Mednotes

L15 MSK Radiology 2 Vertebral Column (changed 3_4)

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tagsmsk, lecture
aliasesL15 MSK Radiology 2 Vertebral Column (changed 3_4)

15 min read

Overview

This lecture covers imaging of the vertebral column: regional anatomy of the spine and the imaging modalities used to assess it, normal radiographic anatomy of the cervical, thoracic and lumbar spine, indications for spine xray (red flags, the Canadian C-Spine Rule), classification and imaging features of spinal trauma (compression and burst fractures, pars interarticularis defects, Spondylolisthesis), degenerative disc disease and the resulting nerve root compression syndromes, vertebral metastatic disease, spinal infection (discitis/osteomyelitis), and image guided spinal procedures (steroid injection, myelography). Each topic is illustrated with a worked clinical case.

Vertebral column anatomy

  • Regions and vertebral counts: 7 cervical (8 cervical nerve roots), 12 thoracic, 5 lumbar, 5 sacral (fused), 1 coccyx.
  • Normal sagittal curvature vs abnormal postures shown: kyphosis and lordosis; hyperkyphosis, hyperlordosis and scoliosis (lateral curvature) as deviations from normal.
  • Generic vertebra, superior view: vertebral body, pedicle, vertebral arch, vertebral foramen, transverse process, superior articular process, lamina, spinous process, articular epiphysis.
  • Generic vertebra, lateral view: vertebral arch, superior articular process, spinous process, inferior articular process; a costal facet (for rib articulation) is present only on thoracic vertebrae.
  • C1 (atlas): anterior tubercle, anterior arch, lateral mass, transverse process, vertebral foramen, articular facet for the dens, transverse foramen, posterior arch, posterior tubercle, superior articular surface of the lateral mass (articulates with the occipital condyle).
  • C2 (axis): dens (odontoid process), superior articular facet, transverse foramen, transverse process, lamina, spinous process, inferior articular process, body.
  • Facet joint orientation becomes progressively more vertical moving down the spine (angle to transverse plane / angle to frontal plane): cervical C3-C7 45°/0°, thoracic 60°/20°, lumbar 90°/45°.

Imaging modalities

  • Xray: first-line assessment of trauma and back pain.
  • Fluoroscopy: procedures, myelography.
  • CT: bone detail, CT-guided biopsy, CT-guided steroid injection.
  • MRI: cord, nerves, cauda equina, vertebral column, muscles.
  • DSA (digital subtraction angiography): spinal angiography, venography, myelography.
  • Nuclear medicine: bone scan.
  • Ultrasound: fetal and neonatal spine only.

Normal radiographic anatomy by region

Cervical spine

  • Standard views: AP open-mouth (peg/odontoid) view and lateral view.
  • Lateral cervical spine landmarks: C1 anterior tubercle, C1 posterior arch, C1 posterior tubercle, C2 body and dens, C2 pars interarticularis, C3 lamina, C3/4 facet joint, C4 vertebral body, C5 spinous process, C6 articular pillar, C7 transverse process.
  • Four alignment lines checked on the lateral film: anterior vertebral line, posterior vertebral line, spinolaminar line, posterior spinous line.
  • Swimmer’s view: an additional lateral projection with its own patient positioning, used alongside the peg view. [slide does not elaborate on the specific indication beyond showing the positioning diagram]

Thoracic spine

  • Standard views: AP and lateral.
  • Numbered structures on the teaching image (key recovered from the duplicate handout thumbnail, not printed on the primary slide): 1 rib, 2 vertebral body, 3 costovertebral joint, 4 spinous process, 5 transverse process, 6 costotransverse joint, 7 intervertebral disc, 8 pedicle, 9 facet joint, 10 inferior articular process, 11 superior articular process, 12 intervertebral foramen.

Lumbar spine

  • AP view landmarks: S (sacrum), T (transverse process), P (pedicle), L (lamina), SP (spinous process).
  • Lateral view landmarks: T11, T12, disc spaces, L1 vertebral body, pedicles, L2, facet joints, L3, spinous processes, L4, pars interarticularis, inferior articular facets, L5, sacrum.

Indications for spine imaging

  • Significant trauma: xray vs CT. Cervical spine xray sensitivity is 50-60%; CT sensitivity is 98%, at roughly 10x the radiation dose.
  • Low back pain: xray has low diagnostic yield relative to its radiation dose; only image if red flags are present.
  • Red flags for low back pain (NZ Acute Low Back Pain Guidelines): features of Cauda Equina Syndrome; severe pain that worsens at night or on lying down; significant trauma; weight loss, history of cancer, or fever; use of IV drugs or steroids; age over 50.
  • Canadian C-Spine Rule (decision pathway for whether to xray after neck trauma):
    1. Any high-risk factor mandating radiography (age ≥65, dangerous mechanism, paraesthesia in the extremities)? If yes, radiograph.
    2. If no high-risk factor: is there a low-risk factor allowing safe assessment of range of motion (simple rear-end motor vehicle collision, sitting position in the ED, ambulatory at any time, delayed onset of neck pain, or absence of midline cervical spine tenderness)? If none present, radiograph.
    3. If a low-risk factor is present: can the patient actively rotate the neck 45° left and right? If unable, radiograph; if able, no radiography needed.

Spinal trauma

The Denis 3-column and AO fracture classifications are shown only as unlabelled schematic diagrams in the source slide; the transcript has no text definitions of the column boundaries or fracture subtypes. General principle given: a fracture involving two or more of the spinal columns is unstable.

  • Compression fracture, characteristic features: wedge-shaped vertebral body; cortical break in the upper anterior wall; horizontal sclerotic band of trabecular impaction; fracture of the superior endplate (less often the inferior endplate); posterior cortex of the vertebral body intact.
  • Burst fracture, characteristic features: retropulsion of a posterosuperior vertebral body fragment (a compression fracture may bulge the posterior cortex but does not displace it posteriorly); sagittal fracture of the vertebral body (90% of cases); sagittal fracture of a posterior element (85%); widening of the interpedicular distance (80%). The intact vs displaced posterior cortex is what distinguishes a burst fracture from a compression fracture.
  • Pars interarticularis defect: seen on oblique/lateral views as a break (the “collar” sign) in the “Scotty dog” outline.
  • Spondylolysis vs Spondylolisthesis: spondylolysis is the pars interarticularis defect itself; spondylolisthesis is the resulting anterior slip of one vertebral body relative to the one below, seen as forward displacement on sagittal CT or lateral xray.
  • Flexion teardrop fracture (case: 60-year-old male, fall from e-bike, immediate onset neck pain, midline tenderness on lateral cervical xray): features are spinal cord injury, ligamentum flavum tear, a teardrop-shaped anteroinferior body fragment, posterior subluxation, facet widening/dislocation, and widening of the interspinous distance.
  • Case (30-year-old male, jumped from a 3 metre wall, immediate back pain, tingling in the lower limbs): imaging showed an L1 burst fracture with retropulsion of the posterior cortex contacting the conus. [this diagnosis is stated only on the duplicate handout thumbnail of the slide, not visible on the primary render]

Degenerative disc disease and nerve root compression

  • Disc pathology spectrum (matched axial/sagittal appearance):
    • Normal disc morphology.
    • Disc bulge: involves more than 25% of the disc circumference (circumferential or asymmetric).
    • Disc protrusion: involves less than 25% of the circumference; the base of the disc material is wider than the herniation.
    • Disc extrusion: involves less than 25% of the circumference; the base is narrower than the herniation.
    • Disc sequestration: a free fragment of disc material with no connection to the parent disc.
  • Nerve root compression syndromes:
    • L4: weakness of quadriceps femoris and hip adductors; loss/diminishment of the patellar reflex; decreased sensation over the posterior thigh, anterior knee, medial leg, and medial malleolus.
    • L5: weakness of gluteus medius, extensor hallucis longus, extensor digitorum brevis; no reflex loss; decreased sensation over the anterolateral leg, dorsum of the foot, and the first web space (between toes I and II).
    • S1: weakness of gluteus maximus, gastrocnemius, fibularis longus, fibularis brevis and fibularis tertius; loss of the Achilles reflex; decreased sensation over the lateral malleolus, lateral foot, and dorsum of the fifth toe.
  • Management, in order: oral analgesia and physiotherapy; radiologically guided targeted analgesia (e.g. CT-guided transforaminal epidural steroid injection, needle placed at the neural foramen); surgery (discectomy, fusion) if these fail.
  • Imaging-symptom correlation caveat: low back pain affects up to two-thirds of people, and degenerative findings on spine MRI are also common in people with no symptoms, so imaging findings need to be correlated with the patient’s symptoms rather than assumed to explain the pain. Age-specific prevalence of degenerative spine MRI findings in asymptomatic people, by decade from the 20s to 80s (Brinjikji et al. 2015 AJNR): [table is small print on the source slide; values transcribed from the rendered image and should be cross-checked against the paper if precision matters]
    • Disk degeneration: 37% / 52% / 68% / 80% / 88% / 93% / 96%
    • Disk signal loss: 17% / 33% / 54% / 73% / 86% / 94% / 97%
    • Disk height loss: 24% / 34% / 45% / 56% / 67% / 76% / 84%
    • Disk bulge: 30% / 40% / 50% / 60% / 69% / 77% / 84%
    • Disk protrusion: 29% / 31% / 33% / 36% / 38% / 40% / 43%
    • Annular fissure: 19% / 20% / 22% / 23% / 25% / 27% / 29%
    • Facet degeneration: 4% / 9% / 18% / 32% / 50% / 69% / 83%
    • Spondylolisthesis: 3% / 5% / 8% / 14% / 23% / 35% / 50%

Vertebral metastatic disease

  • Case (54-year-old female, 6 months of atraumatic back pain, GP-requested AP lumbar xray). [a comparison image illustrating the “absent pedicle / owl’s eyes” sign, pedicle destruction from vertebral metastasis, is referenced on the duplicate handout thumbnail of this slide pairing but is not visible on the primary render, and its exact slide attribution is uncertain from the thumbnail layout]
  • Further work-up once metastasis is suspected: nuclear medicine whole-body bone scan, FDG PET-CT, CT chest/abdomen/pelvis.
  • Case (patient with a vertebral mass presenting with difficulty urinating): MRI showed a large expansile vertebral body lesion with epidural extension. Managed with surgical decompression and stabilisation (posterior pedicle screw and rod instrumentation). Histology: metastatic poorly differentiated adenocarcinoma, in keeping with a breast primary.

Spinal infection

  • Case (70-year-old male, back pain and feeling generally unwell; lumbar xray reviewed in the Emergency Department showed an abnormal process at L2-3): bloods showed an elevated white cell count and CRP 200 (markedly raised); blood cultures were taken; MRI spine was the next investigation.
  • Diagnosis: L1-2 discitis and osteomyelitis, assessed on MRI across T1, T2, STIR and contrast-enhanced (C+) sequences.
  • Complication: a right-sided soft tissue collection (psoas abscess), managed with CT-guided percutaneous drainage (catheter placed into the abscess cavity).

Image guided spinal procedures and safety

  • CT-guided transforaminal epidural steroid injection: needle advanced under CT guidance to the neural foramen.
  • MRI safety: a pacemaker and its leads are shown as a specific safety consideration before MRI scanning. [transcript records the images, a pacemaker on chest xray, but does not state the specific safety rule beyond flagging it as a safety topic]
  • Myelography: contrast is introduced into the subarachnoid space via a spinal needle passed through the epidural space; layers from superficial to deep are epidural space (with epidural needle), dura mater, arachnoid mater, subarachnoid space (containing the cauda equina), pia mater. Patient is positioned side-lying for the procedure.
  • Three ways of visualising the thecal sac and nerve roots: MR myelography (a heavily T2-weighted sequence showing CSF and nerve roots, no injected contrast), a conventional fluoroscopic myelogram (contrast injected into the subarachnoid space), and a CT myelogram (axial CT after intrathecal contrast, e.g. showing the L3, L4 and L5 nerve roots at the midline of their respective pedicles).

Self-test

  1. List the vertebral regions of the spine and the number of vertebrae (and cervical nerve roots) in each.
  2. Describe how facet joint orientation changes from the cervical to the lumbar spine.
  3. List the four alignment lines assessed on a lateral cervical spine xray.
  4. Compare the sensitivity of xray and CT for detecting cervical spine trauma, and the radiation cost of that difference.
  5. List the red flags that make imaging necessary in a patient with low back pain.
  6. A patient presents after a simple rear-end motor vehicle collision, is sitting in the emergency department, has no midline cervical tenderness, and has no high-risk factors. Using the Canadian C-Spine Rule, what determines whether she needs a cervical spine xray?
  7. Distinguish a compression fracture from a burst fracture, including the feature of the posterior vertebral body cortex that separates them.
  8. Distinguish spondylolysis from spondylolisthesis, and name the sign used to detect the pars defect on xray.
  9. Describe the classic history and imaging findings of a flexion teardrop fracture.
  10. Distinguish disc bulge, disc protrusion, disc extrusion and disc sequestration.
  11. Describe the motor, reflex and sensory findings of L4, L5 and S1 nerve root compression.
  12. A patient has weakness of extensor hallucis longus and gluteus medius, no reflex loss, and numbness over the first web space of the foot. Which nerve root is compressed?
  13. Why can spine MRI findings not be used alone to explain a patient’s back pain?
  14. Describe the step-up in management for degenerative disc disease causing back pain.
  15. Describe the “absent pedicle” (owl’s eyes) sign and what it indicates.
  16. Describe the work-up once vertebral metastasis is suspected on plain film, from further imaging to tissue diagnosis.
  17. Describe the typical MRI sequences and blood results used to diagnose discitis and osteomyelitis, and how an associated abscess is managed.
  18. Distinguish MR myelography, a conventional myelogram, and a CT myelogram.
  19. Integrative: a 45-year-old man with 6 months of low back pain develops reduced sensation over the anterolateral thigh and dorsum of the foot, with weakness of great toe extension. Which nerve root is affected, and what imaging would you request next?

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