Q: Spinothalamic tract lesions - Brown Sequard vs syringomyelia?

[MedGeekz]

Hello everyone, I'm pretty new to the forums even though I've been reading the threads a lot, and I would appreciate the help I could get on this issue;

To my understanding, syringomyelia causes compression and damage to the anterior commissure which leads to bilateral loss of pain and temperature due to the decussations of Lissauer's tract.

Brown-Sequard syndrome: hemisection, classic example T10, on the contralateral side, loss of pain and temperature sensation.

1) However my issue is(skipping the decussations and ipsi/contralateral part); why is it so that in hemisection (BS syndrome) you get symptoms BELOW the lesion, all the way to the foot, while in syringomyelia, you only get symptoms more or less at the level of the lesions and nothing BELOW, even though the same tract is affected?

2) Another stupid question; do we have 31 seperate pairs of spinothalamic tracts, or do all dermatomes connect to the one and only tract eventually? This sounds stupid sorry..

Maybe it's a stupid and easy question, but I haven't been able to find an answer to this yet and I've searched around a lot.

Thank you, and again, I appreciate your help!

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[Pepe18]

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[MedGeekz]

Not stupid questions at all. With syringomyelia, it's like a cyst, so it only compresses in the areas where the syrinx is damaged. At each vertebral level, there are sensory nerves carrying pain and temp, they decussate and travel up the contralateral spinothalamic tract. Syringomyelia blocks the spinothalamic nerves at the decussation and only at the level of the pathology. They can continue decussating below and travel up unimpeded. With BS, the spinothalamic tract continues to decussate below the lesion, but they can't continue up to the brain because transmission stops at the hemisection

At each spinal level there are sensory neurons that enter the dorsal horn, they travel about 2 vertebral levels up (this is Lissaur's tract), and then decussate. The fibers from each individual vertebral level meet up in the spinothalamic tracts and travel up together to the thalamus.

And just a heads up, it is anterior white commissure. The anterior commissure is a structural in the brain

Thank you so much for the explanation! I finally think I understood it! appreciated!