Is a 3 MM Disc Bulge the Same thing as a Herniated Disc?

Definition

Area of a bulging disc
Area of a bulging disc. decade3rd

A bulging disc and a herniated disc are often related, but they are not the same thing.  Here's how:

A bulging disc occurs when the nucleus pulposus — the soft, jelly-like center of the disc that gives the disc shock-absorbing capacities — extends beyond its normal position inside the disc structure, yet still stays contained within the annulus fibrosus. (The annulus fibrosus is the tough outer covering of the disc, that, when healthy and without tears, keeps the  nucleus pulposus contained.)

In a healthy intervertebral disc, the edge (i.e., the annulus fibrosus) tends to correspond with the edge of the vertebra to which it is attached. Bulging discs generally don’t go any further than 3 mm out from the edge of the spinal bone.  They are not necessarily painful.

That said, a bulging disc can be the first stage of disc disease.  Or, depending on the individual, it may simply be a variation of anatomy (and not a disease at all.)

Herniated Disc

A herniated disc, on the other hand, occurs when tear or ruptures in the annulus allow ​some of the nucleus pulposus to exit the disc. Pain and other symptoms from a herniated disc are usually due to the escaped nucleus pulposus coming into contact with a spinal nerve root.  

While herniated disc is generally accompanied by symptoms, theoretically speaking at least, this doesn't always happen. If the exiting nucleus pulposus material doesn't land on nerve tissue, then irritation related to its contact with, or pressure on, that nerve isn't elicited, and the common symptoms associated with this injury do not occur.

Bulging Disc is Not an Official Diagnosis

Also called prolapsed discs, bulging disc is not technically a diagnosis, but rather a descriptive term. It refers to one of several forms that degenerative changes in the intervertebral discs may take.  

But herniated disc is a diagnostic term, according to American Society of Neuroradiology, the American Society of Spine Radiology, the North American Spine Society in their PowerPoint presentation entitled, "Nomenclature and Classification of Lumbar Disc Pathology," and published on the American Society of Neuroradiology website.

Authors of a 2011 study published in the December issue of Global Spine Journal, say that a number of things — from the height of your disc to the degree of mobility between the spinal bones above and below — factor into the migration of a bulging disc.  Migration is a movement of the exited disc material away from the tear or other opening in the annulus fibrosus through which the material exits. 

Regardless of the variables, one thing the authors are sure of is that the amount of disc migration is associated with the degree of degenerative changes present in the spine.  Such changes may or may not cause discogenic pain.

Sources:

American Society of Neuroradiology, American Society of Spine Radiology, North American Spine Society. Nomenclature and Classification of Lumbar Disc Pathology. AJNR website. Accessed Jan 2016.

Hu, J., Morishita, Y., Montgomery, Scott R., Hymanson, H., Taghavi, C., Do, D., Wang, J. Kinematic Evaluation of Association between Disc Bulge Migration, Lumbar Segmental Mobility, and Disc Degeneration in the Lumbar Spine Using Positional Magnetic Resonance Imaging. Global Spine J. Dec 2011. Accessed Jan 2016.

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