Radiology · Year 4 · from Radiology

Case 2: MRI Safety - Ferromagnetic Implant Screening

Patient Demographics

  • Age: 58 years
  • Sex: Female

Chief Complaint

Progressive low back pain with radiculopathy, referred for lumbar spine MRI

Presenting Symptoms

The patient reports 6 weeks of progressively worsening low back pain radiating down the left posterior thigh to the calf. She describes numbness in the lateral foot and weakness with toe walking. Medical history includes coronary artery disease with a drug-eluting stent placed 3 years ago and a pacemaker implanted 8 years ago for sick sinus syndrome.

Physical Exam Findings

  • Vital Signs: BP 132/78 mmHg, HR 62 bpm (paced rhythm)
  • Neurological: Decreased sensation in L5-S1 dermatomal distribution on left, weakness of left ankle plantarflexion (4/5), diminished left ankle reflex
  • Spine: Tenderness over lower lumbar spinous processes, positive straight leg raise at 45 degrees on left

Imaging Findings and Interpretation

MRI Safety Screening: The patient's pacemaker implant card is reviewed. The device is a St. Jude Medical Accent PM2112 implanted in 2016 - this is NOT an MRI-conditional device. The manufacturer documentation indicates the device is MRI unsafe due to the following risks:

  • Heating of leads causing tissue damage
  • Induced currents causing inappropriate pacing or inhibition
  • Reed switch activation causing asynchronous pacing
  • Device movement or dislodgement
  • Permanent device damage

Alternative Imaging Decision: Given the absolute contraindication to MRI, CT myelography is recommended as an alternative to evaluate the lumbar nerve roots and detect disc herniation or stenosis.

CT Myelogram Findings: Following intrathecal injection of iodinated contrast, CT imaging demonstrates:

  • Large left posterolateral disc herniation at L5-S1
  • Compression of the traversing left S1 nerve root
  • Moderate central canal stenosis at this level
  • No evidence of cauda equina compression

Diagnosis

L5-S1 disc herniation with S1 radiculopathy; MRI contraindicated due to non-MRI-conditional pacemaker

Management

  1. Conservative management with physical therapy and oral analgesics initially
  2. Epidural steroid injection under fluoroscopic guidance if symptoms persist
  3. Surgical consultation if progressive neurological deficit or failed conservative management
  4. Discussion with electrophysiology regarding upgrade to MRI-conditional pacemaker at next device change if MRI surveillance will be needed

Radiological Image

Image Description: CT myelogram demonstrating contrast within the thecal sac, which outlines the nerve roots and can demonstrate compression from disc herniation. This modality serves as an alternative to MRI when MRI is contraindicated.

Source: Wikimedia Commons - "CT myelogram" URL: https://commons.wikimedia.org/wiki/File:Myelogram_showing_cord_compression.jpg License: Creative Commons Attribution-Share Alike 3.0 Unported

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