Initial chest X-Ray
A 52-year-old male patient, homeless, presented with a rapid onset (days) of chest pain, haemoptysis, fever (39ºC) and weight loss. The laboratory studies demonstrated leukopenia and neutrophilia. Negative serologies. The patient had a history of heavy alcohol and drugs (cocaine) consumption and was a smoker with known chronic obstructive pulmonary disease (COPD).
The chest X-ray revealed a condensation with patent bronchi at the right upper lobe (RUL) and middle lobe (ML) and bulging of the right major fissure (Fig. 1).
Chest Computed Tomography (CT) revealed a consolidation with air bronchogram at the RUL and ML (Figs. 2 and 3). Multiple parenchymal areas without contrast enhancement. Moderate centrilobular emphysema at the upper lobes, mild paraseptal emphysema and bronchial wall-thickening at the lower lobes. Mediastinal lymphadenopathies were present (Fig. 3). No pleural effusion.
The imaging interpretation was necrotising pneumonia probably due to Klebsiella pneumoniae (K. pneumoniae) with underlying alterations due to COPD.
The patient started empiric antibiotherapy, but rapidly progressed to respiratory distress and multiorgan dysfunction due to septic shock and was admitted to the intensive care unit.
K. pneumoniae was then isolated in the bronchial secretions.
Bronchoscopy and transbronchial pulmonar biopsy confirmed bronchial mucosal infiltration by lymphocytes, histiocytes and polymorphonuclear cells, without neoplastic cells.
Community-acquired pneumonia is a lung infection most often caused by bacteria and viruses. It is commonly caused by gram-positive microorganisms, namely Streptococcus pneumoniae . Immunosuppressed individuals or those living in degrading conditions are more sensitive to gram-negative microorganisms such as Haemophilus influenzae, Moraxella catarrhalis or K. pneumoniae. 
K. pneumoniae is an aggressive microorganism, accounting for 0.5 to 5% of pneumonia cases. It can lead to cavitation (30-50% of cases) and necrotising pneumonia (NP) within a short period of time (days). 
NP is a complication of pulmonary infection, where the affected parenchyma is replaced by necrotic tissue and cavitations. It is important to identify associated lung abscesses, usually well-defined small collections (<2 cm), pulmonary gangrene or thrombosis, since they are frequent complications of K. pneumoniae infection. 
Usually the patient presents with fever, cough with sputum production and pleuritic chest pain. Sometimes also haemoptysis, night sweats, anorexia and weight loss are present.
Chest X-ray (CXR) is usually the first imaging performed in the emergency department. Bacterial pneumonia typically demonstrates a lobar consolidation, with air bronchogram sign, sometimes with pleural effusions. In the case of K. pneumoniae, we may see cavitation and the bulging fissure sign, representing a displacement of the adjacent fissure that has been classically associated with K. pneumoniae consolidation. 
Chest CT depicts ground-glass opacities, consolidation with air bronchogram, sometimes with cavitations, reticular opacities, centrilobular nodules or interlobular septal thickening. The intravenous contrast administration is essential to reveal patchy areas of unenhanced parenchyma due to necrosis. It can also depict mature abscesses as a nodular lesion with an enhancing thickened wall. Pleural effusions and mediastinal lymphadenopathies can also accurately be characterised by CT. (4)
Medical treatment with intravenous antibiotics is the mainstay of therapy, sometimes for long periods (2-3 months). It is important to identify associated abscess formation or empyema, because surgical treatment (drainage) may be needed in these cases, particularly when they are very large. Lung-resection can be considered when extensive necrosis is not responding to previous treatments. 
Proper treatment prognosis is favourable, with 90% of abscesses cured with medical treatment alone.
In cases of lobar pneumonia in immunocompromised patients or those with chronic pulmonary pathology, it is important to consider less common diagnoses such as gram-negative bacteria, which tend to progress to NP. CT study, before and after iodinated contrast administration, is essential to identify areas within the parenchyma consolidation without enhancement due to necrosis.
Written informed patient consent for publication has been obtained.
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