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Intracranial haemorrhage: CT appearance and blood stages on MRI
Fresh blood is bright on CT and fades with time; on MRI the state of haemoglobin sets the signal — methaemoglobin is bright on T1, and haemosiderin is dark on all sequences — and the location of the bleed suggests its cause.
Why it matters in the exam
On CT fresh blood is hyperdense (about 50–80 HU), becomes isodense after about 1–2 weeks and hypodense in the chronic stage. In severe anaemia an acute bleed may look isodense. Fluid–blood levels within a haematoma raise suspicion of coagulopathy. On CTA, the "spot sign" (a focus of contrast within the haematoma) predicts haematoma growth. Blood stages on MRI: hyperacute (less than a day) — oxyhaemoglobin, nearly iso on T1 and bright on T2; acute (1–3 days) — deoxyhaemoglobin, dark on T2; early subacute (3–7 days) — intracellular methaemoglobin, bright on T1 and dark on T2; late subacute (a week onward) — extracellular methaemoglobin, bright on both T1 and T2; chronic — haemosiderin, a dark rim on all sequences and especially on SWI.
Cause by location: hypertension — basal ganglia (mainly the putamen), thalamus, pons and cerebellum; cerebral amyloid angiopathy in an older patient — lobar cortical haemorrhage, with cortical microbleeds on SWI and superficial siderosis; a young patient with a lobar bleed — arteriovenous malformation (AVM), cavernous malformation or drug use; haemorrhage with disproportionate oedema — tumour or metastasis; haemorrhage near a sinus with venous infarction — cerebral venous thrombosis. In a younger adult or an atypical bleed CTA is done, and sometimes MRI after the blood has resorbed.
Subarachnoid haemorrhage (SAH): CT within 6 hours of the headache is almost 100% sensitive; if CT is negative after 6 hours — lumbar puncture (xanthochromia). Most spontaneous SAH comes from an aneurysm (most often of the anterior communicating artery), and CTA is the first test to find it. Perimesencephalic SAH — localised blood in front of the midbrain and pons with normal CTA — is non-aneurysmal with a good prognosis. Complications: hydrocephalus, rebleeding and vasospasm on days 4–14. Herniation: subfalcine, descending transtentorial (compression of cranial nerve 3, PCA infarction and Duret haemorrhage in the pons) and tonsillar.
Key points
- Fresh blood is hyperdense on CT, fading within 1–2 weeks.
- Late subacute — bright on T1 and T2.
- Haemosiderin — dark on all sequences.
- Hypertension — basal ganglia; amyloid — lobar.
- SAH: CT within 6 hours, otherwise puncture; CTA for aneurysm.
Summary table
| Stage | Time | T1 | T2 |
|---|---|---|---|
| Hyperacute (oxyhaemoglobin) | Less than a day | Nearly iso | Bright |
| Acute (deoxyhaemoglobin) | 1–3 days | Iso to dark | Dark |
| Early subacute (intracellular methaemoglobin) | 3–7 days | Bright | Dark |
| Late subacute (extracellular methaemoglobin) | A week onward | Bright | Bright |
| Chronic (haemosiderin) | Months | Dark rim | Dark rim |
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Sources
- AHA/ASA Guideline for the Management of Patients With Spontaneous Intracerebral Hemorrhage, 2022 — Imaging
- AHA/ASA Guideline for the Management of Patients With Aneurysmal Subarachnoid Hemorrhage, 2023 — Diagnosis
- ACR Appropriateness Criteria: Cerebrovascular Diseases — Aneurysm, Vascular Malformation, and Subarachnoid Hemorrhage, 2020 — Initial imaging
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.