SF 17a - Paediatric parenchymal lung disease: what imaging technique to choose?
1. To be familiar with paediatric parenchymal lung disease.
2. To learn the advantages and drawbacks of each imaging modalities.
3. To understand the optimal use of the different imaging modalities.
Chest x-ray should be performed prior to considering advanced imaging. It is an useful procedure for evaluating the airways, lungs and others chest components. Ultrasound is a well-known technique to explore to investigate the pleura and the mediastinum. It could be also a tool to explore the lung. To perform this exam, one must know the physical basis of the ultrasonographic method because images of the lung are based on artefacts. Chest CT is the method of choice to explore lung disease. Multidetector CT is now widely available and is characterized by high, almost isotropic resolution. Despite this fact, the main disadvantage of CT is the radiation exposure. Low HRCT protocols are mandatory to explore lung disease in children. MRI combines structural and functional information. MRI could be an effective tool to explore lung diseases because most lung diseases are accompanied by an increase in the quantity of tissue, cells, or blood within the lungs. Recent technical advances have helped MRI to become an effective tool to explore lung diseases.
1. To learn about the aetiologies of paediatric parenchymal lung diseases.
2. To understand the differential diagnosis based on clinical and imaging findings.
3. To discuss the radiographic appearances of paediatric parenchymal lung diseases.
Parenchyma refers to the gas-exchanging part of the lung, consisting of the alveoli and their capillaries. The parameters for a normal lung size are: less than one third of the heart is below the hemi-diaphragm, the diaphragm is not flattened and the sixth anterior rib crosses the diaphragm. Complete increase of transparency of the thorax in association with low flattened diaphragms is commonly associated to air trapping as in asthma, bronchiolitis, cystic fibrosis, etc. In a child with asymmetric lung transparency, usually the lung with less vascularity is the abnormal one. Air bronchogram is the radiological sign of alveolar space involvement. It stands for air in patent airways surrounded by high-density alveolar spaces. This sign is frequent in consolidations and in atelectasis. Consolidation relates to a product of disease that substitutes alveolar air, solidifying the lung (as in infective pneumonia). In atelectasis reduced volume is seen, accompanied by increased opacity. About the aetiologies of pneumonia in infants and young children (<5 years), the majority of infections are viral: respiratory syncytial virus, metapneumovirus and adenovirus. In older children (5-18 years), main causes are viruses and atypical bacteria. Imaging studies have limited value in the differentiation between viral and bacterial respiratory tract infections. Probably, type of pattern is related to age and not to aetiologic agent.
1. To learn about the role of ultrasonography (US) in paediatric parenchymal lung diseases.
2. To discuss the ultrasonographic appearances of parenchymal lung pathology in children.
3. To understand pitfalls and limitations of US of the chest/lung.
According to the basics of lung ultrasound (LUS), from the physics point of view (physical acoustic phenomena that produces special signs: sliding sign, A-lines, B-lines, etc.) the resulting images from LUS do not represent a clear image. Actually images are artefacts that are (or may) combined with disease-specific profiles with the assumption that the disease patterns correlate with the amount of fluid in the lung. Based on the presence or absence of those artefacts and with the estimation of the amount of B-lines, “imaging models” or lung ultrasound (LUS) findings have described both for the lung diseases of new-born (respiratory distress syndrome, transient tachypnoea of the new-born, bronchopulmonary dysplasia, etc.) and for lung diseases of infant and child, e.g. bronchiolitis, community acquired pneumonia etc. Of course, specific LUS findings are present in conditions such as pneumothorax, pleural effusion, opacification, etc. The use of LUS is advantageous in terms of radiation protection but there are a lot of limitations with the inability to have an overview of the entire thorax being the first (but not the only) weakness of the LUS. Furthermore, the acoustic phenomena are not always satisfactory corresponding to the pathology and thus the idea of routinely replacing chest radiography with LUS is unenforceable. The LUS has no ground to replace conventional chest radiology, but when appropriately applied, can save time to achieve a critical diagnosis especially in neonatal intensive care unit and also is a very useful follow-up tool (easy/safe/cheap/without radiation but of course operator dependent).
1. To learn about the role of CT in paediatric parenchymal lung diseases.
2. To discuss the technique and protocols of CT of the lung parenchyma in children.
3. To learn about the differential diagnosis based on clinical and imaging findings.
Despite chest radiograph (CR) being the most used technique for paediatric thoracic imaging, chest computed tomography (Chest-CT) remains the gold standard imaging modality to characterize parenchymal lung diseases. Chest-CT enables high-quality images both in non-collaborative and collaborative children. In non-collaborative children, fast acquisition CT protocols can be used to avoid sedation or anaesthesia without compromising image quality. Conversely, collaborative children can be trained prior to the CT scan to perform specific inspiratory and expiratory manoeuvres using a spirometer. The use of the spirometer improves protocol standardization and image quality. Nonetheless, the main limitation of chest-CT remains radiation exposure, which always conveys a risk of developing cancer related to its stochastic nature. However, dose reduction measures have been introduced to minimize this risk and nowadays chest-CT can be performed at the same radiation dose of a CR. Further radiation dose reduction might be achieved through chest-CT protocol standardization across vendors, which is still lacking. Finally, chest-CT has enabled to shift from qualitative to quantitative radiology. Newly developed imaging analysis techniques allows today to extract numbers from CT images that can be used to assess treatment’s efficacy or to determine patient’s prognosis. In this presentation will be shown a series of clinical examples where the combination of clinical, laboratory and CT imaging data allowed to obtain an integrated report jointly written by radiologist and clinician.
1. To learn about the (potential) role of MRI in paediatric parenchymal lung diseases.
2. To discuss the technique and protocols of MRI of the lung parenchyma in children.
3. To learn about the differential diagnosis based on clinical and imaging findings.
Using magnetic resonance imaging (MRI) for the management of paediatric patients with lung disease has obvious advantages: comprehensive structural and functional imaging without ionizing radiation. Functional imaging with MRI comprises measurements of perfusion, blood flow, ventilation, gas exchange as well as respiratory motion and mechanics. However, MRI of the lung is challenging for three reasons: 1) low tissue density containing few protons to generate signal; 2) multiple air-tissue interfaces causing susceptibility artefacts and fast signal decay; 3) respiratory, vascular, and cardiac motions requiring fast imaging or triggering and gating techniques. Most lung diseases are associated with an increase in tissue per volume (“plus pathology”), due to the interstitial, alveolar, bronchial or pleural accumulation of cells, extracellular matrix or fluid, displacing air content inside a voxel. Subsequently, proton MRI signal is enhanced. On the other hand, lung diseases may present with tissue loss or loss of blood volume attributable to hypoxic vasoconstriction (“minus pathology”), posing additional challenges to MRI. Still, lung MRI has benefited much from recent research in obstructive lung diseases such as cystic fibrosis, propelling its introduction in clinical routine and broadening experience with lung MRI in paediatric population. Nowadays, lung MRI provides robust protocols for paediatric oncology, inflammatory lung diseases (especially pneumonia) and airways disease, which will be discussed in the talk.