Hemivertebrae




KEY POINTS



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Key Points




  • Hemivertebrae are a major cause of congenital scoliosis and kyphoscoliosis.



  • Incidence is 0.3 to 1 per 1000 livebirths. More common in females.



  • Vertebral anomalies develop during first 6 weeks of gestation.



  • Hemivertebrae act as a wedge within the vertebral column, causing curvature away from side of defect.



  • Prognosis for isolated hemivertebra(e) is good.



  • Can be associated with neural tube defects, occult intraspinal defects, renal anomalies, tracheoesophageal atresia/fistula.



  • Associated syndromes in the differential diagnosis include: Goldenhar, Jarcho–Levin, Poland, Robinow, chondrodysplasia punctat, Alagille, and Pallister–Hall.





CONDITION



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Hemivertebrae are vertebral anomalies that can be detected sonographically by the second trimester of pregnancy. These anomalies develop during the first 6 weeks of gestation, when the future anatomical pattern of the spine is formed in mesenchyme. Once the mesenchymal pattern is established in the embryo, subsequent cartilaginous and osseous stages follow (McMaster and Ohtsuka, 1982). At approximately 6 weeks of gestation, a chondrification center appears for each mesenchymal vertebra. Each vertebral body has a dorsal and ventral primary ossification center. These centers fuse, resulting in three primary centers of ossification, which can be visualized sonographically as early as 12 weeks of gestation, but histologically as early as 8 weeks of gestation (Zelop et al., 1993). Abnormalities of the vertebral bodies result from either failure of formation or failure of segmentation (Abrams and Filly, 1985). Abnormalities in vertebral segmentation result in bar or block vertebrae, whereas abnormalities in formation result in hemivertebrae (McMaster and Ohtsuka, 1982). Nasca et al. (1975) classified hemivertebrae by their morphologic appearance and described six different types: single supernumerary hemivertebrae, single wedge-shaped hemivertebrae, multiple hemivertebrae, multiple hemivertebrae with a unilateral bar defect on the contralateral side, balanced hemivertebrae, and posterior hemivertebrae. This latter defect occurs when the anterior part of the vertebral body fails to develop. Clinically this results in a kyphosis rather than a scoliosis. The medical significance of hemivertebrae is that they act as a wedge within the vertebral column, causing a curvature away from the side of the defect (Zelop et al., 1993). The abnormal vertebral body elongates the convex side of the spine. When growth occurs on the affected side, it causes compression of the superior and inferior vertebral end plates, resulting in decreased growth on the concave side (Nasca et al., 1975).



Hemivertebrae are a major cause of congenital scoliosis and kyphoscoliosis. Prenatal detection of this abnormality has become possible only within the past few years, so relatively little is known about the clinical significance of isolated asymptomatic vertebral defects.




INCIDENCE



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In a study of more than 15,000 chest radiographs, the incidence of congenital scoliosis due to vertebral anomalies was 0.5 in 1000 livebirths (Wynne-Davies, 1975). This estimate of vertebral anomalies is low, as only thoracic abnormalities were included in this study. The probable incidence of hemivertebrae is more on the order of 1 in 1000 livebirths (Wynne-Davies, 1975). All vertebral defects are more common in females. The male to female ratio for patients with multiple vertebral anomalies is 0.31 and 0.68 for patients with single vertebral anomalies (Wynne-Davies, 1975). In a retrospective study over a 17-year period (1985–2001) performed in Israel, 26 cases of hemivertebra(e) were identified among 78,500 liveborn infants (Goldstein et al., 2005). Seventeen cases had a single hemivertebra and 9 had multiple vertebral defects.




SONOGRAPHIC FINDINGS



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Examination of the fetal spine should include views in three planes: sagittal, coronal, and transverse (de Elejalde and de Elejalde, 1985). Figures 88-1 and 88-2 demonstrate transverse and sagittal views. The sonographic criterion for hemivertebrae is a disruption in the alignment of one or more vertebral body ossification centers on a coronal section of the fetal spine obtained at 15 weeks of gestation or later. Benacerraf et al. (1986) initially described three cases of hemivertebrae identified sonographically between 17 and 28 weeks of gestation. In a study of 27 fetuses with sonographically detected vertebral anomalies, Zelop et al. (1993) described irregularities along the parallel line formed by vertebral body ossification centers and/or the two posterior neural arch ossification centers on either side (Figure 88-2). In another study, Harrison et al. (1992) described 20 cases of fetal scoliosis. In their study, all fetal spines were examined in the transverse and longitudinal planes for normal vertebral body configuration and curvature. Abnormal spinal curvature was defined as any focal, fixed kyphosis or a fixed curvature of the spine that persisted despite fetal movement. In this latter study, only one case of isolated hemivertebrae accounted for the fetal spinal curvatures. The remaining patients had various associated anomalies. Neural tube defects were the most common, described in 12 of the 20 fetuses studied. This study noted a poor outcome for the fetuses with scoliosis. Only 3 of the 20 infants survived and of these 2 had myelomeningoceles. Twelve of the remaining fetuses were electively terminated, 3 were stillborn, and 2 died on the first day of life.




Figure 88-1


Transverse section demonstrating disruption of the vertebrae. The arrow indicates a cleft in the vertebral body.






Figure 88-2


Sonographic scan in sagittal plane. The arrow indicates an irregularity in the anterior aspect of the vertebral body.





Zelop et al.’s (1993) study is more relevant to the issue of diagnosis and management of the fetus with hemivertebrae. She and her colleagues described 27 fetuses with abnormalities in the spinal ossification centers visualized during the second and third trimesters. Of the 27 patients studied, 11 (41%) had hemivertebrae as the only anomaly documented. The hemivertebrae were distributed all along the spinal column: four were present in the thoracic region, two were present in the thoracolumbar region, and five were lumbar. All of the patients with isolated hemivertebrae had normal karyotypes. Nine of these 11 fetuses were born alive; 1 was electively terminated and 1 died at 32 weeks of gestation after premature rupture of the membranes with sepsis. Of the nine liveborn infants, two required spinal surgery during infancy. The others remained well. In the other 16 cases that comprised this report, multiple additional defects were noted. The following abnormalities were noted: renal in 11 cases, gastrointestinal in 6 cases, cardiac in 4 cases, facial in 4 cases, extremity in 2 cases, cranial in 2 cases, and chest in 1 case. Seven of the fetuses had renal dysgenesis and severe oligohydramnios, consistent with Potter sequence. Four of the patients had polyhydramnios. Of the fetal patients with additional anomalies, seven had a chromosome analysis performed and all had normal karyotypes. Of the 16 patients with additional anomalies, 5 of the 16 survived postnatally, an additional 5 died during the newborn period, and 6 were terminated electively. The study concluded that the prognosis for a fetus with isolated hemivertebrae was good. Of note, however, more than half of the patients with hemivertebrae had significant additional anomalies that affected the prognosis.


Dec 27, 2018 | Posted by in OBSTETRICS | Comments Off on Hemivertebrae

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