Brief Answer:
Typically considered insignificant finding

Detailed Answer:
"Flattening of the thecal sac" in the broadest sense of the statement generally refers to a compression of a sac technically called "the meninges." If there is "flattening" seen on an MRI image the implication is that SOMETHING is pressing on this sac from the other side. That SOMETHING can be a lot of things but mostly likely turns out to be either a herniated/bulging disk or from calcifications or bony spurs of the spinal column which can then NARROW the space through which the sac passes. Inside the sac, of course, is the spinal cord and the nerve roots which ultimately are what the radiologist looks at to tell if there is any reason to suspect compression at the level of these roots which could then, more easily explain the presence of pain.

It is commonly seen in patients just due to the aging process and onset of arthritic changes which we all begin experiencing after about age 40-45 whether we have pain in the neck or back or not. Flattening of the thecal sac is often seen in AYMPTOMATIC patients (patients who are otherwise normal and not complaining of anything).

Usually, when there is THECAL SAC compression or flattening without involvement of the nerve roots at that level then, the finding is merely noted for the sake of completeness and nothing more can be said relative to any symptoms of pain, numbness, tingling, etc. Compression or flattening can be mild, moderate, or more severe in which case the reader usually starts calling out things like NERVE ROOT COMPRESSION or herniation causing thecal sac deformities, etc. etc.

Therefore, in your case and to once again come back to your question as you've asked it...the simple phrase "flattening of the ventral thecal sac" in and of itself is considered insignificant in most cases or at worst, of "unknown clinical significance" which means that more information is needed to make the call clinically as to whether or not that is the explanation of any pain or discomfort you may be having in your neck.

The other statement you just added in the last few minutes of a central disc protrusion with posterior spurring simply underscores my point regarding ARTHRITIC CHANGES which are commonplace and do not necessarily help us always identify the origin or cause to pain and other symptoms but they simply let us know that "arthritis" is present in that joint or at that level. Central disc protrusions by the way, are almost never believed to be bad players when it comes to sac or nerve root compressions since nerve roots come out from the LATERAL RECESS areas. A CENTRAL PROTRUSION (right down the center or in the middle) would anatomically MISS the nerve roots and therefore, not be considered as much of a risk to pain or discomfort that were felt either in the neck or radiating down one arm or another.

Hope that helps.

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