(Radiographics. 2002;22:87-104.)
© RSNA, 2002
Pediatric Ribs: A Spectrum of Abnormalities1
Ronald B. J. Glass, MD,
Karen I. Norton, MD,
Sandra A. Mitre, MD and
Eugene Kang, MD
1 From the Department of Radiology, Mount Sinai School of Medicine, One Gustave L. Levy Pl, New York, NY 10029. Presented as an education exhibit at the 2000 RSNA scientific assembly. Received April 4, 2001; revision requested May 22 and received June 11; accepted June 14. Address correspondence to R.B.J.G. (e-mail: ronald_glass@smtplink.mssm.edu).
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Abstract
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The manifestations of many congenital and acquired conditions can be seen in the ribs of children. Normal variants are usually clinically insignificant; they are occasionally palpated at clinical examination or detected incidentally at chest radiography. Signs of abnormality can appear in the ribs as variations in number, size, mineralization, and shape. These changes can be focal or generalized. Abnormalities detected in the ribs may be the initial indication of previously unsuspected systemic disease. The ribs can yield important diagnostic clues in the work-up of patients with congenital bone dysplasias, acquired metabolic diseases, iatrogenic conditions, trauma (especially child abuse), infection, and neoplasms. Routine evaluation of the ribs on every chest radiograph is important so that valuable diagnostic data will not be overlooked. The diagnostic information obtained from evaluation of the ribs can help tailor the radiologic and laboratory studies that may be necessary to complete a patient’s diagnostic work-up.
© RSNA, 2002
Index Terms: Ribs, 471.21, 471.50, 471.60, 471.80 • Ribs, abnormalities, 471.14, 471.15, 471.16, 471.18 • Ribs, fractures, 471.41 • Ribs, neoplasms, 471.30
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LEARNING OBJECTIVES FOR TEST 4
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After reading this article and taking the test, the reader will be able to:
- Describe the various types of diagnostic features that occur in the ribs of children with bone dysplasias.
- Identify the rib changes that occur in child abuse.
- Recognize the appearances of benign and malignant primary bone tumors of the ribs.
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Introduction
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Chest radiography is frequently the initial imaging study performed in children for a variety of diseases. Important information may be missed if attention is not directed to the ribs on every chest radiograph. Abnormalities detected in the ribs can sometimes be the initial indication of systemic disease. Rib changes can indicate generalized bone dysplasias, metabolic diseases, and trauma, especially abuse. Benign and malignant neoplasms occur in the ribs.
In this article, we review rib development and normal anatomy and techniques for evaluating the ribs and present inherited abnormalities and acquired conditions of the pediatric ribs.
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Rib Development and Normal Anatomy
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Twelve paired ribs develop from cartilaginous costal processes of the developing thoracic vertebrae. Rib development begins at 9 weeks; secondary ossification centers appear at 15 years (1,2). The first seven "true" ribs connect to the sternum via the costal cartilages by day 45. The lower five "false" ribs do not articulate with the sternum. Developmental rib abnormalities may be isolated or occur in association with other congenital anomalies.
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Techniques for Evaluating the Ribs
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The ribs are evaluated in most patients on the frontal chest radiograph. However, routine radiographs of the chest are inadequate for rib detail, and better detail is achieved on dedicated rib views. Such views are obtained by using the overpenetrated grid technique, with additional oblique views centered over the area of maximum interest (3). The best method for evaluation of inflammatory or neoplastic masses is computed tomography (CT) or magnetic resonance imaging.
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Inherited Abnormalities
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Cervical Ribs
Cervical ribs arise from the seventh cervical vertebra. They resemble hypoplastic first thoracic ribs, from which they are reliably differentiated by means of the adjacent transverse process, which is angulated inferiorly in the cervical spine and has a more cranial course in the thoracic spine (Fig 1). The reported prevalence of cervical ribs varies from 0.2% to 8% (4). Cervical ribs occur unilaterally or bilaterally. They are most commonly an incidental finding or are associated with the Klippel-Feil anomaly (Fig 1). Cervical ribs are rarely symptomatic in early childhood; in older children and adults, compression of the brachial plexus or subclavian artery can give rise to the thoracic outlet syndrome (5,6). Cervical rib compression of the subclavian artery can result in aneurysm formation (7).
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Figure 1. Cervical ribs with Klippel-Feil anomaly and esophageal atresia in a 10-year-old boy. Frontal radiograph shows cervical ribs that articulate with the inferiorly directed transverse processes (straight arrows), whereas the thoracic transverse processes extend in a superior direction (curved arrows). The left-sided soft-tissue mass (m) is caused by bowel interposition.
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Abnormal Number of Ribs
Supernumerary ribs may rarely be seen incidentally as a normal variant. Increased numbers of ribs are seen in trisomy 21 syndrome and with the VATER association (Fig 2)(8,9). It is more common to see 11 pairs in the absence of associated anomalies; this situation occurs in 5%–8% of normal individuals. Eleven pairs of ribs occur in one-third of patients with trisomy 21 syndrome (9), as well as in association with cleidocranial dysplasia and campomelic dysplasia.
Abnormal Size or Shortening of Ribs
Short ribs do not extend as far anteriorly as the sternum. The resultant diminished volume of the chest restricts respiratory motion and causes respiratory insufficiency. Short ribs constitute an integral part of several syndromes. Definitive diagnosis of the type of any skeletal dysplasia requires a complete skeletal survey. This survey should optimally be performed early in the neonatal period to exclude a lethal dysplasia so that resuscitation policy can be planned. The differential diagnosis must include the short rib–polydactyly syndromes (Saldino-Noonan, Majewski, and Verma-Naumoff); chest diameter is critically small in these syndromes.
Thanatophoric Dysplasia.—
Thanatophoric dysplasia is a lethal dysplasia transmitted by a dominant gene mutation. It is the most common lethal neonatal skeletal dysplasia after osteogenesis imperfecta type II (10, pp 939–943). Patients present very early with severe respiratory distress. The appearance on the chest radiograph is patho-gnomonic. The ribs are very short and do not ex-tend beyond the anterior axillary line. The vertebral bodies assume an H or U shape, and the humeri are curved and short (Fig 3). Associated findings are cloverleaf skull deformity, polydactyly, and hypoplastic iliac bones. The differential diagnosis includes thanatophoric variants, asphyxiating thoracic dysplasia, homozygous achondroplasia, and achondrogenesis.
Jeune Asphyxiating Thoracic Dysplasia.—
Jeune asphyxiating thoracic dysplasia is an autosomal recessive dysplasia. Patients may present with respiratory distress that may be sufficiently severe to cause neonatal death. The ribs are short, with a horizontal course, and the chest diameter is significantly decreased compared with that of the abdomen (Fig 4). The long bones are shortened. The proximal humeral and femoral epiphyses are frequently ossified at birth, and polydactyly is occasionally encountered. The iliac wings are small, and the acetabula typically have spurs. Although the findings on the chest radiograph are highly suggestive of Jeune dysplasia, the appearance also resembles that of Ellis–van Creveld dysplasia. Less severely affected children who survive into adulthood have a high prevalence of medullary cystic renal disease (11).
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Figure 4a. Jeune asphyxiating dysplasia in a female neonate. (a) Frontal chest radiograph shows short ribs and a very narrow chest diameter. The humeral heads are prematurely ossified (arrowhead). (b) Lateral chest radiograph obtained at 8 months of age shows short ribs that do not reach the sternum.
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Figure 4b. Jeune asphyxiating dysplasia in a female neonate. (a) Frontal chest radiograph shows short ribs and a very narrow chest diameter. The humeral heads are prematurely ossified (arrowhead). (b) Lateral chest radiograph obtained at 8 months of age shows short ribs that do not reach the sternum.
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Ellis–van Creveld Chondroectodermal Dysplasia.—
Ellis–van Creveld chondroectodermal dysplasia is an autosomal recessive dysplasia with a high prevalence among the Amish. The ribs are short, and the chest is narrow (Fig 5). The narrow thorax exaggerates the heart size; cardiomeg-aly is often present because of associated anomalies, especially atrial septal defects. The appearance of the chest and pelvis closely resembles that of Jeune dysplasia. Respiratory insufficiency can be severe, resulting in death in up to 50% of affected neonates (10, pp 786–788). The proximal humeral and femoral epiphyses may be prematurely ossified at birth. Acromelic limb shortening, polydactyly, and cone epiphyses are characteristic. The differential diagnosis includes Jeune dysplasia and the short rib–polydactyly syndromes.
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Figure 5a. Ellis-van Creveld dysplasia in a female neonate. Frontal (a) and lateral (b) chest radiographs show short ribs, which are most obvious on the lateral projection. The cardiomegaly and increased pulmonary vascularity are due to a large atrial septal defect.
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Figure 5b. Ellis-van Creveld dysplasia in a female neonate. Frontal (a) and lateral (b) chest radiographs show short ribs, which are most obvious on the lateral projection. The cardiomegaly and increased pulmonary vascularity are due to a large atrial septal defect.
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Achondroplasia.—
In achondroplasia, the ribs are short and wide with concavity at the rib end (Fig 6). The inheritance is autosomal dominant, with spontaneous mutation in 80% of cases (10, pp 749–751). The chest radiographic findings are highly suggestive of achondroplasia. Rhizomelic shortening of the humeri may be apparent on the chest radiograph. Associated diagnostic features include macrocephaly, depression of the nasion, craniocaudal narrowing of the interpediculate spaces, square iliac bones, and a champagne glass–shaped pelvic inlet. A differential diagnostic consideration is hypochondroplasia.
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Figure 6a. Achondroplasia in a female neonate. (a) Frontal chest radiograph shows short, anteriorly flared ribs and wide humeral metaphyses. (b) Lateral chest radiograph obtained at 3 months of age shows short ribs that are cupped and widened anteriorly. Note the anterior "beaking" of L4 (arrow).
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Figure 6b. Achondroplasia in a female neonate. (a) Frontal chest radiograph shows short, anteriorly flared ribs and wide humeral metaphyses. (b) Lateral chest radiograph obtained at 3 months of age shows short ribs that are cupped and widened anteriorly. Note the anterior "beaking" of L4 (arrow).
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Diminished Bone Density
Four distinct subgroups of osteogenesis imperfecta are recognized, according to the severity of involvement (12). Affected patients have demineralization and bone fragility. Transmission is autosomal recessive in type III and dominant in types I and IV. New dominant mutations account for most cases of type II osteogenesis imperfecta. Type II osteogenesis imperfecta is a lethal condition, characterized by marked osteopenia and deformity of long bones and ribs caused by in utero fractures (Fig 7). Affected neonates present with nonimmune hydrops and respiratory distress. A skeletal survey reveals generalized osteopenia and thin bone cortices. The skull is classically demineralized, and wormian bones are present in most cases. Differential diagnostic considerations include achondrogenesis, hypophosphatasia, and campomelic dysplasia. In older children, the differential diagnosis of osteopenia also includes type I, III, and IV osteogenesis imperfecta; child abuse; and leukemia.
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Figure 7. Type II osteogenesis imperfecta and generalized osteopenia in a female neonate. Frontal chest radiograph shows that all of the ribs are deformed and thickened posteriorly. Periosteal new bone in multiple healing fractures gives the ribs a beaded appearance. Healing fractures are present in the clavicles and humeri.
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Increased Bone Density
Tuberous Sclerosis.—
Tuberous sclerosis is a neurocutaneous syndrome with autosomal dominant transmission. It is characterized by hamartomas and central nervous system tumors. Bone changes are characteristically patchy areas of sclerosis (13). Any bone can be affected. Involvement of the ribs is most commonly seen as expansion and sclerosis (Fig 8). Affected patients have cutaneous manifestations, seizures, and developmental delay. The differential diagnosis includes fibrous dysplasia, chronic infection, trauma, and previous surgical subperiosteal rib resection.
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Figure 8. Tuberous sclerosis in an 8-year-old boy with seizures, developmental delay, and renal hamartomas. Frontal chest radiograph shows sclerosis and widening isolated to the left fifth rib.
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Osteopetrosis.—
Osteopetrosis is subdivided into various subgroups, all of which are characterized by a generalized increase in bone density (Fig 9). The congenital type is transmitted as an autosomal recessive trait and is more severe than the autosomal dominant varieties that manifest later (10, pp 886–891). Neonates and infants experience pancytopenia, hepatosplenomegaly, and premature death. Older children develop cranial nerve palsies, deafness, and blindness. The entire skeleton is dense, and the metaphyses and rib costochondral junctions are splayed. Although the bones are dense, they are brittle and fractures arise from minor trauma. The bone is susceptible to osteomyelitis, and hematopoietic function is decreased. The differential diagnosis includes chronic renal failure, oxalosis, and pyknodysostosis. Caveat: Physiologic sclerosis in neonates should not be mistaken for osteopetrosis.
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Figure 9a. Osteopetrosis. (a) Frontal chest radiograph of a 1-month-old girl shows sclerotic bones and periosteal new bone formation along the lateral aspects of all of the ribs. (b) Frontal chest radiograph of a 5-year-old girl with a family history of osteopetrosis shows that all of the bones are extremely dense but normal in shape. The left upper abdominal fullness suggests splenomegaly.
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Figure 9b. Osteopetrosis. (a) Frontal chest radiograph of a 1-month-old girl shows sclerotic bones and periosteal new bone formation along the lateral aspects of all of the ribs. (b) Frontal chest radiograph of a 5-year-old girl with a family history of osteopetrosis shows that all of the bones are extremely dense but normal in shape. The left upper abdominal fullness suggests splenomegaly.
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Abnormal Rib Shape
Cerebrocostomandibular Syndrome.—
Cerebrocostomandibular syndrome is very rare. The genetic transmission is uncertain (8). Eleven pairs of ribs are usually present. The ribs are characterized by abnormal costovertebral articulations and posterior ossification gaps that resemble fractures (Fig 10); these gaps will ossify in later life. Respi-ratory distress is common in neonates due to flail chest and airway abnormalities. Other features are microcephaly, micrognathia, and congenital heart disease. Multiple fractures must be considered in the differential diagnosis.
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Figure 10. Cerebrocostomandibular syndrome in a female neonate. Frontal chest radiograph shows lucent ossification gaps in all of the posterior ribs. Only 10 rib pairs are present. The costovertebral junctions are abnormal. Several ribs are caudally angulated.
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Rib Notching.—
Concave notches are found on the inferior rib surface and are most commonly a normal variant. Pathologic notching is vascular or neural in origin. Notching associated with aortic coarctation usually affects ribs 4–8 and is rare before the age of 8 years (Fig 11) (13). Rib notching is also encountered in neurofibromatosis and thalassemia. Notching is unilateral (right sided) with coarctation proximal to the origin of the left subclavian artery and a postoperative Blalock-Taussig shunt.
Pectus Excavatum.—
Pectus excavatum is an anomaly that arises from posterior depression of the sternum, which compresses the heart against the spine and deviates it to the left (Fig 12), thus mimicking cardiomegaly. The displaced pulmonary vascularity and obscured right cardiac border resemble a right middle lobe process. The posterior ribs are horizontal, whereas the anterior ribs have a more vertical course. Pectus excavatum is most commonly an isolated anomaly. This chest deformity is also associated with prematurity, homocystinuria, Marfan syndrome, Noonan syndrome, and fetal alcohol syndrome. Surgical correction is undertaken to relieve restrictive airway disease and for cosmetic repair.
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Figure 12a. Pectus excavatum in a 12-year-old boy. (a) Frontal chest radiograph shows steep angulation of the anterior ribs. A poorly defined area of increased opacity along the right cardiac border mimics a pulmonary infiltrate of the right middle lobe. (b) CT scan obtained through the midsternum shows a depressed sternum deviating the heart posteriorly and to the left. (Courtesy of Andrew K. Poznanski, MD, Children’s Memorial Hospital, Chicago, Ill.)
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Figure 12b. Pectus excavatum in a 12-year-old boy. (a) Frontal chest radiograph shows steep angulation of the anterior ribs. A poorly defined area of increased opacity along the right cardiac border mimics a pulmonary infiltrate of the right middle lobe. (b) CT scan obtained through the midsternum shows a depressed sternum deviating the heart posteriorly and to the left. (Courtesy of Andrew K. Poznanski, MD, Children’s Memorial Hospital, Chicago, Ill.)
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Bifid Ribs
Gorlin basal cell nevus syndrome is a rare, autosomal dominant syndrome characterized by multiple nevoid basal cell carcinomas that arise in childhood, jaw cysts, and bifid ribs (Fig 13). The fourth rib has been reported to be the most commonly bifid. Other rib anomalies include agenesis, supernumerary ribs, distorted shape, and fusion of adjacent ribs (14). The lateral clavicle may be deficient. Associated features are mandibular hypoplasia, macrocephaly, and mental retardation. A single bifid rib is most commonly a normal incidental finding and may be detected as a palpable chest wall mass.
Slender Ribs
Trisomy 18 Syndrome.—
Marked phenotypic variability is characteristic of trisomy 18 syndrome. Eleven rib pairs are present, and they are classically hypoplastic and thin (Fig 14). The short sternum causes the typical shield deformity of the chest. The acute iliac angle is diagnostic. These children are spastic and neurologically delayed. The fingers are characteristically maintained in ulnar deviation with flexion deformities. Associated findings are dolichocephaly, micrognathia, and numerous multisystem anomalies. Differential diagnostic considerations include osteogenesis imperfecta, trisomy 13 syndrome, Cockayne syndrome, and Werdnig-Hoffmann disease.
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Figure 14. Trisomy 18 syndrome and severe respiratory distress in a male neonate. Frontal chest radiograph shows very slender ribs. The iliac bones have an almost vertical orientation. Both hips are dislocated.
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Neurofibromatosis.—
Peripheral neural tumors are the hallmark of neurofibromatosis, an autosomal dominant neurocutaneous syndrome. The ribs are slender (Fig 15); they may be twisted, deformed, and separated by neurofibromas that arise from the intercostal nerves (15). The underlying mesenchymal abnormality in neurofibromatosis results in modeling deformity and even bizarre appearance of the ribs. Intercostal neuromas can cause notching of the inferior surface. Sphenoid dysplasia, modeling deformity of the long bones, and posterior vertebral body scalloping are associated findings. The differential diagnosis includes cleidocranial dysplasia, myotonic dystrophy, Melnick-Needles osteodysplasty, and Werdnig-Hoffmann disease.
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Figure 15. Neurofibromatosis in a 15-year-old girl. Frontal chest radiograph shows that several right ribs are thin and ribbonlike. Right ribs 5, 6, and 7 are notched inferiorly (solid arrows). The posterior middle aspect of right rib 9 is expanded, with poorly defined borders and a thinned cortex (open arrow). Note also the bilateral apical neurofibromas.
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Widened Ribs
Mucopolysaccharidosis.—
The storage diseases are a miscellaneous group of autosomal recessive conditions in which specific enzyme deficiencies cause accumulation of abnormal metabolite substrates that are deposited in the bone marrow and multiple viscera (10, pp 672–681). In mucopolysaccharidosis, the ribs are thin proximally at the level of the neck and wider distally (Fig 16). Coarse trabeculation and heterogeneous bone density are due to deposition of accumulated precursor metabolites in the bone marrow. The appearance is variable, and definitive diagnosis is made by means of a complete skeletal survey and biochemical analysis. Helpful associated features include external flaring of the iliac bones, which are inferiorly tapered; vertebral body flattening and anterior beaking; atlantoaxial instability; and brachydactyly. Differential diagnostic possibilities include Gaucher disease and Niemann-Pick disease.
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Figure 16. Hurler syndrome in a 7-year-old boy with developmental delay. Frontal chest radiograph shows that the ribs are thin and tapered proximally; they widen and become very broad distally.
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Thalassemia Major.—
Thalassemia major is the severe homozygous form of this hemoglobinopathy. Symptoms become evident in the first 2 years of life. Hyperplasia of the marrow destroys the trabeculae and expands and thins the cortex (16). The ribs are undertubulated and broad, and ossification is heterogeneous (Fig 17). This appearance is rarely encountered today because patients are aggressively treated with blood transfusions and chelation from an early age. Marrow expansion also causes widened diploë, hypoplasia of paranasal sinuses, paraspinal extramedullary foci, and hepatosplenomegaly. Other diagnostic possibilities include chronic anemias, storage diseases, and fibrous dysplasia.
Expansile Rib Deformity
Lymphangiomatosis.—
Lymphangiomatosis is a rare and idiopathic disease of children and adolescents that is thought to represent a malforma-tion of lymphatic vessels (17). The abnormal lymphatic vessels can be found diffusely in parenchymal viscera and bones. Rib lymphangiomas ap-pear as well-defined areas of lucency (Fig 18). These lucent lesions can coalesce and replace large parts of the affected bone. Lymphangiomatosis of the ribs has been associated with chylothorax (17). Gorham disease is the term used when one or more bones become replaced by abnormal lymphatic vessels. Differential diagnostic possibilities include Langerhans cell histiocytosis, fibrous dysplasia, and hyperparathyroidism (brown tumors).
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Figure 18. Lymphangiomatosis in an 8-year-old boy. Frontal chest radiograph shows multiple corticated areas of lucency in all of the ribs. Focal areas of expansion affect isolated ribs (arrows). The cortices remain intact.
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Fibrous Dysplasia.—
Fibrous dysplasia is a benign condition in which there is proliferation of fibrous tissues in the bones. Involvement may be monostotic or polyostotic. Fibrous dysplasia is the most common cause of a benign expansile lesion of the ribs, and the ribs are one of the most common sites of monostotic involvement (18). The abnormal bone foci are classically lucent with a "ground-glass" matrix; bone expansion, cortical thinning, and modeling deformity are common (Fig 19). The differential diagnosis includes simple bone cyst, enchondroma, and hyperparathyroidism (brown tumors).
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Figure 19. Fibrous dysplasia in an 8-year-old boy. Frontal chest radiograph shows widening of anterior ribs 2 and 3. The ribs have heterogeneous ground-glass opacity. A well-defined area of lucency is present in anterior rib 4 (arrow). Areas of lucency are also present in the scapula (arrowheads).
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Acquired Conditions
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Metabolic Disorders
All the bone manifestations of chronic renal insufficiency (ie, osteopenia, sclerosis, rickets, and hyperparathyroidism) can be seen in the ribs.
Rickets.—
Rickets results from abnormal calcium metabolism due to vitamin D deficiency or disturbance of hydroxylation in the kidney or liver. Dietary vitamin D deficiency is rare today. Rickets is more common with extreme low-birth-weight prematurity and secondary to renal or hepatic dysfunction and anticonvulsant administration. Delayed ossification of the osteoid matrix in immature bones is most marked in the metaphyses around the knees and wrists and the rib ends, which become concave and flared (Fig 20). The hyperplastic rib osteoid may be palpable on the chest wall as the "rachitic rosary." The metaphyseal appearance is indistinguishable from that in phosphate-losing vitamin D–resistant rickets and rickets due to other causes. Other differential diagnostic considerations for rib cupping and flaring include achondroplasia, hypophosphatasia, and metaphyseal chondrodysplasia.
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Figure 20. Nutritional rickets in a 3- month-old boy. Frontal chest radiograph shows that the ribs are flared anteriorly (arrows), as well as widened. The humeral growth plates are irregular (arrowheads).
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Hyperparathyroidism.—
Hyperparathyroidism occurs most commonly secondarily to chronic renal failure. Hyperparathyroidism results in subperiosteal and endosteal bone resorption. Brown tumors are a rare manifestation of hyperparathyroidism, in which well-defined lucent areas of lysis occur without adjacent reactive bone formation. Progressive loss of bone matrix and demineralization can lead to fractures and progressive bone deformity (Fig 21). Renal osteodystrophy can regress with correction of azotemia (19). The other differential diagnostic considerations are Langerhans cell histiocytosis, fibrous dysplasia, and enchondromas.
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Figure 21a. Rapid progression of renal osteodystrophy over 4 years. (a) Frontal chest radiograph obtained during the early stages of azotemia shows no discernible bone abnormality. Cardiomegaly is present, and vagotomy clips are in place. (b) Frontal chest radiograph obtained at the age of 20 years shows that the thorax is deformed. Areas of lucency in the ribs, clavicles, and humerus represent brown tumors (arrows).
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Figure 21b. Rapid progression of renal osteodystrophy over 4 years. (a) Frontal chest radiograph obtained during the early stages of azotemia shows no discernible bone abnormality. Cardiomegaly is present, and vagotomy clips are in place. (b) Frontal chest radiograph obtained at the age of 20 years shows that the thorax is deformed. Areas of lucency in the ribs, clavicles, and humerus represent brown tumors (arrows).
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Iatrogenic Conditions
Generalized new bone formation occurs with prostaglandin administration to children with cyanotic heart disease (Fig 22). The onset has been reported to be as early as 6 days but is more usual after 30–40 days of prostaglandin therapy. The changes are usually more symmetrical than those of infantile cortical hyperostosis (Caffey disease or syndrome). After treatment, periosteal new bone becomes incorporated and remodeled (20). Differential diagnostic possibilities include child abuse, extracorporeal membrane oxygenation, and infantile cortical hyperostosis. Caveat: Motion artifact can mimic the appearance of periosteal new bone.
Trauma
Child Abuse.—
Fractures of the ribs with child abuse are well described and are considered highly specific for child abuse (21). Rib fractures are rare with accidental injury and are unlikely to arise from cardiopulmonary resuscitation (22). Although abuse fractures can occur along any part of the ribs, they are more common in the posterior arc because of the significant posterior levering force inflicted in the abuse situation. Healing fractures are more easily detectable than in the acute phase. Not all fractures are detectable with conventional radiography; some require high-detail radiography, scintigraphy, or CT. The presence of acute and healing rib fractures is diagnostic of abuse (Fig 23). Other diagnostic signs are metaphyseal "corner" fractures, retinal hemorrhage, intracranial hemorrhage, and subdural hygroma. The most important differentialdiagnoses to consider are osteogenesis imperfecta, long-term ventilator therapy in prematurity, birth trauma, and Menkes syndrome.
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Figure 23. Child abuse in an 8-month-old girl with gastric perforation and intraperitoneal air. Frontal chest radiograph shows bilateral healing rib fractures (arrows), which are diagnostic of abuse.
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Surgical Changes.—
Rib resection and deformity that result from thoracotomy are asymptomatic. However, rib fusion will cause scoliosis and restriction of chest wall expansion (Fig 24), which may require surgical intervention. Fused ribs are also encountered in Gorlin syndrome.
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Figure 24. Rib fusion after surgical repair of a diaphragmatic hernia in a 6-week-old boy. Frontal chest radiograph shows fusion of right ribs 5-7. Note the separation between ribs 4 and 5 and the crowding of the interspace between ribs 5 and 6.
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Infection
Rib osteomyelitis is most commonly acquired from an adjacent focus of empyema or pneumonia (Fig 25). Hematogenous spread is extremely rare. When present, hematogenous spread occurs anteriorly near the costochondral junction or posteriorly near the rib angle (23). The changes resemble those of typical chronic long bone infection, in which there is formation of a sequestrum and involucrum in the presence of periosteal new bone formation. Radiographic differentiation from a neoplasm or Langerhans cell histiocytosis may be difficult.
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Figure 25a. Osteomyelitis of the ribs and an extrapleural mass in a 9-year-old boy with chronic granulomatous disease. (a) Frontal chest radiograph shows poorly defined periosteal elevation in anterior ribs 6 and 7 (arrow), which is partially obscured by an inflammatory soft-tissue mass. (b) CT scan shows the periosteal elevation more clearly. The mass has heterogeneous attenuation. Sporotrichosis was proved at culture.
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Figure 25b. Osteomyelitis of the ribs and an extrapleural mass in a 9-year-old boy with chronic granulomatous disease. (a) Frontal chest radiograph shows poorly defined periosteal elevation in anterior ribs 6 and 7 (arrow), which is partially obscured by an inflammatory soft-tissue mass. (b) CT scan shows the periosteal elevation more clearly. The mass has heterogeneous attenuation. Sporotrichosis was proved at culture.
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Neoplasms
The prevalence of primary neoplasms originating in the thoracic wall is 5%–10% of all bone tumors; malignant tumors are more common than benign (24). Large tumors extend intra- and extrathoracically; only that portion of the soft-tissue mass that extends externally will be clinically obvious. As a result, primary rib tumors are significantly larger than bone tumors in other locations (25).
Enchondromatosis.—
The enchondromatoses are a group of disorders characterized by the presence of medullary cartilaginous bone tumors, which are further subdivided by the presence of hemangiomas (Maffucci syndrome) or their absence (Ollier disease). Rib lesions are common in enchondromatosis (10, pp 814–815). Inheritance is sporadic (10, pp 814–815). At radiography, enchondromas appear as areas of lucency in the bones (Fig 26), occasionally with areas of calcification in the cartilaginous matrix. Modeling deformity is not uncommon. The appearance is similar to that of fibrous dysplasia. Enchondromas occur in association with a variety of systemic malignancies and are themselves associated with a 25% prevalence of malignant degeneration (26,27). Differential diagnostic considerations are Langerhans cell histiocytosis and osteomyelitis, if isolated.
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Figure 26. Enchondromatosis in a 16-year-old girl. Frontal chest radiograph shows enchondromas in the right and left ribs (arrows). Isolated ribs are widened anteriorly. A dense mass (m) arises from right rib 6. Note also the areas of lucency and modeling deformity of the left humerus and scapula.
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Osteochondroma.—
Exostoses are benign bony excrescences with a cartilage cap. They can be solitary or associated with multiple hereditary exostoses. It has been estimated that rib osteochondromas arise in almost 50% of patients with multiple hereditary exostoses (4). Those rib exostoses that project externally are palpable on the chest wall. Internal exostoses can be asymptomatic; hemothorax has been reported, likely caused by trauma to the adjacent lung (28). Osteochondromas can mimic pulmonary nodules; calcified osteochondromas resemble granulomas. CT is most helpful in determining the nature of these bone growths (Fig 27).
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Figure 27a. Osteochondroma in a 7-year-old boy who was followed up years after resection of a Wilms tumor. (a) Frontal chest radiograph shows a solitary osteochondroma (arrows), which mimics a pulmonary nodule. (b) CT scan shows that the mass is partially calcified and arises from a rib. (Courtesy of Andrew K. Poznanski, MD, Children’s Memorial Hospital, Chicago, Ill.)
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Figure 27b. Osteochondroma in a 7-year-old boy who was followed up years after resection of a Wilms tumor. (a) Frontal chest radiograph shows a solitary osteochondroma (arrows), which mimics a pulmonary nodule. (b) CT scan shows that the mass is partially calcified and arises from a rib. (Courtesy of Andrew K. Poznanski, MD, Children’s Memorial Hospital, Chicago, Ill.)
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Langerhans Cell Histiocytosis.—
Langerhans cell histiocytosis is thought to be associated with immune dysfunction. Although most bone lesions are asymptomatic, some may manifest with a painful soft-tissue mass (29). The appearance is variable: A well-defined area of lucency in the bone is a classic finding (Fig 28); expansile and poorly defined lesions can appear aggressive. The ribs are commonly involved, and multiple bone involvement is frequent. Differential diagnostic considerations include metastases, hyperparathyroidism (brown tumors), Ewing sarcoma, Askin tumor, and lymphoma.
Xanthogranuloma.—
Xanthogranulomas are rare benign tumors that occur in the ribs and other flat bones. They are invariably solitary lesions and are almost twice as common in male patients (30). The lesions are well defined with reactive bone or a sclerotic margin. They can be expansile and lytic (Fig 29). The tumor is histiocytelike and consists of benign giant cells, cholesterol clefts, and foam cells. Xanthogranulomas may be the residua of previous fibrous dysplasia or Langerhans cell histiocytosis. The tumor has an excellent prognosis, and complete or partial removal is curative (30). The differential diagnosis includes aneurysmal bone cyst, hyperparathyroidism (brown tumor), and Langerhans cell histiocytosis.
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Figure 29. Xanthogranuloma in a 2-year-old boy. Frontal chest radiograph shows a xanthogranuloma of rib 10 (arrows). The rib is focally widened and lucent with indistinct borders. The cortex is intact.
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Ewing Sarcoma.—
Ewing sarcoma is a very aggressive malignant tumor that occurs in adolescents and young adults. This is the most common malignant tumor that affects the ribs of children and adolescents (25). Tumors infiltrate the bone in a permeative, "moth-eaten" pattern. Although most tumors are lytic (Fig 30), sclerotic tumors do occur. Approximately one-third of costal Ewing sarcomas are expansile (31). Most Ewing sarcomas have an associated soft-tissue mass that is significantly larger than the intraosseous tumor (31). Extensive periosteal reaction is not a major feature of primary Ewing sarcoma of the rib (31). The differential diagnosis includes osteomyelitis, Langerhans cell histiocytosis, osteosarcoma, primitive neuroectodermal tumor, metastatic neuroblastoma, and lymphoma.
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Figure 30a. Ewing sarcoma in a 10-year-old girl. (a) Frontal chest radiograph shows a Ewing sarcoma of rib 5. The rib is expanded posteriorly, and the cortex is obliterated superiorly (arrows). A soft-tissue mass arises from the rib. (b) CT scan shows that the rib is infiltrated by the tumor, which extends into the thorax.
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Figure 30b. Ewing sarcoma in a 10-year-old girl. (a) Frontal chest radiograph shows a Ewing sarcoma of rib 5. The rib is expanded posteriorly, and the cortex is obliterated superiorly (arrows). A soft-tissue mass arises from the rib. (b) CT scan shows that the rib is infiltrated by the tumor, which extends into the thorax.
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Primitive Neuroectodermal Tumor.—
Primitive neuroectodermal tumor (Askin tumor) is a rare malignant tumor that arises from the chest wall, occasionally originating in a rib (Fig 31). This tumor very closely resembles Ewing sarcoma, and differentiation depends on detection of neurosecretory granules at electron microscopy (32). Rib destruction occurs in 25%–63% of patients. Pleural extension is common and results in malignant effusion (33). Differential diagnostic considerations include osteomyelitis, Langerhans cell histocytosis, osteosarcoma, Ewing sarcoma, metastasis, and lymphoma.
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Figure 31. Askin tumor originating from a rib in a 7-year-old boy. Frontal chest radiograph shows poorly defined areas of lucency in an anterior rib (arrows). The superior cortex is disrupted. A large, homogeneous soft-tissue mass opacifies the left hemithorax.
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Conclusions
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There is a wealth of information readily available from the ribs because they may indicate many local and systemic processes. Rib abnormalities detected on chest radiographs are an important indicator of known or unsuspected bone dysplasia, cardiac disease, metabolic disease, trauma, and neoplasms. The diagnostic information obtained from evaluation of the ribs can help tailor the pertinent radiologic and laboratory studies that may be necessary to complete a patient’s diagnostic work-up.
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References
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