Thecal sac
Read Your Scan Editorial Team·Last updated
Written from published radiology references and reviewed for plain language. Not written or signed by a physician, and not a diagnosis. How we write these pages →
In plain language
The fluid-filled sheath that surrounds the spinal nerves in the canal. Reports often describe whether it is indented.
Where you’ll see this
This wording turns up on Lumbar Spine MRI reports — MRI imaging of the spine. A lumbar (low-back) MRI shows the vertebrae, the cushioning discs between them, the spinal canal, and the nerves that travel to the legs. Doctors order it for low-back pain, sciatica, leg numbness or weakness, or to plan care. Importantly, many of the changes it describes are extremely common and are seen in people with no pain at all — so the report is read together with how you actually feel.
Questions worth asking your doctor
- Do the findings on the MRI match where I actually feel pain or symptoms?
- Are these changes common for my age, or is anything unusual?
- What are my non-surgical options, such as physical therapy?
- Are there any signs that would mean I should seek care sooner?
- Do I need any follow-up imaging, and when?
Other words on the same report
See this word on your own scan
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Read Your Scan is informational only — not a medical diagnosis, and not a substitute for a licensed radiologist or your doctor. If you have urgent symptoms, seek care.