MRI of the Lumbar Spine
Swollen L5 nerve root
Such a fragment is often surrounded by granulation tissue or hematoma, either or both of which may contribute significantly to the epidural mass. The term herniation should only be used when the more precise terminology is unclear, such as when interpreting a CT scan, myelogram, or low resolution MRI. The term “herniated nucleus pulposus“ is never appropriate, since a herniation may contain a number of tissues, including the nucleus, the cartilaginous endplate, the annulus, and even a rim of
The differentiation of different anatomic types of herniation is more than an academic exercise. A number of studies have shown that people without back pain or radiculopathy may have abnormal MRIs [20,31]. However, there is also evidence that extrusions are in fact specific and not found in asymptomatic populations [11,22,36,
interobserver and intraobserver reliability in making the differentiation by MRI [20,38,40].
SECONDARY SIGNS OF INFLAMMATION FROM DISC EXTRUSIONS
Acute Post “Limbus“ Herniation
A disc fragment extruded into the epidural space or foramen is treated by the body as a “foreign substance“, and the response is that of secondary inflammation. Many investigators believe it is this inflammatory reaction that is the cause of pain, rather than the mass effect. MRI may visualize the inflammatory response. The epidural fat is often indurated and therefore shows increased signal on MRI . A cap of
granulation tissue may develop and contribute to the mass effect [17,24,26,39]. This surrounding mass will enhance after the administration of intravenous gadolinium. It is also brighter on T2 weighted images, a finding that may have prognostic significance since some investigators have shown that disc extrusions that are bright will more likely resolve than those that are “black“ . The bright disc extrusions contain more granulation tissue, and the dark extrusions are desiccated fragments, unlikely to be resorbed. It should also be noted that many of the “bright“ disc extrusions may in fact be spontaneous epidural hematomas adjacent to a small protrusion . These masses will almost certainly disappear within four to six weeks.
It is also possible, using high resolution MRI, to demonstrate either pre or post compressive swelling of an involved nerve root. This can be seen both in and out of the thecal sac, and can be used as further specific evidence for directed single nerve root block or localized epidural injection. While some of these nerve roots may enhance after the injection of intravenous gadolinium, this has not been shown to be of additional help in localizing the symptomatic nerve root .
OSSEOUS INFLAMMATORY CHANGES ADJACENT TO DISC DEGENERATION
Bone marrow adjacent to a degenerating or degenerated disc may show abnormal signal intensity. Instead of the preponderant
Extrusion + granulation (T1)
Extrusion + granulation (T2)
Modic Type 1 (T1) Modic Type 1 (T2)