Neuro Imaging. Types of scan CT MRI CT vs MRI

Neuro Imaging

Types of scan

CT MRI

CT vs MRI

• CT – fast & easy to spot haemorrhage. Fresh blood on CT scan is white.

– Once bleed is ruled out more time for:

• DWI – best for ischaemic damage

Right Anterior Cerebral Artery (ACA) infarct

Left Posterior Cerebral Artery (PCA) infarct

Left Middle Cerebral Artery (MCA) infarct

Indications• Trauma: fractures,hemorrhage• Stroke: Initial evaluation• Hydrocephalus• Mass effect/ midline shift• Detect calcification

Advantages• Detect calcification• Quick, readily available• Better at evaluating the bony structures especially for fractures Disadvantages• Radiation• Not as good as MRI at evaluating the soft tissue structures

CT

Indications• Tumors• Stroke• Epilepsy• Demyelination• Infection• Cranial Nerve palsy• Chronic headache• Dementia

Advantages• Exquisite soft tissue contrast between

normal tissue and pathologic tissue.• Customize imaging technique to answer

specific questions.• No ionising radiation.• Ability to do functional MRI

Disadvantage• Higher cost, limited access• Difficult for unstable pts• Claustrophobia• Not as great for bony detail

MRI

Corpus callosum

Mamillary body

Pituitary gland

Pons

Fourth ventricle

Medulla

Thalamus Fornix Superior sagittal sinus

Cerebellum

Always remember to say left or right!

4. Caudate nucleus

5. Internal capsule

6. Putamen

7. Thalamus

8. Fornix

Transverse sinusSuperior sagittal sinus

Inferior sagittal sinus

Straight sinus

Sigmoid sinus

Circle of Willis

Internal carotid artery

Vertebral artery

Common carotid artery

Subclavian artery

Brachiocephalic trunk

Basilar arteryWhat level does the common carotid artery bifurcate?C4

Anterior cerebral artery

Internal carotid artery

Middle cerebral artery

Posterior communicating artery

Posterior cerebral artery

Watershed infarct: Area supplied by Anterior cerebral and Middle cerebral artery (man in a barrel) OR Area supplied by the Middle cerebral artery and the Posterior cerebral artery.

Intracranial bleeds:

Intra axial – Intraparenchymal, Intraventricular.

Extra axial – Extradural (Epidural), Subdural, subarachnoid.

Intraparenchymal haemorrhage

In this case the bleed has spread into the lateral ventricles.

Usually in a hypertensive patient.The basal ganglia is particularly susceptible to hypertensive bleeds.

Risk factors?

Intraventricular haemorrhage:

Third ventricle

Which ventricle is the bleeding occurring in?

More common in premature babies but can also be due to trauma.

Common presentation?

Extradural haemorrhage:

Between the dura mater and the skull.

Lentiform (lens shape)

Shape?

Injury followed by a lucid interval before sudden onset of symptoms

Trauma (coup)

History?

Middle meningeal artery rupture

Most common cause?

Subdural heamorrhage:

Between the dura mater and the arachnoid mater

Crescent shaped

Shape on a CT?

The elderly and alcoholics – Cerebral atrophy

Babies – Shaken baby syndrome

Who’s most at risk?

Slower onset of symptoms than for an extradural haematoma.

Trauma – Especially involving shearing forces(Contrecoup)

History?

Tearing of the bridging veins

Most commonly?

Sub-arachnoid heamorrhage:

Sometimes a CT is delayed while other causes eg. Meningitis are ruled out.

What would you see on the CT?

Thunderclap headache

Trauma but sometimes spontaneously (aneurism)

History?

Between the arachnoid and pia mater.

Bleed that follows the contour of the brain

Herniations

Midline shift

Sub falcine herniation

Uncal hernation(transtentorial)

Tonsilar herniation

Cushing’s triad

Raised ICP causes compression of the cerebral arterioles, leading to ischaemia. Sympathetic nervous system response causes vascular constriction and so a raised BP (in an effort to restore blood supply to the brain). This is then detected by baroreceptors which causes a decrease in heart rate medicated by the vagus nerve. The pressure on the brainstem leads to irregular breathing.

Irregular breathing

Low heart rate

Raised Blood pressure

Nervous system response to raised ICP. Indication of imminent brain herniation.