(Radiographics. 1999;19:1125-1142.)
© RSNA, 1999
Keep Your Eyes on the Ribs: The Spectrum of Normal Variants and Diseases That Involve the Ribs1
Adam R. Guttentag, MD and
Julia K. Salwen, MD
1 From the Department of Radiology, Albert Einstein Medical Center, 5501 Old York Rd, Philadelphia, PA 19141. Presented as a scientific exhibit at the 1997 RSNA scientific assembly. Received October 5, 1998; revision requested October 15 and received January 14, 1999; accepted January 14. Address reprint requests to A.R.G.
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Abstract
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A variety of normal variants or pathologic conditions of the ribs may be overlooked at chest radiography if the ribs are not evaluated carefully. Rib lesions may simulate pulmonary disease as well. Normal rib variants include cervical, intrathoracic, and pelvic ribs; forked rib; fusion and bridging; and pseudarthrosis of the first rib. Trauma-related lesions are common and usually occur in isolation but can alert the radiologist to other injuries. Metastases may appear as vague areas of increased opacity overlying the lung if seen en face and typically have a smooth interface with the lung on oblique images. Chondroid lesions nearly always arise at or near the anterior end of the rib. Osteochondroma (exostosis) typically manifests as a deformity or expansion of the rib with calcification of the cartilaginous cap. Acute rib infections are seen as focal areas of bone destruction, whereas chronic infections may manifest as periosteal reaction or a bone sequestrum. Inferior rib notching may be seen in a wide variety of pathologic conditions. Rib abnormalities may also be seen in fibrous dysplasia, Langerhans cell histiocytosis, Paget disease, and various hemoglobinopathies. In most cases, radiography is sufficient for the identification and diagnosis of normal variants and pathologic conditions of the ribs.
Index Terms: Ribs, 471.20, 471.21, 471.651, 471.66, 471.84, 471.85, 471.871 • Ribs, abnormalities, 471.14 • Ribs, fractures, 471.41 • Ribs, neoplasms, 471.31, 471.32, 471.34
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INTRODUCTION
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The ribs are too often overlooked at chest radiography, although they are usually easy to evaluate with this modality. Careful observation of the ribs is often rewarding. One may find pathologic conditions of the ribs themselves, evidence of a systemic disease, or clues to significant nearby disease. In addition, radiologists should be familiar with a number of normal variants of the ribs to avoid mistaking them for an abnormality.
In this article, we review normal radiographic findings in the ribs as well as a spectrum of normal variants. In addition, we discuss and illustrate a variety of pathologic findings including fracture related to trauma, neoplastic involvement (metastatic lesions, primary benign and malignant lesions), infectious disease, rib notching, and other abnormalities that may be encountered in everyday practice.
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NORMAL RADIOGRAPHIC APPEARANCE OF THE RIBS
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On a frontal chest radiograph, the posterior parts of the ribs have a horizontal orientation. The lateral and anterior parts of the ribs are situated inferior to the costochondral junction, which may be seen as a "cupped" cortical line in some persons. The costal cartilage typically calcifies with advancing age and is therefore easier to identify on radiographs obtained in older patients.
The superior margin of each rib is normally a smooth, well-defined line that may be followed for the entire length of the rib. However, the groove for the neurovascular bundle thins the inferior margin of the rib. As a result, a portion of the inferior edge is often indistinct on frontal chest radiographs. This finding is symmetric and is most often seen along the posterior portions of the middle ribs (Fig 1a); it should not be mistaken for an erosive or lytic process. The normal rib has a well-defined cortical-medullary junction, which is well seen on both frontal and lateral images. Loss of this sharp interface helps confirm sclerosis of the ribs due to either local or systemic disease.
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Figure 1a. Normal findings at chest radiography. (a) Frontal view shows the inferior margins of portions of the posterior ribs as indistinct (arrows). This finding should not be confused with a destructive process. (b) Lateral view shows the posterior ribs as circular areas of increased opacity (solid arrows) or parallel lines (open arrows), depending on whether the rib is parallel or oblique to the x-ray beam. Loss of this normal appearance on the lateral view may be an important indicator of rib disease (cf Figs 11, 13, 24, 25). The inferior flange of the rib is also seen (arrowhead).
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Figure 1b. Normal findings at chest radiography. (a) Frontal view shows the inferior margins of portions of the posterior ribs as indistinct (arrows). This finding should not be confused with a destructive process. (b) Lateral view shows the posterior ribs as circular areas of increased opacity (solid arrows) or parallel lines (open arrows), depending on whether the rib is parallel or oblique to the x-ray beam. Loss of this normal appearance on the lateral view may be an important indicator of rib disease (cf Figs 11, 13, 24, 25). The inferior flange of the rib is also seen (arrowhead).
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The posterior parts of the ribs are easily seen on properly exposed lateral radiographs. In the midthorax, the ribs lie parallel to the x-ray beam and appear as corticate rings. More inferior, where the ribs are slightly oblique to the beam, the cortex is seen as parallel white lines (Fig 1b). The right rib usually appears slightly posterior and often slightly superior to the matching left rib. Because of geometric magnification, the right rib appears slightly larger than the left rib on standard left lateral radiographs. With this knowledge, one can usually identify a rib as right or left on a lateral radiograph. Because these portions of the ribs are so well seen due to the absence of overlying lung tissue or vertebrae, this area of the radiograph should be scrutinized for abnormalities.
Rib masses and sclerosis, which are often superimposed on the lungs, may simulate pulmonary disease. It is important to consider the possibility of nonpulmonary pathologic conditions in such cases. Findings that may indicate rib lesions include a smooth interface with the lung, expansion or destruction of an overlying rib, orientation of an area of increased opacity along the course of a rib, and the presence of characteristic calcification. Identification of subtle lesions may be difficult in areas where the ribs overlie lung structures or vertebral bodies. Therefore, it is useful to search carefully the areas at the margins of the chest.
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NORMAL VARIANTS
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Radiologists should be familiar with congenital variants of the ribs to avoid unnecessary concern and further evaluation, even though these variants are only rarely clinically significant (1, pp 247–250). Anomalies of the ribs are uncommon but will be seen periodically at clinical examination. Most of these anomalies are isolated findings that occur only sporadically. Some congenital syndromes may include characteristic rib anomalies; for example, forked (bifid) ribs are seen in basal cell nevus syndrome (2). Syndromes that involve multiple congenital bone dysplasias often include rib dysplasia, but these are outside the scope of this article.
In a 1944 review of chest radiographs obtained in 40,000 healthy young male military recruits, Etter (3) found congenital rib anomalies in 544 men (1.4%). Cervical ribs (Fig 2) were present in 68 men (0.2%) in this series; however, other authors have reported a higher prevalence of up to about 8% (1, p 498). This discrepancy may have to do with the type of radiographs studied. Cervical ribs are easier to identify with certainty on dedicated spinal radiographs than on chest radiographs because the vertebra with which the rib articulates is more easily determined. Cervical ribs must also be distinguished from elongated transverse processes of the seventh cervical vertebra. At radiography, cervical ribs may be unilateral or bilateral and range in size from small ossicles to long bones that often fuse or articulate with the first ribs anteriorly. Although generally asymptomatic, cervical ribs have been implicated in cases of thoracic outlet syndrome because of pressure on the brachial plexus nerves by the rib or a fibrous band that often connects the cervical rib to the first rib (4). Selected patients may benefit from resection of the cervical rib. This variant may also cause a spurious "mass" to be palpated in the supraclavicular fossa.
The most frequent anomaly in Etter's series was a forked rib (Figs 3, 4), which was found in 257 men (0.6%) and most often involved the fourth rib (3). In this anomaly, the anterior portion of the rib is duplicated. Figure 4 shows an unusual form of this variant involving cartilaginous duplication of a segment that did not ossify.
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Figure 4a. Forked rib with isolated cartilaginous segment in an asymptomatic 21-year-old man. (a) Frontal chest radiograph shows a widened interspace between the right anterior fourth and fifth ribs with linear intercostal calcifications (arrow). (b) Oblique view shows the calcifications lying within the chest wall in the same plane as the ribs (arrows). This finding represents an unusual form of forking or duplication of the ribs. The calcifications resemble the typical costal cartilage calcifications seen in adults.
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Figure 4b. Forked rib with isolated cartilaginous segment in an asymptomatic 21-year-old man. (a) Frontal chest radiograph shows a widened interspace between the right anterior fourth and fifth ribs with linear intercostal calcifications (arrow). (b) Oblique view shows the calcifications lying within the chest wall in the same plane as the ribs (arrows). This finding represents an unusual form of forking or duplication of the ribs. The calcifications resemble the typical costal cartilage calcifications seen in adults.
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Fusion or bone bridging occurred in 105 men (0.3%) and most often involved the first and second ribs (3). Fusion (Fig 5) may involve posterior or anterior portions of the ribs or may be complete. It is probably related to a segmentation defect because it may be seen in association with vertebral segmentation anomalies. Bone bridging (Fig 6) involves a more focal joining of adjacent ribs by bone outgrowths. It may be posttraumatic or a congenital anomaly and may involve one pair of ribs or several adjacent ones. Bridging may occur anywhere along the ribs. The bridges may be complete, or pseudarthrosis may be present.
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Figure 5. Fusion of the left third and fourth ribs in a 45-year-old man. Frontal chest radiograph shows close apposition of the posterior ribs (white arrow) and broad fusion of the anterior segments (black arrows). These findings represent a failure of normal segmentation. Vertebral anomalies may be found at the same level in some cases.
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Figure 6. Bone bridging in a 34-year-old woman with no history of fracture or trauma. Frontal chest radiograph shows a bone bridge joining the right anterior first and second ribs. Pseudoarticulation is also present (arrows).
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Rudimentary or hypoplastic ribs (usually the first ribs) were found in 79 men (0.2%) in the study. Etter noted that care must be taken not to confuse a rudimentary first rib with a cervical rib (3).
Pseudarthrosis of the first rib (Fig 7) manifested as a radiolucent line through the midportion of the rib with dense sclerotic borders and was seen in 31 men (0.1%). This anomaly may simulate a healing fracture.
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Figure 7. Pseudarthrosis of the right first rib in a 20-year-old man. Frontal chest radiograph shows dense, wavy margins along a rib defect (arrow). This finding is typical in pseudarthrosis and should not be mistaken for a fracture.
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Intrathoracic and pelvic ribs are rare isolated anomalies. Intrathoracic ribs are usually supernumerary, are more often right-sided, and involve the middle of the thorax. Pelvic ribs may arise from any pelvic bone and may have bony, cartilaginous, or ligamentous attachment (5).
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PATHOLOGIC FINDINGS
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Trauma-related Lesions
Rib fractures related to trauma are common and usually occur in isolation. They may be associated with pneumothorax, hemothorax, lung contusion and laceration, and other serious injuries. Some patterns of fracture should raise suspicion for other injuries. Because of the strength and protected location of the first rib, fractures of this rib serve as an indicator of substantial trauma. Although it is no longer considered necessary to perform arteriography in all cases of first rib fracture (6–8), recognition of such a fracture should prompt a clinical and radiographic search for signs of aortic or great vessel injury. One should also look carefully for thoracic vertebral or scapular fractures, which are also seen in the setting of severe trauma. Fractures of the lower ribs should raise the possibility of injuries to the upper abdominal organs or the diaphragm (Fig 8). Fractures of four contiguous ribs in more than one place define a "flail chest" (Fig 9), in which a segment of the chest wall can move paradoxically with respiration. This may compromise ventilation, thus increasing the risk of respiratory failure (8). The bony callus about a healing rib fracture may simulate a pulmonary nodule. In such cases, a simple rib series may be performed to confirm the diagnosis and avoid an unnecessary work-up.
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Figure 8. Ruptured hemidiaphragm in a 62-year-old man who sustained the injury in a motor vehicle accident. Frontal chest radiograph shows a rounded mass in the left lower thorax (white arrowheads). Fractures of the left sixth and seventh ribs (black arrowheads) indicate an area of substantial trauma and are a clue that the mass represents abdominal viscera herniated through a tear in the hemidiaphragm. Pneumopericardium is also present (arrows).
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Figure 9. Flail chest in a 70-year-old man. Frontal chest radiograph shows fractures of the left third through sixth ribs (posterior fractures, arrows; anterior fractures, white arrowheads). An apical pneumothorax is also visible (black arrowheads).
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Metastases
Metastasis is by far the most common cause of malignant involvement of the ribs, and the ribs are a common site of metastasis for a variety of tumors. Metastases may be either lytic (Figs 10, 11) or sclerotic (Figs 12–14). As a mass grows and expands beyond the confines of the ribs, it may appear as a vague area of increased opacity overlying the lung if seen en face. Oblique radiographs may help show the typical smooth interface with the lung that indicates the extrapulmonary location of the mass (Figs 10, 11, 14). Orientation of the long axis of an oblong area of increased opacity along the course of the rib may also provide a clue to its origin (Fig 14). The
ribs underlying any vague area of increased opacity over the lungs should be scrutinized for any destruction of the cortex (Figs 10, 15).
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Figures 10, 11. (10) Multiple myeloma in a 52-year-old man. Frontal chest radiograph shows vague areas of increased opacity over the left side of the chest. Smooth medial margins (arrowheads) indicate a pleural or chest wall origin. Interruption of the cortex of the left anterior fifth rib (straight arrow) and a pathologic fracture of the left eighth rib (curved arrow) are suggestive of a malignancy. (11) Metastatic breast cancer in a 69-year-old woman who presented with hypercalcemia. (a) Lateral chest radiograph shows absence of the ring shadow of the right posterior sixth rib with a mass smoothly indenting the lung (arrowheads). (b) Frontal view reveals destruction of the right sixth rib (arrowheads) as well as a subtler lesion of the left sixth rib (arrow).
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Figures 10, 11. (10) Multiple myeloma in a 52-year-old man. Frontal chest radiograph shows vague areas of increased opacity over the left side of the chest. Smooth medial margins (arrowheads) indicate a pleural or chest wall origin. Interruption of the cortex of the left anterior fifth rib (straight arrow) and a pathologic fracture of the left eighth rib (curved arrow) are suggestive of a malignancy. (11) Metastatic breast cancer in a 69-year-old woman who presented with hypercalcemia. (a) Lateral chest radiograph shows absence of the ring shadow of the right posterior sixth rib with a mass smoothly indenting the lung (arrowheads). (b) Frontal view reveals destruction of the right sixth rib (arrowheads) as well as a subtler lesion of the left sixth rib (arrow).
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Figures 10, 11. (10) Multiple myeloma in a 52-year-old man. Frontal chest radiograph shows vague areas of increased opacity over the left side of the chest. Smooth medial margins (arrowheads) indicate a pleural or chest wall origin. Interruption of the cortex of the left anterior fifth rib (straight arrow) and a pathologic fracture of the left eighth rib (curved arrow) are suggestive of a malignancy. (11) Metastatic breast cancer in a 69-year-old woman who presented with hypercalcemia. (a) Lateral chest radiograph shows absence of the ring shadow of the right posterior sixth rib with a mass smoothly indenting the lung (arrowheads). (b) Frontal view reveals destruction of the right sixth rib (arrowheads) as well as a subtler lesion of the left sixth rib (arrow).
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Figures 12, 13. (12) Metastatic breast cancer in a 34-year-old woman. Frontal chest radiograph shows scattered sclerotic foci that are best appreciated inferolaterally where there are no overlying lung markings (arrows). Diffuse bone metastasis was indicated at concurrent radioisotope bone scintigraphy. (13) Metastatic prostate cancer in a 63-year-old man. (a, b) Frontal (a) and lateral (b) chest radiographs show a diffuse increase in bone density. The loss of distinct cortical lines is especially noticeable in some of the right ribs on the lateral view (arrows in b); the frontal view shows loss of corticomedullary distinction, which is particularly well seen in the fifth rib (arrow in a). (c) On a frontal chest radiograph obtained 5 months later, the change in the appearance of the ribs is striking (arrow). Sclerosis of the vertebral bodies may also be seen, but the lack of overlying lung markings makes evaluation of the ribs easier.
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Figures 12, 13. (12) Metastatic breast cancer in a 34-year-old woman. Frontal chest radiograph shows scattered sclerotic foci that are best appreciated inferolaterally where there are no overlying lung markings (arrows). Diffuse bone metastasis was indicated at concurrent radioisotope bone scintigraphy. (13) Metastatic prostate cancer in a 63-year-old man. (a, b) Frontal (a) and lateral (b) chest radiographs show a diffuse increase in bone density. The loss of distinct cortical lines is especially noticeable in some of the right ribs on the lateral view (arrows in b); the frontal view shows loss of corticomedullary distinction, which is particularly well seen in the fifth rib (arrow in a). (c) On a frontal chest radiograph obtained 5 months later, the change in the appearance of the ribs is striking (arrow). Sclerosis of the vertebral bodies may also be seen, but the lack of overlying lung markings makes evaluation of the ribs easier.
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Figures 12, 13. (12) Metastatic breast cancer in a 34-year-old woman. Frontal chest radiograph shows scattered sclerotic foci that are best appreciated inferolaterally where there are no overlying lung markings (arrows). Diffuse bone metastasis was indicated at concurrent radioisotope bone scintigraphy. (13) Metastatic prostate cancer in a 63-year-old man. (a, b) Frontal (a) and lateral (b) chest radiographs show a diffuse increase in bone density. The loss of distinct cortical lines is especially noticeable in some of the right ribs on the lateral view (arrows in b); the frontal view shows loss of corticomedullary distinction, which is particularly well seen in the fifth rib (arrow in a). (c) On a frontal chest radiograph obtained 5 months later, the change in the appearance of the ribs is striking (arrow). Sclerosis of the vertebral bodies may also be seen, but the lack of overlying lung markings makes evaluation of the ribs easier.
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Figures 12, 13. (12) Metastatic breast cancer in a 34-year-old woman. Frontal chest radiograph shows scattered sclerotic foci that are best appreciated inferolaterally where there are no overlying lung markings (arrows). Diffuse bone metastasis was indicated at concurrent radioisotope bone scintigraphy. (13) Metastatic prostate cancer in a 63-year-old man. (a, b) Frontal (a) and lateral (b) chest radiographs show a diffuse increase in bone density. The loss of distinct cortical lines is especially noticeable in some of the right ribs on the lateral view (arrows in b); the frontal view shows loss of corticomedullary distinction, which is particularly well seen in the fifth rib (arrow in a). (c) On a frontal chest radiograph obtained 5 months later, the change in the appearance of the ribs is striking (arrow). Sclerosis of the vertebral bodies may also be seen, but the lack of overlying lung markings makes evaluation of the ribs easier.
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Figure 14a. Metastatic prostate cancer in a 76-year-old man. (a) Frontal chest radiograph shows a vague area of increased opacity over the lower area of the left lung (arrows). (b) Lateral view shows a similar area of increased opacity with a smooth inferior margin (arrowheads). This finding, as well as the orientation of the area of increased opacity parallel to the anterior ribs, provide clues to the origin of the lesion. (c) Computed tomographic (CT) scan demonstrates a mass arising from the anterior fourth rib with underlying sclerosis of the rib (arrowhead).
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Figure 14b. Metastatic prostate cancer in a 76-year-old man. (a) Frontal chest radiograph shows a vague area of increased opacity over the lower area of the left lung (arrows). (b) Lateral view shows a similar area of increased opacity with a smooth inferior margin (arrowheads). This finding, as well as the orientation of the area of increased opacity parallel to the anterior ribs, provide clues to the origin of the lesion. (c) Computed tomographic (CT) scan demonstrates a mass arising from the anterior fourth rib with underlying sclerosis of the rib (arrowhead).
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Figure 14c. Metastatic prostate cancer in a 76-year-old man. (a) Frontal chest radiograph shows a vague area of increased opacity over the lower area of the left lung (arrows). (b) Lateral view shows a similar area of increased opacity with a smooth inferior margin (arrowheads). This finding, as well as the orientation of the area of increased opacity parallel to the anterior ribs, provide clues to the origin of the lesion. (c) Computed tomographic (CT) scan demonstrates a mass arising from the anterior fourth rib with underlying sclerosis of the rib (arrowhead).
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Figure 15a. Pancoast tumor in a 56-year-old man who presented with right shoulder pain. (a) Initial frontal chest radiograph, which was part of a shoulder series, was interpreted as showing apical pleural thickening related to previous granulomatous disease. The right first rib cortex is intact (arrowheads). (b) On a frontal chest radiograph obtained 8 weeks later, there is early destruction of the medial margin of the first rib (arrowheads). (c) Frontal chest radiograph obtained 3 weeks after b shows nearly complete destruction of the first rib (arrowheads). The irregular interface of the mass with the lung indicates a pulmonary origin. (d) CT scan obtained at the same time as c shows a mass at the thoracic apex that also invades the adjacent T2 vertebral body (arrowheads).
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Figure 15b. Pancoast tumor in a 56-year-old man who presented with right shoulder pain. (a) Initial frontal chest radiograph, which was part of a shoulder series, was interpreted as showing apical pleural thickening related to previous granulomatous disease. The right first rib cortex is intact (arrowheads). (b) On a frontal chest radiograph obtained 8 weeks later, there is early destruction of the medial margin of the first rib (arrowheads). (c) Frontal chest radiograph obtained 3 weeks after b shows nearly complete destruction of the first rib (arrowheads). The irregular interface of the mass with the lung indicates a pulmonary origin. (d) CT scan obtained at the same time as c shows a mass at the thoracic apex that also invades the adjacent T2 vertebral body (arrowheads).
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Figure 15c. Pancoast tumor in a 56-year-old man who presented with right shoulder pain. (a) Initial frontal chest radiograph, which was part of a shoulder series, was interpreted as showing apical pleural thickening related to previous granulomatous disease. The right first rib cortex is intact (arrowheads). (b) On a frontal chest radiograph obtained 8 weeks later, there is early destruction of the medial margin of the first rib (arrowheads). (c) Frontal chest radiograph obtained 3 weeks after b shows nearly complete destruction of the first rib (arrowheads). The irregular interface of the mass with the lung indicates a pulmonary origin. (d) CT scan obtained at the same time as c shows a mass at the thoracic apex that also invades the adjacent T2 vertebral body (arrowheads).
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Figure 15d. Pancoast tumor in a 56-year-old man who presented with right shoulder pain. (a) Initial frontal chest radiograph, which was part of a shoulder series, was interpreted as showing apical pleural thickening related to previous granulomatous disease. The right first rib cortex is intact (arrowheads). (b) On a frontal chest radiograph obtained 8 weeks later, there is early destruction of the medial margin of the first rib (arrowheads). (c) Frontal chest radiograph obtained 3 weeks after b shows nearly complete destruction of the first rib (arrowheads). The irregular interface of the mass with the lung indicates a pulmonary origin. (d) CT scan obtained at the same time as c shows a mass at the thoracic apex that also invades the adjacent T2 vertebral body (arrowheads).
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Primary lung tumors may directly invade the chest wall and destroy adjacent ribs. An irregular interface with the underlying lung (as opposed to the smooth interface seen with chest wall or pleural lesions) indicates the origin of the mass. A Pancoast (superior sulcus) tumor (Fig 15) is a primary lung cancer that may invade the chest wall at the lung apex. Because this tumor may affect the adjacent sympathetic and brachial plexus nerves, patients often present for treatment because of arm or shoulder pain or Horner syndrome. Moreover, because the mass may mimic apical pleural thickening related to tuberculosis, any asymmetric apical area of increased opacity should prompt careful evaluation of the underlying ribs. Although magnetic resonance imaging is generally the best means of assessing the presence and extent of chest wall invasion by a primary lung tumor (9,10), rib involvement seen at chest radiography helps confirm the presence of such invasion.
Primary Neoplasms
True primary neoplasms of the ribs are rare. Chondroid lesions are the most common primary tumors and nearly always arise at or near the anterior end of the rib (11,12). Therefore, lesions at the costochondral junction, especially if calcified, are suggestive of a chondroid origin. Osteochondroma (exostosis) (Fig 16), although not a true neoplasm, is often classified as a tumor and is the most common of these lesions. In cases of multiple familial exostosis, nearly half of patients have a rib lesion (13). The typical appearance is a deformity or expansion of the rib with calcification of the cartilaginous cap. CT allows more definitive evaluation of the mass. Spontaneous hemothorax associated with rib exostoses has been reported (14). It is speculated that bleeding stems from enlarged pleural vessels caused by chronic irritation from an inwardly growing mass. Enchondromas, which cause focal expansion of the rib, may also be seen and may be diagnosed if typical chondroid calcification can be demonstrated.
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Figure 16a. Osteochondroma in a 29-year-old man who presented with fever. (a) Frontal chest radiograph shows an area of increased opacity overlying the right anterior fifth rib. This finding could be mistaken for focal pneumonia. Closer inspection reveals expansion of the rib cortex (arrowheads) and calcification (arrow). (b) Lateral view shows the area of increased opacity oriented along the course of the rib (arrowheads; cf Fig 14b). (c) CT scan shows a sessile mass with cortical and medullary continuity projecting into the lung. Calcification is present in the cartilaginous cap of the mass (arrow).
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Figure 16b. Osteochondroma in a 29-year-old man who presented with fever. (a) Frontal chest radiograph shows an area of increased opacity overlying the right anterior fifth rib. This finding could be mistaken for focal pneumonia. Closer inspection reveals expansion of the rib cortex (arrowheads) and calcification (arrow). (b) Lateral view shows the area of increased opacity oriented along the course of the rib (arrowheads; cf Fig 14b). (c) CT scan shows a sessile mass with cortical and medullary continuity projecting into the lung. Calcification is present in the cartilaginous cap of the mass (arrow).
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Figure 16c. Osteochondroma in a 29-year-old man who presented with fever. (a) Frontal chest radiograph shows an area of increased opacity overlying the right anterior fifth rib. This finding could be mistaken for focal pneumonia. Closer inspection reveals expansion of the rib cortex (arrowheads) and calcification (arrow). (b) Lateral view shows the area of increased opacity oriented along the course of the rib (arrowheads; cf Fig 14b). (c) CT scan shows a sessile mass with cortical and medullary continuity projecting into the lung. Calcification is present in the cartilaginous cap of the mass (arrow).
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A variety of other benign tumors may primarily involve the rib. Osteoblastoma, osteoid osteoma, chondroblastoma, and hemangioma are among those that have been described (15). Although they are not tumors, enostoses (bone islands) are relatively common in the ribs, occurring in 0.4% of patients in one series (16). After the pelvis, the ribs are the most common location of these lesions. Like the callus of healing fractures, enostoses may simulate pulmonary nodules.
Chondrosarcoma is the most common primary malignant neoplasm of the ribs (17), followed by plasmacytoma and lymphoma. Osteosarcoma and malignant fibrous histiocytomas are more rarely seen. Calcified matrix, in either the "rings and arcs" pattern of chondroid lesions (Fig 17) or the cloudlike pattern of osteoid lesions (Fig 18), may provide a clue to diagnosis.
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Figure 17a. (a-c) Chondrosarcoma in a 45-year-old man. (a) Frontal chest radiograph shows a vague area of increased opacity overlying the middle of the right lung. (b) Lateral view shows a mass in the chest wall smoothly bulging into the lung (arrows). Rounded calcifications may be seen in the anterior portion of the mass (arrowheads). (c) CT scan shows the large mass in the chest wall. The mass contains nodular and ring calcifications typical of chondroid matrix (arrow). (d) CT scan obtained in a 30-year-old man shows a smaller chondrosarcoma arising at the costochondral junction. This tumor also contains nodular and ring calcifications (arrow).
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Figure 17b. (a-c) Chondrosarcoma in a 45-year-old man. (a) Frontal chest radiograph shows a vague area of increased opacity overlying the middle of the right lung. (b) Lateral view shows a mass in the chest wall smoothly bulging into the lung (arrows). Rounded calcifications may be seen in the anterior portion of the mass (arrowheads). (c) CT scan shows the large mass in the chest wall. The mass contains nodular and ring calcifications typical of chondroid matrix (arrow). (d) CT scan obtained in a 30-year-old man shows a smaller chondrosarcoma arising at the costochondral junction. This tumor also contains nodular and ring calcifications (arrow).
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Figure 17c. (a-c) Chondrosarcoma in a 45-year-old man. (a) Frontal chest radiograph shows a vague area of increased opacity overlying the middle of the right lung. (b) Lateral view shows a mass in the chest wall smoothly bulging into the lung (arrows). Rounded calcifications may be seen in the anterior portion of the mass (arrowheads). (c) CT scan shows the large mass in the chest wall. The mass contains nodular and ring calcifications typical of chondroid matrix (arrow). (d) CT scan obtained in a 30-year-old man shows a smaller chondrosarcoma arising at the costochondral junction. This tumor also contains nodular and ring calcifications (arrow).
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Figure 17d. (a-c) Chondrosarcoma in a 45-year-old man. (a) Frontal chest radiograph shows a vague area of increased opacity overlying the middle of the right lung. (b) Lateral view shows a mass in the chest wall smoothly bulging into the lung (arrows). Rounded calcifications may be seen in the anterior portion of the mass (arrowheads). (c) CT scan shows the large mass in the chest wall. The mass contains nodular and ring calcifications typical of chondroid matrix (arrow). (d) CT scan obtained in a 30-year-old man shows a smaller chondrosarcoma arising at the costochondral junction. This tumor also contains nodular and ring calcifications (arrow).
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Figure 18a. Osteosarcoma in a 24-year-old woman. (a) Frontal chest radiograph shows an ill-defined area of increased opacity over the lower portion of the right lung. The underlying right anterior sixth rib cannot be discerned. (b) Lateral view shows only a vague area of increased opacity with a smooth inner margin projected over the lower sternum (arrowheads). (c) Unenhanced CT scan reveals a densely calcified mass destroying the rib. Although the location of the mass is typical for the more common chondroid tumors, cloudlike osteoid matrix calcification is present.
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Figure 18b. Osteosarcoma in a 24-year-old woman. (a) Frontal chest radiograph shows an ill-defined area of increased opacity over the lower portion of the right lung. The underlying right anterior sixth rib cannot be discerned. (b) Lateral view shows only a vague area of increased opacity with a smooth inner margin projected over the lower sternum (arrowheads). (c) Unenhanced CT scan reveals a densely calcified mass destroying the rib. Although the location of the mass is typical for the more common chondroid tumors, cloudlike osteoid matrix calcification is present.
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Figure 18c. Osteosarcoma in a 24-year-old woman. (a) Frontal chest radiograph shows an ill-defined area of increased opacity over the lower portion of the right lung. The underlying right anterior sixth rib cannot be discerned. (b) Lateral view shows only a vague area of increased opacity with a smooth inner margin projected over the lower sternum (arrowheads). (c) Unenhanced CT scan reveals a densely calcified mass destroying the rib. Although the location of the mass is typical for the more common chondroid tumors, cloudlike osteoid matrix calcification is present.
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Infectious Disease
Infectious disease that involves the ribs is rare. Bacterial osteomyelitis may occur by means of hematogenous dissemination, trauma, or adjacent infection such as empyema (Fig 19) (18). Fungal infection usually spreads hematogenously in patients with disseminated disease. Acute infections are seen as focal areas of bone destruction. Chronic infections, such as those that occur with tuberculosis, actinomycosis (Fig 20), or other bacteria, may first manifest as periosteal reaction or a bone sequestrum. Rib infections are often associated with chest wall abscesses and cutaneous sinus tracts.
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Figure 19a. Tuberculosis in a 24-year-old man who presented with fever. (a) Frontal chest radiograph shows a loculate pleural effusion and periosteal reaction along the right 9th and 10th ribs (arrowheads). (b) CT scan shows the empyema being forced into the chest wall (arrow).
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Figure 19b. Tuberculosis in a 24-year-old man who presented with fever. (a) Frontal chest radiograph shows a loculate pleural effusion and periosteal reaction along the right 9th and 10th ribs (arrowheads). (b) CT scan shows the empyema being forced into the chest wall (arrow).
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Figure 20. Actinomycosis in a young woman with chest pain and a draining sinus in the chest wall on the left side. Frontal chest radiograph shows periosteal reaction along the left 10th and 11th ribs (arrowheads) as well as soft-tissue swelling in the chest wall (arrows). Patchy pneumonia is seen in the left lower lobe.
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Patients with chronic inflammatory conditions of the lung or pleura, especially tuberculosis, may have enlarged ribs on the affected side. This finding is probably due to chronic reactive periostitis associated with localized hyperemia (19).
Rib Notching
Inferior rib notching may be seen in a wide variety of conditions and generally results from enlargement of some element of the neurovascular bundle. An isolated angulation in the inferior aspect of a posterior rib is a common normal finding and should not be confused with true rib notching, which involves a longer segment of the rib. Because notching is caused by chronic pressure on the rib, the inferior cortex should show reactive sclerosis. The posterior parts of the ribs often have indistinct inferior margins; consequently, this sclerosis can help confirm the presence of notching.
In coarctation of the aorta (Fig 21), the third through the ninth ribs may be involved, the third through the fifth ribs being involved most frequently. The first and second ribs are generally not involved because their accompanying arteries originate from the subclavian arteries and do not provide a collateral pathway to the aorta distal to the usual site of coarctation at the aortic isthmus. Vascular rib notching may also be seen unilaterally after surgical repair of congenital heart disease (Blalock-Taussig shunt), in coarctation between the origins of the innominate artery and the left subclavian artery, or if the coarctation is proximal to an aberrant subclavian artery origin. It is rare to identify rib notching in coarctation in patients younger than 5 years of age (20).
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Figure 21. Coarctation of the aorta in a 36-year-old man. Frontal chest radiograph shows bilateral rib notching related to enlarged, tortuous collateral intercostal arteries (arrowheads). The descending aorta contour is indented at the site of coarctation (arrow).
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In neurofibromatosis type 1 (Fig 22), intercostal neurofibromas may scallop the inferior border of any rib (21,22). An area of increased opacity that corresponds to the neurofibroma may be seen adjacent to the notched ribs. This rib notching should not be confused with the dysplastic "twisted ribbon" ribs also seen in this disorder, which are usually associated with vertebral anomalies such as kyphoscoliosis (23).
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Figure 22. Neurofibromatosis type 1 in a 38-year-old woman. Frontal chest radiograph shows extensive notching and broad scalloping of multiple ribs. Large plexiform neurofibromas indent the lung at multiple levels (arrows).
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Miscellaneous Lesions
Fibrous dysplasia is the most common benign lesion of the ribs (17,24). Ribs are the most common bone location and are involved in up to 30% of patients (25). Fibrous dysplasia and osteochondroma account for most benign rib masses (17). Rib lesions in fibrous dysplasia are almost always asymptomatic and are seen at clinical examination less often than lesions that involve the facial or leg bones. Fusiform enlargement of the rib (Fig 23a) with loss of the normal trabecular pattern and a thin but preserved cortex is the rule, although bizarre deformations (Fig 23b) may be seen. Any part of the rib may be affected, and involvement of the long segment is common and characteristic.
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Figure 23a. Fibrous dysplasia. (a) Abdominal radiograph obtained in a 45-year-old man with McCune-Albright syndrome shows expansion of long segments of the right 11th rib and the left 9th, 10th, and 11th ribs (arrowheads). (b) Anteroposterior rib radiograph obtained in a 33-year-old woman with polyostotic fibrous dysplasia demonstrates involvement of both long (arrows) and short (arrowheads) segments of the lower left ribs.
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Figure 23b. Fibrous dysplasia. (a) Abdominal radiograph obtained in a 45-year-old man with McCune-Albright syndrome shows expansion of long segments of the right 11th rib and the left 9th, 10th, and 11th ribs (arrowheads). (b) Anteroposterior rib radiograph obtained in a 33-year-old woman with polyostotic fibrous dysplasia demonstrates involvement of both long (arrows) and short (arrowheads) segments of the lower left ribs.
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Langerhans cell histiocytosis (eosinophilic granuloma) may involve one or more bones including the ribs, which are a relatively common site of involvement. Poorly circumscribed or "moth-eaten," often expansile osteolytic lesions are most common (26,27).
Paget disease is relatively uncommon in the ribs, occurring in 1%–4% of cases (28). Rib involvement is usually an incidental finding noted during the chronic sclerotic phase of the disease. As in other bones, cortical thickening and bone enlargement are distinctive features (Fig 24). Long segments are involved as in fibrous dysplasia, but the two diseases have distinct radiographic appearances.
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Figure 24a. Paget disease in an asymptomatic 51-year-old man. (a) Lateral chest radiograph shows enlargement and marked thickening of the cortical ring shadow of the right posterior eighth rib (arrow). (b) Frontal view demonstrates thickened cortex over a long segment (arrows). (c) CT scan shows bone enlargement with cortical thickening (arrow), thereby helping confirm the radiographic findings.
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Figure 24b. Paget disease in an asymptomatic 51-year-old man. (a) Lateral chest radiograph shows enlargement and marked thickening of the cortical ring shadow of the right posterior eighth rib (arrow). (b) Frontal view demonstrates thickened cortex over a long segment (arrows). (c) CT scan shows bone enlargement with cortical thickening (arrow), thereby helping confirm the radiographic findings.
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Figure 24c. Paget disease in an asymptomatic 51-year-old man. (a) Lateral chest radiograph shows enlargement and marked thickening of the cortical ring shadow of the right posterior eighth rib (arrow). (b) Frontal view demonstrates thickened cortex over a long segment (arrows). (c) CT scan shows bone enlargement with cortical thickening (arrow), thereby helping confirm the radiographic findings.
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In patients with hemoglobinopathies, various bone changes may be seen. With severe anemia, as is seen in thalassemia major and sickle cell anemia, deossification and cortical thinning due to medullary expansion may be seen. Sickle cell anemia and its variants may also manifest as diffuse or patchy bone sclerosis (Fig 25) related to medullary infarction and fibrosis. The ribs are a common location of this sclerosis (29,30).
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Figure 25a. Sickle cell-hemoglobin C disease in a 54-year-old woman. (a) Frontal chest radiograph shows diffusely increased bone density as evidenced by the absence of the normal cortical stripes along the superior ribs (arrows). (b) Lateral view demonstrates bone sclerosis by loss of the cortical ring shadows posteriorly (arrowheads). Typical central end plate depressions (arrows) provide a clue to the underlying disease. Identical findings may be seen in patients with chronic pure sickle cell anemia.
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Figure 25b. Sickle cell-hemoglobin C disease in a 54-year-old woman. (a) Frontal chest radiograph shows diffusely increased bone density as evidenced by the absence of the normal cortical stripes along the superior ribs (arrows). (b) Lateral view demonstrates bone sclerosis by loss of the cortical ring shadows posteriorly (arrowheads). Typical central end plate depressions (arrows) provide a clue to the underlying disease. Identical findings may be seen in patients with chronic pure sickle cell anemia.
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Multifocal osteosclerosis may also be seen in chronic renal failure and represents renal osteodystrophy, which most often involves the ribs and axial skeleton (31). Affected patients may also have focal lytic masses (brown tumors) in the ribs that may simulate metastases (32). Diffuse osteosclerosis may also be seen with metastasis (Fig 14), Paget disease, and myelofibrosis.
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CONCLUSIONS
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The ribs demonstrate a wide range of normal, congenital variant, and pathologic radiographic appearances. In most cases, radiography is sufficient for the diagnosis. However, one must always keep the ribs in mind and pay careful attention to radiographic findings. Several such findings may be useful in identifying and diagnosing rib diseases and systemic diseases affecting the ribs.
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Abstract
INTRODUCTION
