Intro to Spinal Cord Anatomy

Welcome back to the Neurotransmitters! Today we are talking about spinal cord anatomy. When should you be thinking about a myelopathy (or spinal cord lesion)? Isn't spinal cord anatomy complicated? Join in as we take a lean and practical look at what you need to know to localize clinically!

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Transcript

Audio file 

Spinal Cord.mp3 

00:00:01 

Hello and welcome back to the neurotransmitters, a podcast about everything related to clinical neurology with the goal of reducing your neurophobia. 

I'm your host doctor Michael Kentris. 

Thank you again for joining me today. We are continuing our March through the neuro access, starting at the brain and heading South. And today we are in the spinal cord. 

So when does one consider a myelopathy or a spinal cord localization? There are some key clinical features that can guide you in that direction. A myelopathy shouldn't be causing any abnormalities of cognition, cranial neuropathy, et cetera. So if there's something going on in the head region, we should be revising our opinion. 

There are etiologies that can cause myelopathy. As well as cognitive problems and so on and so forth, but we're going to be focusing on primary myelopathic localizations at this particular junction. So once we've excluded an intracranial localization, we are left with a few key signs that would point us towards a myelopathy versus something more distal down into the peripheral nerves. 

00:01:07 

So some of the things that really attract my eye are signs of upper motor neuron involvement. In particular, I'm looking for things like increased tone, hyperreflexia, abnormal motor reflexes, like a Babinski being present, and the second piece is some sort of crossed sign. 

In particular, if we see motor and vibratory sense being affected, on one side and pain or temperature sense being affected on the contralateral side, that is very suspicious for something going on in the spinal cord. 

00:01:36 

Now let's talk a little bit about spinal cord anatomy and how its structure leads us to these clinical signs and points us in this direction to come to a confident localization. So the spinal cord essentially runs from the lower edge of the brainstem down into the lumbar spine, the L1-2 region. Like many parts of the nervous system, there are a lot of things happening in the spinal cord, but from a clinical assessment perspective, I think there are just a few aspects that will get you 90% of the way there, and that is looking at the tracts. 

00:02:09 

So there are two components to this. One which tract is involved and we'll go through those in a minute. And two, where in the spinal cord are those tracks located? 

00:02:19 

So the three main tracks that we're really looking at are the spinothalamic tract that is responsible for pain, temperature, crude touch sensation. The dorsal columns, which are responsible for proprioception and vibratory sense. And last but not least, is the corticospinal tract, responsible for motor signals from the brain getting to the rest of the body. 

A lot of the clinical interpretation of the signs related to a myelopathy are related to where in the spinal cord. These different tracks run relative to one another, so I think one of the first things to think about is the decapitation or where do the fibers cross? So for the corticospinal and the dorsal columns, these are going to decussate up in the brain stem in the medulla, and this is why weakness, vibratory sense, and proprioception sense will often be ipsilateral to the lesion in myelopathy. 

00:03:09 

The spinothalamic tract is the odd one out as it decussates in the cord usually a couple levels above its point of origin into the spinal cord. So this means that with unilateral spinal cord lesions, the pain and temperature loss will usually be contralateral to the side that is affected. 

00:03:26 

The classic name that you may have heard for this pattern of symptoms is called Brown-Sequard Syndrome, or Hemicord syndrome, where you have ipsilateral weakness, loss of vibratory and proprioception sense on the same side of the lesion and contralateral loss of pain and temperature sense. 

So you may hear people in clinical practice say, “Does the patient have a level or a spinal level,” and what they're referring to is where is the lowest level down where we have the weakness, the numbness, the sensory disturbances, etcetera. And ideally we should be able to put those all together into one place for a proper localization. 

00:04:02 

Another key thing to remember when we're considering localization in the spinal cord, is that if the arms and the legs are involved, we are usually looking at the cervical spinal cord, particularly if weakness is involved, the lowest level in the arms and hands is usually going to be T1 and this is similar for sensory abnormalities as well. So anything that localizes to the myotome or the dermatome above T1 should be involving the cervical spine if we're considering a myelopathy. 

If we have a sensory level to reduce sensation to pinprick across the torso, say, somewhere on the chest, well, then, we're really looking more in the thoracic spine at this point in time, and if there is weakness, it should not involve the arms. 

00:04:46 

Theoretically, if it is in the mid to lower thoracic spine, I will say, anecdotally, that you will sometimes have an exam where you're like, oh, this very clearly localizes to C7 or T2 and you only get the MRI of the cervical or the thoracic spine, and then you find, dang, I just missed the lesion or you've only caught a piece of it, and so then you have to send the patient back for repeat imaging of the piece that you left off. So things that are right on that Cervicothoracic border, I would usually get pictures of both the cervical and thoracic spine, personally speaking 

00:05:20  

Now we've been talking a little bit about the vertical in terms of the spinal cord, but let's, talk a little bit about the cross-sectional anatomy for just a moment. This will be important for conceptualizing the other patterns of myelopathy that we often see in clinical practice. So the lateral corticospinal tracts as the name would suggest, are mostly lateral, little posterior. The dorsal columns are, as you might guess, dorsal or posterior and medial and the anterior lateral or spinothalamic tracts are anterior and lateral. Again, it is nice when things are named in a somewhat descriptive fashion that gives us Useful information just from the name. 

00:05:53 

Now, in addition to these tracks, locations within the spinal cord themselves, they also individually have somatotopic organization. That is to say there is a Pattern of, you know, cervical, thoracic, lumbar, sacral from medial to lateral for each one of these tracts. So for the corticospinal and spinothalamic tracts, cervical is more medial, sacral is more lateral and just because nothing in life can ever be too easy, the dorsal columns are the opposite of that. So the sacral tracts are more medial and the cervical tracts are more lateral got all that? 

00:06:31 

No, let's say it one more time. Corticospinal and spinothalamic tracts, cervical-medial sacral-lateral dorsal columns, sacra-medial, cervical-lateral. Repetition is the mother of all learning, as they say. 

00:06:44 

So let's move on to some clinical syndromes with this knowledge in hand, these spinal cord syndrome, whose identification depends most on knowing this information, is central cord syndrome. 

00:06:55 

Now, central Cord syndrome is most commonly going to be related to something that is causing dilation of the central canal. The most common thing would likely be a syrinx because the central canal is right next door to where the spinothalamic fibers cross, particularly the ones going into the cervical cord. 

This leads to abnormal pain and temperature sensation, primarily in the upper extremities and upper torso. 

00:07:19 

Another spinal cord syndrome to be aware of is anterior cord syndrome, and this is going to involve the tracks in the anterior part of the spinal cord. Which are going to be the spinothalamic and corticospinal tracts primarily because this is often bilateral below the level of the lesion. We are going to see weakness and impaired pain and temperature sensation, but intact proprioception and vibratory sense. 

00:07:42 

Anterior cord syndrome, in particular, is often ischemic in nature, and this has to do with the vascular supply to the anterior spinal cord, the anterior spinal artery tends to receive feeders from different radicular arteries. The most prominent of these is known as the artery of Adamkiewicz, usually found in the lower thoracic area around T9-T10. So in the setting of big drops in blood pressure in someone who maybe has some atherosclerotic disease in that artery or in people who have an abdominal aortic aneurysm or around that level who have to go into. These are all reasons why that artery may become occluded, leading to an acute spinal cord infarction presenting with that anterior cord syndrome, potentially  

00:08:34  

The last spinal cord syndrome that I wanted to mention today is subacute combined degeneration, and this one is a mixture of the dorsal columns and the corticospinal tracts. 

This can be due to several different causes , a classic one being a B12 deficiency, which could be from people who are malnourished from a history of gastric bypass who maybe had a superimposed gastrointestinal illness. 

00:08:45 

You can see similar things with copper deficiency as well, and you can also see similar patterns with things like HIV. One specific pattern to bring up with these entities, particularly B12 and copper deficiency, is a mild low neuropathy and this is what it sounds like. It's a mixture of myelopathy and neuropathy. So you can have mixed upper and lower motor neuron signs, and we're going to talk more. 

00:09:08 

About the approach to weakness in a later episode, but briefly upper motor neuron signs are going to be spasticity, hyperreflexia, and lower motor neuron signs would be more expected to be decreased tone areflexia and potentially fasciculations and atrophy depending on the timeline. 

00:09:25 

So in summary, if you keep your 3 tracks in mind, your corticospinal, spinothalamic and dorsal columns, and their relative relation to one another in mind, you can localize pretty well in the spinal cord and keeping in mind the patterns of different spinal cord syndromes, these localizations all have tendencies to be associated with different pathologies, some more or less likely than others in different clinical contexts. 

00:09:47 

So again, putting the physical exam findings that you see in the context of your patients history is always of the utmost importance. Something occurring over the span of minutes is going to have a much different differential diagnosis than something occurring over the span of months or years. 

00:10:04 

Thank you again for joining me today as we build up these fundamentals of neuroanatomy and clinical neurology and help reduce your neophobia make you into a better clinician, better able to diagnose and treat your patients. I know you have a lot of options out there for where you get your learning, and I appreciate that you spent the time with me today. If you enjoyed this podcast, please consider leaving a 5 star review on Apple, Spotify, or wherever you get your podcast. This really helps with getting the show noticed. 

00:10:29 

And do subscribe for future episodes. If you have any questions, show suggestions, or just want to say hey, feel free to reach out to me on Twitter @DrKentris, that's doctor Kentris. You can also reach me by e-mail at theneurotransmitterspodcast@gmail.com. I hope you have a great day, and keep on localizing out there, we'll see you next time.