Pathology and Pathogenesis

A number of conditions predispose children to the development of pulmonary abscesses, including aspiration, pneumonia, cystic fibrosis (Chapter 395), gastroesophageal reflux (Chapter 315.1), tracheoesophageal fistula (Chapter 311), immunodeficiencies, postoperative complications of tonsillectomy and adenoidectomy, seizures, and a variety of neurologic diseases. In children, aspiration of infected materials or a foreign body is the predominant source of the organisms causing abscesses. Initially, pneumonitis impairs drainage of fluid or the aspirated material. Inflammatory vascular obstruction occurs, leading to tissue necrosis, liquefaction, and abscess formation. Abscess can also occur as a result of pneumonia and hematogenous seeding from another site.

If the aspiration event occurred while the child was recumbent, the right and left upper lobes and apical segment of the right lower lobes are the dependent areas most likely to be affected. In a child who was upright, the posterior segments of the upper lobes were dependent and therefore are most likely to be affected. Primary abscesses are found most often on the right side, whereas secondary lung abscesses, particularly in immunocompromised patients, have a predilection for the left side.

Both anaerobic and aerobic organisms can cause lung abscesses. Common anaerobic bacteria that can cause a pulmonary abscess include Bacteroides spp, Fusobacterium spp, and Peptostreptococcus spp. Abscesses can be caused by aerobic organisms such as Streptococcus spp, Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Aerobic and anaerobic cultures should be part of the work-up for all patients with lung abscess. Occasionally, concomitant viral-bacterial infection can be detected. Fungi can also cause lung abscesses, particularly in immunocompromised patients.

Diagnosis