This document provides information about reading a cranial CT scan, including: 1) Indications for ordering a cranial CT scan such as head trauma, suspected hemorrhage, infection, or mass. 2) The principles of how a CT scan works using X-rays and detecting differences in tissue density. 3) How different tissues like bone, CSF, and gray/white matter appear on a CT scan due to their density properties. 4) Views of axial, sagittal, and coronal that can be obtained from a cranial CT scan. 5) Early signs of infarction that may be seen on a CT scan within hours of a stroke occurring, such as hyperdense MCA sign or obsc

1. How to Read a
Cranial CT Scan

2. Indications
• Acute head trauma
• Suspected acute intracranial hemorrhage
• Vascular occlusive disease (acute and
chronic) or vasculitis
• Mental status change
• Acute neurologic deficit
• Suspected intracranial infection
• Suspected mass or tumor
• Detection or evaluation of calcification
• Increased intracranial pressure
• Headache

3. Principle of CT Scan
•CT scans are created using a series of x-rays,
which are a form of radiation on the
electromagnetic spectrum.
•The scanner emits x-rays towards the patient from
a variety of angles – and the detectors in the
scanner measure the difference between the x-rays
that are absorbed by the body, and x-rays that are
transmitted through the body.

4. • The amount of attenuation is determined by the density
of the imaged tissue, and they are individually assigned
a Hounsfield Unit or CT Number.

5. Tissue Density Differences
• Lower density substances allow more photons to pass through
to the detectors, resulting in a grayer or blacker appearance
on CT (e.g. CSF, air)
• The X-ray beam is attenuated to a higher degree by calcium,
therefore less photons pass through bone to the detectors,
resulting in its ‘white’ appearance on CT
• White matter is less cellular, contains myelinated axons (fat),
and has a higher water content than gray matter, resulting in
slightly lower attenuation values or density

7. Infarction Hemorrhage

8. Normal
Neuroanatomy on
Cranial CT Scans

9. Views
Axial Sagittal Coronal

21. Signs of Hyperacute Infarct

22. Hyperdense MCA sign
• The hyperdense MCA sign refers to
focal hyperdensity of the middle
cerebral artery (MCA) and is the
direct visualization of
thromboembolic material within the
lumen. It is thus the earliest visible
sign of MCA infarction as it is seen
within 90 minutes after the event

23. Gray-white matter differentiation loss

24. Insular ribbon sign
• It is the local hypoattenuation
of the insular cortex region due
to the cytotoxic edema as this
region is susceptible to early
and irreversible ischemic
changes

25. Lentiform nucleus obscuration
• Lentiform nucleus appears
hypoattenuated because of acute
ischemia of the lenticulostriate territory,
resulting in obscuration of the lentiform
nucleus
• This feature may be seen on CT images
within 2 hours after the onset of a stroke

26. Sulcal effacement
• Loss of the definition of the sulci
due to diffuse edema in CSF
containing spaces