Bologna, Italy

Synonyms: Congenital scoliosis (one of the causes of), unilateral aplasia of the vertebral body, complete unilateral failure of formation of the vertebral body.

CODES = MESH Hemivertebra of thoracic vertebrae ICD9  756.14 CDC 756.155

Definition:

Hemivertebra is a congenital anomaly of the spine in which only one half of the vertebral body develops.

Prevalence:

The incidence of hemivertebra is estimated at 5-10:10,000 births with a male/female ratio of 0.31 for multiple vertebral anomalies and 0.68 for solitary vertebral anomalies[1].

Pathogenesis

At 6 weeks gestational age, two lateral chondrification centers arise in the developing vertebral bodies. These chondrification centers then unite by 7 to 8 weeks gestational age to form the primary ossification center of the vertebral body. A hemivertebra results from the failure of one of the lateral chondrification centers to develop[2]. The defective vertebra acts as a wedge in the spine leading to excessive lateral curvature (scoliosis).

Prognosis

The prognosis is directly related to the presence or absence of associated anomalies. The prognosis of isolated hemivertebra is good. Left untreated, 25% of patients with congenital scoliosis show no progression, 50% progress slowly, and 25% progress rapidly during growth[3]. Spinal fusion is the treatment of choice for cases of congenital scoliosis that are progressive or are of the short, rigid type. The treatment of congenital scoliosis should occur before significant deformity occurs.

Etiology

Unknown. The role of genetic factor is controversiale. The occurrence of isolated hemivertebrae in siblings is very uncommon. An association of hemivertebrae with neural defects in siblings has been reported. Wynne-Davies[4] performed a family survey on 337 patients with congenital scoliosis and found that 5 to 10% of sibling of patients with multiple vertebral anomalies with or without spina bifida had either vertebral anomalies or spina bifida. However, she found only one of 245 siblings of 101 infants with a solitary vertebral defect (including isolated hemivertebra) had a spinal defect and concluded that isolated defects were sporadic (non-familial) in nature and carried no risk to subsequent siblings. Connor et al. found an incidence of 4% of neural tube defects among siblings with congenital scoliosis.[5] In contrast to the previous report, they found an increased incidence of neural tube defects in siblings of probands with single hemivertebra as well as those with multiple vertebral defects.

Recurrence risk

Uncertain. There may be an increased risk of neural tube defects in siblings.

Pathology

Only one half of the vertebral body is present, causing a deformation in the shape of the spine.

Associated anomalies

Hemivertebra is commonly associated  with other musculoskeletal anomalies including those of the spine, ribs, and limbs.  Cardiac and genitourinary tract anomalies are the more common extra-musculoskeletal anomalies seen with hemivertebra, with anomalies of the central nervous system and gastrointestinal tract also being reported. Hemivertebra may be part of a syndrome including Jarcho-Levin, Klippel-Fiel, and VACTERL.[6]^,[7] The incidence of karyotypic abnormalities in fetuses with isolated vertebral anomalies is thought to be small. In the largest series, Zelop et al. performed amniocentesis on 18 fetuses with isolated vertebral anomalies and obtained a normal karyotype in all 18 cases[8].

Diagnosis

The sonographic findings associated with fetal hemivertebra include a distortion in the shape of the spine, that can be assessed by both sagittal and coronal scans. A specific diagnosis requires meticolous scanning but it is usually possible by demonstrating, usually in coronal scans, that at the level of the spinal distortion there is triangular bony structure, smaller than a vertebra, that acts as a wedge againts the normal vertebral bodies (Figure 1).

Figure 1. Coronal scan of the spine of a second trimester fetus with hemivertebra

Differential diagnosis

Hemivertebrae may have a similar ultrasonic appearance to the other vertebral abnormalities (wedge vertebra, butterfly vertebra, bloc vertebra, bar vertebra or any combination)  that cause congenital scoliosis and in some cases may only be differentiated after careful neonatal radiologic evaluation.  Open neural tube defects may also be associated with abnormal curvature of the spine but should have other findings differentiating it from hemivertebra. These include the intracranial changes associated with open neural tube defects as well as disruption of the skin over the defect and possibly the presence of a meningocele/myelomeningocele sac.

Diastematomyelia my be associated with sonographic findings very similar to hemivertebra. A specific diagnosis can be difficult at times, but it is usually possible because in a transverse view diastematomyelia results in a typical image: a vertebra with three posterior ossification centers, the central one protruding both towards the skin and the neural canal.

Implications for sonographic screening

It is unlikely that a standard sonographic examination will disclose the presence of hemivertebrae

Implications for targeted examinations

There are no prospective studies available, but we believe that targeted examination should be accurate in predicting hemivertebrae. We recommend an examination at 18 weeks.

Management

When the prenatal diagnosis of hemivertebrae is made, a meticulous search for associated anomalies should be performed. Chromosomal analysis can be offered, especially in the presence of associated anomalies. Amniotic fluid alpha-fetoprotein concentration can be assessed if there is a question of an open neural tube defect and the patient is of appropriate gestational age. Serial ultrasonic evaluation is recommended to follow fetal growth and evaluate for signs of an open neural tube defect that may not be present at an initial early ultrasound.

If there are no other complicating factors, standard management of labor and delivery is recommended. A careful neonatal assessment for associated cardiac and genitourinary anomalies needs to be performed and the infant should receive long term orthopedic follow-up so treatment can occur, if necessary, prior to the development of serious deformity.

References

[1] Wynne-Davies, R: Congenital vertebral anomalies: aetiology and relationship to spina bifida cystica. J Med Genet 12:280-288, 1975.

[2] Moore KL, Persaud TVN: The Developing Human, Fifth ed. Philadelphia: WB Saunders, 358-364, 1993.

[3] Winter RB: Congenital scoliosis. Orthop Clin North Am 19:395-408, 1988.

[4] Wynne-Davies, R: Congenital vertebral anomalies: aetiology and relationship to spina bifida cystica. J Med Genet 12:280-288, 1975.

[5] Connor JM, Conner AN, Connor RAC, Tolmie JL, Yeung B, Goudie D: Genetic aspects of early childhood scoliosis. Am J Med Genet 27:419-424, 1987.

[6] McMaster MJ, David CV: Hemivertebra as a cause of scoliosis. J Bone Joint Surg 68:588-595, 1986.

[7] Connor JM, Conner AN, Connor RAC, Tolmie JL, Yeung B, Goudie D: Genetic aspects of early childhood scoliosis. Am J Med Genet 27:419-424, 1987.

[8] Zelop CM, Pretorius DH, Benacerraf BR: Fetal Hemivertebrae: Associated anomalies, significance, and outcome. Obstet Gynecol 81:412-416, 1993.