In short
Most of the alarming words in a spine MRI report describe normal ageing. Six in ten pain-free 50-year-olds have a disc bulge — what decides treatment is your examination and your symptoms, not the adjectives on the scan.
Emergency if: Go to an emergency department now if you cannot pass urine or lose the feeling of a full bladder, leak urine or stool, become numb around the genitals, buttocks or inner thighs, or develop weakness in both legs. Cauda equina compression must be treated within hours. The same urgency applies to weakness or numbness spreading in both arms or both legs, or a band of numbness around the chest or abdomen, especially with a history of cancer, since cord compression is also measured in hours.
On your report
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01
Bulge, protrusion, extrusion — how they differ
A disc is a cushion with a tough outer ring and a softer centre. The standard radiology nomenclature separates findings by how much of the way around the disc the tissue extends, and by its shape. A bulge is generalised: disc tissue extends beyond the edge of the vertebral rim around most of the circumference — definitions put the cut-off at more than a quarter, and in common radiological use more than half — usually only a short distance out. A herniation is focal, involving less than a quarter of the circumference, or is called broad-based when it involves a quarter to a half.
Within herniation, protrusion and extrusion are distinguished by shape rather than by size. In a protrusion the widest part of the displaced material is no wider than its base, so it sits like a small dome. In an extrusion the displaced material is wider than the neck connecting it to the disc, or has lost continuity with the disc space altogether. A sequestration, or free fragment, is an extrusion that has separated completely from the parent disc.
The clinically useful point is that a bulge is largely a degenerative and age-related finding, common enough to be considered a normal variant at the lowest lumbar level, whereas an extrusion is a more focal, more recent event and is more likely to correspond to a symptom. Even so, the shape word is not a severity score. Whether it matters depends on where it points and what it touches.
02
"Thecal sac indentation": what it means
The thecal sac is the sleeve of tough membrane containing the spinal fluid and, in the lower back, the bundle of nerve roots called the cauda equina. It has a certain amount of give. "Indentation" or "effacement of the thecal sac" means the disc is pressing on that sleeve and flattening it slightly. It is one of the most alarming phrases in a report, and one of the least specific.
What a careful report goes on to say is far more informative: whether the canal is narrowed and by how much, and whether any nerve root is contacted, displaced or compressed. There is no single agreed standard behind those words, but one widely used scheme grades central narrowing as mild when less than a third of the canal is lost, moderate between a third and two-thirds, and severe above two-thirds. A mild indentation with no nerve root contact is a description of anatomy, not of injury.
There is also a straightforward reason indentation is so common: the sac sits directly behind the disc, so almost any posterior bulge touches it. Read the sentence that follows the phrase. If it says the nerve roots are not displaced and the canal is capacious, the indentation is a footnote. If it names a specific nerve root as compressed, and that matches the leg where your pain and numbness are, that is the sentence that matters.
03
PIVD versus cervical spondylosis
PIVD stands for prolapsed intervertebral disc — an older but still widely used label for a disc herniation, most often in the lower back. It describes a focal event at one level: the softer inner material pushing through the outer ring, often producing pain that runs down one leg in a nerve's distribution, sometimes with numbness or weakness in a matching pattern. It is a single-level problem with a single-level symptom.
Cervical spondylosis is a different kind of statement. It is the general, age-related wear of the neck — discs losing height and water content, facet joints thickening, small bony spurs forming — usually across several levels at once. It appears on the report of most people past middle age, and by itself describes ageing rather than disease. It becomes clinically important only when the narrowing it causes actually compresses a nerve root or the spinal cord.
The distinction changes what the report is telling you. A PIVD with matching leg symptoms is a specific finding to correlate with the examination. Cervical spondylosis without neurological findings is background. Symptoms that would move cervical spondylosis into the foreground are hand clumsiness, worsening balance or unsteady walking, and arm weakness — signs that the cord itself may be involved, which needs a proper neurological assessment promptly rather than reassurance, because a compressed cord tends not to recover what it has already lost.
04
Why pain-free people have bulges too
This is the single most useful fact for anyone holding a frightening report. A systematic review of imaging in people with no back pain at all found disc degeneration in 37 percent of 20-year-olds, rising to 80 percent by age 50 and 96 percent by 80. Disc bulges followed the same pattern: 30 percent at age 20, 50 percent at 40, 60 percent at 50, 69 percent at 60 and 84 percent at 80 — all in people who had no symptoms.
Disc protrusions were present in 29 percent of pain-free 20-year-olds and 43 percent at 80. Annular fissures — the tears in the outer ring that reports often describe in worrying detail — were seen in about one in five pain-free 20-year-olds, rising only to just under three in ten by 80. Facet joint degeneration climbed from 4 percent at 20 to 83 percent at 80. The authors concluded that these findings are likely part of normal ageing and often unassociated with pain.
That does not mean your pain is imaginary. It means the scan cannot, on its own, tell which finding is causing it, because the same findings sit silently in the person next to you. This is why clinical correlation is not a formality: a finding counts when its level and side match the pattern of your symptoms and your examination. When they do not match, the finding is probably a coincidence.
05
Why a bad-looking report still usually doesn't mean surgery
Most disc herniations improve without an operation. Reviews of the natural history report that around 90 percent settle within about six weeks of conservative management, with pain persisting at a year in roughly 30 percent — and even then, persistent pain is not automatically a surgical problem. Herniated material also tends to shrink over months as the body reabsorbs it, which is part of why symptoms often improve while the scan still looks abnormal.
Guidelines are correspondingly cautious about imaging in the first place. National guidance advises not routinely offering imaging for low back pain with or without sciatica in a non-specialist setting, and considering it in specialist settings only if the result is likely to change management. Patients being referred for a specialist opinion are told they may not need a scan at all. The reason is precisely the prevalence data above: a scan taken early usually finds something, and that something usually is not the answer.
Surgery is considered when the picture lines up. Spinal decompression is recommended for consideration in sciatica when non-surgical treatment has not improved pain or function and the imaging findings are consistent with the symptoms — both conditions, not either one. Notably, guidance also states that a person's weight, smoking status or psychological distress should not by themselves influence the decision to refer for a surgical opinion.
06
Red flags that need urgent care
Cauda equina syndrome is the emergency to know. It happens when a large central herniation compresses the whole bundle of nerve roots in the lower spinal canal, and the damage becomes permanent if it is not decompressed quickly. The warning signs are new difficulty passing urine or a loss of the sensation of a full bladder, new incontinence of urine or stool, numbness in the saddle area — the buttocks, genitals and inner thighs — new sexual numbness, and weakness in both legs.
These symptoms often develop over hours to days and may worsen fast. The right response is emergency care immediately, not an appointment, not a call the next morning, and not waiting for an MRI slot. Anyone with back pain or sciatica who develops bladder or bowel disturbance, saddle numbness or rapidly progressing leg weakness should be assessed in an emergency department the same day.
Other patterns deserve prompt, if not emergency, assessment: progressive weakness in one leg such as a foot that starts dragging, back pain with fever or with a recent infection, back pain after significant trauma, unexplained weight loss, a history of cancer, or new severe pain in someone taking long-term steroids. None of these are common, but they are the situations where imaging genuinely changes management.
07
Physiotherapy, injections and surgery: what the evidence says
Exercise is the backbone. Guidance recommends an exercise programme as the main component of non-invasive treatment, chosen to fit the person — stretching, strengthening, aerobic work, yoga or tai chi, in a group setting where possible — alongside advice to stay active and continue normal activities rather than resting. Manual therapy such as manipulation, mobilisation or massage is recommended only as part of a package that includes exercise, not on its own.
Several popular options are specifically not recommended: traction, belts and corsets, foot orthotics and rocker-sole shoes, and acupuncture. On medicines, guidance advises against paracetamol alone and against opioids for chronic low back pain. Epidural injection of local anaesthetic and steroid is a considered option for acute and severe sciatica, not a routine treatment for ordinary back pain. Radiofrequency denervation is reserved for carefully selected people with moderate-to-severe pain thought to arise from the facet joints, and only after a positive diagnostic block.
Surgery sits at the end of that sequence, for sciatica that has not responded to non-surgical treatment and where the scan matches the symptoms — and immediately, ahead of everything else, for cauda equina syndrome or progressive neurological loss. Operating earlier tends to relieve leg pain faster, but the difference between surgical and non-surgical outcomes narrows over a year or two for most people, which is why the decision is usually about how much longer you are willing to wait rather than about what the report looks like.
08
Should the MRI be repeated?
Usually not, and rarely for reassurance. Degenerative findings change slowly and do not track symptoms closely, so a repeat scan six months later commonly shows the same words in a slightly different order while you feel considerably better or worse. Since imaging in a non-specialist setting is not routinely recommended even the first time, repeating it without a new question rarely earns its place.
There are clear reasons to repeat it. New or worsening neurological signs — weakness, a dropped foot, new numbness in a new distribution — need re-imaging, and any suspicion of cauda equina needs it urgently. It is also repeated when surgery is being planned and the previous scan is old, when infection or a tumour is suspected, or after an operation when symptoms return in a way that suggests a new problem rather than the old one.
If the honest reason for wanting another scan is that the pain has not gone, the more productive request is a proper reassessment: an examination to see whether anything neurological has changed, a review of what has actually been tried and for how long, and a plan with a defined review point. A second report full of the same degenerative language tends to increase worry without changing a single decision.
How urgently to act on spine symptoms
Routine — see a doctor
Back pain or sciatica with no neurological warning signs: stay active, start a structured exercise programme, and arrange review in about six weeks if it has not settled.
Same-day — call promptly
New or worsening weakness in a leg, a foot that drags, back pain with fever, back pain after significant injury, new hand clumsiness, dropping objects or an unsteady walk alongside neck symptoms, or new severe pain with a history of cancer or long-term steroids — get assessed today.
Emergency — act now
Go to an emergency department now if you cannot pass urine or lose the feeling of a full bladder, leak urine or stool, become numb around the genitals, buttocks or inner thighs, or develop weakness in both legs. Cauda equina compression must be treated within hours. The same urgency applies to weakness or numbness spreading in both arms or both legs, or a band of numbness around the chest or abdomen, especially with a history of cancer, since cord compression is also measured in hours.
Values mentioned in this story
Each one opens a visual guide with its normal range and what moves it — upload a report and we place your own numbers on the same scale.
Sources
- NICE NG59: low back pain and sciatica in over 16s — recommendationsnice.org.uk
- NICE NG59 full guideline, NCBI Bookshelfncbi.nlm.nih.gov
- Brinjikji 2015: spine degeneration on imaging in asymptomatic populationspmc.ncbi.nlm.nih.gov
- Radsource — lumbar disc nomenclature and reporting termsradsource.us
- Disc Herniation — StatPearls, NCBI Bookshelfncbi.nlm.nih.gov
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