When to use computed tomography (CT) scan versus magnetic resonance imaging (MRI) for diagnosing low back pain (lumbar pain)?

From the Guidelines

For diagnosing low back pain, MRI scans are generally preferred over CT scans due to their superior soft tissue contrast and lack of ionizing radiation, especially when evaluating for soft tissue-related issues such as herniated discs, nerve compression, or spinal cord problems 1. When it comes to choosing between computed tomography (CT) scans and magnetic resonance imaging (MRI) for diagnosing low back pain, several factors must be considered, including the suspected underlying condition, the need for soft tissue evaluation, and the presence of any contraindications to MRI, such as certain metallic implants.

Key Considerations for Choosing Between CT and MRI

• Soft Tissue Evaluation: MRI is preferred for evaluating soft tissue-related issues such as herniated discs, nerve compression, spinal cord problems, or ligament injuries because it provides superior soft tissue contrast without the use of ionizing radiation 1.
• Bone-Related Issues: CT scans are typically recommended when there's suspicion of bone-related issues such as fractures, bone infections, or tumors, as they offer better bone visualization and can be performed quickly, making them suitable for emergency situations 1.
• Complex Spinal Structures: CT scans are also useful for evaluating complex spinal structures, especially in cases where MRI might not provide sufficient detail due to artifacts from surgical hardware or other factors 1.
• Previous Lumbar Surgery: In patients with a history of prior lumbar surgery, MRI lumbar spine without and with IV contrast is useful for distinguishing recurrent or residual disc herniations from scar and for evaluating nerve root compression or arachnoiditis 1.

Recommendations Based on Recent Evidence

• MRI for Soft Tissue: For patients with low back pain where soft tissue evaluation is necessary, MRI is the preferred initial imaging modality due to its superior soft tissue contrast and lack of ionizing radiation 1.
• CT for Bone-Related Issues: For suspected bone-related issues, CT scans are recommended as they provide better bone visualization and are quicker to perform, which is advantageous in emergency situations 1.
• Consideration of Patient History and Symptoms: The choice between CT and MRI should be based on the patient's symptoms, medical history, and initial examination findings, with consideration given to the most likely underlying cause of the low back pain 1.

From the Research

Indications for CT Scan

• CT scan is recommended when there is concern for fracture of the lumbar spine 2
• Multidetector CT is preferred in such cases due to its high accuracy in detecting fractures

Indications for MRI

• MRI is recommended for patients with severe or progressive neurologic deficit on presentation and red flags 2
• Patients with low back pain lasting for > 6 weeks having completed conservative management with persistent radiculopathic symptoms may seek MRI 2
• MRI is also indicated for the evaluation of patients with risk factors for neoplastic or infectious disorders or in persons with coexisting evidence of neurologic impairment 3
• MRI is recommended for patients with suspicion of cancer, spinal infection, or fracture, even with a negative X-ray test 4
• MRI is also indicated for patients with inflammatory back pain, severe/progressive neurological deficit, severe and progressive low back pain, or subacute or chronic low back pain with radicular involvement unresponsive to conservative therapy 4

General Guidelines

• Imaging is not necessary for most patients presenting with uncomplicated acute low back pain and/or radiculopathy 2
• National guidelines discourage the use of MRI in non-specific low back pain and recommend reserving it for the investigation of severe or progressive neurological deficits or for those cases in which serious underlying pathology is suspected 5
• Lumbar MRI provides high-resolution, multiaxial, multiplanar views that have high contrast between soft tissues, but its diagnostic accuracy for most lumbar anatomic impairments related to the symptoms of low back pain is low or unknown 3
• MRI cannot be used to guide treatment, and its use should be limited to patients with progressive neurological deficits, suspicion of specific pathology, or in absence of progress of conservative treatment 6