Diagnosis

This CXR shows a large right pleural effusion. This is a significant change over the 13 hour period since the previous CXR suggesting a rapidly progressive pneumonia. This is highly suspicious for a staphylococcal pneumonia. The source of the staph was suspected to be the cellulitis on his arm. The pleural effusion worsened, at which time it was drained through a tube thoracostomy. Gram stain of the fluid revealed gram positive cocci. Cell counts 50,000 RBC's, 29,000 WBC's, 70% segs, 18% bands. Protein 5.4 grams/dl, pH 7.0, glucose 8 mg/dl. He required a second chest tube to drain a loculated empyema. Other than this, he did remarkably well. He did not develop any pneumatoceles or a pneumothorax. He was discharged after 6 weeks of IV Antibiotics. Teaching Points and Discussion Staphylococcal pneumonia is rapidly progressive in all age groups. This is a serious pulmonary infection that is associated with significant morbidity and a high potential for death.

There are two main forms of staphylococcal pneumonia. Primary pneumonia is caused by direct inoculation through the respiratory tract. Secondary or metastatic hematogenous lung infection is due to bacteremic seeding of the lung during the course of endocarditis or septicemia associated with infection at other sites. It is not unusual to see severe impetigo associated with staphylococcal pneumonia. Primary staphylococcal pneumonia is a disease of infancy and childhood with three-quarters of the cases involving patients less than one-year old. Predisposing factors include cystic fibrosis, chronic lung disease, leukemia, pre-existing skin infection, and viral respiratory infection (measles, influenza, adenovirus).

The patients with staphylococcal pneumonia may present with fever, lethargy, severe respiratory distress (tachypnea, grunting, retractions, cyanosis), and gastrointestinal disturbances (anorexia, vomiting, abdominal distention). About 75% of patients present with fever, cough, and dyspnea. The rapid progression of clinical symptoms is characteristic of staphylococcal pneumonia.

Chest radiographs in the early stage of staphylococcal pneumonia may be normal or show a minimal focal infiltrate. In general, there is a rapid progression of radiographic findings over just a few hours. The segmental bronchopneumonia pattern is usually unilateral and then expands to involve other lobes. In the case of our patient here, he presented with abdominal pain and tachypnea.

A small infiltrate was noted which progressed to a large pleural effusion over a few hours. About 71% of pneumonias due to Staph aureus have associated pleural effusions. The effusion is on the right in 65%, on the left in 15% and bilateral 20% of the time. This frequently progresses to an empyema. Ultrasound or CT is often helpful in locating the loculated fluid. A pulmonary pneumatocele is a frequent complication of staphylococcal pneumonia with an incidence of greater than 85%.

There are usually multiple pneumatoceles which vary in size. Pneumatoceles are believed to be caused by a partial airway obstruction by intraluminal exudate or a peribronchial abscess. A lung abscess is another complication of staphylococcal pneumonia. An abscess is a relatively thick-walled cavity, in contrast to a pneumatocele which is usually a thin-walled radiolucent area. Fluid levels may be present in both pneumatoceles and abscesses. The incidence of pneumothorax associated with staphylococcal pneumonia is between 40% to 60%. A pneumothorax may result from a pneumatocele rupture or formation of a bronchopleural fistula (localized bronchial wall necrosis). A pyopneumothorax (pneumothorax + empyema) is highly suggestive of staphylococcal pneumonia. Empyemas require drainage with large bore tube thoracostomies.

The empyema is often rapidly progressive, which leads to compression of the lung and respiratory failure unless the empyema is drained. It is likely to reaccumulate following a thoracentesis. Chest tube thoracostomy also has the benefit of maintaining lung expansion, if a pneumothorax develops. A pathogen is recovered from patients with pneumonia and effusions about 76% of the time. Of these, pleural fluid cultures are positive in 86% and blood cultures are positive in 10%. Although antibiotic coverage with anti-staphylococcal penicillins (e.g., oxacillin) or first generation cephalosporins (e.g.. cefazolin) is usually sufficient, there is a substantial rate of resistance to these drugs.

Methicillin Resistant Staph Aureus will usually be cephalosporin resistant as well. Vancomycin should be added to the anti-staphylococcal antibiotic regimen until sensitivities of the organism are determined. Complications of staphylococcal pneumonia include endocarditis, purulent pericarditis, osteomyelitis, deep tissue abscess, septic arthritis, and meningitis.

References

1. Chartrand SA, McCracken GH. Staphylococcal pneumonia in infants and children. Ped Infect Dis 1982;1:19-23. Forbes GB, Emerson GL.Staphylococcal pneumonia and empyema. Pediat Clin N Amer 1957;4:215-229.
   
   
2. Melish ME. Staphylococcal Infections. In: Feigin RD, Cherry JD (eds). Textbook of Pediatric Infectious Diseases, 2nd edition, 1987,Philadelphia, WB Saunders Company, pp. 1260-1292.

Copyrighted:Radiology Cases in Pediatric Emergency Medicine Volume 2, Case 5 Loren Yamamoto, MD, MPH, Associate Professor of Pediatrics, University of Hawaii John A. Burns School of Medicine loreny@hawaii.edu

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Last created on 01-07-2006