We are presenting this pictorial essay in five categories

1. Normal and normal variants
2. Congenital conditions
3. Metabolic conditions
4. Primary and secondary neoplasms
5. Miscellaneous

1. Normal and normal variants:

1.1. Normal ribs:

1.1.a. Calcification of costal cartilage:

First costal cartilages ossify in the late second or early third decade. The calcification occur­ring in the costal cartilage in the male tends to be in the periphery and band like (railroad track appearance) Fig. 1 ,

whereas in the female the calcification tends to be in the centre and appears nodular (wagging tongue-like appearance). Fig. 2 

1.1.b. Companion shadows:

Companion shadows is a faint soft tissue density that parallels a segment of rib usually first and second ribs, measuring 1 – 5 mm. Fig. 3 

It represents an internal bulge of intercostals tissues, probably composed of extrapleural fat, intercostal muscles, and subcostal muscles. Thickness of companion shadows showed differences between obese patients and normal subjects.

1.2. Normal variants:

1.2.a. Cervical ribs:

Cervical ribs are seen in 1 to 2 % of the population. They are usually bilateral but asymmetrical. Cervical rib is usually asymptomatic, but it can cause thoracic outlet syndrome by compression of the brachial plexus or subclavian vessels. They have to be differentiated from hypoplastic first rib or elongated C7 transverse process. Fig. 4 

1.2.b. Hypoplastic first rib:

Hypoplastic first rib is not uncommon to be encountered in chest radiograph. The reported prevalence is 0.2% of chest radiographs. It can be differentiated from cervical rib by the direction of transverse process of the attached vertebra, as the T1 transverse process is directed superiorly. Fig. 5 

Cervical rib can cause thoracic outlet syndrome and hypoplastic first rib not.

1.2.c. Von luschka’s bifurcated rib:

Von luschka’s bifurcated rib or forked rib is the most common rib anomaly, being found in 0.6% of chest radiographs. Fourth rib is most commonly involved and of no clinical significance. Sometimes it may simulate a lung cavity. Fig. 6 

1.2.d. Fused ribs:

Congenital rib fusion may involve anterior or posterior aspect of rib or complete. Fig. 7 

It may be associated with vertebral segmentation defect.

1.2.e. Rib foramen:

Well circumscribed radiolucent corticated foramen of rib, usually seen in lower and posterior ribs. Fig. 8 

1.2.f. Short rib:

Short rib is an incidental finding in routine chest radiograph, possibly due to early fusion of epiphyseal centre. Short rib is diagnosed if the lateral margin of the affected rib is more than 4 mm medial to a tangent drawn between the lateral margins of adjacent ribs. Fig. 9 

It doesn’t have any clinical significance.

1.2.g. Pseudo-Arthrosis of the First Rib:

An irregular, joint-like cavity with opposing bulbous rib ends can be encountered at midcourse of the first rib. Fig. 10 

This anomaly usually occurs unilaterally and documented in 0.1% of the population. The exact etiology is unknown, may be congenital or post traumatic. It may be a confusing cause for a palpable hard mass in the supraclavicular fossa.

2. Congenital conditions:

2.1. Neurofibromatosis:

Neurofibromatosis is an inherited neurocutaneous disorder, transmitted as an autosomal dominant manner. In neurofibromatosis ribs appear thin, slender, irregular, scalloped and separated by neurofibromas. This deformity of the ribs has been called the twisted ribbon appearance. Fig. 11 

Intercostal neurofibromas may produce erosions on the inferior surface of the ribs, occasionally mimicking coarctation of the aorta.

2.2. Osteopetrosis:

Osteopetrosis is a rare hereditary and familial bone abnormality characterized by the lack of resorption of normal primitive osteochondrous tissue. It is subdivided into various subgroups, all of which are characterized by generalized increase in bone density. The congenital or severe malignant form is autosomal recessive and presents in infantile period. Affected infants show diffuse sclerosis of all bones, splayed costochondral junction and hepatosplenomegaly. Fig. 12 

Pathologic fractures may occur secondary to bone fragility.

2.3. Rib notching:

Rib notching occurs in various conditions. The causes may be arterial, venous or arteriovenous. The notching usually occurs in the inferior aspect of ribs. Fig. 13 

Superior marginal defects can also occur. Classical rib notching is seen in Coarctation of aorta in the inferior aspect of 3rd to 8th posterior ribs. Rib notching may also be seen in Fallot's tetralogy, pulmonary stenosis, after Blalock Taussig shunt, arteritis, aortitis arteriovenous malformations, chronic superior venacaval obstruction, Neurofibromatosis etc. Superior marginal defects are seen in collagen vascular disorders like SLE, Rheumatoid arthritis, osteochondroma, neural tumours, hyperparathyroidism, Osteogenesis Imperfecta, Marfan's syndrome and after chest drainage.

2.4. Klippel feil syndrome:

Klippel feil syndrome is characterised by the clinical triad of short neck, limited neck motion and low occipital hair line. Rib abnormalities are absent or fused ribs, chest wall asymmetry and cervical rib. Fig. 14

3. Metabolic conditions:

3.1. Rickets:

Rickets is characterized by abnormal calcium metabolism due to vitamin D deficiency in children. There will be overgrowth of epiphyseal cartilage at costochondral junction due to inadequate provisional calcification, producing the "rachitic rosary”. Radiologically it shows bulbous enlargement of the costochondral junctions with adjacent cupped anterior rib ends. Fig. 15  Sometimes it can indent the pleural interface or even the thymic shadow.

3.2. Hyperparathyroidism:

Hyperparathyroidism is characterized by overactivity of paratharmone(PTH), which can be primary, secondary or tertiary. The radiological features are subperiosteal resorption, decreased bone density, accentuated trabecular patterns, loss of cortical definition and brown’s tumors. Fig. 16  

The differentials are fibrous dysplasia, expansile lytic metastasis from thyroid or renal carcinoma and enchondroma.

4. Primary and secondary neoplasms:

4.1. Primary bone neoplasm

4.1.1. Enchondroma:

Enchondroma is a common benign bone tumor arising in residual islands of cartilage left in the metaphysis. Most common sites are small tubular bones of the hands and feet. Ribs are rare site for solitary enchondroma accounting for 13% of enchondromas and also frequently involved in multiple enchondromatosis (Ollier’s disease or Maffuci syndrome). The lesions appear as well defined radiolucent area with preserved cortex. Stippled or punctate chondroid type of matrix calcification is found scattered randomly throughout the lucent defect. Lesions involving slender bones such as ribs or fibula may show eccentric expansion, which is described as enchondroma protuberans. Fig. 17 

4.1.2. Osteochondroma:

Osteochondroma is a bony exostosis projecting from the external surface of a bone with a cartilage cap. It usually involves the long tubular bones. Ribs are involved in only 3% of solitary osteochondromas, and almost 50% of patients with multiple hereditary exostosis (MHE). Osteochondroma may be sessile or pedunculated. Spontaneous hemothorax associated with rib osteochondroma has been reported. In multiple exostosis the lesions may be bilateral. Fig. 18 

4.1.3. Osteosarcoma:

Osteosarcomas are the most common primary malignant bone tumors exclusive of multiple myeloma. It commonly involves metaphysis of long bones. Short bones, spine, and flat bones (such as, the ribs, scapula, pelvis, and craniofacial bones) are less frequently involved. Rib osteosarcomas are infrequently reported. Approximately 1 – 2% of osteosarcoma occur in the thoracic bones inclusive of the ribs, sternum, and clavicle. The typical ‘sunburst’ radiological pattern observed in the OS of the long bones may not be evident in the OS of the flat bones. The radiological features of rib osteosarcoma are minimal expansion, cortical breaks, soft tissue component and osteoid type matrix mineralization. Fig. 19 

4.1.4. Ewings sarcoma:

Ewings sarcoma is a relatively common aggressive bone tumor of adolescents and young adults. This is the most common malignant tumor that affects the ribs of children and adolescents. Ewing’s sarcoma of ribs are usually lytic. Mixed lytic sclerotic lesions do occur in case of atypical ribs. Most of the costal ewings sarcoma associated with disproportionate soft tissue component and approximately one third of lesions are expansile. Fig. 20

4.1.5. Chondrosarcoma:

Chondrosarcomas are malignant tumors that produce chondroid matrix. Primary chondrosarcoma is the most common primary malignant rib neoplasm. Conventional chondrosarcomas typically occur in the fourth or fifth decades, however chondrosarcomas involving the ribs and sternum tend to occur in a slightly younger patient population. Anterior ribs are most commonly involved, usually arises at or near the costochondral junction. The radiographic appearance of chondrosarcoma is a lobulated, mixed lytic and sclerotic lesion. Radiologically chondrosarcoma appears as lobulated masses containing the typical stippled, punctate or ring and arc like (chondroid type) calcifications. Fig. 21

4.1.6. Multiple myeloma:

Multiple myeloma is a clonal proliferation of neoplastic plasma cells in the bone marrow that is usually associated with multifocal lytic lesions throughout the skeletal system. It is the most common tumor of bone. Spine is the most common site to be involved, marrow-rich flat bones like  pelvis, skull, ribs, clavicle, and scapula are also frequently involved. Ribs are the second most frequently involved site in multiple myeloma approximately 59%. In multiple myeloma ribs can show diffuse osteoporosis, diffuse osteolytic round to oval lesions, punched out rain drop lesions or expansile lytic lesions with extrapleural soft tissue component. Pathological fractures involving multiple ribs are not uncommon to be encountered in patients with multiple myeloma. Fig. 22

4.2. Secondary neoplastic involvement:

4.2.1. Direct involvement:

Direct invasion into a bone may occur from a soft tissue tumor lying adjacent to or near the ribs. Direct involvement of ribs by neoplastic lesions can be either intrathoracic (most commonly lung) or chest wall (most commonly breast) malignanies.

a. Pancoast tumor:

Pancoast tumors (superior pulmonary sulcus tumors) are non–small cell carcinomas that originate in the lung apex and invade the chest wall or soft tissues of thoracic inlet. The tumor may involve the brachial plexus, cervical sympathetic ganglia, and superior mediastinum. Clinically patients present with Horner’s syndrome and pain radiating to arm. Radiologically it shows apical mass with underlying bone erosion, most often 2^nd rib followed by other ribs and vertebral body.Fig. 23

b. Direct involvement by carcinoma breast:

Direct invasion of ribs by carcinoma breast can be seen in locally advanced carcinoma or in local recurrence after surgery. Chest radiograph shows diffuse haziness with underlying rib erosion which usually involves multiple ribs. Fig. 24

4.2.2. Distant metastasis:

Metastatic bone tumors are the most common malignant tumors of the skeleton. The most common primary sites are in the breast, lung, prostate, kidney, thyroid, and bowel. The metastatic lesions may be lytic, expansile lytic, sclerotic or mixed lytic-sclerotic.

Lytic metastases are more common that usually from carcinoma breast, lung, salivary glands and bowel. Fig. 25

Rib metastases from highly vascular tumors like carcinoma thyroid and kidney are frequently lytic and expansile with extrapleural soft tissue component. The differentials include plasmacytoma, myeloma and brown’s tumor. Fig. 26

Sclerotic metastases are not uncommon and usually involves multiple ribs. Most common primary for sclerotic metastasis is carcinoma prostate in males and carcinoma breast in females. Less frequent primaries include carcinoids, carcinoma lung and colon. The differentials include melorheostosis, osteopetrosis, flurosis and myelofibrosis. Fig. 27

Mixed lytic-sclerotic metastases are less common and usually from carcinoma prostate, breast and lungs. Multiple ribs are involved and associated with pathological fractures. The close differential is multiple myeloma on treatment.

5. Miscellaneous:

5.1. Fractures:

Trauma can produce rib frac­tures. The associated changes that occur in the heart, lungs, pleura, etc are more significant than fractures of the ribs per se. Usually the fractures heal by themselves. The exuberant callus sometimes produced results in opacities over the lungs. Multiple rib fractures may cause pneumothorax, flail chest and haemothorax, which may cause serious morbidity and mortality. Fig. 28

Pathological fractures in the ribs are difficult to heal and may be seen in renal osteodystrophy, metastases, hyperparathyroidism etc. Multiple rib fractures noted repeatedly in a child along with fractures of other bones should arouse suspicion of Battered baby syndrome.

5.2. Fibrous dysplasia:

Fibrous dysplasia is a localized developmental arrest in which all components of normal bone are present, but they fail to differentiate into mature structures. Fibrous dysplasia occurs as one of three clinical patterns: (1) involvement of a single bone (monostotic); (2) involvement of multiple bones (polyostotic); and (3) polyostotic disease, associated with café au lait skin pigmentations and endocrine abnormalities, especially precocious puberty (McCune-Albright syndrome). The affected rib shows expansion, ground glass matrix, thinning of cortex and modeling effect.

Monostotic fibrous dysplasia accounts for 70% of cases. Ribs are the most frequently affected site followed by femur, tibia, jawbones, calvaria, and humerus. Fig. 29

Polyostotic fibrous dysplasia without endocrine dysfunction accounts for 27% of cases. Femur, skull and tibia are most commonly affected bones, rib involvement is rare. Fig. 30

McCune-Albright syndrome accounts for 3% of all cases. The bone lesions are often unilateral.

5.3. Osteoradionecrosis:

Post radiation changes to the ribs include osteoradionecrosis, where the dead areas in the ribs appear very dense on plain radiograph. Osteoradionecrosis of ribs are often seen following radiation therapy to carcinoma breast and carcinoma lung. Multiple ribs are commonly involved and the involvement confined to the field of radiation therapy. Fig. 31

5.4. Postoperative rib:

Postoperative changes are noted in ribs following pneumonectomy, transthoracic esophageal surgeries and resection of chest wall tumors. Remodelling of ribs may be complete after surgery if the periosteum is left behind. Involved ribs may show defect in case of resection, irregular periosteal reaction or postoperative rib fusion. Fig. 32