CT head (an approach)

The approach taken to interpreting a CT scan of the head review will likely be performed differently byis no doubt different depending on the majority ofcircumstances and the reading clinician, however, most radiologists will go through the same steps. So, thisWhat follows is justmerely a proposition of one waysuggested approach to readinterpreting a CT of the head. 

What it does doAn important aspect of this approach is makethe use of windowing to maximise pickup rate. With PACS, windowing appropriatelythe scan to optimize detection of certain pathology is simple, and there is no excuse for not windowing. Reviewing bone-windows and subdural windows should be mandatoryroutine.

The starting point For example, reviewing every scan using not only brain-window but also bone-windows, subdural windows and stroke windows is strongly recommended and will likely dependresult in reduced miss rate.

Scrolling direction

People have surprisingly strong opinions on preference or the way in whichthis. The important part is, obviously, that you need to look at all the images are presented toand especially ensure that you, e.g. whether do not miss the patient was scanned fromones at the very top, down or bottom, up. StartingIt has been argued by many that starting at the top can be helpful in that it gives you the first few images to decide which side has mass effect. If there is not any, you already know it will be something potentially smaller,-effect and you can take more time reviewingthen work your way down to the "busy" slides at the bottom.

Reporting regimeReview pattern

Brain matter

• windowswindow: 80W:80 L:40

Start at the vertex. Look at the brain matter and gyral pattern. Are there any masses, abnormal attenuation or mass effect? Assess

Subarachnoid space and ventricles

Without changing the window setting review the basal cisterns and foramen magnumsulci. Are they visible and commensurate with the patient's age and ventricular size? Do they extend all the way to the bone? If not is there a subacute (isodense) subdural haemorrhage? Is there any subarachnoid blood? Look in the dependent areas for patencyany small volume subarachnoid haemorrhage particularly in the interpeduncular fossa or occipital horns of the lateral ventricles. Next look at the vessels. Is there a hyperdense MCA or basilar tip hyperdensity suggesting thromboembolism? 

Grey-white differentiation

• windowswindow: 40W:8 L:32 or W:40 L:40

From the foramen magnum scrolling up, look at theNow search for subtle cortical hypoattenuation by assessing grey-white differentiation. The cortical grey matter should be readily differentiated from the white matter. The deep grey matter should be distinct from the white matter also. Pay particular attention to the insular cortex and basal ganglia as they are lost early in middle cerebral artery infarction.

Blood/subdural

• windowswindow: 175W:130-300 L:50-100

NowNext, concentrate specifically on reviewing for small collections of subdural or extradural blood that may have blended with the skull on routine windowing. Coronal reformats if available are particularly useful for this. Look for tiny subdural haemorrhage around the tentorium and circumferentially as thin hyperdense crescents. Also, look in the dependent areas for any small volume subarachnoid haemorrhage.

Soft tissues

• windowswindow: 260:80W:350–400 L:20–60

This studyDon't forget that a CT of the head does not just look at the brain. As you scroll back up again, look inSoften the window to something suitable for soft tissues and especially in the anterior face including the globe, sinuses, palate and pharynx. Check the scalp for focal lesions of haematomas. 

Bony review

• windowswindow: 3000:500W:2800 L:600

Now, and lastly, review the bones. This should always be performed, even when a bony algorithm hasn't been provided or where slice thickness is suboptimal. However,Note that if a fracturethere is not seen on a thick slicehistory of trauma, standard algorithm CT,then dedicated thin bony images are required to detect undisplaced fractures. 

Review the negative predictive value is lowskull vault for any fractures or destructive lesions.

Remember Spend some time checking the base of the skull as the increased complexity of this region can make identification of abnormalities more difficult. Don't forget to look atensure that both TMJs are normally aligned. 

Review the petrous air cellsparanasal sinuses for evidence of fluid that may represent acute sinusitis or, maxillary antra andin the auditory canals. Localised opacification may point to the location of a fracture and highlight the need to ask for the bony reformats to be provided.

Other reformats

Increasinglycorrect setting, coronal and sagittal reformats are either provided or available via volume reconstruction softwarefractures. If they are provided, look at them. If you have isotropy, and the ability to use such software, remember to consider using a different reformat to view an area of pathology.

Review areas

Review areas are different for everybody and you will develop your own list over time, usually as the result of misses, but some common review areas for a CT head include:

• tentorium
• orbit and globe
• retropharyngeal space
• foramen magnum