When considering imaging of the lumbar spine, we can try to allocate individual presentations into discrete groups. These groups will have distinctly different utilisation of diagnostic imaging. The goal of this article is to assist the referring practitioner requesting the most appropriate test. A second part article will then discuss the most appropriate utilisation of radiological procedures to treat low back pain and radiculopathy.
In the setting of uncomplicated low back pain, or radiculopathy, with no red flags and no previous surgery, there is no advantage in referring for any diagnostic imaging. The reasons include lack of evidence relating to improved outcomes with imaging versus without imaging; the high prevalence of spinal abnormalities including annular disc bulge and facet joint DJD in asymptomatic patients ; and in the majority of patients, no specific pathology for low back pain can be identified. The current recommendations are for trial conservative management including physical activity, physiotherapy and pharmacological management.
If there is an associated low velocity trauma, osteoporosis, elderly individual, or chronic steroid use all three imaging modalities are considered to be appropriate, including X-ray, CT and MRI lumbar spine. X-ray is particularly useful in patients with osteoporosis or chronicsteroid use. CT has the advantage of detailed of osseous analysis, and is therefore useful if there is a high risk of fracture from trauma, or advanced analysis of facet joints when intervention is being considered. MRI has the advantage of demonstrating bone marrow oedema. MRI can also assist determine the acuity of a fracture and may differentiate malignant from benign compression fractures.
A subset of patients may present with an increased suspicion of cancer, infection or immunosuppression. In these specific cases MRI is highly recommended and CT could be considered only when MRI is not available readily. MRI has an advantage of being able to localise pathology as intramedullary, intradural–extramedullary, and extradural. MRI also offers a greater specificity than bone scan with similar sensitivity and an added advantage of improved anatomical detail. MRI is a necessity to detect abscess in the setting of an infection before there is extensive bone destruction visualised on CT or radiography. Technetium bone scan can be useful for problem-solving and in the setting of metastatic disease to assess the widespread tumour burden.
If the patient has persistent or progressive symptoms of low back pain, or radiculopathy not improving with conservative management, he or she may be a candidate for surgery or CT-interventional procedures. An MRI is strongly recommended, with a moderate recommendation for CT where MRI is unavailable, or if MRI is contra indicated. X-ray lumbar spine is not sufficiently detailed to provide information preoperatively or pre-CT intervention. MRI can accurately demonstrate disc abnormalities which may lead to spinal canal stenosis or nerve root compression. In one study a 57% prevalence of disc herniation was found in patients with low back pain and 65% prevalence in patients with radiculopathy and 28% prevalence in asymptomatic patients.
The patient may also present with new or progressive symptoms – signs with a history of previous lumbar surgery. The causes of these symptoms following surgery could include a free disc or bone fragment, post-operative fibrosis, failure of bone graft fusion, and recurrent disc protrusion. MRI with contrast is required to help differentiate the disc protrusion from surgical fibrosis. CT lumbar spine is recommended in the setting of previous spinal fusion as the metal hardware creates imaging artefact on MRI.
A final, relatively infrequent presentation is low back pain with suspected cauda equina syndrome (CES) or rapidly progressive neurological deficit. CES results from dysfunction of the sacral and lumbar nerve roots within the canal, resulting in impairment of the bladder and bowel, all sexual function and perianal numbness. The most common cause of CES is lumbar disc herniation at L4-5 and L5-S1 levels. MRI has the ability to accurately depict soft tissue pathology, vertebral marrow oedema and central canal patency .MRI is required in the setting as there is a significant limitation with CT lumbar spine which may not demonstrate the degree of spinal canal stenosis or nerve root impingement adequately.
Summary of Recommendations
- Uncomplicated acute LBP and/or radiculopathy are benign, self-limited conditions that do not warrant any imaging studies.
- MRI of the lumbar spine should be considered for those patients presenting with red flags raising suspicion for a serious underlying condition, such as cauda equina syndrome (CES), malignancy, or infection.
- In patients with a history of low-velocity trauma, osteoporosis, or chronic steroid use, initial evaluation with radiographs is recommended. High velocity trauma – CT or MRI.
- If there are persistent or progressive symptoms and the patient is a surgery or CT-intervention candidate, MRI of the lumbar spine has become the initial imaging modality of choice in evaluating complicated LBP. Medicare funding may preclude MRI and lead to CT in some situations.
- MRI is the imaging procedure of choice in patients suspected of cord compression or spinal cord injury.
- Patients with recurrent low back pain and history of prior surgical intervention should be evaluated with contrast-enhanced MRI.
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3. Modic MT, Obuchowski NA, Ross JS, et al. Acute low back pain and radiculopathy: MR imaging findings and their prognostic role and effect on outcome. Radiology. 2005;237(2):597-604.