Introduction
This topic covers how intracranial haemorrhage is recognised and characterised on imaging: the main types and their typical appearances, the time-dependent change in blood density, the search for a underlying cause, and the features that determine urgent management. Non-contrast CT is the first-line investigation in suspected bleeding and is the reference point for all other modalities.
Classification and basic patterns
Intracranial haemorrhage is classified by its anatomical compartment. The compartment largely determines the shape of the collection and how it spreads, which is the first thing to describe in an exam answer.
Imaging modalities and their roles
- Non-contrast CT: first choice in the acute setting; fast, widely available and highly sensitive for acute blood, which is hyperdense (roughly 50 to 70 HU).
- CT angiography (CTA): identifies aneurysms, arteriovenous malformations and dural fistulas; contrast extravasation within the haematoma (the spot sign) predicts haematoma expansion.
- MRI: better for small or subacute lesions, cavernomas and microbleeds (gradient echo or susceptibility-weighted imaging), and for detecting an underlying tumour; diffusion-weighted imaging helps separate haemorrhage from acute infarction.
- Digital subtraction angiography (DSA): the reference standard for characterising aneurysms and vascular malformations and for planning endovascular treatment.