Disc bulge vs. herniation: what do those words mean on my spine MRI?
Short answer: both describe a spinal disc pushing beyond its normal boundary — they differ in how much of the disc is involved and how it's pushing out. A bulge is a broad, generalized outward spreading (like a tire that's a little low). A herniation is a more focused displacement where inner disc material pushes through or against the outer layer (like toothpaste pressing against the tube).
What it usually means on your report
Radiologists follow strict guidelines: if the displaced disc material involves 25% or less of the disc's circumference, it's called a herniation; if it involves more than 25%, it's a bulge. Herniations are further described as protrusions, extrusions, or sequestrations depending on how far the inner material has pushed through the outer ring.
Here's the part that surprises most people: bulges involve more of the disc but are less likely to cause pain — they're usually just age-related wear and tear. Herniations are more likely to irritate a nearby nerve (causing leg or arm symptoms like sciatica), but many herniations cause no symptoms either. The words describe disc shape, not pain level.
What it does NOT mean
- It does not mean your disc "slipped" out of place. Discs don't slip — they change shape.
- A bulge does not mean you need treatment. Most bulges are incidental findings in people without symptoms.
- A herniation does not automatically mean surgery. Many herniations improve with time and conservative care — that decision depends on your symptoms and exam, not the MRI alone.
When to ask your clinician
- "Is this bulge/herniation pressing on a nerve, and does that match my symptoms?"
- "Is this finding new compared to any prior imaging?"
- "What should I watch for that would mean I need to come back promptly?"
This is a plain-English explanation of terms, not medical advice. Talk to your clinician about what your results mean for you.