Disc Herniation, Protrusion, Or Extrusion: Appropriate Diagnosis and Treatment
MRI and CT reports contain some medical terminology that can be confusing to most patients. Obviously, the readings from these imaging studies are translated into medical terminology which is intended for the eyes of medical professionals. I like to share these reports with most of my patients and consequently, many have questions about the terms that are used to describe their clinical findings. The purpose of this article is to help explain the terms used by physicians when diagnosing diseases and injury to the spine.
Each week, our radiologists look over hundreds of MRI or CT scan studies that have been performed for multiple diagnoses. Their job is to relay any pertinent information from the study that may relate to the patient’s diagnosis back to me, the spine specialist. It is important that the request for a particular study expresses the presumed information that should be gathered. For example: In a particular spine MRI scan, the spine specialist will request the study be examined for a potential cause of leg pain, by describing the specific spinal area and side that correlates with the patient’s pain. The radiologist will examine the study, in general, for abnormalities, including misalignments of the spine, abnormal positions of nerves, bones or muscles, as well as unusual masses that may not have anything to do with the reason for the study. The radiologist will then look at the particular question being asked about the patient.
Most of our spine studies are done to evaluate pressure on a particular nerve root, i.e., a pinched nerve. The radiologist will describe the disc spaces at each level of the spine and use adjectives to describe the disc material that is not in its normal position. This is where radiologists will use the words protrusion, herniation or extrusion, which are listed here in relative degrees of abnormality, with protusion being the less abnormal and extrusion being more abnormal.
Discs in the spine are made of soft inner cartilaginous material (nucleus polposus) that is surrounded by a more dense ligamentous material (annulus). The annulus holds the nucleus in the center of the disc and allows the disc to move and cushion impacts applied to the bones. When the annulus starts to wear out, the nucleus material can begin to seep from its central position. As the disc material pushes back into the spine, the nerves can be contacted which can cause irritation and pain. The initial stage of disc degeneration allows the disc to lose its height. This decrease in height is mainly due to the loss of strength of the softer central nucleus cartilage in the disc space. The loss of strength allows the disc to collapse a bit, and forces the stronger annulus to bulge or “protrude”, similar to pressing on the top and bottom of a marshmallow allows the sides to bulge. If the annulus cracks and is unable to contain the central nucleus material, the nucleus will “herniate” through the annulus towards the nerve roots. So a pinched nerve can be caused by a “herniated disc”. If the nucleus continues to push through the annulus, it may become detached from the rest of the disc and is then termed “extruded” disc material.
Not all discs will follow the progressive nature that is explained here. Most disc problems will stabilize themselves in one of these three positions rather quickly from the initial injury. Having said this, the nerves that are near the disc may not be affected at all. The radiologist will often describe some measure of relative nerve pressure that is present on the images, but it is up to the spine surgeon to correlate the imaging studies with the patient’s symptoms. Fellowship-trained spine surgeons have the most advanced training for treating spinal disorders, and are able to discern the optimal treatment plan for patients from the mild muscular sprain to extensive bone and nerve reconstruction surgery.