Neuroimaging Toolkit - Scan Spectrum
| Modality | Bright (Hyperdense/Hyperintense) | Dark (Hypodense/Hypointense) | Key Uses |
|---|---|---|---|
| CT | Bone, acute blood, contrast | Air, fat, CSF, ischemia | Trauma, acute stroke/bleed, fractures |
| T1 MRI | Fat, subacute blood, Gd | Water (CSF), edema, bone | Anatomy, post-contrast lesions |
| T2 MRI | Water (CSF), edema, pathology | Fat (variable), bone cortex, air, flow voids | Pathology (edema, inflammation) |
| FLAIR | Pathology (like T2), MS plaques | CSF (nulled), bone | MS plaques, subtle edema near CSF |
| DWI | Acute ischemia, cellular tumors | Old infarcts, CSF | Early stroke detection (minutes) |
Vascular Events - Clots & Bleeds
- Ischemic Stroke (Clots):
- NCCT: Early signs (hyperdense MCA, loss grey-white differentiation, insular ribbon sign). Later: hypodensity.
- MRI: DWI (hyperintense), ADC (hypointense), MRA (occlusion).
- Thrombolysis: tPA within 4.5 hrs.
- Hemorrhagic Stroke (Bleeds):
- ICH: NCCT shows hyperdense lesion. Common: Hypertensive (basal ganglia, pons), Amyloid (lobar).
- SAH: 📌 "Worst headache of life". NCCT: blood in cisterns/sulci. CTA for aneurysm.
- SDH: Crescent-shaped, crosses sutures. Acute (hyperdense), chronic (hypodense).
- EDH: Lens-shaped (biconvex), doesn't cross sutures. MMA tear. Lucid interval.
⭐ DWI is the most sensitive sequence for acute ischemic stroke, showing restriction within minutes.
Trauma & Tumors - Impact & Invaders
-
Traumatic Brain Injury (TBI):
Feature Epidural Hematoma (EDH) Subdural Hematoma (SDH) Vessel Middle Meningeal Artery (MMA) Bridging Veins CT Shape Biconvex (lenticular) 📌 Lemon Crescentic 📌 Banana Sutures Does NOT cross CAN cross Clinical Lucid interval Gradual (elderly, alcoholics) 
- Diffuse Axonal Injury (DAI):
- Shearing forces. CT: Punctate hemorrhages (corpus callosum, brainstem). MRI (more sensitive): SWI shows microhemorrhages.
- Diffuse Axonal Injury (DAI):
-
Brain Tumors:
- Adults (Supratentorial):
- Glioblastoma (GBM): Most common primary adult. Aggressive. Necrosis, hemorrhage. Butterfly glioma (crosses corpus callosum).
- Meningioma: 2nd most common primary adult. Dural based, homogenous enhancement, dural tail. Often benign.
- Children (Infratentorial - Posterior Fossa):
- Medulloblastoma: Most common malignant (child). Cerebellar vermis (midline), hydrocephalus. Homer Wright rosettes.
- Pilocytic Astrocytoma: Most common benign (child). Posterior fossa. Cystic + mural nodule (enhances). Rosenthal fibers.
- Metastases: Most common intracranial tumor overall. Multiple lesions, grey-white junction, vasogenic edema.
- Adults (Supratentorial):
⭐ Epidural hematoma (EDH) is typically arterial and does not cross suture lines, while subdural hematoma (SDH) is usually venous and can cross suture lines.
Infections & Demyelination - Germs & Glitches
- Brain Abscess: MRI: Central DWI restriction, ring enhancement. MRS: ↑Lactate, amino acids.
- HSV Encephalitis: MRI: Temporal lobe T2/FLAIR hyperintensity, hemorrhage. DWI restriction.
- TBM: MRI: Basal exudates (enhancement), hydrocephalus, tuberculomas.
- Neurocysticercosis (NCC): MRI: Stages (Vesicular + scolex, Colloidal, Granular, Calcified). 📌 VesCo GraCa.
- Multiple Sclerosis (MS): MRI: Periventricular, corpus callosum T2/FLAIR lesions. Active: Gd enhancement.
⭐ Dawson's fingers, ovoid lesions perpendicular to the lateral ventricles, are characteristic of Multiple Sclerosis on MRI.
- ADEM: MRI: Large, fluffy, asymmetric white matter lesions; monophasic.
- PML (JC Virus): MRI: Asymmetric subcortical white matter lesions, no enhancement.
High‑Yield Points - ⚡ Biggest Takeaways
- CT excels for acute hemorrhage, bone detail, and initial trauma assessment.
- MRI offers superior soft tissue contrast for tumors, infarcts (DWI), and demyelinating diseases.
- T1-MRI: Fat bright, CSF dark; shows anatomy. Subacute hemorrhage also bright.
- T2-MRI: Water/edema bright, highlights pathology. FLAIR suppresses CSF, aiding periventricular lesion detection.
- DWI is crucial for acute stroke detection, showing restricted diffusion rapidly.
- Contrast reveals Blood-Brain Barrier (BBB) breakdown in tumors, infections, active inflammation.
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