Summary of Ordering Guidelines
The following summaries are based on the Canadian Association of Radiologists Diagnostic Imaging Referral Guidelines (http://www.car.ca/en/standards-guidelines/guidelines.aspx). Physicians are encouraged to consult the full guidelines for more detailed information on recommended imaging for the wide range of patient conditions.
CT is most appropriate for the following indications:
- Patients with contraindications to MRI
- Patients who are hemodynamically unstable
- Initial assessment for fracture and malalignment in acute trauma
CT is more readily available than MRI and is often adequate for the following indications:
- Suspected uncomplicated lumbar degenerative disc disease (no “red flags”)
- Suspected lumbar spinal stenosis (no “red flags”)
MRI is the appropriate modality for the following indications:
- Myelopathy at any level
- Cervical radiculopathy
- Suspected discitis
- Suspected intraspinal abscess or hematoma
Depending on the condition in question, it may still be most appropriate to refer a patient for a consultant’s opinion prior to requesting an imaging procedure. Please consider the following common neuroimaging requests from this perspective:
Plain films are adequate to document bony changes related to degenerative disc and facet disease. CT does not add significant information about bony changes and resolves soft tissue changes poorly in the cervical spine. Therefore, CT should not be used for the work-up of suspected degenerative disc or facet disease in the cervical spine.
MRI is most appropriate for the depiction of disc bulges, disc herniations, nerve root impingement and cord compression in the cervical spine. However, it should be reserved for cases with clear findings of radiculopathy or myelopathy.
Low back pain
In patients with low back pain, imaging is only indicated after an unsuccessful 4-6 week trial of conservative management. Imaging should be done more urgently in the presence of “red flags” such as: suspected cancer, suspected infection, cauda equine syndrome, and severe/progressive neurological deficit.
Although MRI is better than CT at assessing the contents of the spinal canal, CT is more readily available and is often adequate for initial triage in the lumbar spine.
For patients with acute trauma at any level of the spine, CT is the appropriate first-line imaging for fractures and malalignment. CT imaging of the spine can be combined with CT imaging of the chest, abdomen and/or pelvis to assess for injuries of solid organs and hollow viscera. Unstable trauma patients are better managed in the CT scanner than the MRI scanner. MRI may be required as second-line imaging to assess for ligamentous injury, traumatic disc herniation and intraspinal hematoma in patients who have fractures or malalignment demonstrated on CT, or who have a neurological deficit referable to spinal cord or nerve roots.
MRI scanners can only provide high quality images over a small volume, covered by a dedicated MRI “coil”. Imaging protocols typically cover the cervical spine OR the thoracic spine OR the lumbar spine. Multiple levels of the spine can be scanned in succession, but this can make the examination very long and difficult for patients to tolerate. It is therefore very important, whenever possible, to narrow the level of concern down to a single level by careful history and neurological examination. If this cannot be done, consultation with an appropriate specialist may be helpful to determine the most effective imaging protocol.
Gadolinium enhancement is not necessary for most spine imaging. Notable exceptions are infectious and neoplastic conditions, as well as the postoperative spine (i.e. distinguishing residual/recurrent disc herniation from scar tissue). It is therefore very important to provide relevant history (e.g. fever, leukocytosis, known primary malignancy, known metastatic disease in other parts of the body, or prior surgery at the level to be imaged) with the MRI requisition. If gadolinium enhancement is likely, it is important to provide a recent serum creatinine level with the MRI requisition.