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MR imaging of foraminal and extraforaminal lumbar disk herniations
N Grenier1, J F Gréselle, C Douws
1Service de Radiologie, Hôpital Pellegrin, Bordeaux, France.
Abstract:
Foraminal and extraforaminal disk herniations are less frequent than intraspinal herniations at the lumbar level and more difficult to diagnose. They are undetected by myelography and distinction between them and an enlarged nerve root may be difficult with CT. Thirty-three patients presenting with persistent radiculopathy and showing an image suggesting a far lateral disk herniation on CT at 34 disk levels were prospectively imaged with magnetic resonance (MR). In all cases the disk fragment was identified and its separation from the nerve root was possible. This separation was more readily visible on sagittal or angled coronal views. The exact location of the herniation in relation to the facet joints and the pedicles was best assessed with MR: Ten were purely intraforaminal, 8 extraforaminal, and 15 both. Cephalad migration was noted on the sagittal lateral facet plane in 71% of cases. Surgical correlations were available for 25 disks. Three were falsely positive for disk herniation. Enlarged foraminal veins were responsible for this appearance as confirmed by surgery in two of these. When a prediction of disruption of the lateral extension of the posterior longitudinal ligament was made, it was confirmed at surgery in 52% of cases because of extreme lateralization of the herniations.
Insights
Magnetic resonance (MR) imaging effectively diagnoses far lateral lumbar disc herniations, differentiating them from enlarged nerve roots. MR provides precise localization, aiding surgical planning for these challenging cases.
Area of Science:
- Neurosurgery
- Diagnostic Imaging
- Spinal Anatomy
Background:
- Foraminal and extraforaminal lumbar disc herniations are less common and harder to diagnose than intraspinal types.
- Myelography cannot detect these herniations; CT scans may confuse them with enlarged nerve roots.
Purpose of the Study:
- To evaluate the diagnostic efficacy of magnetic resonance (MR) imaging for far lateral lumbar disc herniations.
- To assess MR's ability to differentiate herniations from anatomical variants and determine their precise location.
Main Methods:
- Prospective imaging of 33 patients with persistent radiculopathy and suspected far lateral disc herniation on CT using MR.
- Analysis of MR images for herniation identification, nerve root separation, and localization relative to anatomical landmarks (facet joints, pedicles).
- Correlation of MR findings with surgical outcomes for 25 disk levels.
Main Results:
- MR imaging successfully identified disc fragments and their separation from nerve roots in all cases.
- Sagittal and angled coronal views enhanced visualization of nerve root separation.
- MR accurately classified herniations as intraforaminal, extraforaminal, or combined (10, 8, and 15 cases, respectively); 71% showed cephalad migration.
- Surgical correlation revealed 3 false positives due to enlarged foraminal veins; 52% of predicted posterior longitudinal ligament disruptions were confirmed.
Conclusions:
- MR imaging is superior to CT for diagnosing far lateral lumbar disc herniations, offering clear visualization and precise localization.
- MR aids in distinguishing herniations from enlarged nerve roots and identifying associated anatomical findings, improving surgical planning.