The mnemonic used by Dr. Andrew Perron who lectures on this topic frequently is: "Blood Can Be Very Bad". Content and images below are taken from his lecture (with his permission).
This stands for
B - blood
C - cisterns
B - brain
V - ventricles
B - bones
Step 1: Blood
Look for any evidence of bleeding throughout all slices of the head CT.
Blood will appear bright white and is typically in the range of 50-100 Houndsfield units.
Basic categories of blood in the brain are epidural, subdural, intraparenchymal/intracerebral, intraventricular, and subarachnoid.
Step 2: Cisterns
Two key questions to answer regarding the four key cisterns (Circummesencephalic, Suprasellar, Quadrigeminal and Sylvian)
- Is there blood?
- Are the cisterns open?
Step 3: Brain
Examine the brain for:
- Symmetry - make sure sulci and gyri appear the same on both sides. (easiest when patient not rotated in the scanner)
- Grey-white differentiation - the earliest sign of a CVA on CT scan is the loss of the grey-white interface on CT scan. Compare side to side.
- Shift - the falx should be in the midline with ventricles the same on both sides. Check for effacement of sulci (unilateral or bilateral).
- Hyper/hypodenisty - blood, calcification and IV contrast are hyperdense (appear lighter) and air, fat and areas of tumor ischemia are hypodense (appear darker).
Step 4: Ventricles
Examine for IIIrd, IVth and lateral ventricles for dilation or compression/shift.
Pathologic processes cause dilation (hydrocephalus) or compression/shift. Communicating vs. Non-communicating. Communicating hydrocephalus is first evident in dilation of the temporal horns (normally small, slit-like). The lateral, IIIrd, and IVth ventricles need to be examined for effacement, shift, and blood.
Step 5: Bone
Bone has the highest density on CT scan (whitest in appearance.) Evaluate for fracture.