Subdural vs Epidural Hematoma: CT Findings and Facts
Save Time with a Video!
Save time by watching the video first, then supplement it with the lecture below!
Click below to view the EZmed video library. Subscribe to stay in the loop!
Become a Member!
Instant Access to All PDF Lectures, Study Guides, and Flashcards!
Instant access to a members-only page of ALL the flashcards, study guides, and PDF lectures. Cancel anytime.
Download the Lecture!
Never forget subdural vs epidural hematomas again with your copy of the lecture below! Enjoy :)
Subdural vs Epidural Hematoma
Subdural and epidural hematomas are abnormal collections of blood within the meninges surrounding the brain.
They are the result of an intracranial hemorrhage that can then form into a subdural or epidural hematoma depending on the location.
The features of a subdural vs an epidural hematoma differ based on CT findings, symptoms, location within the meninges, and pathophysiology.
You will easily learn these differences, along with how to distinguish a subdural from an epidural hematoma on CT and other high yield facts about each.
Every EZmed lecture provides you with simple tricks to learn the content.
This lecture will give you an easy way to remember how a subdural and epidural hematoma appear on CT imaging.
Meningeal Layers
Let’s start by briefly discussing the gross anatomy of the brain.
The brain is surrounded by layers of tissue, called the meninges, that protect the brain and maintain its fluid environment.
The meninges consist of 3 layers - the pia mater, arachnoid mater, and dura mater (inner to outer layer).
Pia Mater
The first layer surrounding the brain is the pia mater.
The pia is a very thin layer that adheres to the surface of the brain.
It is the only layer of the meninges to follow the contour of the brain, including the folded structure of the cerebral cortex.
The pia covers each gyrus (hill) of the brain, and then extends down within each sulcus (valley) as well.
Since the pia mater tightly adheres to the brain, there is no significant space between the pia and the brain.
Arachnoid Mater
The next layer outside the pia is the arachnoid mater.
Unlike the pia mater which adheres tightly to the brain and follows all of its contours, the arachnoid bridges over one gyrus to the next without extending down into each sulcus.
Therefore, a space between the arachnoid mater and pia mater is present, called the subarachnoid space.
Dura Mater
The next layer outside the arachnoid is the dura mater.
The dura is the toughest of the 3 meningeal layers.
The dura has almost no attachment to the underlying arachnoid mater, and therefore a subdural space can be created.
The dura adheres to the overlying cranium (skull).
The dura mater is the outermost meningeal layer adhering to the skull and loosely covering the arachnoid.
The subdural space is a potential space between the dura (outermost layer) and arachnoid (middle layer).
The arachnoid mater is the middle meningeal layer between the dura and pia. It bridges over the gyri without extending into the sulci.
The subarachnoid space is the space between the arachnoid (middle layer) and pia (innermost layer).
The pia mater is the innermost meningeal layer adhering tightly to the brain. It is the only meningeal layer that follows the contour of the brain.
Subdural Hematoma
A subdural hematoma, as the name suggests, is an abnormal collection of blood beneath the dura mater.
Therefore, a subdural hematoma is located between the dura and arachnoid layers of the meninges.
It appears as a concave, crescent-shaped hemorrhage on head imaging.
Subdural hematomas are typically caused by an accelerating-decelerating type injury that leads to shearing stress of the bridging veins.
The bridging veins traverse through the subdural space as they drain venous blood from the brain.
As a result, injury to the bridging veins may lead to the development of a subdural hematoma.
Individuals with brains that have undergone atrophy, or shrinking, are at increased risk of developing a subdural hematoma as their bridging veins are stretched and prone to injury.
These populations include the elderly and individuals with a history of long-standing alcohol use.
Epidural Hematoma
An epidural hematoma, as the name suggests, is an abnormal collection of blood above the dura mater.
Therefore, an epidural hematoma is located between the skull and dura mater.
It appears as a convex, lens-shaped hemorrhage on head imaging.
Epidural hematomas are typically caused by blunt trauma, especially to the temporal region where the skull is thin.
This thin temporal region is called the pterion, and it is the junction of the frontal, parietal, temporal, and sphenoid bones.
The middle meningeal artery travels directly beneath the pterion.
Therefore, trauma to this area may result in injury to the middle meningeal artery and subsequent development of an epidural hematoma.
Many medical examinations like to ask which blood vessel is commonly injured in an epidural hematoma - remember the middle meningeal artery.
Another commonly tested feature of epidural hematomas is how they can cause a “lucid interval”.
Individuals with epidural hematomas may have decreased level of consciousness initially after the injury, followed by improvement in their symptoms.
They can later deteriorate and decline again, having return of altered mental status.
The progression of initial symptoms, followed by improvement, followed by deterioration again is called the lucid interval, and it can be associated with an epidural hematoma.
Banana and Lemon Trick
When first learning about subdural and epidural hematomas, it can be challenging to recall which one is convex shaped and which one is concave shaped on imaging.
Here is a trick you can use to remember the appearance of a subdural and an epidural hematoma on head imaging.
Subdural = Banana
First, we said subdural hematomas were concave, crescent-shaped hemorrhages.
This gives it the appearance of a banana.
You can use the “B” in “sub” for subdural to remember Banana shaped.
Epidural = Lemon
Next, we said epidural hematomas were convex, lens-shaped hemorrhages.
Therefore, the appearance is similar to a lemon.
You can rearrange the letters of “Epi” in epidural to make “Pie”. This will help you remember “Lemon Pie”.
It’s a simple trick that can be used when first learning these hemorrhages.
A subdural hematoma is concave like a banana. You can use the “B” in suBdural to remember Banana.
An epidural hematoma is convex like a lemon. You can rearrange the letters in “EPI” to make “PIE” to help you remember lemon PIE.
Summary
Hopefully this provided you with a quick, concise summary of the differences between a subdural hematoma and an epidural hematoma.
If you found the content useful, leave a comment down below or provide any other suggestions!
Remember these key facts:
Subdural Hematoma - Abnormal collection of blood between dura and arachnoid
Concave, crescent-shaped
Injury to bridging veins
Accelerating-decelerating injury
Elderly, chronic alcoholism
Epidural Hematoma - Abnormal collection of blood between skull and dura
Convex, lens-shaped
Injury to middle meningeal artery
Blunt trauma, especially to pterion
Lucid interval
Before You Go, Make Your Learning Experience Even Easier!
If you enjoyed the content in this post, don’t forget to join the EZmed community for free so you don’t miss out on future posts that make medicine easy!
A weekly notification is sent right to your inbox filled with new blog posts, new videos, and exam prep!
Sign up is on the bottom of this page or in the navigation bar.
Perform well in class, ace your exams, and keep up with your medical knowledge throughout your career using:
Instagram: @ezmedlearning - High yield exam content
YouTube Channel: EZmed - Simple animations and videos
Pinterest: ezmedlearning - Easy illustrations and flashcards
Feel free to use the contact button to reach out with any feedback or suggestions you may have for future topics! Thank you for using EZmed!
https://medlineplus.gov/ency/article/000713.htm