What should a back mri look like

Normally the thecal sac should be symmetrically shaped into a shield-like configuration figure 7 with the lumbar nerve roots visible and lined-up along its periphery this is certainly not always the case.

The delicate thecal sac, however, is vulnerable to compressive forces and may be compressed by central and paracentral disc herniations, osteoarthritic-thickening of the posterior vertebral body or laminae, or hypertrophy of ligamentum flavum.

Any of the aforementioned compression mechanisms would result in central stenosis. Do you see significant compression-related deformity of the thecal sac in figure 7?

Although CT is the gold standard for detecting fractures of the posterior arch, sometimes they are still visible on MRI. Therefore, carefully inspect the posterior arch for signs of cortical disruption breaks in the outlines of the wishbone , especially at the region of the pars interarticularis, is imperative. Also re-assess the "V" of the wishbone in order to make sure that ligamentum flavum thickening or facet thickening is not compressing the thecal sac.

Finally, observe the relationship between the superior and inferior articular processes in order to ensure that there is sufficient coronal orientation of the facet joint. Sometimes the facet joints may be orientated too sagittally, which can allow forward slip to occur—a condition called degenerative spondylolisthesis.

Learn more about this on the spondylolisthesis page. What do you think? How does the posterior arch look in figure 7? The answer is that it looks fine. The facet joints are angled obliquely which means they are coronal enough and no cortical disruption is elucidated. Go through the algorithm I've shown you; what did you come up with? After inspecting the posterior margin of the disc, you should have immediately noticed a focal outpouching bump of the posterior disc which is representative of a moderate-large disc protrusion a.

If you missed it following the disc inspection, then you should have definitely caught it while you were inspecting the thecal sac, which is smashed in the right front region by the herniation.

Look at the thecal sac. Is it hyperintense white? No, it is hypointense dark , which means it is not a T2 and most likely the T1-weighted image. Finally let's look at the neural foramina. How do they look? Notwithstanding the good-sized disc herniation, both lateral foramina are within normal limits and not compressed.

How does the posterior disc margin look? Well, there are no focal outpouchings bumps ; however, the entire disc is "bulging" backwards so that it has narrowed the neural foramina as well as the central canal. This condition is called, as you may have guessed, a bulging disc disc bulge without focal disc herniation.

What about the thecal sac? First of all, I threw you a curveball: this is not a T2 weighted image The thecal sac is not bright white, but the but hypointense dark.

Therefore, for our purposes, it is a T1-weighted image. You should have also noted that the posterior arch is abnormal. Specifically, ligamentum flavum LF which is usually barely seen has greatly hypertrophied second and has compressed the posterolateral corners of the thecal sac.

Central stenosis. Go through your algorithm, and tell me what you see? The posterior and posterolateral contour of the disc are normal, for there is neither disc bulging nor disc protrusion. We cannot see the nucleus pulposus on this T2-weighted image, therefore the patient has degenerative disc disease DDD. Also, particularly noteworthy is the presence of a fairly hyperintense white flattened teepee-like defect in the disc remember, this should be black , which is indicative of a massive bilateral annular tear within the annulus click here to see, yellow arrows.

It looks pretty good as it is symmetrical in shape and is not being compressed or indented by anything. In fact, you can clearly see the traversing nerve roots floating in the CSF without signs of compression. What about the neural foramina? Good job! They look fine and are wide open.

Can you see the dorsal root ganglia? Click here to see, pink arrows. And finally, what about the posterior arch? It looks absolutely fine with no significant ligamentum flavum thickening, obvious fracture, or facet slip. Let's see, the posterior and posterolateral contour of the discs seem to be okay Most of you probably missed this one. If you look very closely you might see I'll tell you later. I would call this mild central stenosis, but that's the least of our worries.

The right one looks fine remember, that is the left side of the image but the left one as a big problem? Do you see it now? This is an example of a very large and left foraminal a. Click here to see it Wow! How could you miss that! You can even see the faint outline of the annular tear which let loose this monster! If this was missed on MRI, which happens more often than you would like to believe, and a traditional microdiscectomy was performed, the surgeon would not have been able to visualize this region of the spine and would have missed seeing the massive herniation; the discectomy would have failed miserably.

Do you see anything else on figure 11? Did you forget to check the posterior arch? There is one more defect in the left posterior arch. Can you see it now? Although you really need a case history here to find out what's going on. I don't see any scar tissue in the epidural space, which would indicate previous discectomy, and this defect is not through the pars interarticularis the weakest part of the posterior arch.

So, at this point, the ideology of this cortical disruption is unclear. I hope you enjoyed the quiz and did well on it. Please come back here from time to time, for I plan on adding more questions in the not so distant future. At the beginning of this page, I promised that I would show you how to figure out what level of the spine you are at on the axial images without purchasing fancy software.

So here goes. With your T2 weighted axial images open, scroll all the way down through the images until you come to the sacral base, which looks like figure If your MRI Center was too lazy to go down this low, at least look for a picture that looks like this click here. Still don't see it? Then your MRI center was either really lazy, or you're not looking hard enough.

The only other thing I can say is try scrolling all the way up through the images and look for T12, which typically has ribs attached to the vertebral body.

If you know which direction is up, then you can scroll all the way down to the wider L5 lumbar vertebra assuming the sacred base is not there. The astute reader might have noticed that there is some different anatomy at this level. Of particular importance are the sacroiliac joints SI joints which are outlined with pink arrows. Also note the sacral base, which is really the vertebral body of the S1 segment.

If instability increases, a pars defect results as the lamina fractures and spondylolysis is a consequence. Spondylolysis describes an unstable spine which ultimately increases the likelihood of surgery. Instability places greater stress on the discs and the outcome is a greater risk of disc herniation, nerve irritation, arthritis and persistent pain. In addition, identify the space between the vertebral bodies for the intervertebral discs.

The disc levels are numbered from L to L5-S1 based on their location in between the vertebral bodies. Discs have a great deal of fluid within them which allow them to act as shock absorbers. Unfortunately, over time the discs dry out and degenerate. With a fracture of the end plate, degenerative disc disease occurs as the fluid within the disc leaks out. A normal intervertebral disc has significant white signal internally figure A which represents normal fluid.

As the intervertebral disc degenerates, the normal white signal darkens figure B and narrows figure C. With loss of the interior supporting fluid, the thick collagen walls of the disc begin to bulge outwards into the central canal from the excessive pressure figure D.

Extrusions described a tear in the disc wall in which the fluid squeezes out into the central canal figure E. If a little material squeezes out it can result in a mild disc herniation. If a great deal of fluid squeezes out it is called a disc extrusion which can migrate figure F. There is a greater chance of severe pain, weakness, numbness, and tingling as more disc material is squeezed into the central canal.

In contrast to the solid structures of the spine, foramen are narrow keyhole-shaped canals located on either side of the spinal column. These foraminal canals allow individual nerve roots to exit from the spine. Borders of the foramen are hard bony pedicles and intervertebral discs shrouded in a thin membrane called the thecal sac which keeps the CSF from leaking out. Patients are at risk of a pinched or irritated nerve with a disc herniation in the narrow foramen compared with the larger central canal.

Nerve root compression occurs in the adjacent area called the lateral recess. Facet joints or associated synovial cysts posteriorly in the foramenal canal compress the nerve roots. The cauda equina horses tail is a bundle of nerve fibers found at the bottom of the spine. The axial images or sliced bread views provide a clearer picture of a specific intervertebral disc and the adjacent nerves. A normal disc figure A provides ample room for the nerves to pass through.

Claudication is traditionally divided into two categories: neurogenic or vasogenic, depending on the underlying cause. It is often described as impaired mobility and dull aching pain in the lower limbs.

Central vertebral canal stenosis is a common cause of neurogenic claudication and has a variable pattern, while vascular claudication it is more consistent and reproducible. The importance of determining symptom chronicity and identifying 'red flags' in the history and clinical examination, such as fevers and perineum paraesthesia, are crucial in the formulation of the clinical diagnosis and differentiating benign causes, such as musculoskeletal strain, from more serious conditions such as epidural abscesses or spinal metastases.

Certain risk factors such as the patient's age, medication history eg. This would direct further investigation with appropriate serum tests and imaging. Guidelines, such as those developed by the American College of Physicians and Pain Society, can direct diagnostic testing for 'red flag' causes of lumbar back pain. Magnetic resonance imaging utilises proton resonance technology to obtain soft tissue cross-sectional representations of the spine.

The quality of these images allows the diagnostician to make more detailed and accurate assessments of the intervertebral disc and its relation to the neural structures when compared with more traditional methods, such as lumbar and computed tomography CT myelograms. A systematic review of the available literature involving spinal MRI found MRI to be a highly sensitive and but less specific imaging modality for lumbar spinal conditions. The lumbar spine consists of five separate vertebrae separated by intervertebral discs and reinforced by multiple ligaments and paravertebral muscles.

The thecal sac containing the conus medullaris and nerve roots are located within the central vertebral canal. The nerve roots then exit the spine via the intervertebral foraminal canal obliquely instead of at right angles, which is observed in the cervical spine. Understanding this anatomical relationship allows the clinician to isolate the exact nerve root being irritated by a herniated intervertebral disc Figure 1.

The exiting nerve roots traverse the neural foramen and this is divided into sections based on its relationship to the pedicle and zygapophysical joint in the axial and sagittal planes Figure 2.

In the axial plane, the exiting nerve root traverses the subarticular recess from the central zone to the foraminal and extra-foraminal zones. Infra-pedicular, supra-pedicular, pedicular and disc levels are used to separate the areas along the longitudinal axis. Figure 2. Intervertebral discs have a hydrated nucleus pulposus contained within concentric rings of annulus fibrosus. With increasing age, the discs progressively dehydrate resulting in a decrease in T2 signal, which are frequently seen in asymptomatic patients.

Nomenclature used in reports of spinal imaging has been confusing and inconsistent. Until a consensus review by several working groups in North America developed a recommendation on terminology 8 used in describing lumbar disc pathology such as disc sequestration and fissures Table 1.

Any separation between annulus fibres or avulsion of annulus fibres from the vertebral bodies is defined as an annular fissure.

These changes often occur in the setting of asymptomatic disc degeneration. Therefore the term 'annular tear' is discouraged as it implies a traumatic trigger. A review of 40 post-discography CT scans found poor correlation between the side of back pain and the side of annular tear in patients with a single level, concordantly painful and fissured discs identified during lumbar discography.

Disc herniation occurs commonly in two scenarios where the spinal column has sustained trauma in the form of abnormal axial loading or altered dynamics secondary to congenital or acquired spinal deformity.

The resulting herniation results in nerve root compression and pain. Any disc material extending beyond the vertebral bodies is considered a herniated disc. This is described further as 'disc bulge', 'protrusion', 'extrusion' and 'sequestration'.

The fundamental aim of using these terms is mainly a descriptive one and allows effective communication to general practitioners. A protruded disc is defined as having a wider base when compared with the extent of disc material spreading beyond the vertebral body Figure 3. Conversely, when the extent of disc spread is greater than the base of the disc extension, it is described as being 'extruded'.

When there is separation between the herniated disc and the parent disc, it is described as being 'sequestrated' Figure 3. Figure 3. In an attempt to correlate clinical findings and radiological evidence, the relation of the herniated disc to the nerve root is carefully examined.

Any contact, displacement or inflammatory changes would be reported to allow accurate localisation of the patient's symptoms to the offending compressive disc lesion. Gradual development of central vertebral canal stenosis where there is compression of the nerve roots in the thecal sac Figure 4 often results in progression of decreasing mobility and neurogenic claudication.

In instances where an acute event has occurred, the initial presentation may occur as cauda equina syndrome, urgent surgical decompression is required. Figure 4. T2-weighted axial slices of the lumbar spine of the same patient at different levels.

There is severe central vertebral canal stenosis at the L4—5 level arrow with no cerebrospinal fluid and crowded cauda equine nerve roots. At L3—4 the nerve roots can be seen as low signal dots surrounded by bright cerebrospinal fluid.

The causes of central vertebral canal stenosis can be divided into congenital and acquired conditions, such as neoplastic and degenerative changes. Degenerative changes include facet osteophytes, ligamentum flavum hypertrophy and disc herniations. The severity of central vertebral canal stenosis is visually graded and currently no universal grading scale is being used. Several centres have assessed various grading methods, including measuring the cross-sectional area and morphology of the thecal sac.