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


