Radiologically a bronchopneumonia is characterized by large heterogeneous, scattered opacities which only later, with worsening of disease, become more homogeneous. Some pneumonias present as spherical- or nodular-shaped consolidations.īronchopneumonia (lobular pneumonia) is characterized histologically by peribronchiolar inflammation manifesting radiologically as patchy airspace nodules with poorly defined margins. As the airways are not primarily involved and remain patent, there is little to no volume loss, and air bronchograms are common. In lobar pneumonia the inflammatory exudate begins in the distal airspaces adjacent to the visceral pleura and then spreads via collateral air drift routes (pores of Kohn) to produce uniform homogeneous opacification of partial or complete segments of the lung and occasionally an entire lobe. Pneumonias are usually divided according to their chest imaging appearance into lobar pneumonia, bronchopneumonia, and interstitial pneumonia. However, many community-acquired pneumonias are still commonly caused by S. The spectrum of causative organisms of CAP includes gram-positive bacteria such as Streptococcus pneumoniae (pneumococcus), Haemophilus influenzae, and Staphylococcus aureus, as well as atypical organisms such as Mycoplasma pneumoniae, Chlamydia pneumoniae, or Legionella pneumophila and viral agents such as influenza A virus and respiratory syncytial viruses. Although the imaging findings do not allow a specific etiologic diagnosis, CAP diagnosis and disease management most frequently involve chest radiography, and other imaging modalities are not usually required. Pulmonary opacities are usually evident on the radiograph within 12 h of the onset of symptoms. Ĭommunity acquired pneumonia refers to an acute infection of the lung in patients who did not meet any of the criteria for HCAP, presenting select clinical features (e.g., cough, fever, sputum production, and pleuritic chest pain) and accompanied by an acute infiltrate on a chest radiograph. The spectrum of organisms known to cause respiratory infections is broad and constantly increasing as new pathogens are identified and an increasing number of patients have decreased immunity due to disease or medications.Įpidemiologically, pneumonia can be classified into community-acquired pneumonia (CAP), hospital-acquired pneumonia (HAP), ventilator-associated pneumonia (VAP), and healthcare-associated pneumonia (HCAP). The number of immunocompromised patients has increased in the last three decades because of three main phenomena: the AIDS epidemic, advances in cancer chemotherapy, and expanding solid organ and hematopoietic stem cell transplantation. Pneumonia is an acute infection of the pulmonary parenchyma that is associated with at least some symptoms of acute infection, accompanied by the presence of an acute infiltrate on a chest radiograph. Respiratory infections are the commonest illnesses occurring in humans, and pneumonia is the leading cause of death due to infectious disease. To appreciate the importance of additional clinical information in the diagnosis of respiratory infections.
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