Congenital absence of a spine pedicle

Last revised by Yuranga Weerakkody on 15 May 2017

Congenital absence of a spine pedicle is a rare congenital condition, but awareness of its characteristic imaging appearance is important to avoid misdiagnosis.

Failure to recognize this entity can lead to misdiagnosis of unilateral facet subluxation/dislocation, leading to unnecessary treatment such as spinal traction. Most reported cases in the literature are incidental finding during trauma scans.

Congenital absence of a spine pedicle is usually asymptomatic, but may become symptomatic due to altered mechanical loading leading to contralateral facet degeneration and contralateral neural foramen stenosis. 

The condition is invariably a unilateral process where absence of the pedicle gives a false impression of an enlarged neural foramen. A spectrum of dysplastic ipsilateral transverse process, dorsally displaced ipsilateral lamina and dysmorphic facets has been described 2. Often the immediately adjacent facets above or below the affected level are also dysplastic 2. Midline fusion anomalies are also a common association. The pseudoenlarged neural foramen has been shown on myelography to contain conjoined nerve roots 2

In addition to unilateral absence of a spine pedicle (absent pedicle sign or winking owl sign), the following items may help to differentiate it from other causes of an absent pedicle:

  • stress hypertrophy (enlargement, cortical thickening and sclerosis) of contralateral pedicle
  • accessory transverse process sign: small inferiorly directed transverse process with a small joint like space separating it from pedicle or vertebral body
  • spinous deviation sign: deviation of spinous process towards contralateral side at the level of involvement

Evidence from the literature suggests that the cervical spine is most commonly affected, followed by the lumbar spine. It is rarely reported in the thoracic spine 2-3.

The condition was first described by Hadley in 1946 1

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Cases and figures

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