Hemivertebrae

► [Absence of one half of the vertebral body]

Hemivertebrae are classified as lateral or dorsal and ventral, depending on whether the developmental defect consists in failure of the contralateral chondral center to develop (lateral hemivertebra) or in failure of the anterior and posterior centers to ossify (dorsal and ventral hemivertebrae, respectively). The first defect occurs at the prechondral stage, while the sec-

Hemivertebrae

Fig. 3.22. Fully segmented hemivertebrae. Isolated lateral hemivertebra at L-3, producing significant structural scoliosis in the lumbar spine with the hemivertebra on the convexity of the curve. Note advanced degenerative osteophyte formation, especially on the concave side of the scoliosis. The inferior disc space is narrowed and the pedicle is enlarged

Fig. 3.22. Fully segmented hemivertebrae. Isolated lateral hemivertebra at L-3, producing significant structural scoliosis in the lumbar spine with the hemivertebra on the convexity of the curve. Note advanced degenerative osteophyte formation, especially on the concave side of the scoliosis. The inferior disc space is narrowed and the pedicle is enlarged ond occurs at the ossification stage of vertebral development. The affected half of the vertebral body may be hypoplastic or absent, as is the pedicle and, at the thoracic level, the corresponding rib. Very often, the neural arch on the side of the affected half of the vertebral body shows a variable degree of fusion or segmentation defect (pediculate or laminar bars). The pedicle on the side of the hemivertebra can be either normal or enlarged. The hemivertebra can exist in the place of a normal vertebra or can be a supernumerary structure. Lateral hemivertebrae, which are by far the most common type, are often supernumerary. Ventral hemivertebrae are exceedingly rare. Hemivertebrae can be fully segmented (nonincarcer-ated), semisegmented, or incarcerated. Fully segmented hemivertebrae are the most common type and usually produce the most severe degrees of spinal deformity, thus requiring prophylactic treatment (McMaster and David 1986) (Fig. 3.22). The so-called semisegmented hemivertebra is fused to one of the adjacent vertebrae above or below, giving rise to osseous fusions that are sometimes of bizarre shape (Fig. 3.23 a,b). In the fully segmented type the disc space is well developed above and below, allowing for differentiation from the acquired disorders, which cause destruction of the vertebral body. Dorsal

Fig. 3.23 a, b. Semisegmented hemivertebra. a The lateral hemivertebra is fused with the next vertebra, giving a trapezoid shape. b Note duplicated pedicles and transverse processes at L-2 owing to the presence of a semisegmented lateral hemivertebra. Scoliosis convex on the side of the hemivertebra is also apparent

Fig. 3.23 a, b. Semisegmented hemivertebra. a The lateral hemivertebra is fused with the next vertebra, giving a trapezoid shape. b Note duplicated pedicles and transverse processes at L-2 owing to the presence of a semisegmented lateral hemivertebra. Scoliosis convex on the side of the hemivertebra is also apparent

Hemivertebra PedicleCuneiform Trapezoidal Vertebral Body
Fig. 3.24. Dorsal hemivertebrae. Isolated dorsal hemivertebra, resulting in gibbus deformity of the thoracolumbar junction

hemivertebrae resemble the anteriorly wedged, or cuneiform, vertebrae (Fig. 3.24). Wedging of the anterior portion of the vertebral body can be primary or secondary to compression injuries or bone softening. When primary, the defect is attributable to failure of the anterior portion of the vertebral body to grow in height and is therefore a defect in formation similar to, although less severe than, a dorsal hemivertebra. Both produce similar effects on spinal alignment. The effects of hemivertebrae on spinal alignment are severe in most cases. Depending on whether the hemivertebra is lateral or dorsal in location, spinal scoliosis or kyphosis, respectively, results (Zidorn et al. 1994). As discussed elsewhere in this section, kyphoscoliosis secondary to hemivertebrae is rapidly progressive in most cases, except when multiple hemivertebrae are present, displaying a balanced effect on spinal alignment (Nasca et al. 1975).

Hemivertebrae have been experimentally induced in fetuses of mice exposed to the teratogenic effect of valproic acid (Padmanabhan and Hameed 1994) and cadmium (Padmanabhan and Hameed 1986). The coexistence in both cases of exencephaly and facial abnormalities underscores the developmental interdependence of the neural plate and the paraxial mesoderm during normal morphogenesis. Failure of midline fusion of the two chondral centers for the vertebral body, possibly secondary to persistence of remnants of the fetal notochord, results in sagittal clefts, a developmental error occurring in early embryonic life (see section headed "Coronal Cleft Vertebrae"). Similarly, failure of midline fusion at the prechondral stage may result in a butterfly vertebra, in which two hemivertebrae are widely separated from each other by persistence of a central canal extending anteriorly and posteriorly on the sagittal plane through the vertebral body (Fig. 3.25). It has been suggested that overdistension of the neural tube soon after its closure (4th week of gestation) caused by an excess of cerebrospinal fluid may spread the developing somite apart, resulting in bilateral hemivertebrae (Gardner 1980). In contrast to the thin fissure of vertebral sagittal clefts, the midline schisis in butterfly

Alagille Syndrome Butterfly Vertebrae
Fig. 3.25. Butterfly vertebra: conventional tomogram showing a typical butterfly vertebra at L-4
Butterfly Apparent Alagille Syndrome
Fig. 3.26. Alagille syndrome. Note multiple butterfly vertebrae in the dorsal spine. (From Berrocal et al. 1997)

vertebrae is a wide cavity filled with cartilaginous tissue continuous with the intervertebral discs above and below. The two hemivertebrae resemble the wings of a butterfly, extending slightly beyond the lateral margins of the neighboring vertebrae, and show oblique superior and inferior end-plates so that they have a funnel-shaped appearance on frontal radiograms. Unlike hemivertebrae, butterfly vertebrae are not associated with segmentation rib defects. The pedicles may be broadened, and the interpediculate distance may be increased. This distinct vertebral configuration is commonly encountered in Alagille syndrome (arteriohepatic dysplasia, OMIM 118450) (Fig. 3.26), an autosomal dominant disorder due to mutation of the JAG1 (Jagged 1) gene at chromosome

20p12. Distinguishing features of the syndrome include deep-set eyes, broad forehead, pointed mandible and bulbous tip of the nose, neonatal jaundice, growth retardation, and defects in the eyes, cardiovascular system (peripheral pulmonary artery stenosis), liver, and bones (vertebral and rib anomalies). In addition to the butterfly-like shape, common features in the spine include hemivertebrae, spina bifida occulta, and decreased interpediculate distance at the lumbar level. A striking histological feature in the liver is the paucity of intrahepatic interlobular bile ducts, resulting in chronic cholestasis (Watson and Miller 1973; Alagille et al. 1975; Rosen-field et al. 1980).

Hemivertebrae can be solitary defects or occur in association with other skeletal and nonskeletal abnormalities. Solitary hemivertebrae are sporadic defects, carrying no risk to subsequent sibs (Wynne-Davies 1975). Moreover, isolated vertebral anomalies detected during fetal life usually have a favorable prognosis and are associated with normal karyotype. By contrast, the presence of associated anomalies in the fetus increases the likelihood of lethality in the perinatal period (Zelop et al. 1993).

The cause and mode of inheritance of hemiverte-brae are unknown. The occurrence of a de novo reciprocal translocation, t(13;17)(q34;p11.2), in a girl with psychomotor developmental delay and congenital scoliosis due to segmented hemivertebra has raised the possibility that 17p11.2 is a candidate region for a hemivertebra locus (Imaizumi et al. 1997). This hypothesis derives credence from the observation that some patients with Smith-Magenis syndrome (OMIM 182290) have both congenital scoliosis and interstitial deletion at 17p11.2.

Hemivertebrae occurring alone or in combination with other anomalies of the spine, especially if located in the low cervical and upper thoracic spine, are commonly associated with urinary tract malformations (Tori and Dickson 1980). Congenital hypoplasia of one lung is often accompanied by hemivertebrae (Silverman 1993). Hemivertebrae are a common finding in subjects with myelomeningocele (Naik et al. 1978).

The acronym VATER (OMIM 192350) stands for a combination of vertebral defects, anal atresia, tracheoesophageal fistula with esophageal atresia, and radial dysplasia. No teratogen or chromosomal abnormality has been recognized, and all recorded cases have been sporadic. Vertebral anomalies are similar to those of spondylocostal dysplasia and include hemivertebrae and fused, hypoplastic, missing, and 'butterfly'vertebrae (Quan and Smith 1972). VACTERL is the acronym for the combination of

Fig. 3.27 a,b. Dyssegmental dysplasia, Silverman type in a stillborn. a Anteroposterior and b lateral radiograms. Note extremely irregular pattern of ossification of the vertebrae, multiple segmentation defects, and anisospondyly. There are hemivertebrae, wedged, oversized, and missing vertebrae, coronal clefts, and lumbos-acral kyphosis. (From Fasanelli et al. 1985)

Fig. 3.27 a,b. Dyssegmental dysplasia, Silverman type in a stillborn. a Anteroposterior and b lateral radiograms. Note extremely irregular pattern of ossification of the vertebrae, multiple segmentation defects, and anisospondyly. There are hemivertebrae, wedged, oversized, and missing vertebrae, coronal clefts, and lumbos-acral kyphosis. (From Fasanelli et al. 1985)

Neonatal Vertebral Anomalies

defects comprising,in addition to those of VATER association, cardiac malformations, renal anomalies including hydronephrosis and urethral atresia, and a wider range of limb anomalies, including hexadacty-ly, humeral hypoplasia, radial aplasia, and proximally placed thumb (Khoury et al. 1983). The designation 'dyssegmental'dysplasia (OMIM 224400) refers to the extensive segmentation defects in the spine (Gorlin and Langer 1978) (Fig. 3.27 a,b). The vertebral bodies are of variable size (anisospondyly), with some vertebrae appearing oversized on lateral radiograms. Vertebral aplasia, especially in the cervical spine, sagittal and coronal vertebral clefts, anterior wedging, and lack of normal craniocaudal interpediculate widening in the lumbar spine are additional findings in the spine. Short and broad long tubular bones with dumbbell femurs, small and flared ilia, narrow chest, and reduced joint mobility are constant features. The autosomal recessive dyssegmental dysplasia of the

Silverman-Handmaker type (OMIM 224410) (Hand-maker et al. 1977) is early lethal and is characterized by more severe radiographic changes. The less severe Rolland-Desbuquois type (OMIM 224400) (Rolland et al. 1972) allows survival beyond the newborn period and is characterized by milder radiographic changes resembling those of Kniest dysplasia (OMIM 156550). A nosologically distinct disorder, dyssegmental dysplasia with glaucoma (OMIM 601561), is associated with severe glaucoma, exophthalmos and corneal opacities (Maroteaux et al. 1996). Spinal dysplasia, Anhalt type (OMIM 601344) resembles dyssegmental dysplasia in some respects, but is a distinct disorder with short stature and significant anomalies in the spine, including hemivertebrae, flat vertebrae, narrow anterior-posterior diameter of the vertebral bodies, and absence of the normal spinous processes (Anhalt et al. 1995).

Teratogens Spine Ribs
Fig. 3.28. Spondylocostal dysostosis. Note extensive vertebral and rib defects, including hemivertebrae, block and butterfly vertebrae, spina bifida, rib hypoplasia, fusion and reduced number of ribs. Left thorax is markedly deformed. The skull and limb bones were normal

Hemivertebrae are characteristic features of spondylocostal dysostosis (OMIM 277300) (Fig. 3.28). Together with spondylothoracic dysostosis (OMIM 122600) and Jarcho-Levin syndrome (OMIM 277300), they are a heterogeneous group of rare disorders characterized by short-neck/short-trunk dwarfism and multiple rib and vertebral anomalies, including hemivertebrae and fused, hy-poplastic, missing, and 'butterfly' vertebrae (Solomon et al. 1978). Although the types and distribution of vertebral anomalies are similar in these disorders, three distinct forms have been recognized: (1) early lethal Jarcho-Levin syndrome, which is of autosomal recessive inheritance, with a symmetrical crab-like chest; (2) autosomal dominant spondylocostal dysostosis, which is associated with a normal life expectancy; and (3) autosomal recessive spondylothoracic dysostosis, with clinical and radiographic features similar to, but usually more severe than, those of spondylocostal dysostosis (Mortier et al. 1996). In Jarcho-Levin syndrome the thorax is small and deformed, with fan-like ribs. In most cases, the small size of the thorax causes respiratory death in infancy. However, survival to the age of 11 years has been reported (McCall et al. 1994). Linkage analysis and combined-haplotype data have identified a critical region between D19S570 and D19S908 on chromosome 19q13 for nonsyndromic spondylocostal dysostosis (Turnpenny et al. 1999). Several skeletal anomalies, including upper and lower limb anomalies, supernumerary ribs, butterfly vertebrae, hypoplastic vertebrae, hemivertebrae, and vertebral coronal clefts, can occur in patients with 22q11.2 deletion (OMIM 188400,192430) (Ming et al. 1997). Nevoid basal cell carcinoma syndrome (Gorlin syndrome, OMIM 109400), an autosomal dominant disorder caused by mutations in PTC, the human homologue of the Drosophila patched gene, comprises multiple basal cell carcinomas, keratocysts of the jaw, palmar/plantar pits, a 'coarse' face, macro-cephaly, frontal bossing, hypertelorism, pectus deformity, Sprengel deformity, calcification of the falx cerebri and tentorium cerebelli, bridged sella, flame-shaped lucencies of the phalanges, metacarpals, and carpals, bifid ribs, fused vertebrae and hemivertebrae (Kimonis et al. 1997). Lumbo-costo-vertebral syndrome consists of congenital lumbar hernia and associated abnormalities, such as absent or hy-poplastic ribs, hemivertebrae, and scoliosis. Ab-dominoschisis and spina bifida occulta are likely associated features (Helderman-van den Enden et al. 1997). Hemivertebrae have been described in two infant sibs as part of a malformation spectrum, referred to as aphalangy with hemivertebrae (OMIM 207620), which includes aphalangy of the hands and feet, and visceral malformations (pulmonary hy-poplasia, ventricular septal defect, and dysgenesis of the urogenital tract and rectum) (Johnson and Munson 1990). X-linked skeletal dysplasia, mental retardation, and abducens palsy (OMIM 309620) is characterized by short stature, fused cervical vertebrae, thoracic hemivertebrae, scoliosis, sacral hy-poplasia, and short middle phalanges (Christian et al. 1977). The disease gene has been mapped to Xq28-qter (Dlouhy et al. 1987). Robinow syndrome, also known as 'fetal face' syndrome, is a mesomelic dwarfing syndrome with a characteristic fetal facies (hypertelorism, midface hypoplasia, and broad mouth with tooth malalignment), small or absent penis, and hemivertebrae (Robinow et al. 1969). Both autosomal dominant (OMIM 180700) (Vallee et al. 1982) and autosomal recessive (OMIM 268310) (Wadlington et al. 1973) inheritance have been documented. The main feature discriminating between the two forms is the occurrence of multiple rib and vertebral anomalies in the recessive form (Glaser et al. 1989). This latter disorder is usually referred to as COVESDEM (costo-vertebral segmentation defect, mesomelia, with normal facies). The gene for autosomal recessive Robinow syndrome has been mapped to chromosome 9q21-q23 and has been identified as ROR2, which encodes an orphan membrane-bound tyrosine kinase (van Bokhoven et al. 2000).

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Responses

  • sabrina oster
    Can butterfly vertebrae cause kyphosis?
    6 years ago
  • NATSNET
    Does hemivertebrae have enlarged pedicle?
    3 years ago

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