Slide 1: Approach to head CTs: Work outside to inside! 1. Start at the scalp. 2. Divide the head into four quadrants. 3. Examine the head in a clockwise fashion to ensure you don’t miss any findings. Keep an eye out for hematomas that disrupt the normal scalp fat architecture, which can help point to fractures/hemorrhages that lie deeper in the head. Next, divide the skill, or calvarium, into quadrants and look for fractures. Use blood products in the sinuses as red flags to look hard for adjacent fractures! Two CT scans with arrows pointing to smooth, clean scalp fat, the frontal sinus, and the calvarium.

Slide 2: Brain parenchyma. There are 3 major components of the intracranial vault, and each has its own density. Grey matter. This is the cortex of the brain where all the cell bodies lie, the densest substance in the brain. Therefore, it is the brightest shade of grey.

White matter. These are the axons of the neurons, deep to the cortex. They are covered with fat-containing myelin, less dense than the cell bodies in the cortex. As a result, the white matter is a slightly darker shade of grey than the cortex.

CSF. The brain floats in a sea of fluid that helps cushion it from trauma. CSF fills the basal cisterns and intercalates between the cortical gyri on the brain’s surface. It is the least dense substance in the head and is, therefore, the darkest shade of grey.

Slide 3: Brain parenchyma. When systematically evaluating the brain parenchyma, you should always see all three shades of grey. Damage to one or another of the brain’s structure will disrupt its architecture. If there is an injury to the brain tissue, it will begin to swell, which will obliterate one or more of these grey layers. Symmetry is key!

Start at the vertex and continue more inferiorly. We still see all three greys. CT scan with arrows pointing to grey matter (brightest grey), white matter (darker grey), and CSF (darkest grey).

Slide 4: Review. To Review: 1. Divide the brain parenchyma into quadrants. 2. Examine the CSF/grey/white differentiation and symmetry.

Injuries to the tissue will usually be asymmetric and result in loss of this layered CSF/grey/white differentiation due to edema.

CT scan showing a stroke. Look how edema from this stroke results in loss of the distinct three shades of grey in this hemisphere (left hemisphere).

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