Case 13
History
38-year-old immunocompromised male with fever and cough.
PA chest radiograph shows diffuse bilateral
reticulnodular interstitial infiltrates with bilateral
cystic changes.
Chest CT confirms the presence of thin walled
pulmonary air cysts.
Findings
Sixty percent of individuals with AIDS present with PCP as the initial manifestation of AIDS. Diffuse bilateral interstitial infiltrates are the most common radiographic appearance of PCP. Less typical presentation of PCP includes localized infiltrate, cystic lesions, hilar nodal enlargement, and spontaneous pneumothorax. Lung necrosis with cavitation, non-cavitating, and cavitating pulmonary nodules have been described. Cavitary and cystic lung lesions are now a recognized feature of PCP infection, although pathogenesis is controversial.
Many etiologic factors have been suggested, including:
- Pneumatocele formation due to check valve obstruction, secondary to necrotic debris or endobronchial invasion.
- Necrotizing and cavitating granulomatous or nodular PCP with upper lobe predilection. Granuloma formation suggests a less advanced form of immunosuppression or improved defenses, secondary to AZT therapy.
- Chronic indolent infection and/or use of aerosolized Pentamidine with formation of thin-walled clustered cystic form of PCP. Aerosolized Pentamidine suppresses the infection, but does not eradicate it from the lung apices and periphery, blood, or lymphatics. Also, the apices become more susceptible to recurrent infection, secondary to poor distribution of the drug at the apices.
- Necrotizing Pneumocystis vasculitis with infarction also has been described as a cause of this form of cystic PCP.
- Emphysematous destruction of the lung due to the release of elastases by macrophages and neutrophils. PCP of the HIV virus or both upset the elastase/antielastase balance, causing direct cytotoxic effect on macrophages.
