How can I determine when to refer a patient for an MRI versus a CT scan for suspected neurological conditions?

When determining whether to refer a patient for an MRI versus a CT scan for suspected neurological conditions, the choice often depends on the specific condition suspected, the urgency, and whether MRI is contraindicated NICE NG234,NICE CKS,NICE CKS,NICE NG232.

Conditions where MRI is generally preferred or indicated:

• For suspected spinal metastases or metastatic spinal cord compression (MSCC), an MRI scan should be offered as soon as possible, ideally within 24 hours for MSCC, or within 1 week for spinal metastases without MSCC NICE NG234. MRI of the spine should include specific sequences to identify metastases and assess cord compression NICE NG234.
• In adults with progressive, sub-acute loss of central neurological function, an urgent direct access MRI scan of the brain should be considered within 2 weeks to assess for brain or central nervous system cancer NICE CKS,NICE CKS.
• For people over 16 who have had a suspected transient ischaemic attack (TIA) or acute non-disabling stroke, after specialist assessment in a TIA clinic, MRI (including diffusion-weighted and blood-sensitive sequences) should be considered on the same day to determine the territory of ischaemia, detect haemorrhage, or identify alternative pathologies NICE NG128.
• For trigeminal neuralgia, an MRI scan is indicated in younger people (advised under 40 years), those with atypical symptoms, individuals who do not respond to initial therapy, or anyone for whom neurosurgery is being considered NICE CKS. Referral to a specialist for MRI assessment is recommended NICE CKS.
• If there is a neurological abnormality that could be attributed to spinal cord injury, an MRI should be performed after a CT scan, regardless of whether the abnormality is evident on the CT NICE NG41.

Conditions where CT is generally preferred or indicated:

• For detecting an acute clinically important traumatic brain injury, CT imaging of the head is the current primary investigation of choice NICE NG232. MRI is generally not used as the primary investigation for acute traumatic brain injury due to safety, logistic, and resource reasons NICE NG232.
• In adults (16 or over) with spinal injury, perform CT if imaging for cervical spine injury is indicated by the Canadian C-spine rule, or if there is a strong suspicion of thoracic or lumbosacral spine injury associated with abnormal neurological signs or symptoms NICE NG41. Whole-body CT is used in adults with blunt major trauma and suspected multiple injuries NICE NG41.
• If MRI is contraindicated for suspected spinal metastases or MSCC, a CT scan should be carried out NICE NG234. Similarly, for suspected brain or central nervous system cancer in adults, a CT scan can be considered if MRI is contraindicated NICE CKS,NICE CKS.
• CT scans can also be considered for multiplanar viewing or 3-plane reconstruction in people with spinal metastases or MSCC to assess spinal stability and plan procedures NICE NG234.

Other considerations:

• Plain X-rays of the spine should not be performed to diagnose or rule out spinal metastases or MSCC NICE NG234. Similarly, plain X-rays of the skull should not be used to diagnose important traumatic brain injury without discussion with a neuroscience unit NICE NG232.
• For suspected functional neurological disorder (FND), structural and functional neuroimaging can help differentiate FND from other neurological disorders, but a neurology consultant with appropriate expertise should ideally make the diagnosis to reduce unnecessary investigations NICE CKS.