A 4-year-old girl, previously healthy, presented with 3 days of cough, sore throat, and fevers. She had a chest radiograph at onset of symptoms, which showed right lower lobe pneumonia and pleural effusion, the latter confirmed by sonography. She was started on antibiotics, but had progressive dyspnea so she was transferred to Children’s Hospital for further management. On physical examination, she had tachycardia and frequent coughing, but was in no apparent distress. Her white blood count was slightly elevated (12,200) with an increased number of bands (41%). Since the patient was not responding to antibiotics, a computed tomography (CT) examination was performed to assess for complicated fluid collections or lung abscess.
A CT examination was performed with a Somatom Definition 64 AS scanner (Siemens, Erlangen, Germany). This scanner has a dose reduction tool called CARE kV, which uses information gathered by the topogram to optimize kilovoltage (kVp) and milliamperage (mAs) so that a user-chosen contrast-to-noise ratio is maintained, and thus optimal image quality and lowest dose are achieved. In this patient, the CT scan revealed multiple air-fluid-filled cavities within the consolidated right lower lobe (Figure 1). Other findings included a large right parapneumonic pleural effusion with enhancing margins consistent with empyema. Several small gas collections were present in the empyema related to the presence of a thoracostomy tube.
The clinical course of community-acquired pneumonia in children is usually benign and responds well to conventional treatment. Occasionally, bacterial pneumonia is complicated by pleural effusion, empyema, lung abscess, pneumatocele, or necrotizing pneumonia (also termed cavitary pneumonia and pulmonary gangrene).1 Complicated pneumonias in children are commonly caused by bacterial pathogens, most often Staphylococcus aureus and Streptococcus pneumoniae.
Necrotizing pneumonia is thought to be a consequence of pulmonary gangrene, tissue liquefaction, and subsequent necrosis, due to either an abnormal cytokine-driven inflammatory response or pulmonary infarction secondary to a thrombotic process.1 Necrotizing pneumonia caused by Staphylococcus has been associated with the presence of Paton-Valentine leukocidin, a cytotoxin-damaging leukocyte. M protein, a virulence factor has been associated with tissue necrosis in group A Streptococcus infection.2 The mechanism of necrotic complications is postulated to be related to thrombotic occlusion of alveolar capillaries secondary to inflammation with subsequent ischemia and eventually necrosis of the lung tissue.3 Pathologically, gross inspection shows necrotic and gangrenous lung with regions of infarctions in the gangrenous areas and thrombi in the pulmonary artery within the areas of infarcted lung.2
Most children present with symptoms of fever and cough for ≤1 week prior to hospitalization. Other clinical findings include failure to respond to medical treatment despite parenteral antibiotic administration. The diagnosis of necrotizing pneumonia can be suspected by plain chest radiography if air collections are seen within consolidation of lung or pleural fluid collections. However, the presence of dense tissue consolidation and pleural effusion may obscure findings of lung necrosis. Computed tomography (CT) scanning is superior to plain chest radiography in revealing parenchymal complications of complicated pneumonia.3-5
The majority of cases of necrotizing pneumonia involve one lobe, although more than one lobe may be affected. CT findings include cystic cavities without well-defined walls or enhancing margins within an area of consolidation. Decreased parenchymal enhancement after administration of intravenous contrast medium is another sign of necrosis, most likely related to ischemia.3,4 Intrapulmonary abscesses and bronchopleural fistulae can occur. The fistula forms when necrosis and abscess formation arise adjacent to the inflamed pleura.5
The differential diagnosis of cavitary pneumonia is lung abscess. Abscesses, unlike the cavities in necrotizing pneumonia, have thick, enhancing well-defined walls and may contain an air-fluid level. Lung abscesses are treated with antibiotics, and large abscesses may require percutaneous drainage. Percutaneous drainage of necrotic lung is not part of the treatment regimen.
Necrotizing pneumonia is important to recognize because most children with this finding need to be hospitalized and require a more aggressive course of antibiotic therapy than do children with uncomplicated pneumonia. Most children recover completely with antibiotic therapy and chest tube drainage of empyema. Rare indications for surgical intervention include persistent bronchopleural fistula, loculated empyema, and lung entrapment. Outcome is usually excellent with normal lungs on long-term follow up imaging.
CT findings of necrotizing pneumonia include a variable number of air-filled cavities in areas of consolidated lung. Most children recover with conservative management with antibiotics and show no long-term sequelae of disease. Low-dose CT is the study of choice to document complicated pneumonia.