Hemivertebra
Hemivertebra is a type of vertebral anomaly and results from a lack of formation of one half of a vertebral body.
Hemivertebra, associated with a failure in the formation and fusion of vertebral body ossification nuclei, are a common cause of thoracic or lumbar scoliosis. A cervical location is rare and even rarer as a cause of cervical subluxation in flexion and extension (for which only one previous case has been found).
Epidemiology
The estimated incidence is at ~0.3 per 1000 live births 2.
Pathology
It falls under the spectrum of segmentational anomalies and can involve one or multiple levels.
A hemivertebra acts as a wedge within the vertebral column, resulting in curvature away from the side on which it is present.
Associations
Recognised associations are many and include:
Aicardi syndrome cleidocranial dysostosis gastroschisis 3 Gorlin syndrome fetal pyelectasis 3
OEIS complex
VACTERL association
mucopolysaccharidosis 9 This list supposed to be lot longer than this. If you know more, do add in with a relevant journal reference.
Classification
A hemivertebra can be classified according to many types which include:
Attachment
fully segmental (free) not attached to either vertebra above or below most concerning semi segmental: half segment is fused with vertebra above or below with no intervening intervertebral disc non segemental not seperated from (i.e. connected to) either level above or below causes less of a concern incarcerated joined by pedicles to levels above and below causes less of a concern Orientation
dorsal hemivertebra: classically results in a kyphosis lateral hemivertebra: classically results in a scoliosis ventral hemivertebra (extremely rare): results in the lordosis Radiographic features
Antenatal ultrasound
A hemivertebra may be seen as an asymmetrical vertebral body on sagittal or coronal scanning, while on axial scanning, a focal defect may be seen at either side of the vertebral column 5.
Plain film/CT
Usually directly outlines the bony anomaly and often seen as a wedge shaped vertebral body.
Prognosis
The prognosis can be variable dependant on the type from being a progressive to non progressive deformity. The strongest negative impact is when a hemivertebra occurs at the lumbo-sacral level 7.
Differential diagnosis
For antenatal sonographic appearances consider: