Bleeds on head CT: epidural, subdural, subarachnoid and intraparenchymal
- Finding
Blood inside the skull is bright on CT. Its shape and place tell which layer is bleeding, how urgent it is and what caused it.
What it is
Intracranial bleeds are named by where the blood lies. An epidural haematoma sits between the skull and the dura, usually from a torn artery after a skull fracture. A subdural haematoma sits between the dura and the arachnoid, usually from torn bridging veins. Subarachnoid blood fills the sulci and cisterns where CSF normally lies; the commonest cause is trauma, and the commonest non-traumatic cause is a ruptured aneurysm. Intraparenchymal (intracerebral) haemorrhage lies within the brain itself. On non-contrast CT fresh blood is bright, and the shape of the collection, whether it crosses sutures or the midline, and its site point to the type and cause. Each type has its own risks: expansion, mass effect, herniation, hydrocephalus and, after aneurysmal bleeding, rebleeding and vasospasm.
What it looks like
- Epidural: lentiform (biconvex) collection that does not cross sutures, because the dura is firmly attached there; it can cross the midline.
- Subdural: crescent that follows the skull and crosses sutures, but stops at the falx and tentorium; it does not cross the midline.
- Subarachnoid: bright blood in the sulci, sylvian fissures and basal cisterns, outlining the brain surface instead of the dark CSF.
- Intraparenchymal: round or irregular bright mass in the brain, often with a dark rim of oedema and possible spread into the ventricles.
- Swirl sign: mixed bright and darker areas inside a fresh haematoma suggest active bleeding.
- A fluid-fluid level inside a haematoma suggests a clotting disorder or anticoagulation.
Why it looks that way
- Epidural blood is usually arterial (classically the middle meningeal artery under a temporal bone fracture), so it can grow fast after a lucid interval.
- Subdural blood is usually venous, from bridging veins stretched by brain atrophy (older age, alcohol) or by shaking in infants.
- Aneurysmal subarachnoid blood is centred on the circle of Willis in the basal cisterns; traumatic blood lies in the convexity sulci near contusions.
- Hypertensive intracerebral bleeds arise in the basal ganglia, thalamus, pons and cerebellum; lobar bleeds in older people suggest amyloid angiopathy.
- Over time haemoglobin breaks down and the blood loses density: bright when acute, isodense when subacute, dark when chronic.
| Bleed | Shape on CT | Usual source | Classic setting |
|---|---|---|---|
| Epidural | Lentiform (biconvex); stops at sutures | Middle meningeal artery | Young adult, temporal fracture, lucid interval |
| Subdural | Crescent; crosses sutures, not the midline | Bridging veins | Older adult, alcohol, anticoagulants, infant abuse |
| Subarachnoid | Blood in sulci and basal cisterns | Aneurysm or trauma | Thunderclap headache |
| Intraparenchymal | Bright mass in the brain with oedema | Small deep arteries, amyloid angiopathy | Hypertension, older age |
Differential and pitfalls
- A subacute subdural can be the same grey as brain: look for effaced sulci and midline shift.
- Mixed density in a subdural suggests acute bleeding into a chronic collection.
- CT is most sensitive for subarachnoid blood in the first hours; it becomes less sensitive after about six hours.
- A lobar bleed in a young person, an unusual site or a fluid level: think of a vascular malformation, tumour, venous thrombosis or drugs.
- Not blood: normal calcification, a dense falx, contrast given earlier, or pseudo-subarachnoid appearance in diffuse brain swelling.
- Bleeding inside an infarct (haemorrhagic transformation) can look like a primary haemorrhage.
Next step
- Any acute bleed: call neurosurgery and the senior now, reassess the Glasgow scale and pupils, and check coagulation.
- On anticoagulants: start the local reversal protocol at once (no waiting for repeat imaging).
- Subarachnoid blood without trauma: CT angiography of the head to look for an aneurysm.
- Intracerebral bleed in an unusual site or young patient: CT angiography (spot sign, malformation) and later MRI.
- Neurological worsening or a bleed likely to grow: repeat CT, usually within the first day.
- Infant with a subdural and an unclear history: follow the suspected abuse pathway (skeletal survey, eye exam).
Test yourself
Think of the answer, then tap the question to see it.
Why does an epidural haematoma not cross the skull sutures?
Because the dura is firmly attached to the skull at the sutures, which limits the collection and gives it a lentiform shape.
Which bleed is crescent-shaped, crosses sutures and stops at the falx?
A subdural haematoma, usually from torn bridging veins.
What is the commonest non-traumatic cause of subarachnoid haemorrhage, and what study looks for it?
A ruptured intracranial aneurysm; CT angiography of the head looks for it.
What does the swirl sign inside a haematoma suggest?
Active bleeding: unclotted fresh blood (darker) mixed with clot (brighter) inside the collection.
Elsewhere in DurgiPedia
- Level of consciousness and the Glasgow Coma Scale
- Meningeal signs: neck stiffness, Kernig and Brudzinski
- Pupils: light reflex and abnormal pupils (Marcus Gunn, Horner, Argyll Robertson)
Connections
Educational content; it does not replace a radiologist's report and is not a clinical instruction. Each study is ordered on the patient's assessment and your institution's protocols.
Sources: Epidural Hematoma (StatPearls (NCBI Bookshelf), 2025); Subdural Hematoma (StatPearls (NCBI Bookshelf), 2026); Subarachnoid Hemorrhage (StatPearls (NCBI Bookshelf), 2023); Intracerebral Hemorrhagic Stroke (StatPearls (NCBI Bookshelf), 2026); Intracranial Hemorrhage Overview (StatPearls (NCBI Bookshelf), 2024).
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Representative model, for educational purposes only.