# Extradural versus Subdural Haematoma

> Extradural versus subdural haematoma for NEET-SS Neurosurgery: CT shapes, suture limits, surgical thresholds, lucid interval and chronic SDH management.

- Canonical URL: https://prepelephant.com/topics/neet-ss/neurosurgery/extradural-subdural-haematoma
- Exam / course: NEET-SS · Subject: Neurosurgery
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Extradural versus Subdural Haematoma", PrepElephant, https://prepelephant.com/topics/neet-ss/neurosurgery/extradural-subdural-haematoma

## Direct answer

An extradural (epidural) haematoma collects between bone and dura, usually from a torn middle meningeal artery at the pterion, and appears on CT as a biconvex, lens-shaped mass that respects cranial sutures. A subdural haematoma collects beneath the dura from torn bridging cortical veins, appears as a crescentic mass that crosses sutures but stops at the falx, and favours the elderly, the alcoholic and the anticoagulated. Surgery is driven by thickness, midline shift and the patient's condition — classically evacuation for an extradural above about 30 mL and an acute subdural thicker than about 10 mm or shifting the midline more than 5 mm.

## What you must remember

- Extradural: temporal fracture over the pterion, arterial bleeding, rapid progression, classically a lucid interval before deterioration; biconvex on CT, limited by sutural dural attachments so it does not cross sutures (a venous posterior fossa or frontal extradural may cross the midline by stripping dural sinuses).
- Subdural: bridging-vein rupture in cortical atrophy, falls from standing, alcohol and anticoagulants; crescentic on CT, crosses suture lines, respects the midline, may be bilateral and interhemispheric.
- CT density tells the age: acute subdural is hyperdense, subacute isodense (look for displaced cortex and effaced sulci), chronic hypodense; mixed density suggests acute-on-chronic rebleed.
- Surgical thresholds in common use: extradural volume above roughly 30 mL whatever the GCS; acute subdural thicker than 10 mm or midline shift above 5 mm regardless of GCS.
- Acute subdural is evacuated by craniotomy; chronic subdural by burr-hole drainage, with recurrence managed by re-drainage, and subdural drains after burr holes reduce recurrence.
- Extradural in the posterior fossa and in children without fracture (vascular-splitting skull) are recognised exceptions to the classic picture; always reverse anticoagulation.
- Both may coexist with underlying contusions — the subdural is often just the marker of a more severely injured brain, which explains its worse prognosis.

## Common confusion

Shape mnemonics get reversed under pressure: lens-shaped (lentiform, biconvex) is extradural because sutures fence it in; crescent (concave inner margin) is subdural because it spreads freely over the hemisphere. The lucid interval is over-read as typical of all extradurals when it occurs in a minority, and candidates forget that a chronic subdural in an elderly patient may present with fluctuating confusion and no history of trauma — the "great imposter" of geriatric neurosurgery.

## Exam-focused takeaway

This pairing is tested by numbers, shapes and populations: a young man with a temporal fracture who talks then deteriorates; an elderly anticoagulated patient with confusion and a crescentic isodense collection; an image asking biconvex versus crescentic with the sutures visible. Expect threshold questions (30 mL, 10 mm, 5 mm) and next-step questions where reversing anticoagulation, urgent CT or theatre wins over observation. The prognosis contrast — extradural with a good outcome if evacuated promptly versus subdural reflecting underlying brain injury — is a recurring viva line.

## Frequently asked questions

### Why is an extradural haematoma biconvex on CT?

Dural attachments at cranial sutures tether the collection, producing a lens shape, whereas the subdural space allows a crescentic spread across sutures.

### What are the surgical thresholds for evacuation?

Classically extradural volume above about 30 mL regardless of GCS, and acute subdural thicker than 10 mm or with midline shift above 5 mm regardless of GCS.

### How does a chronic subdural present and how is it treated?

Often with fluctuating headaches, confusion or focal deficit weeks after trivial or forgotten trauma, treated by burr-hole drainage, with drains reducing recurrence.

### Who gets subdural rather than extradural haematoma?

Elderly, atrophic, alcoholic and anticoagulated brains with bridging-vein rupture after low-energy falls; young temporal fractures favour arterial extradural collections.

### What does mixed density in a subdural mean?

An acute rebleed into a chronic collection — acute-on-chronic subdural haematoma.