How is head injury classified for exams?
Head injury questions in forensic medicine and surgery revolve around three layers: the scalp and skull (fractures and their patterns), the meninges (extradural, subdural and subarachnoid bleeding) and the brain itself (contusions, coup and contrecoup injury, diffuse axonal injury). Severity at the bedside is graded with the Glasgow Coma Scale, and a non-contrast CT head is the key imaging test.
| Layer | Typical injury | Key exam clue |
|---|---|---|
| Skull vault | Linear, depressed, comminuted, gutter, signature fractures | Pattern can point to the weapon or mechanism |
| Skull base | Basilar fracture; ring fracture around the foramen magnum | Battle sign, raccoon eyes, CSF leak |
| Between skull and dura | Extradural (epidural) haematoma | Biconvex; lucid interval |
| Between dura and arachnoid | Subdural haematoma | Crescent; bridging veins |
| Under the arachnoid | Subarachnoid haemorrhage | Blood in sulci and cisterns |
| Brain | Contusion — coup and contrecoup, diffuse axonal injury | Contrecoup lies opposite the impact |
What are the types of skull fracture?
| Fracture | What it is | Typical cause / significance |
|---|---|---|
| Linear (fissure) | A simple, non-depressed crack through the bone | Isolated linear fractures do well; usually observation only |
| Depressed | Bone fragment pushed inward; depression over 1 cm with an open wound raises the risk of cortical laceration | Localised blow with a small heavy object; open or compound depressed fractures need surgery |
| Signature | A depressed fracture whose outline reproduces the striking surface of the weapon | Lets the weapon be matched — but only when the striking surface is small (beyond about 4 × 4 cm a characteristic pattern is unlikely) |
| Comminuted | Bone broken into several fragments | Heavy impact; the commonest skull fracture in an autopsy series of fatal motorcycle crashes |
| Gutter | A furrow cut into the outer table | Tangential gunshot grazing the vault |
| Ring | Fracture encircling the foramen magnum through the skull base | Spine driven up into the skull base or a violent pull from neck hyperextension; can tear the pons–medulla junction |
| Diastatic | Separation along a suture line | Rare — a single case in a fatal motorcycle-crash autopsy series |
| Pond / ping-pong | Smooth indentation without a break in the cortex — a 'green-stick' fracture of the skull | Neonates and infants, whose bones are soft |
Most fractures and bleeds are not visible on plain films; non-contrast CT shows displaced or depressed fractures and the blood beneath, while MRI is better for associated brain injury.
What are the signs of a basilar skull fracture?
Basilar skull fractures most often involve the temporal bone, but may involve the occipital, sphenoid, ethmoid and orbital plate of the frontal bone. They often come with facial and cervical spine injuries, cranial nerve palsies, vascular injury and meningitis from a CSF leak.
| Sign | What you see | Site of fracture |
|---|---|---|
| Battle sign | Bruising behind the ear over the mastoid | Middle cranial fossa / temporal bone |
| Raccoon eyes | Bruising around both eyes | Anterior cranial fossa |
| Haemotympanum | Blood behind the eardrum, which looks purple | Petrous temporal bone |
| CSF rhinorrhoea / otorrhoea | Clear fluid from nose or ear | Dural tear with a fracture |
| Halo sign | Blood-stained fluid dripped on cloth forms a double ring | Suggests CSF but is not specific — saline or tears do the same |
What are the features of an extradural (epidural) haematoma?
An extradural haematoma (EDH) is blood between the inner table of the skull and the dura. It is usually arterial, most often from a torn middle meningeal artery under a temporal bone fracture; venous sources are less common. In adults about 75% occur in the temporal region. EDH is found in about 2% of all head injuries and up to 15% of fatal head injuries; young males are most affected.
- CT: a biconvex (lentiform) hyperdense collection. The dura is tightly attached at the sutures, so an EDH does not cross suture lines.
- Lucid interval: brief loss of consciousness, a period of near-normal alertness, then rapid deterioration as the clot expands. It occurs in only about 14–21% of patients, so its absence does not exclude EDH.
- Danger: rapid expansion causes uncal herniation — ipsilateral fixed dilated pupil, contralateral weakness, falling GCS.
| Surgery (evacuation) | Non-operative care possible only if ALL present |
|---|---|
| Volume over 30 mL, regardless of GCS | Volume under 30 mL |
| GCS below 9 with anisocoria — prompt surgery | Clot thickness under 15 mm and midline shift under 5 mm |
| Outcomes best when done early (within 12 hours of symptoms in one series) | GCS above 8 and no focal deficit, with close observation |
What are the features of a subdural haematoma?
A subdural haematoma (SDH) is blood between the dura and the arachnoid, most often from rupture of bridging veins that cross this space from the brain surface to the dural sinuses, torn by shearing forces. Because the blood spreads freely in the subdural space, it forms a crescent that crosses suture lines but is limited by the falx and tentorium.
- Elderly and alcohol-related atrophy: a shrunken brain stretches the bridging veins, so even a minor ground-level fall can cause SDH; antithrombotic drugs add risk.
- Infants: SDH, especially with an inconsistent history, raises the possibility of abusive head trauma.
- Time course: acute SDH follows trauma and behaves as an expanding mass; chronic SDH is defined after about 3 weeks and is an inflammatory membrane disease with repeated small bleeds.
- Surgery for acute SDH: evacuate if thickness is over 10 mm or midline shift is over 5 mm, regardless of GCS.
How do EDH, SDH and SAH differ?
| Feature | Extradural (EDH) | Subdural (SDH) | Subarachnoid (SAH) |
|---|---|---|---|
| Space | Skull – dura | Dura – arachnoid | Under the arachnoid, in CSF spaces |
| Source | Middle meningeal artery (arterial) | Bridging veins (venous) | Trauma, or a ruptured berry aneurysm (about 85% of non-traumatic SAH) |
| CT shape | Biconvex / lentiform | Crescent | Blood in sulci, fissures and basal cisterns |
| Sutures | Does not cross | Crosses | Not relevant |
| Typical patient | Young adult, temporal fracture | Elderly, alcoholic, on anticoagulants; abused infant | Sudden 'worst headache of my life' |
| Classic clinical clue | Lucid interval | Chronic SDH may present weeks later with slowly worsening symptoms | Thunderclap headache, neck stiffness |
- Non-traumatic SAH: about 85% come from a ruptured intracranial aneurysm. If the early CT is normal, lumbar puncture looks for xanthochromia.
- Complications of SAH: rebleeding, vasospasm, hydrocephalus, seizures and delayed cerebral ischaemia; oral nimodipine is the only treatment with consistent evidence for reducing delayed cerebral ischaemia.
What is a contrecoup injury?
A coup contusion lies directly under the point of impact. A contrecoup contusion lies directly opposite the impact site: after the first impact the brain rebounds and strikes the opposite inner surface of the skull, typically at bony prominences.
- Classic setting: a fall backwards onto the occiput. The contusions appear at the frontal and temporal poles — the brain is injured near the irregular floor of the anterior and middle cranial fossae.
- Contrecoup bleeds are reported in 13% to 77% of such patients and are most often linked to occipital and temporal impact sites.
- Theories: positive pressure, negative pressure (cavitation), rotational shear stress and angular acceleration.
- Unlike diffuse axonal injury or brain swelling, contrecoup injury is a focal lesion.