Learn to see the lumbar disc herniation CT and MRI magnetic resonance film superb tutorial (Note: very practical tutorial, applicable to medical science, professionals look after it is also very good to learn and review. I don’t know who the original is, right to share.) The first lesson, we first learn a little bit of preparatory knowledge . Lumbar intervertebral disc consists of three parts, the middle is the nucleus pulposus, the nucleus pulposus is surrounded by the annulus fibrosus, and the upper and lower is the cartilage plate. For detailed knowledge about the composition of the lumbar disc, please see the relevant articles in the lumbar spine knowledge hall, here mainly talk about and MRI / CT film with lumbar disc disease related to a few key anatomical structures. Take a look at the axial view of the lumbar disc film. These key structures are important for diagnosis: ・Tendon sheath sac, also called Thecal Sac ・Exiting Spinal Nerve Roots (L5) ・Traversing Spinal Nerve Roots (S1). Looking at this diagram carefully, the key “culprits” to look for are: ・Nucleus pulposus ・Posterior longitudinal ligament ・Posterior fibrous ring ・Small joints Problems with any of these structures can lead to low back pain as well as pain in the lower extremities (sciatica). The correct way to see where and what is being compressed is to look at the MRI/CT axial view (from top to bottom). Whereas from a sagittal view (viewed from the side) you can only roughly tell if there is compression, bulging or herniation. As you study the following, you may feel that the CT and MRI images do not distinguish the various parts as clearly as this diagram shows, and that you sometimes have to use your imagination to see the actual CT/MRI films ^_^ Lesson 2: Locate the disc we want to look at. Without a localization map of the lumbar spine, it would be almost impossible for a “layman” to tell the difference between the 5 discs in the lumbar region. A localization chart is like a road map that tells us exactly where to scan at each level of the lumbar spine, so it is essential even for very experienced physicians. This localization map labels the 20 MRI slice layers of the lumbar spine from a sagittal plane view. Each number represents an MRI image taken through that plane. The image layers in this slice cover only the L3, L4, and L5 segments. For example, layer 11 (the layer above layer 10 labeled in red) passes right through the L4 disc. If you have a problem with your L4 disc, look at this layer. Layer 18 information is also very useful; it corresponds to the L3 disc. For patients with very thin discs, the thickness of the layer should ideally be a little thinner (6mm) to ensure that it passes right through the thinned disc. So, if you go back to your MRI or lumbar CT now, you will have learned how to find it through the “localization map”. On many MRI films, each large image is accompanied by a small localization map, which makes it easy to know which disc we are looking at. Lesson 3, Learn to see the lumbar MRI/CT slice axial view . Figures (a) and (b) are axial views of the L5 disc. Although this patient has moderate lumbar disc degeneration (the black disc is seen on the film) and a small non-compressive 4mm central disc herniation, he has a large “central canal” that is well represented by the axial MRI anatomy. The nucleus pulposus of the disc is not visible in these two images because the disc is too dehydrated to separate the annulus fibrosus from the nucleus pulposus region, and because these images are T1-weighted (higher resolution), so they do not separate the watery nucleus pulposus from the drier annulus fibrosus region. However, on a normal, non-degenerative disc T2-weighted image, it is easy to see the nucleus pulposus region and the annulus fibrosus region on a T2-weighted image (see Figure III). The “posterior neural structures” include the traversing Nerve Roots, the Thecal Sac, and the Exiting Nerve Roots. The Exiting Nerve Roots are located within the intervertebral foramen (see the pink area of the IVF in the image) and are not visible in this image. If you use your imagination, you can find a “Mickey Mouse”-like image in the image, with the dural sac as the Mickey Mouse’s head and the two Exiting Nerve Roots as the Mickey Mouse’s ears. To repeat, although this disc has a 4mm herniation, there is no contact between the patient’s passing nerve root S1 and the herniation. In most cases, the disc herniation or scar tissue will obscure one of the passing nerve roots (Mickey Mouse ears), which is usually a sign of nerve root compression. Figure (c) shows an axial view of the L4 disc in another healthy 45-year-old male. We can now distinguish between the nucleus pulposus region and the surrounding ciliated annulus region. Note that the “Mickey Mouse” will not be visible in this plane. Also note the concavity of the posterior edge of the disc near the nerve root of L5, which is a sign of a normal, healthy disc; L4 emanates from the nerve root a little more laterally. It is easy to see why, in the case of a large disc herniation or spinal stenosis, the emanating nerve root, L4, and the passing nerve root, L5, would be compressed at the same time. In this image, the tiny nerve roots (L5 and S1) hanging within the dural sac can be clearly seen, and they are arranged in an imperfectly organized fashion. Note that the neural foramina are very open (light yellow areas), indicating that there is no existing spinal stenosis due to adjacent intervertebral joint problems.T2-weighted images are best for visualizing degenerative disc disease because the T2-image shows water-rich structures as bright white and areas of low water content as black. In Lesson 4, learn to look at a lumbar CT/MRI sagittal view. Figure (d) is a lateral, or sagittal, view of the lumbar region of the spine. Note that this image is between T2 and T1, is called a proton density image, and is the best image for determining whether a disc herniation has penetrated the posterior longitudinal ligament (PLL). Like the T1 image, it uses high magnetism, so the subtle parts show up surprisingly well. Let’s look at the basic structure first: the intervertebral discs that lie between the vertebrae should be white (more water). Note the black-colored (dehydrated) L5 disc (the disc between L5 and the sacrum), which represents moderate to severe degenerative disc disease. The posterior longitudinal ligament (PLL small blue arrow) is shown in the image as a black line running vertically down along each vertebra and the posterior edge of the disc. Interestingly, even though this patient had a 9mm herniated disc (HNP) with some buckling of the bone and nucleus pulposus material visible above the disc plane, the posterior longitudinal ligament continued to contain the herniated nucleus pulposus material without freeing it. This condition is academically referred to as a large inclusive disc herniation. The dural sac (red star) appears as a “super-white” structure that fills the central canal behind the vertebral body. This sac contains free-floating spinal nerve roots (cauda equina) composed of motor nerve fibers and sensory nerve fibers. The ligamentum flavum (green star) lies between each vertebra and enhances the stability of the spine. This structure can become enlarged or thickened, contributing to the formation of centralized spinal stenosis, a condition to which older people are susceptible. Lesson 5, Finding the herniated lumbar disc: the anterior epidural space Now let’s use some CT axial views to learn about the different areas of the anterior epidural space where lumbar disc herniation occurs. If you have ever read an MRI report, some of the terminology may sound familiar, as these areas are often used by radiologists to describe the exact location of a herniated disc. Blue Zone: This is the “central zone,” which is immediately posterior to the disc and encircles the anterior aspect of the dural sac. Because the posterior longitudinal ligament is thickest in this area, a herniated disc is usually either slightly to the left or to the right in this area. Pink area: This is the “paracentral region” or lateral recess, which is located immediately lateral to the central region. Because the posterior longitudinal ligament is not as thick in this area as it is in the central area, disc herniation often occurs in this area. In fact, this is the number one location for herniated discs to occur. It is common to see passing nerve roots contacted, displaced and compressed by a herniated disc in this zone. (Remember, a herniated disc at L5 in the lateral recess is compressing the passing nerve root S1, not the sending nerve root L5, which is located in the foramen magnum.) Green Zone: This is the “intraforaminal zone,” also called the “subarticular zone,” which is located within the foramen magnum. It is rare for a disc to herniate into this area or beyond. In fact, only 5 to 10 percent of herniated discs occur in this zone or further out. When a disc herniation does occur in this area, it is usually more problematic for the patient. This is due to the fact that the “dorsal root ganglia” (DRG), with its ultra-fine neural structures, are located in this area. Any compression of the DRG will result in severe sciatica and neuronal damage. Yellow area: This is the “extraforaminal area”, which is located immediately outside the foramen. Again, this is a rare area for herniated discs to occur, but when it does, it can be tricky for both the patient and the doctor. Herniated discs in this area can also stimulate the “sympathetic nervous system” causing lower extremity reflex sympathetic dystrophy (RSD)-like symptoms. Lesson 6, looking at axial CT myelography. Now let’s look at some CT myelograms. The one in Figure (VI) is from a layer immediately above the L5 disc and below the vertebral body (remember that both CT and MRI are thin slices through different planes of the spine). Because this layer is a layer on the horizontal plane of the disc, only the posterior neural structures can be seen and not the disc itself. Note the bright white annulus (not labeled) that indicates the outer contour of the vertebral body (upper part of the image). The cauda equina (dural sac) is completely filled with “white” contrast (injected during the myelogram) making the dural sac and dural sheath appear bright white. The dorsal root segments of L5 are not well visualized because the contrast only fills the root sheath below the dorsal root segments. I have drawn a black line in the center of the dorsal root joint on each side. Note also the intervertebral joints (angled black splits), which resemble a sandwich between the superior sacral synchondrosis and the inferior L5 synchondrosis. The CT slice in Figure (VII) is from below the left layer and shows the posterior portion of the disc quite well. We can understandably see that the posterior disc has both a bulge and a protrusion to the left past the nerve root S1, so obscuring (flooding) the S1 nerve root (the color is not as white as S1 on the right). A line (thin white smiley line) is now drawn on the posterior part of the annulus to illustrate how the diseased disc is bulging outward. Any time disc tissue is seen outside the annulus posterior to the vertebral body, the disc is considered to be bulging. A bulging disc is usually no more than 2 to 3 millimeters in size and is either concentric or nonfocal in shape. The bulging disc in this picture is an outward-facing pouch with an eccentric shape that has partially reached the left “lateral socket”. This outward-facing pocket is the bulge that occurs after a disc injury, allowing the left S1 nerve root to be lost (submerged) due to the fact that it is not able to fill with contrast properly due to the compression at this level. You may notice a white, surface-to-air missile-like firing beam below the affected left S1 nerve root. This is the result of an “accidental” leakage of contrast into the epidural space after the myelogram, rather than an intentional semi-epidural contrast effect. The same L5 disc image is not labeled. Try to see it for yourself without the auxiliary lines and labeling. Do you see the herniation? I’m sure you see it now! This is a large basal herniation with a larger base than the bulging end. One thing to remember: CT myelography looks for “filling defects” and is not the best way to visualize the discs in the body. MRI is much better at showing disc detail. On the CT myelogram (left), if the disc herniation is large, it will darken the nerve root, or disappear. This is because the compression exerted on the nerve root prevents the contrast from filling the nerve, so the bright white nerve root cannot be seen. This means there is a problem! For Lesson 7, look at an example of an MRI look at a 9mm lumbar disc herniation . Figure (9) shows a T1 axial and sagittal view of a large 9mm herniation (red star). The herniation has completely obscured (not visible) the right passing nerve root S1 (left side of the image) and extruded it into the vertebral plate (small green arrow). Moderate to severe compression of the dural sac from this large herniation can be observed in the axial and sagittal views (between the blue arrow and the red five stars). This patient is a 24-year-old who has avoided surgery and is doing well. Notice how his spinal canal is much smaller than that of the young man in Figures 10 and 11; a large spinal canal is far more tolerant of lumbar disc herniation than a small one. Lesson 8, it’s time for the test ~ let’s see what we know now! Using what you have learned, answer the following five questions: 1. Name the structures represented by each number in the axial view of MRI in Figure (x). 2. Name the location of the lumbar disc herniation using the correct regional classification. 3. Which nerve root has been replaced by the disc herniation? 4. What type of MRI image is this? Hint: T1, T2, or proton density? 5, What two tissue structures are being contacted by the disc herniation? First, use your mind to think about it, do not immediately look at the following answers Oh ~ ~ Publish the answer: 1. In numerical order, the labels in Figure (X) are: (1) L5 disc (2) 9mm disc herniation. (3) Left S1 nerve root. (4) Dural sac. (5) Epidural space. (6) Right vertebral plate (7) Sphenoid process (8) Left intervertebral joint (2) This is a 9-mm-large, non-inclusive right paracentral herniated disc located in the right lateral saphenous fossa. 3, Right S1 nerve root. 4, T1-weighted image 5, Right S1 nerve root and dura.