CT head

Question 1

How would you structure a CT head interpretation?

Answer 1

1. Confirm details
2. Blood
3. Cisterns
4. Brain
5. Ventricles
6. Bone

Question 2

How does a CT work?

Answer 2

Demonstrates the extent to which a material can be penetrated by an X-ray beam

Distilled water at standard temperature and pressure has 0 Hounsfield units HU, whereas air under the same conditions has -1000 HU.

Question 3

What would you check about patient details?

Answer 3

Patient name, hospital number and date of birth
Date and time the scan was acquired
Previous scans (if available) for comparison

Question 4

What would you look for when looking for blood?

Answer 4

1. Extradural haematoma (extra-axial)
2. Subdural haematoma (extra-axial)
3. Subarachnoid haemorrhage (SAH): may be very subtle. Remember a SAH can extend into the ventricular system so always look at the posterior horns as blood may collect in the dependant portion.
4. Intracerebral haemorrhage (intra-axial): this may be intraventricular (within the ventricles) and/or intraparenchymal (within the brain tissue).

Question 5

How would you spot an extradural haematoma on a CT?

Answer 5

An extradural haematoma is a collection of blood which forms between the dura mater and skull

Extradural haemorrhage is often preceded by a clear history of trauma, therefore you should look carefully for evidence of an associated fracture.

The majority of cases of extradural haematoma result from trauma to the middle meningeal artery

Intracranial pressure can rise rapidly and without prompt evacuation of the haematoma, brainstem herniation can occur.

Question 6

How would you spot a subdural haematoma on a CT?

Answer 6

A subdural haematoma forms between the dura and the arachnoid mater and typically develops secondary to trauma (as a result of tearing of bridging veins).

In elderly patients who have experienced a fall, the inciting traumatic event may be less obvious.

Question 7

How would you spot a subarachnoid haematoma on a CT?

Answer 7

A subarachnoid haemorrhage involves bleeding into the subarachnoid space (between the arachnoid and pia mater).

This space normally contains CSF and the vasculature of the brain.

The most common cause of subarachnoid haemorrhage is trauma, however, they can also develop spontaneously (e.g. aneurysmal rupture).

Question 8

How would you spot an intrracerebral haematoma on a CT?

Answer 8

Intracerebral haemorrhage involves bleeding within the brain secondary to a ruptured blood vessel. Intracerebral haemorrhages can be intraparenchymal (within the brain tissue) and/or intraventricular (within the ventricles).

Question 9

How would you assess the cisterns?

Answer 9

There are four key cisterns that which should be assessed for effacement, the presence of blood and asymmetry:

1. Ambient cistern: surrounding the midbrain.
2. Suprasellar cistern: superior to the sella turcica.
3. Quadrigeminal cistern: adjacent to the corpora quadrigemina.
4. Sylvian cistern: across the insular surface and within the Sylvian fissure.

Question 10

What would you say about the brain?

Answer 10

1. Sulcal effacement
2. Grey-white matter differentiation
3. Abnormal shifts of brain tissue
4. Hypo/hyper-dense foci
5. Tumours

Question 11

What is sulcal effacement?

Answer 11

Sulcal effacement is the term used to describe the loss of the normal gyral-sulcal pattern of the brain, which is typically associated with raised intracranial pressure.

Question 12

What causes poor differentiation between grey and white matter?

Answer 12

Suggests the presence of oedema which may develop secondary to a hypoxic brain injury, infarction (e.g. ischaemic stroke), tumour or cerebral abscess.

Question 13

What are common abnormal shifts in brain tissue?

Answer 13

1. Subfalcine: beneath the falx cerebri
2. Uncal: inferomedial displacement of the uncus
3. Transcalvarial: brain shift through the calvarium
4. Transtentorial: may be superior or inferior
5. Tonsillar: downward displacement of the cerebellar tonsils into the foramen magnum

Question 14

What is a hypodense foci?

Answer 14

Hypodensity on a CT head may be due to the presence of air, oedema or fat:

1. Oedema is often seen surrounding intracerebral bleeds, tumours and abscesses.
2. Pneumocephalus (air within the cranial vault) may be noted after neurosurgery or adjacent to the inner table in cases of calvarial fractures.

Question 15

What is a hyperdense foci?

Answer 15

Hyperdensity on a CT head may be due to the presence of blood, thrombus or calcification:

A hyperdense middle cerebral artery (MCA) is sometimes noted in total anterior circulation strokes (TACS) and indicates the presence of a large thrombus within the vessel.

Question 16

What are the radiological features of a tumour?

Answer 16

1. Surrounding haemorrhage: may be hyperdense, isodense or hypodense depending on the maturity of the bleed.
2. Calcification: hyperdense on CT and typically associated with meningiomas.
3. Mass effect: displacement of tissue due to the tumour or associated bleeding/oedema.
4. Oedema (hypodense): may be present in the brain tissue surrounding the tumour.

Question 17

What would you say about the ventricles?

Answer 17

1. Intraventricular haemorrhage and the choroid plexus
2. Hydrocephalus
3. Ventricular effacement
4. Other intraventricular pathology

Question 18

How does intraventricular haemorrhage present?

Answer 18

Hyperdensity within the ventricular system.

However, not all hyperdensity in the ventricles represents acute bleeding: the choroid plexus is frequently calcified and often appears bright on CT

Question 19

How would you spot hyddrocephalus on a CT?

Answer 19

Hydrocephalus is a term that describes the abnormal accumulation of CSF in the ventricles of the brain. It can be broadly divided into communicating (i.e. non-obstructive) and non-communicating (i.e. obstructive). An early sign of hydrocephalus on a CT head is dilation of the temporal horns.

Question 20

What does ventricular effacement describe?

Answer 20

Ventricular effacement describes a thinning in the appearance of the ventricles. This may result from cerebral oedema secondary to a mass or an intracranial haemorrhage. The shift in CSF that occurs in these cases follows the Monro-Kellie doctrine.

Question 21

What is the Monro-Kellie doctrine?

Answer 21

The cranium, enclosing the brain, forms a fixed space comprising three components: blood, cerebrospinal fluid, and brain tissue.

These components remain in a state of dynamic equilibrium, therefore any increase in any one of them results in a compensatory decrease of the other two.

Once the other compartments have reached their point of maximum compensation, any further increase in the size of one results in increased intracranial pressure.

Question 22

What are other intraventricular pathologies?

Answer 22

Cysts
Tumours
Infective lesions

Question 23

What would you say about the bone?

Answer 23

Assess the bones of the skull using the appropriate windowing.

Look for fractures of the calvarium and skull base. Subtle areas of low density within the inner table of the skull may represent small locules of air in the soft tissue windows. Careful evaluation to look for subtle fractures here is essential.

Superficial soft tissue injury may be associated with underlying fractures.