welcome to stanford medicine and to the stanford radiology youtube video channel hello i'm eric tranvin clinical assistant professor of neuroradiology at stanford university and today we'll be discussing the basics of mri lumbar spine interpretation we'll start by discussing a normal mri lumbar spine protocol looking at some normal anatomy and then we'll talk about establishing a search pattern finally we'll talk about lumbar disc nomenclature a typical lumbar spine mri protocol will have sagittal images a series of images oriented as if we were looking at a person from the left a stack of axial images oriented along the long axis of the sagittal images as if we were looking at a patient from the top their head or the bottom of their feet and in some cases an additional series of axial oblique images will be performed through the lower lumbar discs to better show the disc morphology there are different sequences and all the sequences show the same anatomy however the signal intensity or the relative brightness and darkness of tissues with respect to one another will differ depending on the sequence used for example on t1 weighted sequences fat is bright and you can see the bright signal of the subcutaneous fat as well as the epidural fat inside the spinal canal outside the the sac csf signal is low and you can see that dark signal inside the thecal sac here muscle is of intermediate signal intensity between csf and fat t2-weighted sequences are similar to t1-weighted sequences in that fat is brightened signal and muscle is relatively intermediate however in this sequence csf as you can see here is bright on the stir sequence the csf remains bright however the signal intensity of the fat as well as the signal intensity of the bone marrow becomes dark and this highlights areas of edema within the bone marrow looking at the anatomy on the sagittal images we're starting at a sagittal section and we can see the vertebral body this is l5 this is s1 we can see the intervertebral disc the epidural fat surrounding the thecal sac on this t1 weighted image on the tt weighted image you can actually see the nerve roots and we as and as we move further laterally we end up inside the neural foramen here where we can see the exiting nerve root as well as some small vessels in the foramen this is the pedicle of l5 superior articular process of l5 inferior articular process of l5 on the axial images as we scroll down we can see the thegel sac which is this ovoid dark area here surrounded by epidural fat on the axial t2 weighted images we can see the nerve roots within the the sac here we are at the pedicle level as we go a little bit lower we end up in the neural foramen and we can see the nerve roots exiting the neural foramen on either side here we are at the intervertebral disc level on the t1 weighted image the disc is relatively uniformly intermediate in signal intensity on the t2 weighted image you can see that the annulus fibrosis is a little bit darker than the nucleus pulposus essentially which is brighter if you're interpreting imaging it's important to have a search pattern to make sure you don't overlook anything i use the abcde approach outlined here a is for alignment and can be assessed in multiple planes on the sagittal plane you can assess the degree of lordosis or kyphosis and you can also evaluate for any list thesis that is displacement of one vertebral body anteriorly or posteriorly with respect to another if you have a coronal sequence or your localizer images capture the lumbar spine in a coronal plane you can assess for scoliosis as well the next thing we'll do is look at the bones not only are we looking at the integrity of the spinal column looking for any fracture or any evidence of post-operative change but also looking at the bone marrow signal intensity this is mri of normal bone marrow bone marrow is composed of red marrow or hematopoietic marrow which is the blood forming element of marrow as well as yellow marrow which is composed primarily of fat and as we discussed earlier fat is bright on t1 weighted sequences such as this one and as a result bone marrow is relatively bright in comparison to disc and skeletal muscle and that's your internal reference on stir sequences the fat signal intensity of the bone marrow is relatively suppressed which is why on the stir the bone marrow is dark when you're looking at axial t1 weighted images of the spine be sure to scroll all the way down to the bottom of the stack so you can evaluate the marrow in the sacrum especially the sacral ayla and the illac bones which might be excluded from the field of view on your sagittal images also note that bone marrow changes with age in younger patients there is a greater proportion of hematopoietic camera or red marrow so the bone marrow will be relatively darker than in a patient who is older and has a higher proportion of yellow mirror try to become familiar with the normal signal intensity of bone marrow on t1 weighted images on these first three images we see different examples of what's considered normal bone marrow in all situations the bone marrow is brighter than skeletal muscle or disc although in this image over here on the right it appears a little bit more heterogeneous in a patient who has some degree of red mirror reconversion this is an example of abnormal bone marrow the bone marrow is diffusely hypointense or dark on t1-weighted images darker than skeletal muscle darker than disc in a patient who has all bone marrow signal abnormalities can be focal such as in this patient with metastatic disease to the l2 vertebral body diffuse such as in this patient that has acute myeloid leukemia or mixed as in this patient that has red mirror reconversion due to a chronic illness as well as superimposed disciples osteomyelitis at the l4 l5 level where we see increased signal intensity in the disc as well as within the vertebrae on stir with corresponding decreased signal on the t1 weighted image the most common focal bone marrow abnormality we see however is benign these are examples of modic changes which are degenerative and plate marrow signal changes type 1 is vascularized fibrous tissue which has similar signal intensity to edema bright on t2 dark on t1 and bright on stir and then you have type 2 modic changes where there's fatty marrow replacement adjacent to the end plate and then finally type three where you get sclerosis where the signal intensity of the end plates decreases on all sequences the next thing we want to look at is the spinal canal and this includes everything in the spinal canal including the epidural space which is best assessed on the t1 weighted images as well as the contents of the canal such as the csf the distal cord the codis medullaris and the akata koana some findings in the spinal canal are obvious such as this schwannoma that presents as a mass inside the thecal sac some findings are more subtle such as edema within the deconus medullaris in a patient with a spinal dural arterial venous fistula we want to look at the cauda equina and make sure they're normal in appearance in the upper right hand image is an example of arachnoiditis where there's aggregation and clumping of nerve roots of the cauda equina the normal image is below for reference and the next thing we'll do is catalog the degenerative changes we'll start by reviewing the standard lexicon for describing lumbar discs this and more is described in great detail in lumbar disc nomenclature version 2.0 the reference you can find at the bottom of this slide in this lexicon you have disc bulges and disc herniations disc bulges exists when angular tissue extends beyond the edges of the vertebral hypotheses disc bulges can be symmetric or they can be asymmetric herniations in contrast are by definition localized or focal you have localized displacement of this material beyond the limits of the disc space but this encompasses less than 25 percent of the total circumference of the disc herniations can have different morphologies a protrusion exists when the herniated disc material is smaller than the base of the disc an extrusion exists when the displaced or herniated disc material is larger than the base of the disc such as in this middle example you can even have a sequestration where the disc herniation loses contact or continuity with the parent disc as in this example in this example we see that there's disc material within the dorsal epidural space on the sagittal image as well as on the axial image herniations can occur in different locations with respect to the spinal canal best viewed on axial images the central zone is situated between the medial margins of the facet joints the sub-articular zone or lateral recess is situated between the medial margin of the facets and the medial margin of the pedicle the foramen is situated between the medial margin and the lateral margin of the pedicle and the extra framal zone is lateral to the pedicle this is an example of a central disk protrusion as you can see on the sagittal t2-weighted image at l4 l5 there is this localized extension of disk material beyond the disk space here and here it doesn't look like it's contacting or compressing any adjacent nerve roots this is an example of a subarticular or lateral recessed zone disc protrusion in this case we see similar to the previous case localized extension of disc material beyond the disk space this is in the subarticular zone because much of it is located between the medial margin of the facet and the meter of the margin of the pedicle you can see that the disc is compressing the nerve that traverses the lateral recess at this level because this is the l4 l5 disc the nerve that is being compressed is the left l5 nerve this is another example of a subarticular zone disk extrusion in this case however there is a significant superior migration of disk material over here and as we page down on the axial image you can see this disk material within the lateral recess encroaching on the adjacent nerve roots in the lateral recess right here here we have a disc extrusion located in the framel zone or foramen disc extrusion on the sagittal t2-weighted image at the level of the pedicle we see this bright ovoid t2 hyperintense structure within the frame and here we can actually see the nerve root as it's displaced superiorly and compressed against the vertebral body posterior margin and the pedicle on the axial image you can see this foraminal disc extrusion here we can't see the nerve in relation to the disc because it's being displaced and compressed this is an example of a predominantly extraframing disk extrusion on the axial tt weighted image we see the soft tissue mass in the right extraframal zone partially extending probably into the lateral aspect of the neural foramen on the parasagital image at the level of the pedicle we see that there's some degree of foramen stenosis at this level due to disc height loss a bolting disc as well as as facet hypertrophy but as we move further laterally within the neural foramen we can see that it's filled up with the soft tissue and that looks different than the adjacent normal nerve and this is all disc material filling the foramen also extending into the extra foraminal zone displacing the nerve facet and ligamentum flavon hypertrophy can cause foraminal subarticular zone and central spinal canal stenosis synovial cysts which form as a result of facet joint degeneration can also cause nerve compromise when they project into the spinal canal or into the neural foramen fecal sac narrowing can be significant and can be caused by epidural lipomatosis when there's this excess of epidural fat as we can see on the sagittal t1 weighted image here epidural fat can be so voluminous that it can compress the thecal sac and here we see a very small thecal sac and all the nerve roots are aggregated within that tigal sac the grading of lumbar central canal stenosis as well as neural framelessnesses for that matter can be subjective although there have been attempts to standardize this this is the system that i use it takes into consideration the amount of csf that's left inside the the sac as well as what's happening to the nerve roots in the normal situation there's no stenosis csf is preserved and there's no aggregation of nerve roots in the thegal sac when there's mild stenosis there's some effacement of the thecal sac and some effacement of csf although the nerves remain separated from one another when there's moderate stenosis we begin to see some aggregation of nerves in the thecal sac and when there's severe stenosis as in this case you don't see any csf between the nerve roots and the cauda equina this is related to a large disk extrusion right here you can use also use this grating when you're assessing the sac narrowing due to epidural fat or epidural lipomatosis various scales have been proposed to grade the degree of framal stenosis on the right-hand table is a scale that takes into consideration the presence and morphology of perineural fat around the nerve root inside the foramen on the scale on the left-hand side of the table perineural fat is taken into consideration as well as the presence or absence of nerve root collapse or morphologic change as it turns out the findings that are most likely clinically relevant and may have symptoms associated with them are either loss of perineural fat in all four directions or complete obliteration of paranormal fat in the fourth row of this table as well as the presence of nerve root collapse or morphologic change personally i use the table on the right but i also mentioned when i see nerve root displacement or compression that being said it's important to recognize that degenerative changes are a normal part of aging and that many patients will have one or more degenerative changes that can be described in mri lumbar spine reports that are asymptomatic and the prevalence of these findings just increased with age therefore imaging base degenerative changes must be interpreted in the context of the patient's clinical condition so what imaging findings might matter things that are likely clinically important moderate or severe stenosis disc extrusions nerve root displacement or compression as we talked about before and plate edema which is type 1 mode exchange or grade 2 or higher list thesis as a quick recap of our search pattern we looked at the abcdes of mri spine evaluation we can assess alignment primarily on the sagittal images and any available coronal imaging we're looking at spine curvature as well as this thesis we'll look at the bones or the spinal column we want to make sure it's intact but we're also going to evaluate the bone marrow regarding the spinal canal we want to look at the epidural space as well as the contents of the thecal sac the distal core the conus the cauda equina then we'll catalog degenerative changes using our standard lexicon and then of course we'll look at everything else including the localizer image the visualized abdomen pelvis and retroperitoneum and last but not least we should look at the clinical history and try to find the imaging finding that might explain the patient's symptoms so in summary we talked about the normal mri sequences using lumbar spine imaging we talked about some normal anatomy we developed a search pattern that we'll utilize when we're looking at lumbar spine mris and we developed a vocabulary to describe disc pathology you