Chest Imaging: Pneumonia

Imaging in lung anomalies is usually started off by plain film radiography. This projection technique gives a first overview of the anatomical situs and allows for a first assessment of expected anomaly. Depending on the individual setting an ultrasound of the chest can be added for further assessment of the vascular structures or cystic components. A more sophisticated imaging technique like computed tomography or magnetic resonance imaging will allow for definite classification of the anomaly. The different imaging techniques and especially CT and MRI protocols used will be covered. Anatomical variants are most often detected within the tracheobronchial tree, namely with anomalous branching pattern of the upper lobe bronchi. Congenital lung anomalies are a heterogeneous group of developmental disorders with a wide distribution in imaging appearance and clinical manifestations. The most frequent ones are: congenital pulmonary airway malformation (CPAM), congenital lobar hyperinflation, bronchial atresia, bronchiogenic cyst and pulmonary sequestration. For these anomalies, the embryologic background, clinical presentation and imaging findings will be demonstrated.

Inflammation is a response of vascularised tissues to infections to eliminate the offending agents. Pneumonia occurs when the host mounts an inflammatory response, centred on the lung parenchyma, usually against a microorganism which has reached this normally sterile site. Bacteria are the most common causative microorganisms. Pneumococci usually spare alveolar walls and cause lobar pneumonia that resolves completely, whereas Staphylococci and Klebsiella species destroy alveolar walls and form abscesses that heal with scar formation. Combination of pattern recognition with knowledge of the clinical setting is the best approach to pulmonary infectious processes. When pulmonary infection is suspected, knowledge of the varied radiographic manifestations will narrow the differential diagnosis, helping to direct additional diagnostic measures, and serving as an ideal tool for follow-up examinations. Management of immunocompromised patients is challenging and difficult because of the diversity of causative organisms. Although diagnostic information may also be obtained by means of bronchoalveolar lavage and transbronchial needle aspiration, the radiologist plays an important role in the diagnosis and management of patients with suspected pneumonia.

Non-small cell lung carcinoma (NSCLC) comprises the largest group of which the imaging appearance can be variable. It can present as centrally or peripherally located nodule or mass that may invade mediastinal structures or the chest wall. Tumour margins may be smooth, lobulated, ill defined, irregular or spiculated. Other findings include cavitation, consolidation and ground glass opacity (GGO). Accompanying post-obstructive pneumonia and/or lung collapse can be seen in central tumours. Small cell lung carcinoma (SCLC) is the most common primary pulmonary neuroendocrine tumour. Most SCLCs are a centrally located large mass invading or metastasising to regional lymph nodes. 5-10% of SCLCs present as a peripherally located spiculated nodule without associated lymphadenopathy. Pulmonary metastasis: the lung is frequently involved in metastatic disease. Typical radiological features include multiple round nodules with variable size, peripherally located (haematogenous metastasis) and diffuse thickening of the interstitium (lymphangitic carcinomatosis). Atypical features such as cavitation, calcification, air bronchogram and GGO are often encountered. Pulmonary lymphoma imaging findings of parenchymal disease in both primary (rare entity) and more frequently occurring secondary pulmonary lymphoma are variable and non-specific. They include single or multiple nodules, masses or consolidations, cavitation and air bronchogram. Ancillary findings include lymphadenopathy, bronchial wall thickening, interlobular septal thickening and pleural effusion. CT is the workhorse of imaging in bronchogenic carcinoma, metastasis and lymphoma, and plays together with PET/CT a crucial role in staging bronchogenic carcinoma and lymphoma. Due to the variety in CT imaging appearances, tissue confirmation is usually warranted to confirm the diagnosis.

Community-acquired pneumonia (CAP) refers to pneumonia acquired outside of hospitals or extended-care facilities and is one of the most common infectious diseases. CAP is an important cause of mortality and morbidity worldwide. According to the IDSA/ATS/AAFP guidelines, a chest radiograph is required for the routine evaluation of patients with suspected CAP to exclude conditions that mimic CAP (e.g. acute bronchitis) and to confirm the presence of an infiltrate compatible with the presentation of CAP. Although chest radiography findings usually do not allow identifying the causative organism, they may be helpful in narrowing down the differential diagnosis, prognosis, and detection of associated conditions. Serial chest radiography can be performed to observe the progression of CAP. CT scanning is increasingly used in clinical practice. Performing CT should be considered if any of the abnormalities at presentation or at follow-up are not consistent with the diagnosis of pneumonia, or if concomitant disease is suspected such as an underlying bronchogenic carcinoma, for the confirmation of pleural effusion and for the detection of pulmonary complications. The aim of the presentation is to provide an overview of the imaging findings of the most common aetiologic organisms in patients with CAP. In addition, imaging findings that may help in the differentiation between pneumonia and other common non-infectious causes of abnormal chest radiographs in patients with suspected CAP will be discussed.

Pulmonary tuberculosis (TB) remains a common worldwide infection that produces high mortality and morbidity, especially in developing countries. In 2013, an estimated 9.0 million (360 000 of whom were HIV-positive) people developed TB and 1.5 million died from the disease.
Chest radiographs play a major role in the screening, diagnosis, and response to treatment of patients with TB. However, the radiographs may be normal or show only mild or nonspecific findings in patients with active disease. We will review the chest radiographs findings of TB, which vary widely in the function of several host factors, age, prior exposure to TB, and underlying immune status. CT is useful in detecting TB incidentally, in resolving cases with inconclusive findings on chest radiographs, and in assessing disease activity. Cavities, centrilobular nodules, and tree-in-bud appearance are the most common CT findings of active pulmonary tuberculosis. We will discuss the classic, and some not-so-classic, signs that should suggest the diagnosis of TB.

The radiological characterisation of infiltrates gives a first and rapid hint to differentiate between different types of infectious (e.g. typical bacterial, atypical bacterial, fungal) and non-infectious aetiologies. Follow-up investigations need careful interpretation according to disease, recovery, concomitant treatment and eventually vessel arrosion requiring contrast-enhanced angio-CT. Due to a high incidence of fungal infiltrates in immunicompromised hosts, interpretation of the follow-up of an infiltrate must use further parameters besides the lesion size.