The ability to assess a CT head scan for serious pathology can be considered a vital skill for any intensivist. There is often a delay in receiving a specialist radiology report whilst appropriate care interventions often need to be implemented as soon as possible. The brilliant website www.neuroicu.guru has a simple guide as to how to do this to identify the important pathology that you want to detect as soon as possible. These notes are a simple summary of their guidance as well as being a place for me to store my links on the topic. This is an area where it is pretty much vital to have the actual images to hand, so please use the links below to get access to a huge range of these.
Check you have the correct scan (patient name, correct date)
Select the scan window to ‘brain’ setting (this is often the default, but check)
Start at the top and work down
Scroll up and down twice and assess for anything big first
Then apply a systematic approach for looking for things. A Good mnemonic is ‘Blood Can Be Very Bad’ - Blood, cisterns, brain, ventricles, bone
Apply a top to bottom scrolling approach, looking for important features.
At top, make sure the sulci meet the skull (isodense subdural haematomas can be spotted this way) Identify the central sulcus – looks like the Greek letter omega Look for big abnormalities – there should be symmetry between the sides Look at the interface between grey and white mater in the cerebrum, as this is often the location to spot abnormalities Identify choroid plexus (can be calcified in older patients) Look at the deep grey structures (the basal ganglia) Look at the occipital horns (ventricles) – Blood in the ventricles can collect here as the patient will be in the supine position Look at the Sylvian fissure – CSF is usually well visible here Look at the midbrain – it should look lie Mickey Mouse’s head – a possible place for blood to collect is between Mickey’s ears. Mickey’s ears represent the cerebral peduncles. Look at the suprasellar cistern – this is where the circle of Willis is Move down to posterior fossa – this is important as it is a small space (a box in a box). It is also very close to medulla so small mass lesion can cause big problems Look at the middle cranial fossa – as it is at the base of the brain it is also a common site for subdural blood to collect. The irregular surface of the skull here can also result in damage and bleeding in deceleration injuries. Cerebellar tonsils – these are next to medulla and it is important to specifically look for herniation – the medulla should still have a full ring of CSR around it normally.
Look specifically for signs of herniation. There are 3 main patterns of herniation to look for:
Subfalcine Herniation Also known as ‘Midline shift’, and such an effect is seen on the scan – the concern is of vascular compromise, particularly the anterior cerebral circulation (because of traction on the arteries)
Uncal Herniation Compression of the cerebellar peduncles by the medial temporal lobe – this squashes Mickey’s ear This can result in a 3rd nerve palsy. Greater degrees can result in the ‘false localising sign’. This is ipsilateral hemiparesis cause by pushing of the contralateral cerebral peduncle into Kernohan’s notch.
Tonsillar Herniation (Coning) Passage (or threatened) of the cerebellar tonsils through the Foramen Magnum. There is compression of the medulla and thus compromise of it’s vital functions. The well known impact is Cushing’s response and rapid death. Normally a full ring of CSF around the medulla. In herniation this is gone.
Then use the ‘Blood Can Be Very Bad’ mnemonic to look for abnormalities.
Blood Use colour to help determine age. White is acute, isodense at 7 days and hypodense beyond 7 days. Is it extra axial, or intra-parenchymal?
Extra-axial has specific patterns – subdural, extradural, subarachnoid How do you tell if it intra-parenchymal? Almost always there is an oedema outline of the blood (dark grey)
Consider specific pathology whilst doing this. Importantly, there are 3 main sites of primary hypertensive haemorrhage:
Cisterns These areas of CSF that can be affected by intracranial pathology. There should be a clear ring around the midbrain, and also clear at the foramen magnum. The suprasellar cistern is where the Circle of Wilis lies, so is the most common site for aneurysmal bleeds to show. Are they present? Are they effaced? Do they contain blood?
Brain The grey-white matter border is an important area to look for abnormalities. Look around clockwise for any abnormalities in the differentiation. Assess the deep structures from symmetry.
Ventricles Assess their size shape and symmetry. Is there any effacement?
Bone Switch to the bone window setting Assess the cranium for any clear bony abnormalities. Look at the sinuses – can demonstrate loss of air if they are filled with blood or infectious matter.
Last edited 26/01/2017
References and links
Neuroicu.guru. Radiology 1: CT head interpretation. 2016. (Available at http://www.neuroicu.guru/radiology-i-ct-head. Accessed 26/01/2017)
Navigating Radiology. Introduction to CT head. (Available at https://www.navigatingradiology.com/. Accessed 26/01/2017)
Radiopaedia.org. (Available at https://radiopaedia.org/)