Neuroradiology and Head and Neck Radiology
Stroke
Non-contrast CT excludes haemorrhage and allows ASPECTS scoring; early signs are loss of the insular ribbon, a hyperdense vessel and sulcal effacement. Diffusion-weighted imaging is positive within minutes and the ADC map confirms restricted diffusion. ADC pseudonormalises at about one week, so a delayed scan can be falsely reassuring. Perfusion imaging identifies the penumbra in large-vessel occlusion.
Haemorrhage
Epidural haematoma is biconvex and limited by sutures; subdural haematoma is crescentic, crosses sutures and does not cross the midline; subarachnoid blood fills basal cisterns and sulci. Aneurysmal subarachnoid haemorrhage is detected on CT within hours; later, lumbar puncture or CT angiography is used.
Tumours and white matter
Intra-axial lesions show surrounding oedema and heterogeneous enhancement; extra-axial lesions broaden the adjacent cistern and may show a dural tail. Multiple sclerosis plaques are periventricular, juxtacortical, infratentorial and spinal, ovoid and perpendicular to the ventricles (Dawson fingers).
Head and neck
Know nodal levels I to VI and the drainage of the nasopharynx (retropharyngeal nodes, level II). Understand imaging of sudden sensorineural hearing loss and cholesteatoma.
Traps
Posterior reversible encephalopathy syndrome is parieto-occipital and often reversible. Wernicke encephalopathy affects the medial thalami and periaqueductal grey. Examiners repeatedly test epidural versus subdural and the hyperdense MCA sign.
Rule of thumb
Acute infarct: DWI bright, ADC dark. If both DWI and ADC are bright, consider T2 shine-through rather than acute infarction.