Type:
Educational Exhibit
Keywords:
Paediatric, Respiratory system, CT, Plain radiographic studies, Education, Other
DOI:
10.26044/ranzcr2022/R-0198
Background
Pulmonary alveolar proteinosis (PAP) is a rare condition characterised by the accumulation of lipoproteinaceous material within the alveoli. First described in 1958, its pathophysiology was initially poorly understood with a highly variable prognosis(1). With developments in molecular genetics, however, a greater understanding of its pathogenesis has been elucidated. Acquired anti-GM-CSF antibodies which disrupt surfactant homeostasis, are the most common cause in adult cases(2). Concurrently, there were case reports of atypical forms of PAP occurring in the paediatric population. It is now known that most cases of paediatric PAP are due to a genetic defect in surfactant metabolism or are associated with a primary immunodeficiency(3).
Chest x-ray is a useful first step in diagnostic imaging for PAP, but findings are nonspecific. Classically there are bilateral, symmetrical and central lung opacities, with relative sparing of the lung apices and costophrenic angles. Less often, PAP can cause multifocal asymmetrical opacities or diffuse extensive consolidation(1).
The characteristic radiological feature on CT in PAP is a “crazy paving” pattern. This is a nonspecific finding with a broad differential. More common aetiologies include bacterial pneumonia, acute interstitial pneumonia, and acute respiratory distress syndrome. Less commonly, “crazy paving” is caused by pulmonary oedema, pulmonary infections, radiation or drug-induced pneumonitis, pulmonary haemorrhage, usual interstitial pneumonia, cryptogenic organising pneumonia, sarcoidosis, chronic eosinophilic pneumonia, invasive mucinous adenocarcinoma of the lung, lipoid pneumonia, or pulmonary veno-occlusive disease(1).