How to read HeadCT

January 9, 2021

This blogs talks about how to read head ct scans and how to identify different types of bleeds.


Head CT is also called Brain CT. It refers to computed tomography examination of the brain and surrounding structures. It can be performed in 2 ways:

  1. Non-Contrast Study
  2. Contrast Study


Without Contrast: No preparation is required.

With Contrast:

  1. Only one CT contrast study should be scheduled within a 48 hour period.
  2. BUN & Creatinine must be done within 72 hours of the scan.
  3. Nothing but clear liquid after midnight before the scan.
  4. NPO 4 hours prior to exam (no food or drink).

During examination of CT scans, it is important to review old scans as they may provide information which is as clinically important as the current scans

For example:

Example of how past cases may influence diagnosis and treatment.

This elderly patient - who presented with acute confusion - has a large area of low density in the right frontal lobe seen on the current CT Review of a previous CT revealed that the abnormality in the brain was not new, but related to an infarct which occurred 5 months earlier The current CT appearances were not the cause of the acute confusion (urinary tract infection in this case)



In emergency situations radiologists tend to follow this mnemonic: Blood Can Be Very Bad (BCBVB).

B: blood

look for epidural hematoma, subdural hematoma, intraparenchymal hemorrhage, intraventricular hemorrhage, subarachnoid hemorrhage and (also) extracranial hemorrhage

C: cisterns

look for the presence of blood, effacement and asymmetry in four key cisterns (perimesencephalic, suprasellar, quadrigeminal and Sylvian cisterns)

B: brain

look for asymmetry or effacement of the sulcal pattern, gray-white matter differentiation (including the insular ribbon sign), structural shifts and abnormal hypodensities (e.g. air, edema, fat) or hyperdensities (e.g. blood, calcification)

V: ventricles

look for intraventricular hemorrhage, ventricular effacement or shift and for hydrocephalus

B: bone

look for skull fractures (especially basal) on bone windows (soft tissue swelling, mastoid air cells and paranasal sinuses fluid in the setting of trauma should raise the possibility of a skull fracture; intracranial air means that the skull and the dura have been violated somewhere)


To look for these neuropathology, there is a 3 step process:

Step 1
Step 2
Step 3

For this blog, we focus on bleeds/hemorrhage and its subtypes.

The following points can be used as a guide to assess a brain CT to demonstrate/exclude a hemorrhage.

Brain parenchyma


Ventricular system


Old examinations

Hemorrhage Categorization

When a blood vessel within the skull is ruptured or leaks, it is called Intracranial hemorrhage (ICH)

ICH encompasses many conditions characterized by the extravascular accumulation of blood within different intracranial spaces. Following categorization is based on locaiton:

Intra-axial hemorrhage is bleeding within the brain itself, or cerebral hemorrhage. This category includes intraparenchymal hemorrhage (bleeding within the brain tissue) and intraventricular hemorrhage (bleeding within the brain’s ventricles).


intracerebral hemorrhage

Intracerebral hemorrhage also called intraparenchymal cerebral hemorrhage, is a subset of an intracranial hemorrhage. It is the acute accumulation of blood within the parenchyma (tissues) of the brain.

Extra-axial hemorrhage, bleeding that occurs within the skull but outside of the brain tissue, falls into three subtypes: Epidural hemorrhage (extradural hemorrhage) which occur between the dura mater (the outermost meninx) and the skull, is caused by trauma.


Lets look at above mentioned neuropathology based on 3 steps metioned in Introduction:

Brain Parenchyma

Intra-axial hemorrhages

Lobar hemorrhage

Location : Lobar -> Lobes

Hyperdense collection of blood, located superficially within the lobes of the brain (i.e. not in the basal ganglia).

They are usually large and more common in elderly patients.

Case courtesy of Assoc Prof Frank Gaillard, From the case rID: 10678

Extension into the subdural or subarachnoid and even intraventricular(common to basal ganglia hemorrhage - hypertensive) space may be seen.

Hypertensive hemorrhage

Distribution that matches incidence of hypertensive hemorrhages:

Hypertensive hemorrhages

1- Basal ganglia hemorrhage

Name pretty much gives away the location of hemorrhage: around basal ganglia.

Abnormal Hyperdensity centered on the basal ganglia or thalamus. It will be characterized as intraparenchymal hemorrhage.

Case courtesy of Assoc Prof Frank Gaillard, From the case rID: 2764

Often times there may be an intraventricular extension. In this case it also becomes intraventricular hemorrhage.

Case courtesy of Dr Jeremy Jones, From the case rID: 6223

2- Pontine hemorrhage

location: pontine -> pons

These bleeds frequently rupture into the 4th ventricle as shown in figure.

Case courtesy of Assoc Prof Frank Gaillard, From the case rID: 11062

3- Cerebellar hemorrhage

location: cerebellar hemispheres

It appears as hyperdensity within the cerebellar hemispheres. Extension into the fourth ventricle or subarachnoid space is relatively common.

Case courtesy of Dr Farzad Pirzad, From the case rID: 9620

Outside Brain Parenchyma

Extra-axial hemorrhage

Extradural hemorrhage

location: between the inner surface of the skull and outer layer of the dura

shape: bi-convex (or lentiform)

Case courtesy of Dr Matt Skalski, From the case rID: 21542

Extradural hematoma (EDH), also known as an epidural hematoma.

EDHs are hyperdense. Depending on their size, secondary features of mass effect (e.g. midline shift, subfalcine herniation, uncal herniation) may be present.

Case courtesy of Dr Sandeep Bhuta , From the case rID: 4458

Intralaminar dural hemorrhage

location: between the two layers of the dura mater

Intralaminar dural hematomas in the intracranial space, are exceedingly rare.

Subdural hemorrhage

location: between the dura and arachnoid mater of the meninges around the brain

Case courtesy of Dr Matt Skalski, From the case rID: 21542

The aspect of a Subdural hemorrhage (SDH) on a CT may vary: from hyperdense/heterogeneous in the acute phase to iso/hypodense during the chronic phase. In a mixed picture, fresh hemorrhages are seen in a chronic subdural hematoma.


appearance: relatively isodense (same density) to cortex with swirled appearance.

mass-effect: cerebral swelling accentuates the mass-effect created by the collection of the clot, serum and ongoing unclotted blood.


shape: crescent-shaped

appearance: hyperdense relative to the cortex


duration: takes 3-21 days

appearance: isodense to the adjacent cortex

Isodense appearance makes it hard to detect

key-id’s : mass-effect, thickening of cortex, CSF-filled sulci do not reach the skull but rather fade out into the subdural.


duration: ~3 weeks

shape: crescentic shape may change to a biconvex

appearance: hypodense

Chronic subdural hematoma (= hypodense) at right with an acute bleeding component (= hyperdense). Source

Please refer to ct scans for all above stages here.

Subarachnoid hemorrhage (SAH)

location: subarachnoid spaces

The subarachnoid spaces include the basal cisterns (= space around the brain stem), the Sylvian fissure, the cerebral sulci, the intraventricular space and the interhemispheric fissure

Case courtesy of Dr Matt Skalski, From the case rID: 21542

Small amounts of blood can sometimes be appreciated pooling in the interpeduncular fossa, appearing as a small hyperdense triangle, or within the occipital horns of the lateral ventricles.

Subarachnoid blood in the prepontine cisterns (hyperdense obliteration of the moon shape).Source
Blood along the right cerebral convexity. The blood follows the cortical gyri sulci pattern, characteristic of subarachnoid blood.Source
Extensive intraventricular blood in the left lateral ventricle, the aqueduct and the 4th ventricle.Source

Intraventricular hemorrhage

Intraventricular hemorrhage (IVH) denotes the presence of blood within the cerebral ventricular system.

IVH is divided in 2 types: \(P(primary) < P(secondary) \rightarrow\) P being probablity

  1. Primary - blood in the ventricles with little (if any) parenchymal blood
  2. Secondary - a large extraventricular component is present (e.g. parenchymal or subarachnoid) with secondary extension into the ventricles

In above sections on hypertensive hemorrhage and subarachnoid hemorrhage, IVH CT scan is shown.

Subpial hemorrhage

location: between the cortical surface and the pia mater

Difficult to distinguish from subarachnoid hemorrhage.

It is very rare type of extra-axial intracranial hemorrhage.

Cerebral hemorrhagic contusion

location: in the frontal lobes adjacent to the floor of the anterior cranial fossa and in the temporal poles.

appearance: hyperdense foci

Case courtesy of Assoc Prof Frank Gaillard, From the case rID: 7149

Hemorrhagic contusion are common to see in significant head injury. Most contusions represent the brain coming to a sudden stop against the inner surface of the skull (contrecoup) accentuated by the natural contours of the skull.

Contusions vary in size and can appear as small petechial foci of hyperdensity/hemorrhages involving the grey matter and subcortical white matter or large cortical/subcortical bleed.

Key Findings

Midline Shift

Midline of the brain is curved due to pressure build up inside brain either due to swelling or bleeding.

Case courtesy of UoE Radiology, From the case rID: 34098

Caused due to following:

  1. extra-axial collection causing mass effect
  2. parenchymal tumor causing mass effect
  3. stroke with associated edema causing mass effect

Mass Effect

Mass effect describes what happens around a tumor in the brain. It may be caused by:

  1. tumors
  2. cerebral abscess
  3. infarction and associated edema
  4. hemorrhage


It describes the situation where the intracranial ventricular system is enlarged because of increased pressure. It may be caused by:

  1. obstruction of CSF flow.
  2. altered CSF dynamics.
How to read HeadCT - January 9, 2021 - Ujjwal Upadhyay