interpreting-neuroradiology

# Interpreting Neuroradiology

Structures brain and spine imaging interpretation with stroke, mass, and degenerative disease assessment.

## Why This Skill Exists

Neuroimaging drives some of the most time-sensitive decisions in medicine — acute stroke management, hemorrhage evacuation, and tumor resection planning all depend on rapid, accurate interpretation. The AHA/ASA guidelines mandate CT or MRI brain imaging within 25 minutes of ED arrival for stroke code activations, with interpretation expected within 45 minutes of symptom onset for thrombolytic eligibility. Missed intracranial hemorrhage, unsuspected herniation, and incorrectly characterized brain masses are high-stakes diagnostic errors with catastrophic consequences.

The ACR Practice Parameter for Neuroradiology requires structured evaluation of brain parenchyma, ventricles, extra-axial spaces, calvarium, and visualized portions of the skull base and orbits. For spine imaging, the ACR mandates systematic assessment of alignment, vertebral bodies, disc spaces, spinal canal, neural foramina, and paraspinal soft tissues. This skill provides the systematic framework for brain and spine interpretation using established grading scales, classification systems, and critical-finding recognition patterns.

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## Checkpoint A: Pre-Draft Intake (Mandatory)

1. **What study type?** (Default: CT head non-contrast — specify MRI brain, CTA, MRA, spine CT/MRI)
2. **What is the clinical indication?** (Default: Obtain actual indication — stroke, headache, trauma, mass)
3. **Is this a stroke code/alert?** (Default: No — if yes, time-critical workflow applies)
4. **Are prior neuroimaging studies available?** (Default: No priors)
5. **Was contrast administered?** (Default: Non-contrast for CT; specify for MRI)
6. **Is the patient pediatric?** (Default: Adult — pediatric requires age-appropriate assessment)
7. **Is there neurosurgical hardware present?** (Default: No — if yes, assess for complications)

### Documents to Request

- Current imaging study (all sequences/reconstructions)
- Prior neuroimaging for comparison
- Clinical presentation (GCS, focal deficits, symptom onset time)
- Requisition with specific clinical question
- Neurosurgical/intervention notes if post-procedure
- Relevant lab values (coagulation studies if hemorrhage, tumor markers)

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## Step 1: CT Head Non-Contrast — Systematic Review

Evaluate in a fixed sequence to prevent missed findings:

**1. Gray-White Matter Differentiation**
- Loss of gray-white differentiation = acute ischemia (earliest CT sign, visible 6–12 hours)
- Insular ribbon sign, obscured lentiform nucleus = MCA territory infarct
- ASPECTS score for anterior circulation stroke (10-point scale, each region = 1 point deducted)

**2. Hemorrhage Assessment**
| Hemorrhage Type | CT Appearance | Key Features |
|----------------|---------------|-------------|
| Epidural | Biconvex, lenticular | Does not cross sutures; temporal squamous bone fracture |
| Subdural | Crescent-shaped, crosses sutures | Acute (hyperdense), subacute (isodense), chronic (hypodense) |
| Subarachnoid | Hyperdense in sulci, cisterns, fissures | Modified Fisher scale for vasospasm risk |
| Intraparenchymal | Focal hyperdensity within brain parenchyma | Location suggests etiology (hypertensive = basal ganglia, thalamus, pons, cerebellum) |
| Intraventricular | Hyperdense layering in ventricles | Graeb score for severity; hydrocephalus risk |

**3. Ventricles and CSF Spaces**
- Ventricular size: Evans index (frontal horn width / biparietal diameter; >0.3 = ventriculomegaly)
- Temporal horn dilatation = earliest sign of hydrocephalus
- Asymmetry suggesting mass effect or trapped ventricle

**4. Midline Shift**
- Measure at septum pellucidum
- >5 mm = significant; consider surgical evaluation
- Subfalcine, transtentorial, tonsillar herniation patterns

**5. Calvarium and Skull Base**
- Fractures: linear, depressed, basilar (opacified mastoid air cells, pneumocephalus)
- Bone window review is mandatory in trauma

**6. Extracranial Structures**
- Scalp hematoma, foreign bodies
- Paranasal sinuses (air-fluid levels in trauma = fracture)
- Orbits (if included)

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## Step 2: MRI Brain — Sequence-Specific Interpretation

| Sequence | Primary Role | Key Findings |
|----------|-------------|-------------|
| T1 | Anatomic detail | Subacute hemorrhage (bright), fat, melanin, protein |
| T2 | Fluid/pathology detection | Edema, gliosis, CSF bright |
| FLAIR | Periventricular/cortical pathology | MS plaques, subarachnoid hemorrhage (bright CSF), cortical infarcts |
| DWI/ADC | Acute ischemia detection | Restricted diffusion = bright DWI + dark ADC = acute infarct (minutes-days) |
| GRE/SWI | Hemorrhage (all ages) | Blooming artifact from blood products, microbleeds, vascular malformations |
| T1 post-contrast | Blood-brain barrier breakdown | Enhancing masses, infection, active demyelination |
| MRA | Vascular anatomy | Stenosis, occlusion, aneurysm, dissection |
| Perfusion (DSC/ASL) | Hemodynamic assessment | Mismatch with DWI = penumbra (salvageable tissue) |
| Spectroscopy (MRS) | Metabolite analysis | NAA (neuronal), choline (membrane turnover), lactate (anaerobic), lipid (necrosis) |

### Acute Stroke MRI Protocol Interpretation
- **DWI-FLAIR mismatch**: DWI positive + FLAIR negative = onset likely <4.5 hours (thrombolysis eligible)
- **Perfusion-diffusion mismatch**: Perfusion deficit > diffusion deficit = salvageable penumbra (thrombectomy candidate)
- **ASPECTS on DWI**: Same 10-region scoring as CT

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## Step 3: Brain Mass Characterization

| Feature | Intra-axial (within brain) | Extra-axial (outside brain) |
|---------|--------------------------|---------------------------|
| CSF cleft | Absent | Present (between mass and cortex) |
| White matter buckling | Present | Absent |
| Cortex | Involved/disrupted | Displaced but intact |
| Dural tail | Absent | Present (meningioma) |
| Common types | Glioma, metastasis, abscess, lymphoma | Meningioma, schwannoma, epidermoid, arachnoid cyst |

### WHO Tumor Grade Features on MRI

| Feature | Low Grade (II) | High Grade (III–IV) |
|---------|---------------|-------------------|
| Enhancement | Minimal/none | Heterogeneous, ring-enhancing |
| Necrosis | Absent | Present (GBM hallmark) |
| Edema | Minimal | Extensive vasogenic |
| Perfusion (rCBV) | Low | Elevated (>1.75 relative to normal white matter) |
| Spectroscopy | Elevated choline, preserved NAA | Markedly elevated choline, reduced NAA, lipid/lactate peaks |

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## Step 4: Spine Imaging — Systematic Approach

### Alignment
- Anterior vertebral body line, posterior body line, spinolaminar line, spinous process tips
- Listhesis: measure as percentage of vertebral body width (Grade I: 0–25%, Grade II: 25–50%, etc.)

### Vertebral Bodies
- Height loss: mild (<25%), moderate (25–40%), severe (>40%)
- Signal abnormality: edema (acute fracture), fat (chronic/healed), enhancing (tumor, infection)
- STIR sequence is the gold standard for differentiating acute vs. chronic compression fractures

### Disc Assessment
- Protrusion: focal, broad-based; location (central, paracentral, foraminal, far lateral)
- Extrusion: extends beyond disc space; migration (superior/inferior)
- Sequestration: free fragment separated from parent disc
- Disc nomenclature per NASS/ASSR/ASNR consensus terminology

### Spinal Canal and Neural Foramina
- Central canal stenosis: mild, moderate, severe (effacement of CSF, cord compression)
- Neural foraminal stenosis: mild, moderate, severe (fat obliteration, nerve root compression)
- Cord signal: myelomalacia (T2 bright, T1 dark) vs. edema (T2 bright, normal T1)

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## Step 5: Report Structure

### Impression — Prioritized
1. Critical/emergent findings first (hemorrhage, acute stroke, cord compression)
2. Primary diagnosis addressing clinical question
3. Secondary findings with management implications
4. Incidental findings with appropriate follow-up recommendations

### Stroke-Specific Reporting
- ASPECTS score
- Vascular territory
- Estimated time of onset (if DWI-FLAIR mismatch available)
- Large-vessel occlusion site (if CTA performed)
- Hemorrhagic transformation (if present)

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## Checkpoint B: Post-Draft Alignment (Mandatory)

1. Was every anatomic compartment evaluated (parenchyma, ventricles, extra-axial, calvarium)?
2. Is hemorrhage excluded or characterized with appropriate grading?
3. For stroke, is ASPECTS calculated and vascular territory identified?
4. Is mass lesion characterized as intra-axial vs. extra-axial with differential?
5. Is midline shift quantified and herniation assessed?

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## Quality Audit

- [ ] Systematic review covers all compartments (parenchyma, ventricles, extra-axial, bone)
- [ ] Gray-white matter differentiation is assessed
- [ ] Hemorrhage is characterized by type, location, and grading scale
- [ ] Midline shift is measured in millimeters at septum pellucidum
- [ ] ASPECTS score is documented for anterior circulation strokes
- [ ] DWI/ADC maps are reviewed for acute ischemia
- [ ] All MRI sequences are individually assessed
- [ ] Brain masses are characterized as intra-axial vs. extra-axial
- [ ] Spine alignment is assessed using standard reference lines
- [ ] Disc pathology uses consensus nomenclature (protrusion, extrusion, sequestration)
- [ ] Canal and foraminal stenosis are graded (mild, moderate, severe)
- [ ] Cord signal abnormality is documented and differentiated (edema vs. myelomalacia)
- [ ] Critical findings trigger immediate communication per institutional policy
- [ ] Bone windows are reviewed in CT trauma studies

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## Guidelines

1. For stroke code activations, provide a preliminary verbal interpretation within minutes — document the formal read afterward.
2. Always review bone windows on CT head — skull fractures and calvarial metastases are invisible on brain windows alone.
3. Use ASPECTS scoring for anterior circulation strokes — scores <6 predict poor outcome and influence thrombectomy decisions.
4. DWI-FLAIR mismatch on MRI indicates onset within approximately 4.5 hours and may qualify the patient for thrombolysis even with unknown onset time (WAKE-UP trial criteria).
5. Characterize brain masses by location (intra-axial vs. extra-axial), enhancement pattern, and associated features before offering a differential — this determines neurosurgical approach.
6. On spine MRI, use STIR sequences to differentiate acute (edema-bright) from chronic (fat-signal) compression fractures — this distinction determines whether vertebroplasty/kyphoplasty is appropriate.
7. Document cord compression as an emergency — spinal cord compression with neurologic deficit requires surgical evaluation within hours.
8. Apply the modified Fisher scale for subarachnoid hemorrhage to predict vasospasm risk — this guides neurocritical care management intensity.