BOOP is a condition characterized pathologically by the presence of polypoid granulation tissue in the lumen of bronchioles and alveolar ducts. The classical clinical presentation is of a subacute onset of flulike symptoms and nonproductive cough. The majority of cases are idiopathic, some precipitating causes include connective tissue disorders, drug toxity (most commonly amiodarone), thyroiditis and UC.
Classic imaging findings are peripheral patchy consolidations or ground glass opacities. Consolidation is nonsegmental and commonly 2-6cm in diameter. These consolidations are similar to eosinophilic pneumonia but typically show a basilar predominance (vs an apical predominance in eosinophilic pneumonia). BOOP is generally self-limiting process, recovery is hastened by steroids.
Differential entities include infectious pneumonia (patients with BOOP are generally not that sick), Eosinophilic pneumonia (patients with EP have a eosinophilic infiltrate on biopsy and +/- blood eosinophilia). Less likely differential entities include alveolar cell carcinoma (this will not get better with steroids) and sarcoid (generally younger patients).