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The Ribs: Anatomic and Radiologic Considerations

¹ Departments of Radiology (Y.K., Y.K.Y., J.M., T.I.)
² Anatomy (K.H.), St Marianna University School of Medicine, 2-16-1 Sugao, Miyamae-Ku, Kawasaki City, Kanagawa, Japan 216.

View larger version (145K): [in a new window]   Figure 1.  Big rib sign. On a left lateral chest radiograph, the comparable portions of the posterior and anterior ribs appear very different in size (arrowheads). The posterior rib (right) is farther from the film and is magnified more than the anterior rib (left), which is in contact with the film.

View larger version (38K): [in a new window]   Figure 2.  Vertical displacement sign. Schematic demonstrates how the vertical divergence of the x-ray beam results in the progressive vertical separation of the paired ribs as one moves in either the cephalic or caudal direction from the midthorax.

View larger version (129K): [in a new window]   Figure 3a.  Vertical displacement sign. (a) Left lateral chest radiograph (magnified view) shows one pair of ribs projecting at the horizontal level (H). In the inferior pair of ribs (I), the posterior rib (arrow) is slightly lower than the anterior rib. In contrast, in the cranial rib pair (S), the posterior rib (arrowhead) is higher than the anterior rib. Thus, the posterior ribs are farther from the film and are on the right. (b) Left lateral chest radiograph (magnified view) obtained at a slightly different angle shows the upper anterior rib (arrowhead) cephalad and the lower anterior rib (arrow) caudad to the posterior ribs (ie, the anterior ribs are on the right). (c) Left lateral chest radiograph (magnified view) demonstrates how the vertical displacement sign is usually applicable even when the posterior ribs are partially superimposed. The higher rib (arrowhead) and lower rib (arrow) could be identified even when they overlapped.

View larger version (121K): [in a new window]   Figure 3b.  Vertical displacement sign. (a) Left lateral chest radiograph (magnified view) shows one pair of ribs projecting at the horizontal level (H). In the inferior pair of ribs (I), the posterior rib (arrow) is slightly lower than the anterior rib. In contrast, in the cranial rib pair (S), the posterior rib (arrowhead) is higher than the anterior rib. Thus, the posterior ribs are farther from the film and are on the right. (b) Left lateral chest radiograph (magnified view) obtained at a slightly different angle shows the upper anterior rib (arrowhead) cephalad and the lower anterior rib (arrow) caudad to the posterior ribs (ie, the anterior ribs are on the right). (c) Left lateral chest radiograph (magnified view) demonstrates how the vertical displacement sign is usually applicable even when the posterior ribs are partially superimposed. The higher rib (arrowhead) and lower rib (arrow) could be identified even when they overlapped.

View larger version (118K): [in a new window]   Figure 3c.  Vertical displacement sign. (a) Left lateral chest radiograph (magnified view) shows one pair of ribs projecting at the horizontal level (H). In the inferior pair of ribs (I), the posterior rib (arrow) is slightly lower than the anterior rib. In contrast, in the cranial rib pair (S), the posterior rib (arrowhead) is higher than the anterior rib. Thus, the posterior ribs are farther from the film and are on the right. (b) Left lateral chest radiograph (magnified view) obtained at a slightly different angle shows the upper anterior rib (arrowhead) cephalad and the lower anterior rib (arrow) caudad to the posterior ribs (ie, the anterior ribs are on the right). (c) Left lateral chest radiograph (magnified view) demonstrates how the vertical displacement sign is usually applicable even when the posterior ribs are partially superimposed. The higher rib (arrowhead) and lower rib (arrow) could be identified even when they overlapped.

View larger version (150K): [in a new window]   Figure 4.  Rib counting at CT with the clavicle as an anatomic landmark. Axial CT scan shows the medial third of the clavicle (*) and the relative position of the first two ribs (1, 2).

View larger version (102K): [in a new window]   Figure 5.  Rib counting at CT with the xiphoid process as an anatomic landmark. Axial CT scan shows the xiphoid process (*), the seventh rib (7), and the relative position of the lower ribs (6–9). It is important to identify the transverse portion of the costal cartilage (arrows), at which point one stops counting down and starts counting up (ie, moves from medial to lateral). 5 = fifth rib.

View larger version (102K): [in a new window]   Figure 6a.  Rib counting at CT with the sternal angle as an anatomic landmark. Sequential axial chest CT scans of the ribs and sternum show identification of the sternal angle (*) with the second costal cartilage and rib (2) followed by the counting of the third, fourth, and fifth ribs (3–5) in numeric order (a). The fifth rib is traced as the reference rib in sequential planes (b–d). Note that the rib moves slightly anterior in the caudal planes. The target rib with the metastatic lesion (arrowhead in d) is identified by counting ribs in numeric order from fifth (5) to fourth (4) in the same axial plane.

View larger version (100K): [in a new window]   Figure 6b.  Rib counting at CT with the sternal angle as an anatomic landmark. Sequential axial chest CT scans of the ribs and sternum show identification of the sternal angle (*) with the second costal cartilage and rib (2) followed by the counting of the third, fourth, and fifth ribs (3–5) in numeric order (a). The fifth rib is traced as the reference rib in sequential planes (b–d). Note that the rib moves slightly anterior in the caudal planes. The target rib with the metastatic lesion (arrowhead in d) is identified by counting ribs in numeric order from fifth (5) to fourth (4) in the same axial plane.

View larger version (107K): [in a new window]   Figure 6c.  Rib counting at CT with the sternal angle as an anatomic landmark. Sequential axial chest CT scans of the ribs and sternum show identification of the sternal angle (*) with the second costal cartilage and rib (2) followed by the counting of the third, fourth, and fifth ribs (3–5) in numeric order (a). The fifth rib is traced as the reference rib in sequential planes (b–d). Note that the rib moves slightly anterior in the caudal planes. The target rib with the metastatic lesion (arrowhead in d) is identified by counting ribs in numeric order from fifth (5) to fourth (4) in the same axial plane.

View larger version (113K): [in a new window]   Figure 6d.  Rib counting at CT with the sternal angle as an anatomic landmark. Sequential axial chest CT scans of the ribs and sternum show identification of the sternal angle (*) with the second costal cartilage and rib (2) followed by the counting of the third, fourth, and fifth ribs (3–5) in numeric order (a). The fifth rib is traced as the reference rib in sequential planes (b–d). Note that the rib moves slightly anterior in the caudal planes. The target rib with the metastatic lesion (arrowhead in d) is identified by counting ribs in numeric order from fifth (5) to fourth (4) in the same axial plane.

View larger version (79K): [in a new window]   Figure 7a.  Rib counting at lateral chest radiography with the sternal angle as an anatomic landmark. (a) Diagram of the ribs and sternum (lateral view) shows the second costal cartilage attached to the sternal angle (*), which is characterized by a slight anterior convex angulation. The second rib (darkened area) courses upward obliquely. (b) Lateral chest radiograph shows the second rib (arrowheads) and costal cartilage attached to the sternal angle (*).

View larger version (103K): [in a new window]   Figure 7b.  Rib counting at lateral chest radiography with the sternal angle as an anatomic landmark. (a) Diagram of the ribs and sternum (lateral view) shows the second costal cartilage attached to the sternal angle (*), which is characterized by a slight anterior convex angulation. The second rib (darkened area) courses upward obliquely. (b) Lateral chest radiograph shows the second rib (arrowheads) and costal cartilage attached to the sternal angle (*).

View larger version (121K): [in a new window]   Figure 8.  Determining the number of vertebrae with the 12th rib as an anatomic landmark. Lateral chest radiograph demonstrates the 12th (ie, the lowest) rib as the most caudal arch (arrow). The L1 vertebral body is compressed.

View larger version (151K): [in a new window]   Figure 9.  Bifid (forked) rib. Posteroanterior chest radiograph (magnified view) shows a bifid or forked deformity of the anterior end of the fifth rib (* and white arrows). An associated spurlike process or incomplete fusion of the ribs (black arrow) is seen.

View larger version (135K): [in a new window]   Figure 10.  Cervical rib. Posteroanterior chest radiograph (magnified view) shows a supernumerary bone arising from the seventh cervical vertebra (arrow).

View larger version (120K): [in a new window]   Figure 11.  Short rib. Posteroanterior chest radiograph shows a short midthoracic rib arch (arrow).

View larger version (111K): [in a new window]   Figure 12a.  Costal shape in the normal thorax. (a) Photograph of a right rib shows the smooth, hemispheric curvature of the rib. (b) Posteroanterior chest radiograph shows the overlying arc of the ribs.

View larger version (146K): [in a new window]   Figure 12b.  Costal shape in the normal thorax. (a) Photograph of a right rib shows the smooth, hemispheric curvature of the rib. (b) Posteroanterior chest radiograph shows the overlying arc of the ribs.

View larger version (29K): [in a new window]   Figure 13a.  Funnel chest. (a, b) Schematic (a) and posteroanterior chest radiograph (b) show accentuation of the downward angulation of the anterior portions of the ribs, which run almost parallel to each other. (c) Lateral chest radiograph shows depression of the sternum (arrow).

View larger version (144K): [in a new window]   Figure 13b.  Funnel chest. (a, b) Schematic (a) and posteroanterior chest radiograph (b) show accentuation of the downward angulation of the anterior portions of the ribs, which run almost parallel to each other. (c) Lateral chest radiograph shows depression of the sternum (arrow).

View larger version (109K): [in a new window]   Figure 13c.  Funnel chest. (a, b) Schematic (a) and posteroanterior chest radiograph (b) show accentuation of the downward angulation of the anterior portions of the ribs, which run almost parallel to each other. (c) Lateral chest radiograph shows depression of the sternum (arrow).

View larger version (162K): [in a new window]   Figure 14a.  Barrel-shaped thorax in a patient with diffuse panbronchiolitis (Asian bronchiolitis). (a) Axial chest CT scan shows a barrel-shaped thorax characterized by a relatively long anteroposterior diameter of the osseous thorax. (b, c) Posteroanterior chest radiograph (b) and schematic (c) show the straight, downward angulation of the lateral portion of the ribs (arrows in b), which become elongated as the sagittal diameter of the thorax increases.

View larger version (157K): [in a new window]   Figure 14b.  Barrel-shaped thorax in a patient with diffuse panbronchiolitis (Asian bronchiolitis). (a) Axial chest CT scan shows a barrel-shaped thorax characterized by a relatively long anteroposterior diameter of the osseous thorax. (b, c) Posteroanterior chest radiograph (b) and schematic (c) show the straight, downward angulation of the lateral portion of the ribs (arrows in b), which become elongated as the sagittal diameter of the thorax increases.

View larger version (30K): [in a new window]   Figure 14c.  Barrel-shaped thorax in a patient with diffuse panbronchiolitis (Asian bronchiolitis). (a) Axial chest CT scan shows a barrel-shaped thorax characterized by a relatively long anteroposterior diameter of the osseous thorax. (b, c) Posteroanterior chest radiograph (b) and schematic (c) show the straight, downward angulation of the lateral portion of the ribs (arrows in b), which become elongated as the sagittal diameter of the thorax increases.

View larger version (142K): [in a new window]   Figure 15.  Rib companion shadows. Posteroanterior chest radiograph (magnified view) shows rib companion shadows projecting adjacent to the inferior and inferolateral margins of the second rib (arrows).

View larger version (130K): [in a new window]   Figure 16a.  Rib companion shadows. (a) Posteroanterior chest radiograph reveals thick companion shadows (arrows). (b) Anteroposterior chest radiograph fails to demonstrate these shadows.

View larger version (121K): [in a new window]   Figure 16b.  Rib companion shadows. (a) Posteroanterior chest radiograph reveals thick companion shadows (arrows). (b) Anteroposterior chest radiograph fails to demonstrate these shadows.

View larger version (84K): [in a new window]   Figure 17.  Rib companion shadows. Sagittal reformatted CT scan of the thorax shows the posterior or posterolateral portion of the second rib (2) located at the superoposterior aspect of the lung. Note the slightly protruding soft tissues in the second intercostal space (arrow), which may cause the rib companion shadow below the second rib. 1 = first rib, 3 = third rib, 4 = fourth rib.

View larger version (128K): [in a new window]   Figure 18.  Sharp lines along the lower costal margin. Posteroanterior chest radiograph shows sharp, thin lines along the lower margin of the ribs (arrows).

View larger version (119K): [in a new window]   Figure 19a.  Costal groove. (a) Photograph of a right rib shows the normal anatomy of the costal groove (arrows). (b) Radiograph of the same rib shows a thin, sharp hairline caused by the cortex of the costal groove (arrows).

View larger version (101K): [in a new window]   Figure 19b.  Costal groove. (a) Photograph of a right rib shows the normal anatomy of the costal groove (arrows). (b) Radiograph of the same rib shows a thin, sharp hairline caused by the cortex of the costal groove (arrows).

View larger version (136K): [in a new window]   Figure 20.  Rib overlying shadows. Posteroanterior chest radiograph shows two types of short, linear opacities projecting over the lateral portion of the ribs. White arrows indicate anterior overlying opacity, black arrow indicates posterior overlying opacity.

View larger version (113K): [in a new window]   Figure 21a.  Rib overlying shadows. (a) Photograph of a right eighth rib shows a blue catheter along the superior margin and a guide wire along the inferomedial margin. (b) Radiograph of the same rib shows the catheter (thick line) and the guide wire (thin line) crossing between the external and internal margins at the lateral portion of the rib. The course of the guide wire at the lateral portion of the rib is very similar to the medial border of the anterior overlying opacity. The course of the catheter corresponds to the posterior overlying opacity. (c) Schematic demonstrates the relationship between the rib margins and the overlying opacities. The gray area corresponds to the overlying shadow, which results from overlap of the bone structure; the blue line indicates the superior margin of the rib; and the red line indicates the inferomedial margin of the rib.

View larger version (57K): [in a new window]   Figure 21b.  Rib overlying shadows. (a) Photograph of a right eighth rib shows a blue catheter along the superior margin and a guide wire along the inferomedial margin. (b) Radiograph of the same rib shows the catheter (thick line) and the guide wire (thin line) crossing between the external and internal margins at the lateral portion of the rib. The course of the guide wire at the lateral portion of the rib is very similar to the medial border of the anterior overlying opacity. The course of the catheter corresponds to the posterior overlying opacity. (c) Schematic demonstrates the relationship between the rib margins and the overlying opacities. The gray area corresponds to the overlying shadow, which results from overlap of the bone structure; the blue line indicates the superior margin of the rib; and the red line indicates the inferomedial margin of the rib.

View larger version (22K): [in a new window]   Figure 21c.  Rib overlying shadows. (a) Photograph of a right eighth rib shows a blue catheter along the superior margin and a guide wire along the inferomedial margin. (b) Radiograph of the same rib shows the catheter (thick line) and the guide wire (thin line) crossing between the external and internal margins at the lateral portion of the rib. The course of the guide wire at the lateral portion of the rib is very similar to the medial border of the anterior overlying opacity. The course of the catheter corresponds to the posterior overlying opacity. (c) Schematic demonstrates the relationship between the rib margins and the overlying opacities. The gray area corresponds to the overlying shadow, which results from overlap of the bone structure; the blue line indicates the superior margin of the rib; and the red line indicates the inferomedial margin of the rib.