The first job is to exclude haemorrhage. The second is to find early ischaemic change, which needs a narrow stroke window, not the standard one.
Orient first
- The immediate question before thrombolysis is HAEMORRHAGE, not infarct. Answer that first and communicate it.
- Early ischaemic change is a subtle LOSS OF GREY–WHITE DIFFERENTIATION caused by cytotoxic oedema. It is a density difference of only a few Hounsfield units, which is why the standard brain window hides it.
- A NARROW window (roughly 30–40 window width, centre around 35) exaggerates that small difference and makes early change visible. Reading a stroke CT on a standard window is the commonest reason early change is missed.
- A normal CT in acute stroke is expected and does not argue against the diagnosis.
Acquire the study
- Non-contrast CT head, thin slices, reviewed on BOTH the standard brain window and a narrow stroke window.
- Compare the two hemispheres SIDE BY SIDE at the same level, symmetrically — the diagnosis is made by asymmetry.
- Know the time from onset; it changes what you expect to see and what can be offered.
The manoeuvre
- Exclude haemorrhage first: intraparenchymal, subarachnoid, subdural, extradural, intraventricular.
- Switch to the narrow stroke window.
- Look for loss of the INSULAR RIBBON — the insular cortex losing its distinction from adjacent white matter.
- Look for obscuration of the LENTIFORM NUCLEUS.
- Look for cortical sulcal effacement and loss of grey–white differentiation in each vascular territory.
- Look for a HYPERDENSE VESSEL sign — dense MCA, or the dot sign in a sylvian branch — and compare with the contralateral vessel before calling it, since a high haematocrit makes all vessels dense.
- Score the extent (for example ASPECTS in the anterior circulation) if that is the local protocol, and state the territory involved.
- Look for established infarction, old infarcts, and small-vessel disease that alter the interpretation.
- Assess for mass effect and midline shift.
What confirms it
- Loss of grey–white differentiation in a vascular territory, asymmetrical to the other side, on a narrow window.
- A hyperdense vessel supports large-vessel occlusion but is neither necessary nor sufficient.
What licenses you to exclude it
- ⚠️ A NORMAL NON-CONTRAST CT DOES NOT EXCLUDE ACUTE STROKE — it is the expected finding in the first hours, and it is exactly the patient who should be treated. Never write anything that implies otherwise.
- What the study does exclude, when adequate, is haemorrhage.
- Diffusion-weighted MRI is the test that positively excludes acute infarction.
The classic misread
- Reading the study only on the standard brain window.
- Reporting "no acute infarct" in a way a clinician reads as "not a stroke".
- Calling a hyperdense MCA without comparing sides.
- Missing an old infarct and attributing the deficit to it.