Pictorial review of the many faces of bronchioloalveolar cell carcinoma.

Bronchioloalveolar cell carcinoma (BAC) has a varied appearance on CT that often leads to an incorrect or delayed diagnosis. The purpose of this pictorial review is to define common CT characteristics that are specific to BAC. A retrospective review was undertaken of 20 CT scans of pathologically proven cases of BAC; tumours were categorized as focal or diffuse, single or multiple, and infiltrative or well defined. Additional radiological features noted include the density (solid, part solid, non-solid), the presence of unaffected vessels within the tumour(s), and the presence of internal air bronchograms. We illustrate cases of localized and diffuse BAC presenting as (i) solitary or multiple pulmonary nodules, with and without air bronchograms, (ii) bubble-like lucencies of pseudocavitation associated with nodules of varying density, (iii) unifocal or multifocal ground-glass opacities, (iv) crazy paving, (v) nodules and airspace opacities with unaffected vessels coursing through them and (vi) lobar or multilobar consolidation and cavitating nodules. In conclusion, BAC may present with a variety of CT appearances. However, there are typical features such as the CT-angiogram sign or air-brochochograms in solitary nodules and in the periphery of larger consolidations, persisting pure ground-glass opacities, unresolving consolidation and the combination of diffuse nodules and consolidation. These features should alert the radiologist to the diagnosis of BAC.