Radiodiagnosis
Neuroimaging
Neuroimaging for MBBS and NEET-PG: non-contrast CT in stroke and trauma, extradural and subdural haematoma, subarachnoid haemorrhage and MRI for ischaemia, mapped to NMC code RD1.5.
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Neuroimaging
Neuroimaging for MBBS and NEET-PG: non-contrast CT in stroke and trauma, extradural and subdural haematoma, subarachnoid haemorrhage and MRI for ischaemia, mapped to NMC code RD1.5.
This chapter covers the imaging of the brain and spinal cord, centred on the acute presentations of stroke, trauma and headache. It teaches why non-contrast CT is the first test in an emergency, the shapes and behaviour of intracranial haemorrhage, the superior sensitivity of MRI for ischaemia and posterior fossa disease, and the signs of raised pressure and hydrocephalus.
High-yield: Neuroimaging
- Non-contrast CT of the head is the first-line investigation in acute stroke and head trauma because it is fast and reliably detects acute haemorrhage.
- Acute intracranial blood is hyperdense (bright white) on non-contrast CT, while chronic blood becomes hypodense over weeks.
- An extradural haematoma is biconvex or lens shaped, does not cross suture lines, and is classically associated with middle meningeal artery injury.
- A subdural haematoma is crescent shaped, crosses suture lines, and is common in the elderly and in those on anticoagulants.
- Subarachnoid haemorrhage shows blood in the sulci, basal cisterns and fissures on CT, and a negative CT with a suggestive history warrants lumbar puncture.
- Early ischaemic stroke may show a hyperdense middle cerebral artery sign and loss of grey-white differentiation before frank hypodensity appears.
- MRI with diffusion-weighted imaging is the most sensitive test for acute ischaemic stroke, showing restricted diffusion within minutes.
- MRI is the modality of choice for posterior fossa lesions, demyelination, epilepsy work-up and spinal cord pathology.
- A ring-enhancing lesion has a wide differential including cerebral abscess, glioblastoma, metastasis, tuberculoma and toxoplasmosis.
- Midline shift, effacement of the ventricles and loss of basal cisterns are radiological signs of raised intracranial pressure.
- CT venography or MR venography is used to diagnose cerebral venous sinus thrombosis, which may show the empty delta sign.
- Hydrocephalus is recognised by dilated ventricles out of proportion to the sulci, with periventricular lucency in acute obstruction.
- CT angiography identifies the aneurysm responsible for a subarachnoid haemorrhage and guides treatment.
- Contrast is avoided in the immediate stroke pathway on non-contrast CT, but is used to characterise tumours, infection and vascular lesions.
Intracranial haemorrhage patterns
- **Extradural:** Biconvex lens shape, does not cross sutures. Middle meningeal artery.
- **Subdural:** Crescent shape, crosses sutures. Elderly and anticoagulated patients.
- **Subarachnoid:** Blood in sulci and basal cisterns. Aneurysm on CT angiography.
- **Acute ischaemia:** Best seen as restricted diffusion on MRI within minutes.
NMC competencies in this chapter
- **RD1.5:** Radiological investigation and interpretation in common internal medicine and neurological conditions
Frequently Asked Questions
Why is non-contrast CT first in acute stroke?
It is fast, widely available and reliably detects acute haemorrhage, which must be excluded before thrombolysis. Early ischaemic changes may be subtle, so MRI diffusion imaging is added when the diagnosis is uncertain.
How do extradural and subdural haematomas differ on CT?
An extradural haematoma is biconvex and does not cross suture lines, arising from arterial injury. A subdural haematoma is crescent shaped, crosses sutures, and results from torn bridging veins, common in the elderly.
What is the differential for a ring-enhancing brain lesion?
It includes cerebral abscess, glioblastoma, metastasis, tuberculoma and toxoplasmosis. The clinical setting, number of lesions and additional imaging features help narrow this classic differential.
When is MRI preferred over CT for the brain?
MRI is preferred for acute ischaemia with diffusion imaging, posterior fossa lesions, demyelination, epilepsy work-up and spinal cord disease, where its soft-tissue contrast far exceeds that of CT.
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