How To Interpret Lumbar Spine MRIs
Orthopedic surgeons and other spine specialists have agreed that describing disc problems should be standardized. Several groups have proposed terms to describe disc pathology such as bulging, protrusion, extrusion, and sequestration. The American Society of Spine Radiology, American Society of Neuroradiology, and the Combined Task Force of the North American Spine Society are included in the groups advocating the standardization of terms. This study attempts to find out if these guidelines are being followed.
An ongoing clinical trial called SPORT (Spine Patient Outcomes Research Trial) provided the data for the study. Information was collected from 13 multidisciplinary teams treating spine patients in 11 states. MRIs used to make the diagnosis were read by a radiologist and the physician examining the patient. The results between these two groups were compared.
Most of the 396 patients enrolled in the study were working men with confirmed disc herniation at the L5-S1 level. The three areas or categories reviewed were spine level, morphology, and location. Although the majority of problems were in the L5-S1 area, some patients had changes at L2-3, L3-4, or L4-5 instead.
Morphology refers to the extent of disc damage. This ranges from mild bulge to protrusion (inner disc material pushing into the outer covering of the disc). More progressive damage leads to extrusion (inner disc material pushing through the outer disc covering) and finally, sequestration. Sequestration refers to disc fragment that breaks off and becomes a free-floating loose body in the spinal canal.
The location of most disc problems is usually posterolateral. This means the disc pushes back toward the spinal canal and off to one side or the other. Disc protrusion can be central (straight back), lateral (just to one side), or foraminal. Foraminal describes a disc that has moved into the space where the spinal nerve root exits the spine. Lateral and foraminal discs can occur on the right or left side.
MRIs were read by the spine specialist taking care of the patient (neurosurgeons, orthopedic surgeons, and nonoperative spine specialists). The same MRIs were also interpreted by radiologists. Each person looking at the MRIs filled out a form answering questions about the level, morphology, and location of the disc pathology. Then the answers were compared between the two groups.
For the most part, both groups agreed on the level of disc problems and the location within the level (central, right, left, posterolateral). In fact, agreement was calculated at 93.4 per cent. When there was disagreement about the vertebral level affected, it was usually because of a transitional vertebra confusing the numbering.
The biggest stumbling block was in describing the morphology (protrusion, extrusion, sequestration). Almost half the time, the radiologist didn't describe the morphology at all. In cases where both groups described the abnormal disc, the clinician (attending physician) was more likely to give it a higher grade indicating a more severe progression of disease than the radiologist.
For example, the examining physician would label the morphology as a disc extrusion when the radiologist would call it a protrusion. In cases where the radiologist didn't see a herniation, the morphology was labeled as a bulge. The attending physician would interpret that as a herniation.
A bulging disc describes the inner disc material (called the nucleus) as pressing against (but not into) the outer covering (called the annulus). With a herniation, the inner disc material has pushed into the outer covering. The reason for this difference in categorization may be because the clinicians were influenced by knowing the patient's symptoms. It's also possible that differences in training account for differences in the way clinicians interpret lumbar MRIs.
There were a few cases of human error where the reader labeled the side of involvement incorrectly (e.g., saying it was on the right when it was really on the left). This can affect treatment and result in a less successful response than hoped for -- sometimes even sending the patient to surgery when conservative care failed to resolve symptoms. Obviously operating on the wrong side would not be good either. So the authors warn anyone reading MRIs that even experienced radiologists can make this mistake and to guard against it.
The authors conclude that radiologists are not routinely following the guidelines. Standardizing terminology used to describe disc pathology is important in providing studies that can be compared. Without this kind of cooperation, attempts to improve research and treatment results will be hampered. Lumbar spine MRI readers are strongly urged to follow these published guidelines.
Jon D. Lurie, MD, MS, et al. Magnetic Resonance Imaging Interpretation in Patients with Symptomatic Lumbar Spine Disc Herniations. In Spine. April 2009. Vol. 34. No. 7. Pp. 701-705.