How to Read a CT Head Opening Patient information; orientation; contrast vs non-contrast Blood Acute - Initially white (active bleeding is dark) More hyperdense for 1 st few hours / days becomes isodense Chronic – Hypodense at 4-6/52 Epidural haematoma – biconvex; doesn’t cross sutures; usually arterial injury Subdural haematoma – concave; crosses sutures but not midline; usually venous injury / Subarachnoid haemorrhage – blood in cisterns or cortical sulci Brain Look for: tumour, atrophy, abscess, mass effect, CVA, intracranial air, grey-white differentiation, symmetry, hyper/hypodensities; compare gyri for evidence of effacement; trace falx for evidence of midline shift Hyperdense: blood, IV contrast, calcification Hypodense: air, fat, ischaemia, tumour; active bleeding / old blood Infarct: no abnormality in 1 st few hours (sensitivity 50% at 6hrs, specificity >95%) Early changes suggest large infarct: loss of grey-white differentiation is 1 st sign, parenchymal hypodensity, effacement of sulci, ventricular compression, local mass effect, loss of insular ribbon, obscuration of lentiform nucleus, hyperdense MCA or other (100% specificity, 30% sensitivity for MCA) hypoattenuation at 24 hours (max at 3-5/7) increased attentuation (for few weeks) decreased attenuation with mass effect and ill defined margins isodense at Ventricles Symmetrical with no dilation, effacement, shift, blood Bone Skull fractures (especially basal skull fracture); sinuses and air cells