Hemivertebra

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

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

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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

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

Unknown. The role of genetic factors is controversial. The occurrence of isolated hemivertebrae in siblings is very uncommon. An association has been reported between hemivertebrae and neural defects in siblings. Wynne-Davies³ 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, they found in a study of 101 infants with a solitary vertebral defect (including isolated hemivertebra), only one of their 245 siblings 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.⁴ 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.

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

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, while anomalies of the central nervous system and gastrointestinal tract are also reported. Hemivertebra may be part of a syndrome including Jarcho-Levin, Klippel-Feil, and VACTERL.^5-6 The incidence of karyotypic abnormalities in fetuses with isolated vertebral anomalies is thought to be small.⁷ 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

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

The sonographic findings associated with fetal hemivertebra include a distortion in the shape of the spine, which can be assessed by both sagittal and coronal scans. A specific diagnosis requires meticulous scanning but it is generally possible by demonstrating, usually by coronal scans, that at the level of the spinal distortion there is triangular bony structure, smaller than a vertebra, which acts as a wedge against the normal vertebral bodies.^9-13 Three-dimensional ultrasound can help to confirm diagnosis.¹⁴ There are some reports of early diagnosis in the first trimester.¹⁵ 

Hemivertebrae may have a similar ultrasonic appearance to the other vertebral abnormalities (wedge vertebra, butterfly vertebra, block 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 in these cases, additional findings are associated. These include intracranial anomalies as well as disruption of the skin over the defect and possibly the presence of a meningocele/myelomeningocele sac.
In diastematomyelia, sonographic findings may be very similar to those seen in cases of hemivertebra. A differential  diagnosis can be difficult, but it is usually possible because in a transverse view diastematomyelia results in a typical image: a vertebra with three posterior ossification centres, the central one protruding both towards the skin and the neural canal.
 

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

There are no prospective studies available, but we believe that targeted examination should be accurate in detecting hemivertebrae. Three-dimensional ultrasound may be of help in confirming the antenatal diagnosis.

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 . 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 be performed before significant deformity occurs.¹⁶

When the prenatal diagnosis of hemivertebrae is made, a meticulous search for associated anomalies should be performed. Chromosomal analysis can be offered, especially when associated anomalies are present. 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 labour and delivery is recommended. A careful neonatal assessment for associated cardiac and genitourinary anomalies should be performed and the infant should receive accurate orthopedic follow-up so treatment can occur, if necessary, prior to the development of serious deformity.

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. Wynne-Davies, R: Congenital vertebral anomalies: aetiology and relationship to spina bifida cystica. J Med Genet 12:280-288, 1975.
4. 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.
5. McMaster MJ, David CV: Hemivertebra as a cause of scoliosis. J Bone Joint Surg 68:588-595, 1986.
6. 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.
7. Alvarez de la Rosa M, Padilla Pérez AI, de la Torre Fernández de Vega FJ, López García J, Troyano Luque JM. Genetic counseling in a case of congenital hemivertebrae. Arch Gynecol Obstet. 2009 Oct;280(4):653-8.
8. Zelop CM, Pretorius DH, Benacerraf BR: Fetal Hemivertebrae: Associated anomalies, significance, and outcome. Obstet Gynecol 81:412-416, 1993.
9. Harrison LA, Pretorius DH, Budorick NE. Abnormal spinal curvature in the fetus. J Ultrasound Med. 1992 Sep;11(9):473-9.
10. Varras M, Akrivis C. Prenatal diagnosis of fetal hemivertebra at 20 weeks' gestation with literature review. Int J Gen Med. 2010 Jul 21;3:197-201.
11. Benacerraf BR, Greene MF, Barss VA. Prenatal sonographic diagnosis of congenital hemivertebra. J Ultrasound Med. 1986 May;5(5):257-9.
12. Basude S, McDermott L, Newell S, Wreyford B, Denbow M, Hutchinson J, Abdel-Fattah S. Fetal hemivertebra: associations and perinatal outcome. Ultrasound Obstet Gynecol. 2015 Apr;45(4):434-8. 
13. Wax JR, Watson WJ, Miller RC, Ingardia CJ, Pinette MG, Cartin A, Grimes CK, Blackstone J. Prenatal sonographic diagnosis of hemivertebrae: associations and outcomes. J Ultrasound Med. 2008 Jul;27(7):1023-7.
14. Wen Y, Xiang G, Liang X, Tong X. The Clinical Value of Prenatal 3D Ultrasonic Diagnosis on Fetus Hemivertebra Deformity- A Preliminary Study. Curr Med Imaging Rev. 2018 Feb;14(1):139-142.
15. Chen M, Chan B, Lam TP, Shek T, Lee CP, Tang MH. Sonographic features of hemivertebra at 13 weeks' gestation. J Obstet Gynaecol Res. 2007 Feb;33(1):74-7.
16. Winter RB: Congenital scoliosis. Orthop Clin North Am 19:395-408, 1988.
 

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