A focal lung pneumatosis,  is an enclosed pocket of air or gas in the lung and includes blebs, bullae, pulmonary cysts, and lung cavities. Blebs and bullae can be classified by their wall thickness. A bleb has a wall thickness of less than 1 mm. By radiology definition, it is up to 1 cm in total size. By pathology definition, it originates in the pleurae (rather than in the lung parenchyma). A bulla has a wall thickness of less than 1 mm. By radiology definition, it has a total size of greater than 1 cm. By pathology definition, it originates in the lung parenchyma (rather than in the pleurae). A lung cyst has a wall thickness of up to 4 mm. A minimum wall thickness of 1 mm has been suggested, but thin-walled pockets may be included in the definition as well. A cavity has a wall thickness of more than 4 mm.The terms above, when referring to sites other than the lungs, often imply fluid content. Lung cysts are seen in about 8% of the general population, with an increased prevalence in older people, and are not associated with emphysema. They may be part of the aging changes of the lungs, and cause a slight decrease in their diffusing capacity. The presence of multiple pulmonary cysts may indicate a need to evaluate the possibility of bullous or cystic lung diseases. Cavitation indicates workup for serious infection or lung cancer.
Although infection is not the reason or cause of chronic bronchitis, it is seen to aid in sustaining the bronchitis. Diagnosis
A physical examination will often reveal decreased intensity of breath sounds, wheezing, rhonchi, and prolonged expiration. During examination for physicians rely on history and the presence of persistent or acute onset of cough, followed by a URTI with no traces of pneumonia. Acute bronchitis is typically a clinical diagnosis that relies on patients history and exam, and should be suspected in patients with an acute onset of cough, which often follows a URTI without traces of pneumonia.Although there is no universally-accepted clinical definition for acute bronchitis, there is a proposed set of practical criteria (Macfarlane, 2001) that include:

An acute illness of less than three weeks. Cough as the predominant symptom. At least one other lower respiratory tract symptom, such as sputum production, wheezing, chest pain. No alternative explanation for the symptoms.A variety of tests may be performed in people presenting with cough and shortness of breath:
A chest X-ray is useful to exclude pneumonia which is more common in those with a fever, fast heart rate, fast respiratory rate, or who are old. A sputum sample showing neutrophil granulocytes (inflammatory white blood cells) and culture showing that has pathogenic microorganisms such as Streptococcus species. A blood test would indicate inflammation (as indicated by a raised white blood cell count and elevated C-reactive protein).Decreased breath sounds, crackles, wheezing, and rhonchi that clears with coughs may be heard in the chest.