CT of localized lucent lung lesions

Abstract

OCALIZED lucent lung lesions depicted by the standard chest radiograph are relatively rare, except for those occurring in patients with generalized chronic obstructive pulmonary disease. The standard chest radiograph provides an inexpensive, sensitive means for determining the presence of most clinically significant focal, thinwalled, sharply demarcated areas of avascularity. Some of the limitations of the chest radiograph in this regard are: (a) it permits only a broad differential diagnosis; (b) it sometimes does not define the full extent of disease; (c) it sometimes does not allow localization to the precise anatomic compartment; and (d) it sometimes fails to demonstrate a small accompanying lesion adjacent to or remote from the lesion under investigation. Even with these radiographic limitations, other available data including clinical history, pulmonary function studies, and laboratory results significantly enhance the radiologist’s diagnostic accuracy. For those few but potentially life-threatening localized lucent lesions, more aggressive and risky procedures must be employed for diagnostic or therapeutic purposes, such as biopsy, chest tube insertion, or even thoracotomy. With the advent of CT, considerable improvement in the overall diagnostic accuracy of these localized lucent lung lesions has been obtained. By defining more precisely the location, margins, thickness, contents, and overall configuration, CT significantly narrows the differential diagnosis. If the CT characteristics of the lesion are nondiagnostic, interventional procedures such as bronchoscopy or percutaneous aspiration biopsy can more easily be obtained by CT guidance. The CT cross-sectional display and geometric resolution sometimes more clearly define previously recognized standard radiographic features of complicated versus uncomplicated and benign versus malignant lucent lung lesions. In addition, CT uniquely distinguishes pleural from subpleural lucent lesions. Probably the most important role CT serves is in demonstrating occult opaque or lucent lesions in proximity to the original lucency or in the contralateral lung. The presence or absence of abnormal pulmonary vascularity, adenopathy, calcification, or small pleural