Ischemic Stroke – CT Brain (Non-contrast) | Key Radiological Features

 

Ischemic Stroke – CT Brain (Non-contrast) | Key Radiological Features 

 

1. Hyperacute Phase (0–6 hours)

Often subtle / may be normal

• Dense artery sign (e.g., Dense MCA sign) → acute thrombus
• Loss of gray–white differentiation
  • Insular ribbon sign
  • Lentiform nucleus obscuration
• Sulcal effacement (early edema)
• No hemorrhage (key to thrombolysis decision)

2. Acute Phase (6–24 hours)

• Hypodense area in vascular territory (wedge-shaped)
• Cytotoxic edema → ↓ attenuation
• Progressive loss of gray-white differentiation
• Mass effect
  • Sulcal effacement
  • Ventricular compression

3. Subacute Phase (1–7 days)

• Well-defined hypodensity
• Peak mass effect (3–5 days)
• Fogging effect (transient normalization ~1–2 weeks)
• Gyriform (cortical) enhancement (if contrast)
• ± Hemorrhagic transformation

4. Chronic Phase (>2–3 weeks)

• Encephalomalacia (CSF density area)
• Volume loss → ex vacuo ventricular dilatation
• Gliosis
• No mass effect

High-Yield Signs (Rapid Recall)

• Dense MCA sign → thrombus
• Insular ribbon loss → earliest cortical sign
• Obscured lentiform nucleus → deep gray involvement
• Wedge-shaped hypodensity → territorial infarct
• Mass effect peaks at 3–5 days
• Fogging effect → pseudo-normal CT (pitfall)

ASPECTS (MCA Stroke) – Quick Note

• 10-point score (NCCT)
• 1 point deducted for each early ischemic change region
• ≤6 → poor prognosis / large infarct core

Radiological features of Raised ICP on CT Brain (in a nutshell)

Radiological features of Raised ICP on CT Brain (in a nutshell)

🧠 Key CT Findings

1. Sulcal effacement

• Loss/obliteration of cortical sulci
• Earliest sign of diffuse cerebral edema

2. Ventricular compression

• Slit-like or reduced size of lateral and third ventricles
• May progress to near-complete effacement

3. Basal cistern effacement

• Obliteration of:
  • Suprasellar cistern
  • Perimesencephalic cistern
  • Ambient cistern
• Strong indicator of significant ICP rise

4. Midline shift

• Displacement of septum pellucidum
• Indicates mass effect (quantify in mm)

5. Diffuse cerebral edema

• Loss of gray–white matter differentiation
• Generalized hypodensity of brain parenchyma

6. Herniation signs

• Subfalcine → cingulate gyrus shift under falx
• Uncal (transtentorial) → medial temporal lobe displacement
• Tonsillar → cerebellar tonsils descending (better on MRI but indirect CT signs present)

7. Effacement of CSF spaces

• Narrowing/obliteration of:
  • Cortical sulci
  • Ventricles
  • Cisterns

🔑 Compact Mnemonic

“SVeB MeD Her”

• Sulci effaced
• Ventricles compressed
• Basal cisterns obliterated
• Midline shift
• Diffuse edema (↓ G-W differentiation)
• Herniation signs

⚠️ Practical note (high-yield)

• Basal cistern effacement + GCS drop = impending herniation
• Always correlate with cause: mass lesion, hemorrhage, edema, hydrocephalus

Pneumocephalus — CT Brain (Key Radiological Features)

 

Pneumocephalus — CT Brain (Key Radiological Features)

1. Density

• Very low attenuation (black)
• HU ≈ −1000 (air)

2. Typical Locations

• Subdural (most common)
• Epidural
• Intraventricular
• Intracerebral / intraparenchymal
• Subarachnoid / cisternal

3. Characteristic Signs

• Mount Fuji sign (tension pneumocephalus)
  → Separation + compression of frontal lobes by subdural air
• Air bubble / multiple loculi sign
  → Scattered small air pockets
• Air-fluid level
  → Suggests CSF leak or communication

4. Mass Effect (if tension)

• Sulcal effacement
• Ventricular compression
• Midline shift
• Frontal lobe compression

5. Distribution Pattern Clues

• Non-dependent air (rises anteriorly/superiorly)
• Often frontal region in supine CT
• May outline cisterns → “negative contrast effect”

6. Associated Findings

• Skull base fracture
• Postoperative changes (craniotomy)
• Sinus/mastoid air communication
• CSF leak

One-line clinical correlation

• Simple pneumocephalus → incidental, small, no mass effect
• Tension pneumocephalus → neurosurgical emergency (mass effect + Mount Fuji sign)

Radiological features of hydrocephalus on CT brain (concise)

 

Radiological features of hydrocephalus on CT brain (concise)

1) Ventricular dilatation (core feature)

• Enlargement of lateral ventricles (rounded frontal horns)
• Dilated 3rd ventricle
• ± Dilated 4th ventricle (helps localize obstruction)
• Temporal horns early dilatation (sensitive early sign)

2) Disproportionate ventriculomegaly

• Ventricles enlarged out of proportion to cortical sulci
• Helps differentiate from cerebral atrophy (where sulci also enlarged)

3) Periventricular lucency (transependymal CSF seepage)

• Hypodense rim around ventricles
• Indicates raised intraventricular pressure

4) Effacement of cortical sulci & cisterns

• Sulcal effacement (compressed brain parenchyma)
• Basal cisterns may be compressed

5) Ballooning of ventricular horns

• Frontal and occipital horns become rounded/bulbous
• Loss of normal concavity

6) Signs suggesting type (useful clinically)

• Obstructive (non-communicating):
  • Dilatation proximal to block
  • e.g., enlarged lateral + 3rd ventricle, normal 4th → aqueductal obstruction
• Communicating:
  • All ventricles enlarged uniformly

7) Ancillary features

• Periventricular edema severity correlates with acuity
• Possible midline shift if asymmetric cause
• Identify cause: mass, hemorrhage, cyst, aqueduct stenosis

Ultra-short mnemonic

“VEPES”

• Ventricular dilatation
• Effaced sulci
• Periventricular lucency
• Early temporal horn enlargement
• Size disproportion (vs sulci)

Midline Shift CT Scan

 

Midline Shift on CT Brain — Key Radiological Features (Concise)

1. Septum Pellucidum Displacement (Most sensitive marker)

• Shift from midline (measured at level of foramen of Monro)
• Quantified in mm (clinically significant ≥5 mm)

2. Third Ventricle Shift

• Deviated from midline
• Often compressed or slit-like

3. Pineal Gland Displacement

• Normally midline → shift indicates deep central displacement
• Useful when calcified (acts as a marker)

4. Lateral Ventricle Asymmetry

• Ipsilateral ventricle: compressed
• Contralateral ventricle: dilated (± obstructive hydrocephalus)

5. Effacement of Sulci

• Loss of cortical sulci on affected side due to mass effect

6. Subfalcine Herniation (Cingulate Shift)

• Cingulate gyrus displaced under falx cerebri
• Often accompanies significant MLS

7. Basal Cistern Compression

• Indicates raised ICP and possible transtentorial progression

Measurement (Standard)

• Distance between:
  • Ideal midline (line through falx)
  • Actual septum pellucidum position

Clinical Correlation Thresholds

• <5 mm → mild
• 5–10 mm → moderate (often surgical consideration)
• >10 mm → severe, high risk of herniation

Quick Mnemonic

“3 S + V + H”

• Septum shift
• Sulcal effacement
• Side ventricle asymmetry
• Ventricle (3rd) deviation
• Herniation (subfalcine)

Depressed Skull Fracture — CT Brain (Non-contrast)

 

Depressed Skull Fracture — CT Brain (Non-contrast)

Key radiological features:

1. Bony Abnormality

• Inward displacement of skull fragment(s) below adjacent inner table
• Step defect in calvarium
• Often comminuted fragments
• Best seen in bone window

2. Depth Criteria (Clinical relevance)

• Depression > thickness of adjacent skull → significant
• Associated with higher risk of dural tear & brain injury

3. Intracranial Complications

• Underlying contusion / intracerebral hemorrhage
• Extradural hematoma (EDH)
• Subdural hematoma (SDH)
• Subarachnoid hemorrhage (SAH)
• Pneumocephalus (air entry)

4. Soft Tissue Findings

• Scalp swelling / hematoma
• Possible foreign body (in compound fractures)

5. Dural / Brain Involvement

• Dural breach (suggested by pneumocephalus or deep fragment)
• Brain laceration in severe cases

6. Special Situations

• Open (compound) fracture → air, contamination
• Over venous sinus → risk of sinus injury/thrombosis
• Frontal sinus involvement → CSF leak risk

One-line summary:

Inwardly displaced skull fragment(s) on bone window + frequently associated underlying intracranial injury (contusion/hematoma ± pneumocephalus).

Skull Fracture (Non-depressed) — CT Brain Features

Skull Fracture (Non-depressed) — CT Brain Features 

1. Linear (most common)

• Thin radiolucent line in bone window
• Sharp, non-sclerotic margins
• Often crosses vascular grooves (vs grooves: branching, sclerotic margins)
• May cross sutures (vs sutures: serrated, symmetric)
• No displacement or depression

2. Diastatic fracture

• Widening of cranial sutures beyond normal
• Common in children
• Typically along coronal, sagittal, lambdoid sutures

3. Comminuted (non-depressed)

• Multiple intersecting fracture lines
• Bone fragmented but no inward displacement

4. Basilar skull fracture

• Often indirect signs predominate:
  • Pneumocephalus
  • Air-fluid levels in paranasal sinuses
  • Opacification of mastoid air cells
• Fracture line may be subtle (bone window essential)
• Common sites: temporal bone, sphenoid, occipital base

General CT Clues (All Types)

• Best seen in bone window
• Look for overlying scalp swelling/hematoma
• Assess for associated intracranial injury (EDH, SDH, contusion)
• Use multiplanar reconstructions (MPR) for subtle fractures

Quick Differentiation

• Fracture line → sharp, straight, may cross sutures
• Suture → zig-zag, symmetric, sclerotic edges
• Vascular groove → branching, tapered

Intracerebral Hemorrhage (ICH) — CT Brain (Non-contrast)

 

Intracerebral Hemorrhage (ICH) — CT Brain (Non-contrast)

Key radiological features (concise):

1. Hyperdense Intraparenchymal Lesion

• Acute blood = hyperdense (bright) (≈60–80 HU)
• Common sites: basal ganglia (putamen), thalamus, lobar, cerebellum, brainstem

2. Surrounding Edema

• Hypodense rim around hematoma (perihematomal edema)
• Develops within hours → increases over days

3. Mass Effect

• Effacement of sulci, ventricles
• Midline shift (quantify if needed)
• Compression of adjacent structures

4. Intraventricular Extension

• Hyperdense blood in ventricles
• May show fluid–fluid level / layering
• Risk of acute hydrocephalus

5. Shape & Margins

• Typically irregular or round/oval
• May have heterogeneous density (active bleed, clot retraction)
• “Swirl sign” → hypodense areas within clot (ongoing bleeding)

6. Location Clues (Etiology hint)

• Deep (putamen/thalamus) → hypertensive
• Lobar → amyloid angiopathy, tumor, AVM
• Multiple → metastasis, coagulopathy

7. Evolution (brief)

• Hyperacute (0–6 h): hyperdense ± swirl
• Subacute (days): density ↓ (isodense ~1–2 weeks)
• Chronic: hypodense cavity ± encephalomalacia

Mnemonic: “HEMATOMA”

• Hyperdensity
• Edema
• Mass effect
• Atypical density (swirl)
• Topography (site clues)
• Outflow into ventricles
• Margins irregular
• Age-dependent change

Subarachnoid Hemorrhage (SAH) — CT Brain (Non-contrast)

Core radiological features (concise):

1) Hyperdensity in subarachnoid spaces

• Acute blood appears hyperdense (bright)
• Typical locations:
  • Basal cisterns (suprasellar, interpeduncular, ambient)
  • Sylvian fissures
  • Interhemispheric fissure
  • Cortical sulci

2) “Star sign” (basal cistern pattern)

• Star-shaped hyperdensity in basal cisterns around Circle of Willis
• Classic for aneurysmal SAH

3) Sulcal effacement with hyperdense sulci

• Blood outlines sulci → prominent hyperdense cortical sulci
• May coexist with early cerebral edema → sulcal effacement

4) Intraventricular extension (common)

• Hyperdensity within ventricles (especially occipital horns)
• May show fluid–fluid levels

5) Hydrocephalus

• Acute obstructive or communicating hydrocephalus
• Findings:
  • Ventricular dilatation
  • Periventricular lucency (transependymal CSF seepage)

6) Loss of gray–white differentiation (severe cases)

• Due to global cerebral edema (esp. massive SAH)

7) Distribution clues to etiology

• Aneurysmal SAH → basal cistern dominant
• Traumatic SAH → cortical sulci over convexities
• Perimesencephalic SAH → localized around midbrain, limited spread

One-line mnemonic

“Bright blood in cisterns, sulci, fissures ± ventricles + hydrocephalus”

Subdural Hematoma (SDH) — CT Brain (Non-contrast) Key Features

 

Subdural Hematoma (SDH) — CT Brain (Non-contrast) Key Features

Typical Appearance

1. Shape & Location

• Crescent-shaped (concavo-convex) extra-axial collection
• Lies between dura and arachnoid
• Crosses sutures, but does NOT cross midline (limited by falx/tentorium)

2. Density (depends on age)

• Acute (0–3 days): Hyperdense (bright)
• Subacute (3–21 days): Isodense → may be subtle (“CT occult”)
• Chronic (>3 weeks): Hypodense (dark)
• Mixed density: Rebleed → fluid-fluid levels / layering

3. Mass Effect

• Sulcal effacement
• Midline shift
• Compression of ventricles
• Possible subfalcine / transtentorial herniation

4. Internal Characteristics

• Homogeneous (acute) or heterogeneous (chronic/rebleed)
• May show septations/membranes (chronic SDH)

5. Associated Findings

• Underlying cerebral edema
• Cortical contusions
• Skull fracture less common than in EDH

High-yield Differentiation (SDH vs EDH)

• SDH: Crescentic, crosses sutures
• EDH: Biconvex (lens-shaped), does NOT cross sutures

Rapid Mnemonic

“SDH = Sickle, Spreads, Slowly changes density”

• Sickle (crescent)
• Spreads across sutures
• Slow evolution → density changes

Normal CT Brain (Non-contrast) — Key Radiological Features (Concise)

 

1. Symmetry

• Bilateral cerebral hemispheres symmetrical
• No midline shift
• Falx cerebri in midline

2. Grey–White Matter Differentiation

• Clear distinction:
  • Grey matter (cortex, basal ganglia) → slightly hyperdense
  • White matter → slightly hypodense
• Preserved corticomedullary junction

3. Ventricular System

• Lateral, 3rd, 4th ventricles:
  • Normal size and configuration
  • Symmetrical
• No dilatation or compression

4. Cisterns & Sulci

• Basal cisterns (suprasellar, ambient, quadrigeminal) → open and well-defined
• Cortical sulci:
  • Normal for age
  • No effacement (→ edema) or prominence (→ atrophy)

5. Basal Ganglia & Thalami

• Normal density and symmetry
• No focal hypo/hyperdense lesions

6. Brainstem & Cerebellum

• Normal size, contour, and density
• No focal lesion or compression

7. No Abnormal Densities

• No:
  • Hyperdensity → hemorrhage
  • Hypodensity → infarct/edema
• No calcification (except physiological: pineal, choroid plexus)

8. Midline Structures

• Falx, septum pellucidum → central
• No mass effect or shift

9. Bone & Extra-axial Structures

• Skull vault intact (no fracture)
• No:
  • Extradural/subdural collection
  • Scalp swelling

10. Orbits & Sinuses (Screening)

• Orbits normal
• Paranasal sinuses:
  • Air-filled (no fluid level or opacification)

Ultra-short Mnemonic: “S G V C B B M B O”

• Symmetry
• Grey–white differentiation
• Ventricles
• Cisterns/sulci
• Basal ganglia
• Brainstem/cerebellum
• Midline
• Bones/extra-axial
• Orbits/sinuses