disc herniation and compression - cord level

[acciddropping]

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Hi guys,
I didn't see a good summary of the cord level that's compressed with each possible disc lesion - and I have not come across a good summary chart either.... Can some of you help summarize? I know how the spinal nerves run (C1-7, above and the rest, from below)

Can you fill in the answers below -
disc between C3/4 compresses on C___
disc between T3/4 compresses on T___
disc between C7/T1 compresses on ___

Thanks.

I think the anwers are:
C4
T4
C8
But, not 100% sure but that's what I picked up from doing questions... - because for T and L segments, we count one segment below but for C's we count at the level where herniation occurs... do you guys know why it's the case?

 

[bulldogmed]

Hi guys,
I didn't see a good summary of the cord level that's compressed with each possible disc lesion - and I have not come across a good summary chart either.... Can some of you help summarize? I know how the spinal nerves run (C1-7, above and the rest, from below)

Can you fill in the answers below -
disc between C3/4 compresses on C___
disc between T3/4 compresses on T___
disc between C7/T1 compresses on ___

Thanks.

I think the anwers are:
C4
T4
C8
But, not 100% sure but that's what I picked up from doing questions... - because for T and L segments, we count one segment below but for C's we count at the level where herniation occurs... do you guys know why it's the case?

You're correct on all three counts, though thoracic herniations are not nearly as common as cervical or lumbar herniations.

From Blumenfeld, p. 321, "For both cervical and lumbosacral disc herniations, the nerve root involved usually corresponds to the lower of the adjacent two vertebrae...thoracic, lumbar, and sacral nerve roots exit below the correspondingly numbered vertebral bone. Cervical nerve roots, on the other hand exit above the correspondingly number vertebral bone--except for C8, which has no corresponding vertebral bone and exits between C7 and T1. Cervical nerve roots have a fairly horizontal course as they emerge from the dural or thecal sac near the intervertebral disc and exit through the intervertebral foramen. Cervical discs are usually constrained by the posterior longitudinal ligament to herniate laterally toward the nerve root, rather than centrally toward the spinal cord."

 

[Miracoli]

So following the above method what will be your answer for this Q and why?
disc herniation between L5/S1 compresses on__

 

[Pisiform]

I think it depends on what kind if herniation you have ... All those of the above are correct for postero-lateral herniation.

 

[bulldogmed]

So following the above method what will be your answer for this Q and why?
disc herniation between L5/S1 compresses on__

It's helpful to see an image here. Posterolateral herniations below L1, i.e., in the cauda equina, produce lesions to the nerve root for the lower section. Far lateral herniations do just the opposite, they hit the nerve root for the upper section. Herniations to the center will produce a lesion to a section below the IV disc segment. In this case, L5/S1, central will affect S2 and below possibly.

 

[Miracoli]

It's helpful to see an image here. Posterolateral herniations below L1, i.e., in the cauda equina, produce lesions to the nerve root for the lower section. Far lateral herniations do just the opposite, they hit the nerve root for the upper section. Herniations to the center will produce a lesion to a section below the IV disc segment. In this case, L5/S1, central will affect S2 and below possibly.

Thanks!
I found this, similar to your explanation.
understanding whether the disc herniations will compress the nerve root
above the level of the disc (e.g. the exiting nerve root), or below (e.g. the traversing
nerve root), is essential. The location of herniation is described as either: (Figure 3)
1. Central (red) – Causes compression of the traversing root. Although
very rare, if the disc herniation is large enough it can cause cauda equina
syndrome. If the herniation is at the level of the conus this can lead to conus
medullaris syndrome.
2. Posterolateral (orange)-- Most common location as it takes advantage of
he weakness between the annulus and the lateral margin of the posterior
longitudinal ligament. Typically causes compression of the traversing root.
If sequestered superiorly (dotted arrow), the disc can compress the exiting
nerve root. The superiorly sequestered disc may also compress at the axilla
of the exiting nerve root above and the traversing nerve root of the level
below (solid arrow), causing a double-root injury.
3. Far lateral (yellow) – Disc herniates into the foramen or even further lateral,
causing compression of the exiting nerve root.

Figure 3 - Anatomy of lumbar disc herniation and nerve root impingement