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Shape of the thecal sac: L3/4 interspace compared with L4/5.
M Naji1, M Williams, M D Hourihan
1Huddersfield Royal Infirmary, Huddersfield, UK.
Anaesthesia
|December 18, 2008
Summary
The thecal sac
Area of Science:
- Radiology and Imaging
- Anatomy
- Neurosurgery
Background:
- The thecal sac's shape can vary.
- Understanding this anatomy is crucial for procedures like lumbar punctures.
Purpose of the Study:
- To investigate the anatomical shape of the thecal sac at L3/4 and L4/5 vertebral levels.
- To determine the prevalence of shape changes between these levels.
Main Methods:
- Retrospective review of 60 normal magnetic resonance imaging (MRI) scans.
- Assessment of thecal sac morphology at L3/4 and L4/5 interspaces.
Main Results:
- The thecal sac was consistently oval at L3/4.
- A significant proportion (43%) of scans showed a transition from an oval to a triangular thecal sac shape at L4/5.
- The triangular shape had its apex pointing towards the posterior epidural space.
Conclusions:
- Anatomical variation in thecal sac shape, particularly at L4/5, is common.
- This variation may explain difficulties in obtaining cerebrospinal fluid (CSF) via lumbar puncture at lower levels, potentially leading to 'dry taps'.
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