Plain Radiograph: The retention of excess gas in all or part o fthe lung at any stage of expiration; to be used only when excess air is demonstrated by a dynamic study, such as inspiration/expiration films or fluoroscopy. Not to be used for overinflation
CT: Decreased attenuation of pulmonary parenchyma, especially manifest as less than normal increase in attenuation during expiration. To be differentiated from decreased attenuation of hypoperfusion secondary to locally increased pulmonary arterial resistance.
The inspiratory and expiratory images shown below demonstrate air-trapping in the left lower lobe secondary to obliterative/constrictive bronchiolitis
Radiology (CT): Focal region or regions of low attenuation, usually without visible walls, resulting from actual or perceived enlarged air spaces and destroyed alveolar walls. May be associated with air trapping. (panacinar, distal acinar, centrilobular)
CT A round, parenchymal space with a well-defined wall; usually air-containing when in the lung but without associated pulmonary emphysema; commonly used to describe enlarged air spaces in end-stage fibrosis of interstitial lung diseases and also in Langheran's cell histiocytosis and lymphangiomyomatosis
Fig. 1 shows cysts of honeycombing, whereas Fig. 2 shows cysts of histiocytosis X
Pathology: A multitude of irregular cystic spaces in pulmonary tissue that are generally lined with bronchiolar epithelium and have markedly thickened walls comprised of dense fibrous tissue, with or without associated chronic inflammation
Plain Radiograph: A number of closely approximated ring shadows representing air spaces, 5-10mm in diameter with walls 2-3mm thick that resemble a true honeycomb: a finding whose occurrence implies "end-stage" lung. Often mistaken for bronchiectasis.
Radiology & Pathology A thin-walled, gas-filled space within the lung, usually occuring in association with acute pneumonia (most commonly of staphyloccal etiology) and almost invariably transient. Fig. 2 shows an associated pneumothorax (arrowhead).
Pathology: A sharply demarcated region of emphysema; a gas-containing space that may contain nothing but gas or may contain overdistended and ruptured alveolar septa and blood vessels
Plain Radiograph: A sharply demarcated area of avascularity within the lung, measuring 1.0cm or more in diameter and possessing a wall less than 1mm in thickness - this is the preferred term fo all thin-walled air-containing spaces in the lung with the exception of pneumatocele On CT, a bulla is a round, focal air space, 1cm or more in diameter, demarcated by a thin wall; usually multiple or assocated with other signs of pulmonary emphysema