=====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).

see [[cervical hemivertebra]]

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

[[Jarcho Levin syndrome]]

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:

[[Block vertebra]]