A 72-year-old female presents with a complete right sided hemiparesis. She is conscious and alert. Cranial nerves are normal. She has had a non-contrast CT scan of her brain which is normal. Clinical examination reveals loss of pain sensation in her left arm, with intact light touch.
a) What is the site of the lesion? (25% marks)
Right half of cervical cord.
Important features to process here are:
- A completely intact level of consciousness with normal cranial nerves
- Right sided motor weakness over the whole body
- Left sided loss of pain sensation in the upper limb
Now, for some localisation, showing the working:
- A completely intact level of consciousness with normal cranial nerves virtually excludes a lesion above the level of the medulla
- Because the arm is involved, we can establish that the lesion is above the level of the thoracic cord.
- Nociceptive tract decussation occurs at or slightly above the level of their nerve root entry, and so the fibres from the left arm cross over to the right side shortly after joining the spinal cord.
- Motor tracts decussate at the level of the pyramids, which means to generate a right-sided hemiparesis with a lesion below the medulla, the spinal cord lesion must also be right-sided.
In case it helps, here is a crude diagram of these decussations:
Oh's Manual: Chapter 78 (pp. 795) Spinal injuries by Sumesh Arora and Oliver J Flower
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