The following discussion is about CT interpretation in the context of trauma. This is a link to an Edinburgh course on CT interpretation in the context of stroke.
Mnemonic for approaching trauma head CT interpretation
Blood Can Be Very Bad
- Using a systematic approach will help to ensure that significant neuropathology will not be missed
- The CT slice is regarded as being viewed from the patient’s feet, so the left side of the picture as you view it is the right side of the patient.
- Determine if scans have been taken with or without IV contrast, as contrast may mimic the presence of blood. IV contrast does not cross the normal blood brain barrier and is used if there is a suspicion of tumour, infection (e.g. abscess) or vascular abnormality (e.g. AVM or aneurysm)
B – Blood
- Acute blood is bright white (once it clots)
- Blood becomes isodense at 1wk (exact time depends on size of clot)
- Blood becomes hypo dense at 2wks (exact time depends on size of clot)
- Extracerebral (axial) haemorrhage occurring within the skull, but outside the brain
- Extradural haemorrhage (EDH)—biconvex lesion that does not cross suture lines; usually secondary to arterial injury. Low mortality only if treated early.
- Subdural haemorrhage (SDH)—crescent-shaped blood collection that can cross suture lines; usually secondary to venous disruption of surface and/or bridging vessels.
- Subarachnoid haemorrhage (SAH)—haemorrhage into the CSF and cisterns secondary to aneurysms, trauma and arteriovenous malformation.
- Intracerebral (axial) haemorrhage occurring within the brain itself
- Cisterns are collections of CSF, which surround and protect the brain. Examine each for evidence of effacement,asymmetryandthe presence of blood.
B – Brain matter
- Compare the sulcal pattern (gyri) for evidence of effacement and relative volumes of the left and the right sides of the brain for asymmetry. Trace the falx through the series of scans, looking for mid-line shift secondary to compartmental mass effect.
- Look for inconsistencies in the grey–white differentiation (e.g. evolving embolic stroke). Patients with CVA may have a normal CT head scan on presentation with subtle oedema beginning at 6-12 hours, hypo-attenuation after 24 hours and maximal oedema at 3-5 days.
- Identify hyperdense regions associated with blood, IV contrast or calcification.
- Identify hypodense regions associated with air, fat, ischaemia or tumour.
- Examine the lateral ventricles, 3rd and 4th ventricles for asymmetry, dilatation (hydrocephalus), effacement and haemorrhage.
B – Bone
- look for skull fractures (especially basilar) in bone windows
- Soft tissue swelling, mastoid air cells disruption and paranasal sinuses fluid should raise the possibility of a skull fracture;
- intracranial air means that the skull and the dura have been violated somewhere.
- Always check for upper c-spine fractures.
- If you see an interesting CT which would be useful for educating your colleagues then just drag and drop it into the anonymous folder ‘ED Abnormalities’ on our PACs system.
Basic CT interpretation
Cases to work through
- I have created a play list of images to work through on Radiopaedia.com Head trauma CT’s
Further anatomy resources
- Anatomy of TBI from EmergencyMedicineIreland.com
- Headneckbrainspine.com lovely illustration of anatomical structures