Can MRI neurography help diagnose a thermal burn to a nerve in a patient with a sacral nerve stimulator (SNS) after MRI radiofrequency exposure?

MRI Neurography for Diagnosing Thermal Nerve Injury from Sacral Nerve Stimulator RF Exposure

Yes, MRI neurography can help diagnose thermal nerve injury to sacral nerves following radiofrequency exposure during MRI, as it is superior to CT for detecting soft-tissue nerve pathology including thermal injury, edema, and inflammation.

Diagnostic Capability of MRI Neurography for Nerve Injury

MRI neurography is the optimal imaging modality for evaluating nerve injury because:

• MRI demonstrates superior soft-tissue contrast and spatial resolution for directly assessing nerve integrity, edema, inflammation, and injury patterns that would be expected from thermal burns 1

• MRI can detect intraneural signal abnormalities, nerve edema, and inflammatory changes that characterize thermal injury to neural tissue 1

• MRI is superior to CT in identifying soft-tissue pathologies including nerve injury, with the ability to characterize the extent of nerve damage 1

Specific Findings Expected with Thermal Nerve Injury

If thermal injury occurred to the sacral nerves from RF heating, MRI neurography would likely demonstrate:

• Abnormal intraneural T2 signal hyperintensity indicating nerve edema and inflammation from thermal damage 1

• Nerve thickening and enhancement if contrast is administered, reflecting inflammatory response to thermal injury 1

• Surrounding soft-tissue edema and inflammation in the region of the nerve stimulator leads 1

Critical Safety Context: RF Heating Risk

The clinical scenario raises important safety considerations:

• Phantom studies demonstrate that intact sacral neuromodulation systems show minimal heating (<1°C) during 1.5T MRI of lumbar and pelvic regions, with no significant temperature rise detected in intact device configurations 2

• However, isolated intact leads can show heating up to 5°C, which could potentially cause thermal nerve injury 2

• Clinical studies of patients with InterStim sacral nerve stimulators undergoing 1.5T MRI (with devices deactivated and scans performed outside the pelvis) showed no adverse effects, though these were not pelvic/sacral region scans 3, 4

• RF heating sensation increases approximately 10-fold from 1T to 3T MRI, though the presence of metallic implants did not significantly increase heating sensation in spine studies 5

Imaging Protocol Recommendations

For suspected thermal nerve injury from sacral nerve stimulator RF exposure, obtain dedicated MRI lumbosacral plexus/sacral nerve imaging with the following specifications:

• MRI without and with IV contrast is preferred to differentiate vascular structures from nerves and to detect enhancement patterns suggesting nerve inflammation 1

• Delay imaging approximately 1 month after the suspected thermal injury to allow acute edema and hemorrhage to evolve into more characteristic patterns of nerve injury 1

• Use dedicated nerve imaging sequences optimized for neurography rather than standard pelvic MRI, as these provide superior nerve visualization 1

Common Pitfalls to Avoid

• Do not perform standard pelvic MRI instead of dedicated lumbosacral plexus/nerve imaging, as standard protocols are not optimized for nerve visualization 1

• Avoid immediate post-injury imaging, as acute hemorrhage and edema may obscure nerve pathology; waiting 3-4 weeks allows better characterization 1

• Recognize that the device itself creates significant artifact that may limit visualization of immediately adjacent neural structures, though more distant nerve segments should be evaluable 1

Clinical Decision Algorithm

1. If thermal nerve injury is suspected clinically (new neurologic symptoms, pain, sensory changes after MRI exposure): Obtain dedicated MRI lumbosacral plexus with and without contrast 1

2. If imaging is performed acutely (<1 month): Expect suboptimal visualization due to edema/hemorrhage; consider repeat imaging at 4 weeks 1

3. If MRI demonstrates abnormal intraneural signal, enhancement, or nerve thickening in the distribution of sacral nerve stimulator leads: This supports thermal injury diagnosis 1

4. Correlate imaging findings with electrodiagnostic studies (EMG/nerve conduction) to confirm functional nerve injury 1