Nerve Root Compression Flashcards
Possible levels of nerve root compression?
- Disc level
- Lateral recess
- Foramen
- Extra foraminal
Where are nerves most commonly compressed?
Disc level; mostly by herniated discs (less frequently = spinal stenosis)
What is the lateral recess?
Area below disc where nerve runs more laterally towards the foramen
What causes narrowing of the lateral recess?
Decreased stability of vertebral column –> facet joint hypertrophy and arthritis, disc bulging, flavum ligament hypertrophy.
Facet arthrosis +/- hypertrophy of ligamentum flavum +/- disc bulge
What causes narrowing of the foramen?
- Facet arthrosis
- Spondylolisthesis
- Foraminal disc herniation (usually a migrated disc from a lower level)
Cause of extra foraminal compression?
Area lateral to the foramen; uncommon but usu due to laterally herniated disc
What is the ligament flavum?
Ligament on interior posterior side of vertebral canal connecting laminae of adjacent vertebrae
What causes ligamentum flavum hypertrophy?
Ageing and instability of vert column due to facet arthrosis; more stress on flavum ligament causing hypertrophy and fibrosis
What do facet arthritis and ligamentum flavum hypertrophy both produce?
Stenosis of the lateral recess; if bilateral = spinal stenosis
What is epidural fat?
fat surrounding the dural sac (contains nerves).
When is epidural fat increased?
- steroid therapy
- extreme obesity
- rare = idiopathic
Approach to MRI for ?spinal stenosis (protocol)?
Sagittal T1 and T2 with correlation on transverse sections (T2) at level of suspected pathology
Interpretation of ?spinal stenosis MRI?
Sag T1: 1. Prevert soft tissue (aorta) 2. Bone marrow / end plates 3. Four levels of compression Correlate with Tra T2
What is disc herniation?
Displacement of disc material (nucleus pulposus, annulus fibrosus, cartilage) beyond limits of IV disc space
What are the types of disc herniation? (related to size)
-Focal 180)
Protrusion v extrusion of disc?
Protrusion: distance between edges herniation
When are synovial cysts commonly seen?
In combo with facet arthrosis
What do synovial cysts most commonly cause?
- Stenosis of the lateral facet
- if XL can cause foraminal stenosis
What are the most common causes of spinal stenosis?
Bilateral facet arthrosis in combination with bulging of the disc and hypertrophy of ligamentum flavum
Less common causes of spinal stenosis?
- Congenital narrowing with short pedicles
- Spinal injury and epidural haematoma
- Bone tumours
- Spondylodiscitis or epidural abscess
- Spondylolisthesis
What is epidural lipomatosis?
Excessive fat within the epidural space compressing thecal sac. Presents with CFx of spinal canal stenosis.
What is spondylolisthesis?
One vertebra slips forward over the one below it (usu L4 on L5).
What is spondylolysis?
Stress fracture of the pars interarticularis
Annular tear v disc herniation
Tear: =annular fissure. Separations of annual fibres, avulsion from their vert insertions or breaks in annular lamellae
Herniation: displacement of disc material beyond limits of iv disc space
Bulging disc?
Circumferential disc tissue (180-360”) beyond edge of ring apophyses; not considered form of herniation. NP covered by intact AF
Migration v sequestration?
Migration: displacement of disc material away from site of extrusion
Sequestration: displaced material has completely lost continuity with parent disc
Descriptions of axial localisation herniated discs (midline to lateral)?
i) Central
ii) Paramedian/-central
iii) Foraminal
iv) Extraforaminal / lateral
Where and why are discs herniations most common?
Paramedian: PLL (posterior longitudinal ligament) is thinner in this region
