Basics of lumbar MRIs: A Thread
Do you want to know what you’re looking at on a lumbar MRI?
Being a Physiotherapist I have to deal with a number of patients coming with the complaint of low back pain and most of the time they already have MRI SCAN. So for the Purpose of Education images are taken from the Google.
We’ll look at some images & try and figure out what’s ‘normal’ in the MRI
Disclaimer: As a Spinal Physiotherapist I spend a lot of time staring at MRIs but I’m not a radiologist. So test what I say & challenge me (kindly!) if you think I’ve got it wrong.
Let’s look at a ‘normal’ MRI first...
MRIs produce images based on the prevalence of hydrogen in the tissue. Water and fat are abundant in hydrogen so show as ‘high signal’ (ie, whitesih) on a ‘T2 weighted’ image.
On the T2 weighted image below, can you identify the cerebrospinal fluid & the subcutaneous fat?
See below to check if you got it right.
Can you see the dark strands within the CSF? These are the nerve roots which make up the cauda equina. Remember the pt is supine in the scanner, hence the nerve roots lying to the back of the spinal canal.
So because water shows as high signal on T2 images, a healthy disc will present with higher signal in the nucleus than the annulus as the latter has a lower water content.
We’ll come back to the concept of a ‘healthy disc’
Sometimes, we might see a high signal area on an T2 weighted MRI and it is unclear whether it is fat or water. ‘T1 weighted’ images can be used to work it out.
You can see areas with high water content (CSF/nucleus) are dark on the T1 image below. Fat is still white.
Can you work out whether the circled area is mostly fat or water? Left image is T2 weighted (fat and fluid are bright). Right image is T1 weighted (fat is bright, fluid is dark).
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| FAT IN THE MRI |
answer: mostly fat.
this is a haemangioma. these are benign and usually asymptomatic. further reading here:
so we’re starting to know what we’re looking at… but what is a ‘normal mri’ or ‘healthy disc’?
This well-known study looked at MRI findings in painfree populations.
Circled examples suggest that 80% of painfree people in their 50s have ‘disc degeneration’ & 40% of painfree people in their 30s have a disc bulg
So maybe MRIs aren’t helpful in identifying pain sources…?
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| MRI IN NORMAL POPULATION IS NOT NORMAL |
This well-known study looked at MRI findings in painfree populations.
Circled examples suggest that 80% of painfree people in their 50s have ‘disc degeneration’ & 40% of painfree people in their 30s have a disc bulge.
So maybe MRIs aren’t helpful in identifying pain sources…?
Or perhaps they are. This lesser known paper by the same authors did find correlation between degenerative discs on MRI and back pain.
The key is to consider MRI findings in context of symptoms & physical assessment.
It’s also important to interpret the images & the report together. These are both disc bulges – If I had to guess which one was causing symptoms, I know which one I’d pick!
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| MRI SCAN SHOWING DISC EXTRUSION AND COMPRESSION OF THE SPINAL NERVES |
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MRI SCAN SHOWING DISC BUILDING AT LUMBAR SPINE
Like a lot of things in healthcare, I think we have to take the research with a pinch of salt & consider the person in front of us on a case by case basis.
Know the research and consider the person.
