Pneumocystis, Jiroveci Pneumonia

Jud W. Gurney, MD, FACR

Key Facts

Terminology

Opportunistic fungal infection often affecting individuals with T-cell immunodeficiency

Imaging Findings

Ground-glass is dominant finding; opacities symmetric and diffuse with sparing of lung periphery (40%)
- Mosaic attenuation pattern (30%)
- Upper lobe distribution in some, may be associated with aerosolized pentamidine prophylaxis
Cysts (30%), thin-walled, usually in ground-glass opacities
Prior irradiated lung protected: PCP will develop only outside radiation ports
Extremely rare to have PCP with normal HRCT examination

Top Differential Diagnoses

Pathology

Patients with impaired cell-mediated immunity predisposed to PCP
Organism can be found in normal lungs
Even with highly active antiretroviral therapy (HAART), PCP remains most prevalent opportunistic infection in AIDS

Clinical Issues

Axial CECT shows diffuse ground-glass opacities

with lobular sparing. Small holes

may represent early pneumatoceles.

Coronal CECT reconstructions shows diffuse perihilar distribution of ground-glass opacities

and small pneumatoceles

TERMINOLOGY

Abbreviations and Synonyms

Definitions

Opportunistic fungal infection often affecting individuals with T-cell immunodeficiency
- 2 major forms: Trophozoites and cysts

IMAGING FINDINGS

General Features

Best diagnostic clue: Diffuse symmetric ground-glass opacities in hypoxic immunocompromised patient
Patient position/location
- Diffuse perihilar with peripheral sparing
- Less common upper lobe predominant with cysts
Morphology: Ground-glass opacities with cysts (30%)

CT Findings

Radiographic Findings

Nuclear Medicine Findings

Historically, gallium scan used for questionable cases, now replaced by CT due to long imaging times (24 hours)
- Widespread lung activity is present with PCP

Imaging Recommendations

DIFFERENTIAL DIAGNOSIS

Hypersensitivity Pneumonitis

Antigen source identified with careful work and personal history
- Onset of dyspnea and nonproductive cough tends to be more subacute or chronic
- Hypoxia often more mild and fever less common
Diffuse ground-glass most common imaging manifestation
Ill-defined centrilobular nodules more common than in PCP
Air-trapping common at expiratory CT, uncommon with PCP
May also have cysts

Lymphocytic Interstitial Pneumonia

Diffuse Alveolar Hemorrhage

Anemia common
Clinical history, tissue sampling, and laboratory investigation required to differentiate different etiologies of DAH
Diffuse or extensive bilateral ground-glass and consolidative opacities similar to PCP

Cytomegalovirus Pneumonitis