Sternal Abnormalities

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As mentioned in previous sections, disturbances of endochondral ossification and growth of the sternum and ribs are key elements in the development of pectus deformities in children and adolescents (Haje et al. 1999; Sadler 2000). Growth and development of the sternum is not only influenced by genetic factors, but also just as much by biomechanical factors (Wong and Carter 1988). A considerable number of developmental defects of the sternum and anterior chest wall are recognized. Some are anatomical variations or minor anomalies, representing at worst an aesthetic and psychological problem. Examples include tilted sternum, prominent convexity of anterior rib or costal cartilage, prominent asymmetrical costal cartilage, well-defined paracostal subcutaneous nodule, mild pectus excavatum, and mild pec-tus carinatum (Donnelly et al. 1999).

Several other congenital sternal defects represent definite abnormalities occurring in isolation or as part of the malformation spectrum of syndromes and bone dysplasias. Two such major abnormalities, pectus excavatum and pectus carinatum, have been discussed in specific sections. A brief review of some other sternal abnormalities is included here. An increased number of ossification centers in the sternal manubrium is seen approximately four times as frequently in patients with Down syndrome as in normal children. An accessory ossification center located ventral to the manubrium sterni, an anomaly termed the 'double-layered manubrium' (Currarino 2000), is frequently seen in diastrophic dysplasia (OMIM 222600) (Fig. 2.55 a,b). A reduced number of the sternal ossification centers, resulting in a short sternum, is found in trisomy 18 syndrome (Fig. 2.56). Premature fusion of the sternal sutures, or Currarino-Silverman syndrome (OMIM 184800), results in shortening of the sternum and high carinate chest deformity. This type of sternal deformity is typical of Noonan syndrome (OMIM 163950) and sometimes also occurs in Aarskog syndrome (OMIM 305400). Mineralization of the sternum fails to occur in campomelic dysplasia (OMIM 114290,211990) and in achondrogenesis type I and II (OMIM 200600,200610,200700). Failure of the two halves of the sternum to fuse on the midline results in sternal cleft. Depending on the degree of separation, partial (75%) and complete (25%) forms are recognized. When the defect is severe the sternum is entirely missing (Altschuler 1999) and there is associated schisis of the abdominal wall. Prenatal diagnosis by ultrasonography is possible. The clinical significance of the cleft lies in the fact that the heart and great vessels are left unprotected (Fokin 2000). Therefore, early surgical repair is recommended, especially in the presence of complete clefts (Domini et al. 2000). Sternal cleft can be an isolated defect (Moto et al. 1996; Hoeffel et al. 1999) or occur in association with other anomalies or as part of well-defined malformation syndromes. The association of sternal fusion defects with various cardiac, diaphragmatic, and anterior body wall defects is currently regarded as a ventral midline developmental field complex - as defined by Opitz and Gilbert (1982) - that includes the pentalogy of Cantrell and ectopia cordis (Martin et al. 1992). Thus, the pentalogy of Cantrell, an asso

Fig. 2.55 a,b. Diastrophic dysplasia in a female child a during the neonatal period and b at 2 years of age. Note the developmental anomaly of the manubrium sterni consisting of two ossifications, with the accessory ossification center located ventral to the normal manubrium (double-layered manubrium). Subsequent fusion of the two segments usually results in residual sternal deformity. (From Currarino 2000)

Double Manubrial Ossification
Fig. 2.56. Trisomy 18 syndrome in a 5-month-old infant. Note short sternum with only two small sternal segments below the manubrium, and mild pectus carinatum deformity

ciation of: (1) sternal cleft defects, (2) midline ventral abdominal wall defects, (3) ectopia cordis, (4) in-trapericardial herniation of abdominal organs through diaphragmatic defects, and (5) cardiac anomalies, formerly described as a separate entity of sporadic occurrence (Cantrell et al. 1958; Casey et al. 1975), is now included under the designation 'thora coabdominal syndrome' (OMIM 313850) (Carmi and Boughman 1992). Thoracoabdominal syndrome, or midline defects syndrome,is inherited as an X-linked dominant condition, with the gene involved mapping to Xq25-q26.1 (Carmi et al. 1990; Parvari et al. 1996). The high prevalence of midline or midline-associat-ed malformations, including hydrocephalus, anen-cephaly, cleft lip, congenital heart defect, renal agenesis, and hypospadias, in five males in the same kindred suggests that a single X-linked gene mutation may disrupt development (Toriello and Higgins 1985). The association of sternal cleft, midline abdominal defect, and cutaneous craniofacial heman-giomata is referred to as 'sternal malformation-vascular dysplasia spectrum' (OMIM 140850). Multiple hemangiomas may be located in the mucosa of the small bowel, mesentery, and pancreas. Occasional manifestations include absent pericardium, cleft lip, micrognathia, and glossoptosis. This entity is clearly related to the midline defects described above. The etiology is unknown, and all reported cases have been sporadic (Hersh et al. 1985). An association of midline thoracoabdominal defects and limb defects is known (Pivnick et al. 1998). The affected infant showed absent sternum, ectopia cordis, diaphragmatic defects with abdominal contents in the chest, eye defects, unilateral absence of the middle third of the clavicle, 11 pairs of ribs ipsilaterally, ipsilateral hypoplasia of the tibia and aplasia of the fibula and foot, and also ectrodactyly of the ipsilater-al hand and contralateral foot. A short and bifid ster num, with pectus carinatum or excavatum, occurs in Coffin-Lowry syndrome (OMIM 303600). Shortening of the sternum is an occasional feature in the following conditions: Coffin-Siris syndrome (OMIM 135900), de Lange syndrome (OMIM 122470), Marshall-Smith syndrome (OMIM 602535),multiple synostosis syndrome (OMIM 186500), popliteal pterygium syndrome (OMIM 119500), and Schinzel-Giedion syndrome (OMIM 269150).

Several acquired lesions may affect the sternum, which is a relatively common site of metastasis. Primary tumors are less common, and include lymphoma, chondrosarcoma, plasmocytoma, chordoma, and giant cell tumors (Martini et al. 1974). Fractures or dislocations of the sternum sometimes occur after direct trauma to the lower anterior part of the thoracic cage. Commonly, the site of fracture is the upper body of the bone near the manubriosternal junction. Cardiovascular, pulmonary, and tracheal injuries are serious complications of direct sternal trauma (Brookes et al. 1993). Indirect mechanisms, such as a blow to the upper thoracic spine, can also be responsible, although less commonly, for sternal fractures (Gkopalakrishnan and el Masri 1986). Osteomyelitis of the sternum and septic arthritis of the sternoclavicular and manubriosternal joint can result from direct hematogenous inoculation or secondary contamination attributable to local injury, surgery, or a therapeutic or diagnostic procedure. Abscess formation and mediastinitis may complicate the course of a sternoclavicular joint infection (Biesecker et al. 1973).

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  • fikru
    Why sternum bone is tilted ?
    2 years ago

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