Pathological accumulation of blood within the cranium, either within brain tissue (parenchyma) or surrounding meninges.
Classification by Location of Bleeding
1. Bleeding within the Meninges (Extra-axial hemorrhages)
- Extradural (Epidural) Hematoma (EDH)
- Subdural Hematoma (SDH)
- Subarachnoid Hemorrhage (SAH)
2. Bleeding within the Brain Parenchyma (Intra-axial hemorrhages)
- Intraparenchymal Hemorrhage
- Cerebral Infarction (Hemorrhagic transformation)
Basic Head CT Scan Interpretation Points
- Use 5–10 mm slice thickness , typically 14 slices per study.
- CT without contrast is used for acute hemorrhage detection because blood appears hyperdense (white), whereas CSF appears hypodense (black).
- Compare both hemispheres for:
- Localized altered density
- Mass lesions
- Midline shift
- Acute blood is bright white initially, becoming darker with time; after ~1 month, density equals CSF.
1. Extradural Hematoma (EDH)
Location: Between the skull and dura mater (potential space).
Etiology: Usually arterial bleed — middle meningeal artery laceration after skull fracture, commonly temporoparietal region.
Clinical: Rapid ICP rise; classic "lucid interval" in ~1/3 patients (brief unconsciousness, then normal, then deterioration).
Management: Urgent clot evacuation (craniotomy or burr hole if no neurosurgical facilities).
CT Features:
- Lens-shaped (biconvex/lentiform) hyperdense extra-axial collection.
- Does not cross suture lines (dura adheres at sutures).
- Air within hematoma suggests open fracture.
2. Subdural Hematoma (SDH)
Location: Between dura mater and arachnoid mater.
Etiology: Venous bleeding from bridging veins, often after trauma or in at-risk groups (elderly, alcoholics, cerebral atrophy). Also seen in shaken baby syndrome and coagulopathy.
Clinical: May cause raised ICP, neurological deterioration, mass effect, herniation syndromes. Chronic SDH can present weeks later with headaches, confusion, hemiparesis.
CT Features:
- Crescent-shaped (concave) hyperdense extra-axial collection conforming to brain convexity.
- Crosses suture lines (not limited by dura attachments).
- Can cause midline shift and mass effect.
- In interhemispheric SDH, falx cerebri may appear thickened and irregular.
3. Subarachnoid Hemorrhage (SAH)
Location: Bleeding into the subarachnoid space (between arachnoid and pia mater).
Etiology: Most commonly due to ruptured aneurysm in the Circle of Willis; can also be traumatic.
Clinical: Sudden severe “thunderclap” headache; neurological damage mainly from complications like hydrocephalus and vasospasm.
CT Features:
- High-density blood in CSF spaces: basal cisterns, Sylvian fissure, ventricles, sulci.
- Confirmed SAH → CT angiogram or cerebral angiography.
- If CT negative but suspicion high → lumbar puncture for xanthochromia .
Summary Table of CT Features
| Hematoma Type | Location | Shape on CT | Crosses Sutures? | Usual Cause | Key Clinical Notes |
|---|---|---|---|---|---|
| Extradural Hematoma | Between skull & dura mater | Lens-shaped (biconvex) | No | Middle meningeal artery injury | Rapid ICP rise, lucid interval (~1/3) |
| Subdural Hematoma | Between dura & arachnoid mater | Crescent-shaped | Yes | Bridging veins (venous) | Elderly, alcoholics, chronic presentation common |
| Subarachnoid Hemorrhage | Subarachnoid space | Blood in CSF spaces | N/A | Ruptured aneurysm | Sudden severe headache, vasospasm risk |
