The ribs: Anatomic and radiologic considerations

The ribs are essential structures of the osseous thorax and provide informa tion that aids in the interpretation of radiologic images. Techniques for m aking precise identification or the ribs are useful in detection or rib les ions and localization of lung lesions, The big rib sign and the vertical di splacement sign can be used to differentiate the right and left ribs on lat eral chest radiographs. The clavicle, the xiphoid process, and the sternal angle may be used as anatomic landmarks for rib counting on computed tomogr aphic scans. For rib counting on lateral chest radiographs, the sternal ang le or the 12th rib may be used. Anatomic rib variants include developmental deformities, cervical rib, and short rib and may mimic true rib diseases. Detection of thoracic deformities such as funnel chest (pectus excavatum) a nd barrel-shaped thorax requires an awareness of the strong correlation bet ween the transverse appearance of the thorax and costal shape. Shadows arou nd the rib cage (eg, rib companion shadows, sharp lines along the lower mar gin of the ribs, rib overlying shadows) may mimic pleural and extrapleural disease on frontal chest radiographs. It is imperative that the radiologist be familiar with normal rib anatomy, normal rib variants, and the radiolog ic appearance of the ribs to prevent misdiagnosis.