Does size on the MRI matter?

How does the size of the disc protrusion on the MRI correlate to the amount of disc material removed ?

To be honest, I’m not sure if there is a way to calculate a figure in terms of weight or volume, but there is one thing I can tell you from a subjective perspective. The amount of disc removed during a discectomy often seems larger than what I would expect from what I see on the MRI. I’m not sure why this is, but perhaps the disc fragment seen on the MRI is maximally compressed compared to its size after removal from the body where there is nothing but atmospheric pressure affecting its size.

Here is an example that I removed recently. The MRI shows a fairly large protrusion at L5-S1 occupying the lateral recess with S1 nerve root compression and severe symptoms of pain. The interlaminar approach was chosen to adequately decompress the lateral recess in this male with elevated iliac crests typical for a male patient. 

Of course I was expecting a good size fragment, but nothing like this amount of disc (This qualifies as a Moby Disc). In all fairness, about 30-45% of this material came out of the inside of the disc space so you can see that it’s really worthwhile to spend time reaching around inside the disc space to look for fragments that could reherniate. 

For some reason, when I look at the MRIs, I never expect this much disc to pop out. The reason I mention this is that it’s good to know about how much disc you  expect to remove when you look at the MRI. Whether you do a discectomy with the transforaminal or interlaminar approach, it’s good to lay out the disc fragments on a sponge or towel to see how much material you are removing. If it’s not enough material, keep probing around till you mobilize the fragment(s)  and it pops out. 

Keep track in your mind how big the protrusion looks on the MRI and how much disc material you see on your sponge. For some reason, I’m always a little surprised to see more disc material than I think I will.

Onward and Upward

Dr. Tony Mork

Endoscopic Spine Specialist