Written & reviewed by: Kinase Medical Team · Last reviewed: 30 September 2026 · Editorial policy
Key features
- Biconvex (lentiform) hyperdense collection, most often under the squamous temporal bone.
- Limited by sutures (dura is tightly attached there) but can cross dural venous sinuses.
- Skull fracture in about 75%; bleeding usually from the middle meningeal artery (about 75%).
- Classic lucid interval occurs in fewer than 20% of cases.
- 'Swirl sign' (mixed density) indicates active bleeding at the time of the scan.
Differential diagnosis
| Condition | How to tell it apart |
|---|---|
| Acute subdural haematoma | Crescent-shaped, crosses sutures and spreads widely over the hemisphere. |
How it appears in NEET PG
CT head images of trauma are asked frequently: shape (biconvex vs crescent), vessel involved and the relation to sutures are the usual questions, often with a GCS calculation.
Frequently asked questions
Why is an extradural haematoma biconvex?
Blood collects between the skull and the dura and is usually held back by the suture lines, so instead of spreading it bulges inward into a lens shape.
Which vessel is usually injured?
The middle meningeal artery, commonly torn by a temporoparietal skull fracture.
How does a subdural haematoma differ on CT?
A subdural collection is crescentic and crosses suture lines because it lies beneath the dura.
Sources
- Radiopaedia — Extradural haemorrhage
- Harrison's Principles of Internal Medicine (textbook)
Keep practising
- NEET PG Radiology previous-year questions
- Concept page: glasgow coma scale
- Pneumoperitoneum (Air Under the Diaphragm)
- Sigmoid Volvulus (Coffee Bean Sign)
- Boot-Shaped Heart (Tetralogy of Fallot)
- All clinical images
For exam preparation and medical education only — not a substitute for clinical judgement, diagnosis or treatment of any patient.