<prompt> Most common cause of Pneumatocele:Streptococcus pneumoniaeHaemophilus influenzaSerratia marcescensStaphylococcus Aureus  <response>: Ans. d Staphylococcus AureusRef: Harrisonss 19 th ed. Pulmonary pneumatoceles are thin-walled, air-filled cysts that develop within the lung parenchyma. They can be single emphysematous lesions but are more, often multiple, thin-walled, air-filled, cystlike cavities. Pneumatoceles are generally observed soon after the development of pneumonia and can be observed on the initial chest radiograph. They are commonly caused by Staphylococcus Aureus. Other agents also causes pneumatocele including: Streptococcus pneumonia H. Influenza, E. Coli Group A streptococci Serratia marcescens Klebsiella pneumoniae, adenovirus, and tuberculosis. Noninfectious etiologies include hydrocarbon ingestion, trauma, and positive pressure ventilation. 