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How to Read Emergency Images

How to read a head CT

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

Steps: Blood Cisterns Brain Ventricles 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.

Epidural (lens shaped, does not cross suture lines)

CT scan of brain

Subdural (crescent shaped, does cross suture lines)

Subdural (crescent shaped, does cross suture lines)

Intraparenchymal /intracerbral hemorrhage (high density bleeds most often in the basal ganglia area if due to HTN)

CT scan of brain

Intraventricular hemorrhage

CT scan of brain

Subarachnoid hemorrhage (due most often to aneurysms, CT sensitivity decreases sharply with time)

Subarachnoid hemorrhage

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?

Circummesencephalic cistern

Circummesencephalic cistern

Suprasellar cistern

CT scan of brain

Quadrigeminal cistern

Quadrigeminal cistern

Sylvian cistern

CT scan of brain

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.

Labeled CT scan of brainLabeled CT scan of brainLabeled CT scan of brainLabeled CT scan of brain

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.