What is pulmonary alveolar proteinosis (PAP), and what is the difference between primary and secondary PAP?
PAP is a rare lung disease characterized by the accumulation of an abnormal surfactant-like material within the alveoli. PAP can be primary (idiopathic) or secondary. The primary form is more common and is seen in young and middle-aged adults, whereas the secondary form is seen in the setting of hematologic malignancy, inhalational lung disease, or immunodeficiency states. Patients with PAP have subacute or chronic symptoms and can even be asymptomatic.
What is the classic CT appearance of PAP?
PAP is characterized by bilateral fairly symmetric and geographic areas of crazy paving. Although the crazy paving pattern has classically been associated with PAP, a multitude of disease conditions can result in a crazy paving pattern.