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The 90 % who recover sufficient activity tolerance within one month do not warrant further diagnostic testing.  Half of those with neurologically positive (but not cauda equina) sciatica are well on their way to recovery within a 4 week period.  If back or sciatica symptoms continue to limit activity unabated, especially at work, for more than four weeks, it is reasonable to seek some physiologic evidence like EMG for neurological problems or labs and even a Bone Scan for non-neurological findings before deciding if MRI might define a strongly obvious and concordant correctable lesion  (Patient discussion Handout # 2).  Remember that anatomic studies alone can be confusing (see chemical irritation).      
Imaging Considerations - Normal aging changes (“degeneration” present 30% of the time in asymptomatic 30 year olds and up to 100% of those age 65 years) are at times interpreted as a diagnosis, such as Osteoarthritis. Table 7, is a compilation of imaging for people without back symptoms. Note the chances at different ages of an imaging test providing a diagnosis exclusive of any symptoms Thus, gaining physiologic evidence first helps guide us past the limitations of imaging studies done in isolation.   
Analogy: A picture of a telephone does not tell you if it is ringing.  A picture of a box does not tell you how heavy it will be if you drop it on your foot.  A picture of something adjacent to the dural sac does not tell you if it is compromising the function of a nerve root - even if it seems to be pressing on it.  Only physiologic evidence tells us if nerve root is compromised and how much.  Our best data supports surgical outcomes performed to decompress compromised neural contents due either to herniated disc or spinal stenosis, guided by physiologic studies.  Pictures from imaging studies only guide the surgical approach by defining a correctable lesion - whether or not it is concordant with evidence of physiologic compromise (concordant symptoms, physical examination or special neurological testing).   
Thus, demanding concordance between obvious physiologic evidence and obvious anatomic testing increases clarity. Still, coming to a conclusion about surgical considerations for the spine without a fracture or dislocation to guide our efforts is like being on quiz show where you have to guess the phrase or name seeing only a few letters.  The more letters you can read, the greater the chance of identifying the phrase correctly. Remember only strong concordant findings predict a reasonable surgical outcome.  Table 8 lists relative physiologic evidence to avoid the possible confusion with imaging studies alone.  
Table 7: Radiographic diagnoses studying people without symptoms (note the increase in frequency of specific diagnoses with increasing Age, especially early discogram, disk cracks and radiographs). 
On the graph in Table 7, look for your age along the age in years line and move your finger toward the top of the page to see your chances of having something labeled an abnormality on your imaging studies before you ever have back symptoms.  This emphasizes the need for gaining some physiologic evidence of the potential cause of symptoms before risking the common confusion possible with imaging pictures which are only indicated to localize a specific location for already obvious structural (x-ray/ bone scan) or neurological compromise (PE or EMG). 
Be aware of the different contributions of diagnostic techniques.  Note in Table 8 that no physiologic evidence comes from imaging studies, and using them in isolation often introduces confusion differentiating all to common aging changes from a cause for present symptoms. 
Table 8: Types of contributions toward a specific diagnosis ( 0 to ++++ estimates relative ability)  
Physiologic Evidence- In the absence of a fall or other event that may cause a fracture, consider the following testing order for persistent symptoms (a month or more): 
Back Pain only a month or more (no neurological findings) 
-Laboratory studies (TSH, RA, ESR, CBC, UA, Chem.Panel) are used as a metabolic general screen. 
 -Bone Scan indications include structural general screen for bony Physiologic reactions to change in structural stresses of fracture/dislocation or architecture (tumor, infection, spondylitis even aging). Tc-99 Diphosphinate with a radioactively tagged bone metabolism metabolite provides an indications of increased or decreased bone turnover.  Increased bone turnover recordings are greatest with acute fracture or infection more than dislocation or tumor, which tend to be much more than old fracture or aging changes (Degenerative Joint Disease common in the AC joint, 1st metacarpal-carpal, spine and feet).  Fractures heal but in adults the increased turnover noticeable with bone scan remains for at least half a decade from just adult cracked ribs with less and less but discernible expression over time.  Bone turnover can be decreased in bone infarct like Aseptic Necrosis of the hip or shoulder and some tumors. Higher ratios Sacroiliac ratios can be an indication of early Sero-negative Spondyloarthropathy that cool down after fusion of the joint. 
Sciatica without obvious Radiculopathy 
-EMG ((Electromyography) are considered for constant or near constant limb symptoms without obvious Radiculopathy persisting for four or more weeks with severe limitations (Testing before 3-4 weeks commonly provides false negative).  In limb muscles seek more than one Positive Sharp wave or Fibrillation Potential (if S1 is effected then look for a slowed h-reflex) as indications of motor nerve compromise before considering anatomic verification (if any muscle is 3+ or more anatomic studies are probably prudent).  An EMG is not needed if combined motor, sensory and reflex changes indicate obvious L4, L5 or S1 nerve root involvement. [Remember we are seeking strong finding that predict a reasonable outcome!]  Polyphasic waves indicate old lesions not, alone respond poorly to decompression and increased insertional activity do not meet the criteria for strong findings that predict a reasonable outcome.  Multiple limb muscles with positive sharp waves and or fibrillation potentials and h-reflex slowing with S1 nerve root involvement are strong physiologic evidence to explain a limitation of 4 or more weeks of leg symptoms as an indication for seeking concordant imaging. CAUTION: Paraspinal changes are only additive information not to be acted upon alone or only in combination with Extensor Digitorum Brevis changes. Experienced Electromyographers rarely test the Extensor Digitorum Brevis EMG as changes are common due to shoe wear.  
-SEP (Sensory Evoked Potentials as either Dermato-Sensory Evoked Potentials (DSEP) - or Somato-Sensory Evoked Potentials(SSEP) are helpful in the patient with spinal stenosis symptoms and some EMG changes of motor function.  SEP's can provide sensory information of slowed nerve roots transmission since they tend to be more sensitive though less specific for active compromise than EMG motor changes. 
Table 9: Example of seeking Physiologic measures first to avoid confusion with Imaging studies 
Before discussing imaging findings to indicate obvious correctible lesion, it is worthwhile to review the lumbar spine anatomy. 
Relative Anatomy of the Lumbar Spine 
       The areas of most interest, from an evaluation and treatment standpoint, relate to possible compression on neural contents within the dura below the first lumbar body. Here the spinal cord ends and cauda equina of nerve roots continues until finally exiting around and under the pedicles that attach the vertebral body to the posterior elements. (see Figure 7). 
Note the relative relationships between pedicles, transverse processes, facet joints and ligamentum flavum to the disc space neural foramen and neural contents of the dural sac, which includes the nerve roots in Figure 8. 
       Studying Figure 8 posterior elements and Figure 9 lateral view relative to the neural contents in Figure 7 helps to understand why disc herniations usually catch the nerve root that exits at the next lower level nerve root foramen.  For instance - herniation at L4-5 usually impacts the L5 nerve root that exits through the L5-S1 foramen, and L5-S1 herniation usually impacts the S1 nerve root that exits through the sacrum. 
Note also the relationship of the pedicles as you would see them on a plain radiograph. An absence of pedicles hints at tumor involvement due to the tendency for metastatic tumors to affect the pedicle's junction with the body of the vertebra.  The pedicle is an important landmark for finding the nerve root, as can be seen in Figure 7. 
       A break in the pars interarticularis (between the upper and lower facet articulation of the same vertebra) known as spondylolysis, allows the body, pedicle and superior facet to move forward (known as spondylolisthesis) leaving the spinous process, lamina and inferior facet behind to articulate with the adjacent superior facet.  
Figure 7  The relationship of the dura, dural sleeves and nerve roots to the pedicle and central spinal canal. 
Figure 8.  The posterior elements (facet joints, lamina, spinous processes and interlaminar space covered by the ligamentum flavum) relative to neural contents. 
Figure 9  The lateral relationship of the nerve roots to the foramen formed by the facet joints, pedicle and vertebral body. [Foraminotomy enlarges the foramen for the nerve root's exit] 
Imaging Studies - Anatomic Pictures are used to define a reason for physiologic evidence. 
       - X-rays are only helpful in identifying fracture or dislocation, otherwise helpful in but one of 2500 films relative to radiation.  If findings are positive for fracture or dislocation a specialist commonly seeks further definition with CAT Scan or MRI
       - CT Scans (Computerized Tomography) define bony pathology much better than neural compromise (many times gray shades of soft tissue do not allow accurate evaluation of the neural canal contents). 
      - MRI (Magnetic Resonant Imaging) scans outline potential anatomic reason for physiologic evidence especially intradural and extradural defects (not bone) contrasting ligamentous and disc tissues from dural contents.  Unfortunately, the images can be distorted should the patient be unable to lie still for thirty minutes (up to 15% of patients are found to be claustrophobic).  MRI is contraindicated on anyone with metal within soft tissue, i.e., foreign body in the eye or abdomen. 
     - Myelogram and CT-Myelogram is helpful for patients who can't lie still, are too claustrophobic for MRI's or have metal imbedded. The myelographic dye provides better intra-canal differentiating than with CT alone. Myelography requires dye injected into the spinal dural sac and provides good information about extradural defects. 
       Myelogram or CT-Myelogram are invasive and both require radiation- disadvantages not shared by MRI.  In the face of inadequate pathology on MRI or CT, the chance is remote for Myelogram or CT-Myelogram to display the strong findings that would predict a reasonable. Non-invasive MRI has similar clarity without radiation.   
       The goal of imaging is usually three-fold.  Imaging seeks information about pressure upon the spinal cord which ends above L2 or nerve roots continuing below L1 in the lumbar spinal canal or in the intervertebral foramen through which the nerve roots pass to exit the spinal canal where they become exclusively postganglionic peripheral nerves.  Imaging also hemps verify other suggestions of the rare "Red Flags." 
      While 88% of back symptoms are bereft of a true diagnosis, a history of significant trauma (compatible with fracture or dislocation) piques concern about compromise of structural integrity. Similarly, a history and compatible examination for sciatica warrants consideration of neurological compromise in the spinal canal and nerve root foramen.  At present, the most commonly used imaging techniques for defining a potentially correctable cause for structural or neurologic compromise, are MRI or CT, as neither is invasive as is Myelography.  
A reasonable approach to reading MRI scans is as follows.  T1 weighted images make fat appear white and T2 weighted images make appear water white. 
       1. The MRI T1 Parasagittal views best evaluate fat in the foraminal canal. This fat vanishes before nerve roots can be compressed.  The parasagittal MRI T1 weighted lateral images make fat white in contrast to the nerve and other tissue in the canal (demonstrated in Figure 5).   
Figure 5. Parasagittal T1 images seeking loss of white fat due to foraminal compression. 
The parasagittal lateral views of the spine as depicted in Figure 5, are usually displayed from left to right allowing first view in the upper left hand corner to be of the far left aspect of the left nerve root foramen with each picture thereafter moving to the right until the lowest right image is right most of the right nerve root foramen.  Look for fat surrounding the exiting nerve root in the foramen (white on T1 weighted images) since any pressure will eliminate the fat before affecting the nerve.  Do not be alarmed if you cannot find fat on all foramen views, if fat is present in at least 2 parasagittal views there is probably no significant neural compromise.  Remember to record the level according to the 5th vertebra as the one above the sacrum, 4th is two above, et cetera.  The foramen is described according the vertebral body above and below, e.g., L5-S1 (Lumbar 5th-Sacral 1st) foramen or interspace, L4-L5 (Lumbar 4 - Lumbar 5).  
2. Next, quickly look at the Parasagittal MRI T2 weighted lateral images. In T2 the water is white (use the mnemonic that the 2 in H20 as an aide to memory).  Thus the white water contrasts with the other tissues.  The parasagittal view gives a lateral view similar to a lateral Myelo-CT where the myelographic dye makes the CSF (cerebrospinal fluid)  white as does the T2 weighted image.  Here, look at the contours of the spinal canal and potential indentations upon white fluid filled dural sac that contains the nerve roots before they exit through the foramen.  Evaluate the alignment of the vertebral bodies that form the anterior wall of the spinal canal. 
3. Finally, evaluate the T2 weighted cross-sectional images to evaluate indentations upon the dural sac, with its white watery fluid contents and nerves.  Think of the sac as a long water filled balloon that should be concave unless resting upon something that flattens or indents it.  We are most interested in the indentations that cause the sac to be convex.  This may indicate pressure on the neural contents and explain physical findings or EMG abnormalities relative to complaints of sciatica.  
Figure 6a. T2 weighted cross-sectional MRI image of extra-dural defect on right distinguished by displacement of herniated disc on dural sack filled Cerebral Spinal Fluid (H2O white) with dark nerve roots. 
The transverse T2 weighted images as demonstrated in Figure 6a allow the cross-sectional evaluation of extra-dural compression of the long water balloon like dural sac that contains the nerves to the lower extremities and perineum.  Look for the normally round, oval or at most a flattened surface of the dural sac.  When the normal round to flat contours of the sac become concave rather than convex there may be nerve roots compression, possibly causing pain into the extremities and interfering with their function (as seen on physical examination or EMG.    
Figure 6b. Aging changes on the right that sometimes cause Neuro-claudication due to Spinal Stenosis
Nerve roots can become choked by the aging process in the central canal or in the nerve root foramen (as seen with the obliteration of the fat in the foramen in T1 weighted parasagittal images).  Flattening of the aging disc reduces the anterior dimension of the canal and the posterior ligaments enfold as their distance shortens with collapse of the discs with subsequent osteophyte formation further limits the neural canals.  Decompression results are best for symptoms of neuroclaudication (walking less than 3 blocks due to leg symptoms). 
In summary, T1 (fat-white) parasagittal lateral views let you look for fat in the foramen that is obliterated before there is pressure on the nerve root.  T2 (H20-white) parasagittal views of the canal allow you to assess the contours of the vertebral alignment and compression of the water filled dural sac.  T2 (H20-white) cross-sectional views provide evaluation of the normally concave or flat dural sac that might have a concavity due to pressure on the sac and its contents.  If any doubts arise about the numbering of left to right or right to left on parasagittal views initiate a phone call to the reading neuroradiologist for verification.   
Remember, on all imaging studies over-reading is a necessity for the neuroradiologist.  Only emphasis can satisfy all potentially interested parties who might review the scan and alert the less adroit to points of interest, significant or not. 
Table 10: Major diagnostic entities related to specific treatment 
Go to Correctable Lesions found in work-up. 
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