High Yield Overview
Spine Imaging: Systematic Interpretation
Comprehensive Vertebral Column Assessment
ABCSSystematic Approach
3-ColumnDenis Classification
CTTrauma Gold Standard
MRISoft Tissue/Cord
Spine Imaging Modality Selection
Plain Radiograph
PatternFirst-line, alignment, gross pathology
TreatmentLow dose, limited sensitivity
CT
PatternTrauma, fracture detail, bone pathology
TreatmentGold standard for bony injury
MRI
PatternSoft tissue, disc, cord, ligaments, infection
TreatmentNo radiation, superior soft tissue
CT Myelogram
PatternWhen MRI contraindicated
TreatmentInvasive, good for stenosis
Critical Must-Knows
- Alignment: Anterior vertebral line, posterior vertebral line, spinolaminar line, spinous process tips.
- CT for trauma: Gold standard for bony injury. Reconstructions in sagittal and coronal planes essential.
- MRI for cord/soft tissue: Disc herniation, ligamentous injury, cord compression/signal, infection.
- Instability indicators: PLC injury on MRI, translation greater than 3.5mm, angulation greater than 11 degrees (cervical).
- Red flags: Cord signal change, epidural hematoma/abscess, pathological fracture features.
Examiner's Pearls
- "Hangman fracture: Bilateral C2 pars fracture - check for C2-3 disc injury on MRI.
- "Jefferson fracture: C1 burst - lateral mass overhang greater than 7mm suggests TAL rupture.
- "Chance fracture: Horizontal splitting through vertebra - high association with abdominal injury.
- "STIR sequence best for detecting bone marrow edema and ligamentous injury.
- "Modic changes: Type 1 (edema), Type 2 (fatty), Type 3 (sclerosis).
Never Clear C-spine on Plain Films Alone in Major Trauma
Plain radiographs miss up to 50% of cervical spine injuries. CT is mandatory for clearance in obtunded patients or those with high-risk mechanisms. MRI is indicated if neurological deficit, suspected ligamentous injury, or CT findings suggest instability.
Systematic Approach
ABCS Method for Spine Radiographs
Mnemonic
ABCSSystematic Spine X-ray Interpretation
A
Alignment
Four lordotic lines: anterior vertebral, posterior vertebral, spinolaminar, spinous tips
B
Bone
Vertebral body height, pedicles, facets, spinous processes
C
Cartilage/Disc
Disc space height, end plates, facet joints
S
Soft Tissue
Prevertebral swelling (cervical), paraspinal lines (thoracic/lumbar)
Memory Hook:Always Be Checking Systematically
Alignment Assessment
Four Lines to Trace:
- Anterior vertebral body line
- Posterior vertebral body line (anterior spinal canal)
- Spinolaminar line (posterior spinal canal)
- Tips of spinous processes
Normal Measurements:
- Predental space: Less than 3mm adult, less than 5mm child
- Retropharyngeal space (C2-4): Less than 7mm
- Retrotracheal space (C6): Less than 22mm
- Basion-dens interval: Less than 12mm
Plain Radiograph Interpretation
Cervical Spine Views
Cervical Spine Radiograph Views
| View | Assessment | Key Findings |
|---|---|---|
| AP | Spinous process alignment, lateral masses | Unilateral facet dislocation (rotation) |
| Lateral | Alignment, vertebral bodies, disc spaces | Fractures, subluxation, soft tissue swelling |
| Odontoid (Open Mouth) | C1-C2 articulation, dens | Odontoid fractures, Jefferson fracture |
| Oblique | Neural foramina, facet joints | Foraminal stenosis, facet pathology |
| Flexion/Extension | Dynamic stability | Ligamentous instability (when safe) |
Thoracolumbar Spine Views
AP View
- Vertebral body alignment
- Pedicle integrity (winking owl sign)
- Transverse process fractures
- Paraspinal soft tissue lines
- Spinous process alignment
Lateral View
- Vertebral body height (anterior vs posterior)
- Disc space height
- Posterior vertebral body line
- Facet joint alignment
- Kyphotic angle measurement
Soft Tissue Signs
Prevertebral Soft Tissue Swelling
Cervical spine - suggests occult injury:
- C1-C4: Should be less than 7mm (less than 1/3 vertebral body width)
- C5-C7: Should be less than 22mm (less than vertebral body width)
Causes: Fracture, ligamentous injury, hematoma, abscess, tumor
Thoracolumbar:
- Paraspinal line displacement suggests hematoma/mass
- Loss of psoas shadow may indicate retroperitoneal pathology
CT Interpretation
CT for Spinal Trauma
CT is the Gold Standard for Spinal Fracture Assessment
Advantages over plain radiography:
- Detects fractures missed on X-ray (especially upper/lower cervical)
- Characterizes fracture pattern precisely
- Multiplanar reconstructions (sagittal, coronal)
- 3D reconstruction for complex injuries
- Rapid acquisition in trauma setting
Standard protocol:
- Thin slices (less than 1mm) for quality reconstructions
- Bone and soft tissue windows
- Sagittal and coronal MPR essential
Fracture Assessment on CT
CT Fracture Analysis
| Feature | What to Assess | Significance |
|---|---|---|
| Vertebral body | Compression, burst, height loss | Load-bearing capacity |
| Posterior elements | Pedicles, laminae, facets | Stability, canal compromise |
| Spinal canal | Fragment retropulsion, stenosis | Cord compression risk |
| Facet joints | Dislocation, fracture, widening | Instability indicator |
| Transverse processes | Fractures | Associated injuries (lumbar plexus) |
Three-Column Model (Denis)
Mnemonic
AMPDenis Three-Column Spine Model
A
Anterior Column
Anterior longitudinal ligament, anterior 2/3 vertebral body and disc
M
Middle Column
Posterior 1/3 vertebral body and disc, posterior longitudinal ligament
P
Posterior Column
Pedicles, facets, laminae, spinous processes, posterior ligamentous complex
Memory Hook:Two or more column injury suggests instability
MRI Interpretation
MRI Sequences for Spine
Spine MRI Sequences
| Sequence | Best For | Key Findings |
|---|---|---|
| T1-weighted | Anatomy, marrow, fat | Vertebral body infiltration, anatomy |
| T2-weighted | CSF, cord, disc hydration | Cord compression, myelopathy signal |
| STIR | Bone marrow edema, ligament injury | Acute fractures, PLC injury, infection |
| T1 + Gadolinium | Enhancement, infection, tumor | Abscess rim, tumor vascularity |
| T2* GRE | Hemorrhage, disc osteophyte | Cord hemorrhage, calcification |
Disc Assessment
Disc Bulge: Circumferential extension beyond vertebral body margins (greater than 50% circumference)
Disc Herniation: Focal extension (less than 50% circumference)
- Protrusion: Base wider than apex
- Extrusion: Apex wider than base, may extend above/below disc level
- Sequestration: Free fragment, no continuity with parent disc
Imaging Gallery: Lumbar Spine MRI Systematic Assessment
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Spinal Cord Assessment
Cord Signal Abnormalities
T2 Hyperintensity in Cord:
- Myelopathy/edema
- Cord contusion
- Myelitis
- Ischemia
- Tumor
T1 Hypointensity:
- Edema (acute)
- Myelomalacia (chronic)
- Syrinx
T2 Hypointensity (dark):
- Hemorrhage (acute)
- Hemosiderin (chronic)
Expansion: Tumor, syrinx, acute contusion Atrophy: Chronic myelopathy, prior injury
Ligamentous Injury (MRI)
Posterior Ligamentous Complex (PLC) Assessment
Components:
- Supraspinous ligament
- Interspinous ligament
- Ligamentum flavum
- Facet capsules
MRI findings of PLC injury:
- STIR hyperintensity in interspinous region
- Discontinuity of ligaments
- Facet widening/fluid
- Spinous process widening
Significance: PLC injury is key determinant of instability in thoracolumbar fractures (TLICS)
Specific Conditions
Degenerative Disease
Modic Changes (Vertebral Endplate)
| Type | T1 Signal | T2 Signal | Pathology |
|---|---|---|---|
| Type 1 | Low (dark) | High (bright) | Edema, inflammation (active) |
| Type 2 | High (bright) | High/iso | Fatty replacement (stable) |
| Type 3 | Low (dark) | Low (dark) | Sclerosis (end-stage) |
Infection
Spondylodiscitis MRI Features
Classic triad:
- Disc space narrowing and T2 hyperintensity
- Adjacent vertebral body edema (STIR bright)
- Endplate erosion/destruction
Additional findings:
- Epidural abscess (rim enhancement)
- Paraspinal abscess
- Loss of intranuclear cleft sign
- Enhancement of disc and endplates
Differentiation from Modic 1: Infection destroys endplate, Modic 1 preserves it
Tumor/Metastases
Spinal Metastases Imaging
MRI findings:
- T1 hypointense lesion (marrow replacement)
- T2 variable (often hyperintense)
- Enhancement with gadolinium
- Pedicle involvement (winking owl on X-ray)
- Soft tissue mass, epidural extension
Red flags for pathological fracture:
- Pedicle destruction
- Posterior element involvement
- Convex posterior vertebral body
- Paraspinal mass
- Multiple levels
- Known primary malignancy
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
VIVA SCENARIOStandard
Cervical Spine Clearance
EXAMINER
"A 45-year-old is intubated after a high-speed MVA. How do you clear the cervical spine?"
EXCEPTIONAL ANSWER
For this obtunded patient who cannot be clinically assessed, I cannot clear the cervical spine clinically, so imaging is essential. Plain radiographs alone are insufficient - they miss up to 50% of injuries. I would obtain a CT of the entire cervical spine with sagittal and coronal reconstructions, which is the gold standard for bony injury detection. I would systematically assess alignment using the four lines (anterior vertebral, posterior vertebral, spinolaminar, spinous process tips), examine each vertebral body, the atlantoaxial articulation, facet joints, and look for prevertebral soft tissue swelling. If CT shows no fracture or malalignment, I would consider whether MRI is needed. Current evidence suggests that in an obtunded patient with a normal CT, MRI may still detect clinically significant ligamentous injury in 1-5% of cases. Many protocols now recommend MRI for obtunded patients before collar removal, particularly looking for STIR signal in the posterior ligamentous complex, disc injury, or cord signal abnormality. The collar stays on until the spine is cleared.
KEY POINTS TO SCORE
CT is gold standard for bony injury (not plain films)
Plain films miss up to 50% of cervical injuries
MRI for ligamentous injury assessment in obtunded patients
Collar remains until definitively cleared
COMMON TRAPS
✗Clearing spine on plain films alone
✗Forgetting about ligamentous injury with normal CT
✗Not knowing the four alignment lines
LIKELY FOLLOW-UPS
"What MRI findings indicate ligamentous instability?"
"What is the predental space and normal values?"
"When would you obtain flexion-extension views?"
VIVA SCENARIOStandard
Thoracolumbar Fracture Assessment
EXAMINER
"Describe how you assess a thoracolumbar fracture on CT and MRI for stability."
EXCEPTIONAL ANSWER
I assess thoracolumbar fracture stability using the Denis three-column model and the TLICS classification. On CT, I evaluate: (1) Anterior column - anterior longitudinal ligament and anterior two-thirds of vertebral body; (2) Middle column - posterior third of body and posterior longitudinal ligament; (3) Posterior column - pedicles, facets, laminae, spinous processes, and posterior ligamentous complex. Two or more column involvement suggests mechanical instability. I measure vertebral body height loss, kyphotic angle, and canal compromise from retropulsed fragments. On MRI, the critical finding is posterior ligamentous complex integrity - I look for STIR hyperintensity in the interspinous space, widening between spinous processes, facet joint fluid or widening, and ligamentum flavum disruption. PLC injury is the single most important determinant of instability in the TLICS system, adding 3 points. I also assess for cord compression or signal change, which determines neurological status. A TLICS score of 4 or less suggests non-operative management, 5 or more suggests surgery.
KEY POINTS TO SCORE
Denis three-column model for mechanical stability
PLC injury on MRI is key instability determinant
STIR sequence best for ligamentous assessment
TLICS score guides management
COMMON TRAPS
✗Only looking at CT without MRI for soft tissue
✗Forgetting PLC assessment
✗Not knowing TLICS scoring
LIKELY FOLLOW-UPS
"What is the TLICS classification?"
"What defines a burst fracture vs compression fracture?"
"What percentage canal compromise requires surgery?"
VIVA SCENARIOStandard
Disc Herniation Imaging
EXAMINER
"Describe the MRI features of a lumbar disc herniation and how you report the location and type."
EXCEPTIONAL ANSWER
On MRI, a disc herniation appears as focal extension of disc material beyond the normal disc margin. On T2-weighted images, the herniated portion is typically intermediate to low signal (degenerated disc) and may compress the thecal sac or nerve roots. I describe the herniation by type and location. Types include: protrusion (base wider than apex, contained by outer annulus), extrusion (apex wider than base, through outer annulus), and sequestration (free fragment with no continuity). Location is described axially as central (midline, compresses thecal sac), paracentral (in the lateral recess, affects traversing nerve root), foraminal (within the neural foramen, affects exiting root), or extraforaminal (far lateral). In the sagittal plane, I note if it's at disc level or migrated superiorly or inferiorly. For example, 'L4-5 left paracentral disc extrusion with inferior migration, causing severe compression of the traversing L5 nerve root with displacement and effacement of the lateral recess.' I also assess for cord or cauda equina compression and any cord signal change in the cervical/thoracic spine.
KEY POINTS TO SCORE
Types: protrusion, extrusion, sequestration
Axial locations: central, paracentral, foraminal, extraforaminal
Paracentral affects traversing root, foraminal affects exiting root
Report level, side, type, location, and nerve root affected
COMMON TRAPS
✗Confusing which nerve root is affected by location
✗Not knowing the difference between protrusion and extrusion
✗Forgetting to assess for cauda equina compression
LIKELY FOLLOW-UPS
"At L4-5, which root does a paracentral herniation affect?"
"What are the MRI features of cauda equina syndrome?"
"How do you differentiate disc herniation from osteophyte?"
Spine Imaging Exam Day Cheat Sheet
High-Yield Exam Summary
ABCS Systematic Approach
- •A: Alignment (4 lines - anterior, posterior vertebral, spinolaminar, spinous)
- •B: Bone (vertebral bodies, pedicles, facets, processes)
- •C: Cartilage/Disc (disc height, endplates, facet joints)
- •S: Soft tissue (prevertebral swelling, paraspinal)
Modality Selection
- •Plain films: First-line, alignment, gross pathology
- •CT: Gold standard for trauma, fracture detail
- •MRI: Soft tissue, disc, cord, ligaments, infection
- •STIR: Best for edema and ligamentous injury
Key Measurements
- •Predental space: Less than 3mm (adult), less than 5mm (child)
- •Prevertebral soft tissue C2-4: Less than 7mm
- •Retrotracheal C6: Less than 22mm
- •Translation: Greater than 3.5mm = instability (cervical)
Stability Assessment
- •Denis 3-column: 2+ columns = unstable
- •PLC injury on MRI = key instability marker
- •TLICS score 5+ suggests surgery
- •Cord signal change = urgent decompression