Aim from post-operative spine aassessment by MRI or CT

Our aim is to assess the following

1-Site of surgery.

-Take care of the level of laminectomy, if the operation is done at the level of L4-L5, so the lamina removed is of L4, if you are not sure, just say spinal laminectomy at level of L4-L5 disc.

2-Degree of thecal decompression(Do not write this in your report).

-Types of operation:

*Spinal laminectomy resulting in removal of both laminae and spinous process resulting in decompression of the thecal sac posteriorly.

*Spinal hemi laminectomy resulting in removal of one lamina only leaving other one and spinous process in situ.

*Laminar fenestration in which they produce a hole in the lamina.

Recently, they do not remove laminae, producing a small groove in one of them, introducing medical endoscopy and doing the operation, this is the most safe type of operation resulting in almost no instability.

3-Post-operative complication to differentiate between post-operative scar or recurrent disc lesions.

4-Post-operative complications (more clear with MRI than CT due to hypo intensity of the bones):

-Scar tissue versus recurrent disc.

 To differentiate between both, use contrast injection, in case of scar tissue it will take enhancement, while in case of recurrent disc, it will not take.
In T1 image, you will see a hypo intense mass in the epi dural space and peri neural area(space around nerve roots) compressing one root, if you give contrast, this mass will be enhanced if it is scar tissue and vice versa if it is recurrent disc.
Do not injects contrast within the first two months after operation(due to effect of the operation itself), after this period you can inject contrast and the coming 15 years.


-Disc space infection.

*Discitis appears as hypo intense lesion affecting disc material in T1 and hyper intense in T2 and if you give contrast, the disc material will enhance.
*Usually is associated with infection of the vertebral body above and below resulting in what is known bone marrow edema which take contrast.
*How to differentiate between discitis and degenerative changes
Both gives narrowed disc space.
To differentiate gives contrast, if it takes it, so it is discitis and not degenerative changes.
Another issue is looking in T2 image, you will find the disc material in case of discitis hyper intense due to water content resulting from infection, while in case of degenerative changes, it will appears hypo intense.
 
-Arachnoiditis (adhesion between cauda equina nerve roots or adhesion between nerve roots and thecal sac ).
In the past, myodil injection was one of the most common cause leading to arachnoiditis.
Other causes of arachnoiditis are operations and viruses.
It is better to use T2 image for evaluation of arachnoiditis, as you can see the nerve roots hypo intense within hyper intense CSF.
We have two types of arachnoiditis, the first one known as pseudo cord sign in which the nerve roots are attached together simulating a cord, the second  type is known as empty thecal sac where nerve roots are attached to thecal sac resulting in that the thecal sac appears empty.