such as the cardiovascular system, digestion system, and central nervous system. Intrapulmonary inflammation or extrapulmonary lesions may become macrolide-resistant, with a refractory or severe clinical course, which complicates clinical treatments.^[4] An imaging examination is the preferred choice for confirming pneumonia.^[5] Moreover, imaging characteristics also offer additional information on the pathology and the clinical course. Therefore, a comprehensive and deep understanding of chest imaging findings of MPP in children is important. We summarize various imaging findings, corresponding pathological characteristics, and clinical values in children with MPP in this review.

Imaging Diagnosis

Imaging is a tool for diagnosing pneumonia. Ultrasound (US) without irradiation is an ideal imaging tool for monitoring disease. However, lung US has a low diagnostic sensitivity for pneumonia in children, which has contributed to pediatricians' reluctance to use it.^[6] Chest radiography (CR) is the first-line imaging method for diagnosing pneumonia.^[5] CR is the first choice clinically for suspected CAP in children.^[7] Computed tomography (CT) is used with caution in children because of the radiation dose. CT is recommended in patients with complex conditions.^[8] With the development of imaging technology, thoracic magnetic resonance imaging (MRI) has gradually been implemented to evaluate pneumonia and its complications.^[9] Furthermore, with the advent of the era of artificial intelligence, machine learning based on imaging has been attempted to assess pneumonia.^[10] We discuss the various imaging findings of MPP in detail below.

Typical chest imaging features

As early as 1977, Camron et al. reported that acute Mycoplasma pneumonitis manifested as a reticular pattern on CR, showing early peribronchial thickening and late involvement of alveolus.^[11] Interstitial changes accompanied by vascular congestion are the most common pattern. In 1981, Finnegna et al. found that consolidation and nodules were the main patterns of lesions in adult patients, and lesions were usually located in the unilateral lung or in the lower lobe of the lung. Patchy consolidation of one lobe was also more common in female patients, while nodules frequently occurred in male patients, the reason for which is still unknown.^[12] Radiographic findings in pediatric MPP were investigated in a study of 120 children.^[13] However, the radiographic features found in children with MPP were similar to those with viral illness of the lower respiratory tract. Reticulonodular infiltration localised to a single lobe may be more common in MPP than in other types of respiratory infections in children. In addition, patchy or ground-glass consolidations occur in M. pneumoniae infections, but dense and homogeneous consolidations are uncommon. Hsieh et al. described the following four radiographic patterns of MPP: peribronchial and perivascular interstitial infiltrates, airspace consolidations, reticulonodular changes, and nodular or mass-like opacification.^[14] High-resolution CT is superior to CR in showing the pattern and distribution of lesions. CT findings of M. pneumoniae infections were compared with those of CR in a study of radiographic and CT features in 28 adult patients with M. pneumoniae.^[15] This study showed that consolidation had more obvious lobular distribution on CT than on CR. Nodules and bronchovascular bundle thickening were also more common on CT than on CR. The patterns of CT features of M. pneumoniae infection in patients of different ages were furthermore analyzed. A study of 16 patients showed different distinctive patterns of CT features obtained in children aged <18 years and adults aged ≥18 years. Lobar or segmental consolidation, along with parapneumonic effusion, is more common in children with MPP than in adults with MPP, which is similar to bacterial pneumonia.^[16] The incidence of pleural effusion ranges from approximately 5% to 26%.^[13],[17] Thoracic MRI findings in pneumonia have been reported. Consolidation and pleural effusion are clearly shown by MRI in cases of MPP, but other features, such as peribronchial and perivascular interstitial changes and reticulonodular infiltration, are poorly visualised.^[18] In summary, a large variety of imaging features in MPP have been observed, which could explain the varying stages of this disease [Table 1]. The pattern of the lesions includes interstitial changes, parenchymal changes, or mixed changes. The distribution of the lesions varies from focal to multilobar to diffuse. Other features include hilar lymphadenopathy, pleural effusion, and atelectasis. In most cases, multiple features co-exist.

Table 1: Relationships of imaging characteristics and clinical variables of Mycoplasma pneumoniae pneumonia

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Chest imaging differential diagnosis

In general, an interstitial pattern indicates a viral etiology, while an alveolar lesion suggests a bacterial status. However, there are interstitial and/or alveolar patterns of MPP. Therefore, children with MPP need to have a differential diagnosis made. A differential diagnosis from imaging features of MPP was investigated in the early 1990s. There was no significant difference in imaging findings in a study of community-acquired Legionnaires' disease, pneumococcal pneumonia, M. pneumoniae, and psittacosis. Among them, lymphadenopathy was restricted to M. pneumoniae infection and the clearance of radiographic shadows of MPP was fastest.^[19] With regard to the relation between imaging features and etiological agents, patchy alveolar opacities on CR are more commonly observed in children with MPP than in those with Streptococcus pneumoniae pneumonia. The relationship between radiological features and different pathogens has been found to be minimal.^[20] However, Miyashita et al. found that bronchial wall thickening and centrilobular nodules on CT were more frequent in patients with MPP than in those with S. pneumoniae pneumonia.^[21] A scoring system of combined clinical, hematological, and radiographic parameters likely helps to differentiate the diagnosis between MPP and pneumonia by other pathogens.^[22] Therefore, there are some limitations to imaging being used to determine the etiology of MMP. Fortunately, deep learning based on chest X-ray has been developed, which is promising for determining the etiology of pneumonia.

Relationship between Chest Imaging Features and Pathology

Imaging characteristics are closely associated with histopathological information. Once M. pneumoniae successfully adheres to the host epithelium, inflammation and the immune response play a pathogenic role.^[3] Therefore, when M. pneumoniae arrives in the lower respiratory tract, macrophages start to activate, phagocytosis occurs, and then there is chemotactic migration to the site of infection. Finally, neutrophils and lymphocytes, such as CD4⁺ T lymphocytes, B lymphocytes, and plasma cells, exude into the lung, and can be seen radiologically as pulmonary infiltrates.^[23],[24] Pulmonary infiltrates include some patterns. Nodules seen on CT indicate histological bronchiolitis, and consolidation or ground-glass attenuation is confirmed as bronchopneumonia by histopathology. A combination of diffuse alveolar damage and fibrinous exudates may occur in severe cases of M. pneumoniae.^[15],[25] There are three associations of radiological features and pathological findings in patients with MPP, as follows. First, bronchovascular bundle thickening on CT indicates mononuclear cell infiltration around the peribronchovascular interstitium. Second, cellular bronchitis in the small airways characterised by exudates or granulation tissue is associated with nodules on CT. Third, exudates accompanied by neutrophils in the alveolar lumen are radiologically shown as ground-glass opacities or airspace consolidation.^[26] A study showed that host cell-mediated immunity levels were correlated with pathological changes in Mycoplasma-infected mouse experiments.^[1],[26] This finding provided the theoretical basis for the different types of imaging features in children with MPP. Patients with a high level of cell-mediated immunity are more likely to show centrilobular nodules, while ground-glass opacity and consolidation are commonly seen in patients with a low level of cell-mediated immunity.^[27] Therefore, we conclude that imaging findings in Mycoplasma-infected children are dependent not only on the stages of disease, but also on the state of the host immunity.

Role of Chest Imaging Findings in the Clinic

Many studies have suggested that chest imaging features play a main role in the assessment of the clinical outcome of MPP. Yeon et al. reported that patients characterised by consolidation were likely to have a worse clinical situation, such as a higher rate of hypoxia, tachypnea, tachycardia, prolonged fever, and hospitalisation.^[28] Complications, such as atelectasis and/or pleural effusion, are important variables for predicting a bronchial mucus plug in children with MPP.^[29] M. pneumoniae-infected patients with atelectasis exhibit many symptoms, such as dyspnoea, changes in local ventilation and the blood flow ratio, and an irritant cough, which make atelectasis a refractory course in the clinic.^[30] Patients with macrolide-resistant M. pneumoniae and macrolide-susceptible M. pneumoniae show no differences in radiographic findings.^[31] Radiographic clearance is also an important concern in the clinical course of MPP. A longer time to radiographic clearance is required in patients with refractory MPP.^[32] Refractory MPP accompanied by the formation of a bronchial mucus plug is associated with delayed radiographic resolution and pulmonary complications.^[33] Children with refractory MPP accompanied by corticosteroid resistance also have delayed resolution on CR.^[34] In light of the abovementioned research, the presence of atelectasis and delayed resolution on CR are likely to be two important factors influencing the clinical course of MPP.

Potential Shortcomings and Future Efforts

On the basis of the above mentioned findings, we consider that chest imaging characteristics of MPP are dependent on the immune state of patients and the stage of development of MMP. These variables could result in insufficient specificity, which may present with interstitial inflammation, such as bronchovascular bundle thickening due to viral pneumonia, or with consolidation characterised by bacterial pneumonia. Imaging-based diagnosis has a moderate accuracy in children with MPP. Additionally, drug resistance and mixed infections complicate the clinical course of MPP. Over the years, radiologists have not made obvious gains in the imaging diagnosis of MPP.

Other diagnostic tests for MPP in clinical work need to be developed including culture, nucleic acid amplification, and serological tests, to determine the pathogen.^[4] With the advent of the era of artificial intelligence, imaging-based automated medicine will allow a precise and differential diagnosis. In addition, taking into consideration, the radiation dose in children, low-dose CT or MRI without radiation may be available as the ideal imaging modality.

Conclusion

In summary, M. pneumoniae is a common causative pathogen of pneumonia in children. Pneumonia caused by M. pneumoniae has various clinical courses. Imaging characteristics in children with MPP on CR and CT vary from the patterns of lesions to distribution, which are dependent on the stages of MP and the level of host immunity. Low-dose CT or MRI has potential advantages in the future assessment of children with MPP.

Acknowledgments

We thank Ellen Knapp, PhD, from Liwen Bianji (Edanz) (www.liwenbianji.cn/), for editing the English text of a draft of this manuscript.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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