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MRI and CT-Myelography 
 
Panel findings and recommendations: 
 -   In the presence of Red Flags suggesting cauda equina syndrome or progressive major motor weakness, the prompt use of CT, MRI, myelography, or CT-myelography is recommended.  Because these serious problems may require prompt surgical intervention, planning for use of such imaging studies is best done in consultation with a surgeon. (Strength of Evidence = C.) 
 -   CT, MRI, myelography, or CT-myelography and/or consultation with an appropriate specialist is recommended when clinical findings strongly suggesting tumor, infection, fracture, or other space-occupying lesions of the spine.  (Strength of Evidence = C.) 
 -   Routine spinal imaging tests are not generally recommended in the first month of symptoms except in the presence of red flags for serious conditions.  After 1 month of symptoms, an imaging test is acceptable when surgery is being considered (or to rule out a suspected serious condition).  (Strength of Evidence = B.) 
 -   For patients with low back problems who have had prior back surgery, MRI with contrast appears to be the imaging test of choice to distinguish disc herniation from scar tissue associated with prior surgery.  (Strength of Evidence = D.) 
 -   CT-myelography and myelography are invasive and have an increased risk of complications.  These test are indicated only in special situations for preoperative planning.  (Strength of Evidence = D.) 
 -   The following are minimal quality criteria for imaging studies of the lumbar spine (Strength of Evidence = B): 
1.  CT and MRI cuts to be made no wider than 0.5 cm and parallel to the vertebral endplates. 
2.  MRI scanners to have a magnetic field strength no less than 0.5 T (tesla) and to allow a scanning time adequate for optimal image acquisition. 
3   Myelography and CT-myelography to use water-based contrast media. 
4   The technical protocols for these imaging tests to be described on radiologist reports.   
 
  Introductory Discussion.  The four imaging tests commonly used in assessing the anatomy of the lumbar spinal canal and its contents are plain myelography, CT scan, MRI scan, and CT-myelography.  These four tests are discussed as a group because they are used in similar clinical situations, provide similar types of information, and are often compared with each other in research studies.  Evaluation is limited by lack of a gold standard for evaluating efficacy.  Each test and the type of information it provides are described briefly as follows: 
 -   CT scans use multiple x-ray beams projected at different angles and levels to produce computer-generated axial cross-sectional images of the body. 
 -   MRI scans use magnetic fields to produce computer-generated axial and sagittal cross-sectional images of the body. 
 -   Plain myelography is invasive using plain x-rays, taken after a nonionic water- soluble contrast media is injected into the spinal canal via lumbar puncture needle, to produce images of the borders and contents of the dural sac. 
 -   CT-myelography uses a CT scan, done after a contrast media has been injected into the dural sac in the same manner as for plain myelography, to produce axial cross-sectional images of the spine that enhance distinction between the dural sac and its surrounding structures. 
 
  Significant technological advances have taken place in these imaging modalities over the past several years.  Kent, Haynor, Larson, et al.297 have suggested technical criteria for the performance of these imaging tests to assure a minimal level of quality.  Studies of imaging tests were not considered by the panel if the technical protocols were inadequately described or if the protocols varied significantly among subjects within a study.  The panel used the following technical criteria for including studies of individual imaging modalities: 
 -   For myelography, contrast media should be water based, not oil based. 
 -   For CT scans, the axial images (cuts) should be no wider than 0.5 cm and should be parallel to the vertebral endplates. 
 -   For MRI scans, the image quality should be equivalent to or better than scans with magnetic field strength >0.5 T with an adequate scanning technique.  Because of significant advances in technology, studies of MRI scans before 1985 were not considered. 
 
  The objective of using these imaging tests for patients with low back problems is to define medically or surgically remediable anatomic pathological conditions.  Therefore, the tests are not done routinely, but are generally used only for patients who present with one of these three clinical situations: 
 -   Back-related leg symptoms and clinically specific detectable nerve root compromise with symptoms severe enough to consider surgical intervention. 
 -   A history of neurogenic claudication and other findings suggesting spinal stenosis with symptoms severe enough to consider surgical intervention. 
 -   Clinical examination findings or other test results suggesting other serious conditions affecting the spine (such as cauda equina syndrome, spinal fracture, infection, tumor, or other mass lesions or defects). 
 
  This section assesses the usefulness of the four imaging tests for diagnosing nerve root compromise due to herniated discs or spinal stenosis. The use of imaging tests for evaluating other serious conditions affecting the spine is beyond the scope of this guideline and is not discussed in detail here. 
 
Imaging for Nerve Root Compromise (Suspected Disc Herniation
Literature Reviewed     Evidence on Efficacy   Potential Harms and Costs      Summary of Findings     Author's Example 
 
Imaging Tests for Neuroclaudication (Suspected Spinal Stenosis
Literature Reviewed     Evidence on Efficacy   Potential Harms and Costs      Summary of Findings     Author's Example 
 
Spinal Imaging Findings Subjects without Symptoms  
Literature Reviewed     Evidence on Efficacy   Potential Harms and Costs      Summary of Findings     Author's Example 
 
 
Imaging Discussion 
The AHCPR Guide #14 for back problems published in 1994 realized that imaging studies (MRICT scans) can be very confusing because of the aging changes common in asymptomatic people (Imaging in subjects without pain).  Thus, they recommend reducing the confusion of imaging studies by being guided by confirming physiologic findings (of obvious L5 or S1 radiculopathy on exam or EMG evidence of nerve root compromise, Bone Scan or X-ray evidence of structural compromise) to use imaging more appropriately.  A quick review of an approach to understanding the MRI reading is available (Author's Example).  The general approach to avoid confusion is in the Author's Examples about logical Diagnostics for slow recovery to limit the confusion with early use of imaging. 
 
  Summary of AHCPR Findings.  Given the benign natural history of low back problems, with 80 to 90 percent of patients expected to improve at 1 month even without treatment, routine spinal imaging tests are not generally necessary during the first month of symptoms except when a red flag (suggesting a medically emergent condition) is noted on medical history and physical examination.  After 1 month of symptoms, the use of imaging tests may be appropriate when surgery is being considered for a specific detectable loss of neurologic function or to further evaluate possibly serious spinal pathology in the presence of red flags (Pengel et al.`03).   
 
Carragee`05 article on persistent low back pain suggests over-use of imaging studies risks reinforcing the suspicion of serious disease, magnifying the importance of nonspecific findings, labeling patients with spurious diagnoses.  Indications for imaging include strong neurologic signs, "Red Flags" for cauda equinae symptoms, systemic symptoms, risk factors for cancer, infection, or occult fractures and persistent symptoms >4-8 weeks.  He warns "Patients should understand that imaging is to rule out serious conditions, and to expect degenerative findings".  
 
Be aware that studies find 70-80% of chronically disabled patients to have psychological distress on psychometric testing or have disputed compensation issues compared to an extremely generously 20-30% at most to have definite pathologic or destructive processes imaging studies reveal(, Carragee`01 ,Cairns`03). Thus, confounded clinicians should not become too desperate in not finding the cause of symptoms even when sensing an exaggerated fear of pain with beneficial activities, psychological distress, disputed compensation claims, involvement in a tort-compensation system or patient dissatisfaction (Burton`95, Carragee`05, Boos`00, Cassidy'03)  (See also Neck Imaging
 
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