Should MRI's be taken for acute injuries after a car crash?

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Welcome back to the Forensic Chiropractor podcast.

A often have patient’s that have been in motor vehicle collisions and went to the emergency room and had multiple CT scans done and sent home with no acute findings.  Following an exam in my office an MRI is ordered and we see acute findings.  The insurance company or more likely an attorney representing the insurance company later on will argue that I should have never ordered the MRI.  There are false ideas about what a CT scan and an MRI are used for.  Today’s study helps me explain some of the differences and why MRI can be so important and why it is important to order early in most cases.  Today’s study in Rol of Magnetic Resonance Imaging in Acute Spinal Trauma: A pictorial review published by Yogesh Kumar and Daichi Hayashi in the BMC musculoskeletal disorders journal in 2016. 

The study starts by addressing what CT scans do well and that is fractures and an adequate assessment of spinal stability for a surgical decision.  This translates into CT scans are so much faster than an MRI and can be used to rule out most fractures and gross instability.  In contrast the study shows that MRIs are the modality of choice for evaluation of ligamentous and other soft tissue structures, discs, spinal cord and occult or hard to see boney injuries.

The study talks about reasons to order MRIs.  The first is CT or x-rays showing findings of ligament injury.  The second is to look for epidural hematoma or disc herniations.  Third to identify spinal cord abnormalities in patients with impaired neurological status.   Fourth is to exclude suspected ligamentous or occult bony injuries.  Fifth to determine stability of the cervical spine and need for a collar and 6^th to determine difference between bleeding and nonbleeding spinal cord injuries. 

For those unfamiliar with an MRI I want to give a brief explanation.  The patient enters the MRI which is a really large magnet.  This large magnet gets all of the hydrogen protons to align with the magnet.  Then a radio wave is placed through the body.  This radio wave knocks all of the protons out of alignment with the magnet.  Then the radio wave is turned off and all of the protons return to alignment with the magnet and this realignment causes a release of energy that can be detected at turned into an image. 

The different anatomy will release energy at different times.  The standard spine MRI was record this energy release at 2 separate times.  We call these Time 1 and time 2 or T1 and T2.   This allows us to see different types of anatomy and injuries.  Fat tissue can throw off a T2 view when looking for edema.  The MRI has a way to suppress the fat signal on a T2 and this is typically called a STIR view.  So long story short an MRI can see different anatomy and different signals on the T1, T2 and STIR views.  

The T1 is mainly used for bony anatomy and fractures.   The T2 view is best for cord edema, bleeding, ligaments, and discs.  The STIR view is best for edema and diagnosing acute soft tissue injuries.  New injuries will create edema that can be seen on imaging.  The edema is often seen only in the first few hours.  Today’s study reported that ideally the MRI is done within 72 hours of the injury.

Today’s study talks a little about stability of the spine.  The spine is split into 3 columns.  A spine is considered unstable in any 2 of the 3 columns are affected.  The first column is the anterior longitudinal ligament, anterior 2/3 of the vertebral body and the anterior 2/3 of the disc.   The second column is the posterior 1/3 of the vertebral body, posterior 1/3 of the disc and the posterior longitudinal ligament.  The third column is everything posterior to the posterior longitudinal ligament including pedicles, facet joints, articular processes, ligamentum flavum, neural arch and interconnecting ligaments.     

Beyond 2 of the 3 columns being affected today’s study showed many other findings suggestive of instability.  These findings are translation of a vertebra over 2mm indicates a ligamentous injury, widening of the facet joints, widening of the interspinous space, disruption of the posterior vertebral body line, greater than 20 degrees of kyphosis. 

Today’s study reported that although a CT scan can show many of these findings an MRI offers additional benefits to visualize instability injuries. 

Today’s study reported that normal ligaments on an MRI will have a low or dark signal intensity on all sequences besides the interspinous ligament which may have striated appearance with low signal intensity areas interspersed with high signal or bright areas related  to fat.

A partial ligament tear on an MRI will be seen as high signal areas on a STIR view due to the edema and bleeding in the ligament.   Complete tears will also show high intensity signals and complete lack of the intact low intensity signals. 

Today’s study showed that the most common mechanism for ligament injuries in the spine comes from hyperextension and hyperflexion injuries.  The hyperextension injuries commonly damage the anterior column and hyperflexion injuries typically damage the middle and posterior columns. 

When it comes to ligamentum flavum injuries today’s study showed we typically see fractures.  When we have interspinous or supraspinous ligament damage we will have an increased signal in the spaces of the ligaments on a STIR view due to the edema. 

Today’s study talked about facet joint injurie. Facets are the joints of the spine posterior to the vertebral bodies.  Facet joints should have fluid in them and this fluid will appear bright on a T2 and STIR view.  If we have widening of the facets with an increased signal we have facet damage.  This can be tricky since healthy facets will have increased signals. I like to compare the above and below facets to assess for widening facets at any level.  We can have a one sided facet injury and in that case the once facet will be wider than the other side. 

Today’s article addresses acute traumatic disc herniation findings on MRI.  They state that a disc herniation is an injury to the annulus fibrosus with nucleus pulposus herniating or moving outside.  They reported that disc herniations can appear similar to other disc damage on an MRI.  I have talked about that on prior podcasts.  We need to look at all aspects of an MRI to assess what type of story the MRI is telling.  Is it showing a degenerative old injury or a new injury.  It is important to get an MRI when patients have neurological deficits.  The MRI can be helpful to find undetected disc herniations. 

MRIs can be very helpful when assessing spinal cord injuries.  The most common spinal cord injury seen on an MRI is an increased or hyperintense signal on a T2 view.  This suggests cord edema. If we see a hypointense signal in the spinal cord on a T2 view we are likely looking at bleeding.  Today’s study reported that the most common cause for spinal cord injuries is hyperextension injuries and more particularly hyperextension injuries in older patients with degenerative changes in the spine. 

Often insurance companies will argue that degenerative spine changes are pre-existing and unrelated to the collision.  They then report that all other findings the patient’s have must have been from these pre-existing degenerative changes.  That thought is only half true.  Degenerative changes take years to develop and when seen on imaging after trauma would indicate that these changes were not caused by the injury.  The problem is that as seen in today’s article and others I have covered in the past that these degenerative changes make patients prone to more significant injuries from the trauma.  As in this case older degenerative patients have more spinal cord injuries.  These spinal cord injuries were reported in today’s study as decreased motor function, bladder dysfunction, sensory loss all below the level of the spinal cord injury. 

A hard truth to learn is that all imaging has the potential to miss things we are specifically looking for.  There are very difficult pathologies to see on imaging.  Rib fractures are one very hard to see pathology on x-rays.  Sternal fractures are another difficult fracture to see.  There are lots of osseous fractures that are not easily seen on x-ray or even CT scan.  Today’s study showed that MRI is very sensitive for seeing these hard to imaging fractures.  The MRI is very good at seen marrow edema and bleeding. 

Even injuries such as a muscle strain will have edema and this can been seen on MRI with increased T2 and STIR views.    

Vertebral compression fractures are typically never missed on x-ray or CT scans and an MRI is not needed to see these.  The problem we have is it can be very difficult from an x-ray or CT scan to know if a compression fracture is new or old.  It also might be an old compression fracture with a superimposed new fracture.  MRI can be quote “very helpful by showing the bone marrow as low signal on a T1 images and a high signal of T2 and STIR views.  This can be one of the best ways to determine if a compression fracture is new or old.  A chronic fracture will often have the marrow replaced by fat and this is also easily seen on an MRI and different from edema. 

There are different types of fractures.  We can have traumatic fractures.  We can have acute fractures caused by osteoporosis and we can have acute fractures caused by malignancies.  Today’s study showed how we can use MRI to distinguish the different causes of fractures.   Osteoporotic fractures that are new have horizontal bands of abnormal signal intensity separated by a straight line from the normal fatty marrow and typically a lack in posterior elements being involved.  Osteoporotic causes of fractures typically leaved an angulated and concave appearance of the posterior vertebral margin.    In contrast the fractures caused by malignancy will have abnormal bone marrow edema that extends into the posterior elements and a convex appearance of the posterior vertebral wall.  There will typically be surrounding osseous and soft tissue involvement with the malignancy related fractures. 

One of the most important parts of today’s study as related to forensic work is that they showed bone marrow edema will have resolution in 6-8 weeks.  This is shown to be a partial or complete resolution of bone marrow edema.  This means that when we see edema in the bone it will only likely be there for 6-8 weeks.  This is another important reason to get imaging relatively fast after an injury. 

The end of todays study covers the pitfalls of MRI.  They report that artifacts due to metal like surgery hardware or dental work can make imaging with an MRI very difficult.  On occasion if the fat saturation or STIR view is incomplete fat signal can persist and simulate edema.  Another one I see a lot is prominent epidural veins can mimic disc herniations.  Another problem I have talked about in the past for MRIs is technicians or imaging centers that do poor quality work.   Slice thickness and angles of slices can be very important.  We can only see what has been imaged.  If corners are cut while taking the MRI was will easily miss pathology. 

To summarize today’s podcast we covered that MRIs often have an important role even if a CT scan was just done.  The MRIs need to be done sooner vs later to assess for edema.  Another assessment for spinal stability would be problems in 2 of the 3 columns, 2mm of movement, widening of the facet joints, widening of the interspinous space, disruption of the posterior vertebral body line and kyphosis greater than 20 degrees.  These are all really important findings to assess for stability in the cervical spine. 

This study also covered what spinal ligaments look like on an MRI and what damaged ligaments look like.  A healthy ligament is dark and a break in the dark ligament is a tear and a high signal shows edema in the ligament.  This study also showed that increased facet space compared to opposite side or above and below can show an acute injury.    They also showed that MRI is great at showing spinal cord problems.  They covered that MRI is very helpful to determine the cause of a fracture.  They showed what a osteoporotic caused fracture and a malignancy fracture will look like.   One of my favorite parts of this study is showing that edema will have partial or complete resolution in 6-8 weeks.  This helps us understand that edema or a type 1 modic change will be best visualize in 6-8 weeks and may not be seen after this time.   Also shows that if we have edema and lots of edema the injury is likely new and in the last 6-8 weeks. 

MRIs are an important part of forensic work and needs to done sooner vs. later.  Working with a good imaging center that doesn’t cut corners can be very important. 

Real world example

My prior podcasts 4-7 covered many different ways to time date a disc injury with an MRI.  Today’s article can help add a few items to the list of ways to time date a disc injury.  Not just a disc injury, but any injury.  MRI is so helpful with time dating injuries.  Like I have said many times before there is no way to know exactly the time an injury happened by just using an MRI.  We look at a lot of different things on imaging and can paint a picture of causation.  Does the picture show a degenerative osseous spine with disc space height loss, circumferential bulge with a desiccated disc?  That would paint a picture of an old problems unlikely related to new trauma.  Or does the MRI show no degenerative osseous changes, no loss of disc space height, focal herniation with increased signal in the herniation and type 1 modic changes surrounding the herniation?  That would clearly paint a picture of a new injury. 

Today’s study helps add that edema seen on an MRI typically resolves or at minimum partially resolves at 6-8 weeks.  If we have an MRI taken 2 years after an injury with edema that might not be from the injury 2 years prior.  Keep in mind we still need to look at all evidence not just this one aspect.  Facet joint widening seen on an MRI is another part of the picture.  If we have facet joint widening with increased signal at the same level as a disc herniation this is one more indication of a new injury.  This is especially true if there are no degenerative hypertrophy of the facet joints. 

Similarly if we have widening of the interspinous space this is another indication of a traumatic injury and would help paint a picture of a new injury.  I think the more objective findings we can include with our causation opinion the more accurate it will be.  Findings from today’s article can be important to assess if a new injury has occurred or if we are dealing with an older injury.