Lumbar Paraspinal Denervation. Lumbar MRIs are likely the most common MRIs people would report but to see acute denervation changes from disc herniation is uncommon So what does denervation look like?
Denervation MRI Findings:
In the acute to subacute stage there is an ” oedema” type pattern to the signal with increased T2 signal, isointense T1 signal and enhancement of the affected muscle/s post contrast. Muscle atrophy and fatty infiltration is progressive and as this case shows, can be quite significant even within 2 weeks.
In the chronic stage the “oedema” type signal resolves and there is muscle atrophy and fatty infiltration.
This man presented with sciatica after coughing and the scan was done about two weeks after onset of symptoms.
Image above: Compare both sides to appreciate the loss of volume, increased T2 signal and fatty change on the right posterior paraspinal muscles. Easy to not notice if we concentrate just on the canal.
Image above T2 scans: Compare both sides to appreciate the loss of volume, particularly of quadratus lumborum ( anterior arrow) increased T2 signal and fatty change on the right posterior paraspinal muscles.
So in this patient 2 weeks after the acute disc prolapse we see muscle oedema, loss of volume with fatty infiltration and enhancement of the right posterior paraspinal muscles and the right iliacus which has a supply from L3. The T2 hyperintensity is easy to pass by if you are not looking carefully and would be more obvious if a T2 fat sat or STIR scan was performed. On the post contrast scans though the signal abnormality is much easier to appreciate.
As lumbar imaging is mostly without contrast and without a T2 FS or STIR sequence its quite easy to not notice denervation changes if we concentrate just on the canal when reporting.