Figure 1: CT head scan showing both an extradural haematoma on the right and subdural haematoma on the left side. The high signal intensity indicating an acute bleed.

(Click on image to enlarge)

Figure 2: CT head scan from Figure 1a. The extradural haematoma because of the restriction by the meninges is shaped like a half lemon as depicted by the picture of the lemon on the right side while the subdural haematoma without restriction by the meninges, then to spread out over the surface of the cerebrum and is shaped like a banana as shown by the banana depicted on the left.

(Click on image to enlarge) 




One of the most common causes for Out-Of-Hours imaging is head trauma, requiring the need for a CT head to be undertaken without delay.


Quick, cheap, easy and massively important in management, rapid access CT imaging is essential in contemporary medicine.


The chief concern of clinicians is BLOOD.

Is there any and does it require neurosurgical input?

Is an operable survivable abnormality present on the CT?

If blood is present, where is it and is it isolated or in several sites?


These are:

-       Extra-axial collections: extradural and subdural haematomas

-       Subarachnoid (Figure 1a and b)

-       Intraparenchymal ( haematoma or contusions )

-       Intraventricular


Of these the extra-axial collections are the most immediate and straightforward to surgically treat through evacuation with a bore hole, especially if there is significant mass effect on the brain itself.


An extradural haematoma is a collection of blood which forms between the inner surface of the skull and outer layer of dura.  They are typically lentiform in shape and hence why the appearance is often referred to as looking like a lemon.


A subdural haemorrhage is a collection of blood accumulating in the ‘potentia’l space between the dura and arachnoid mater of the meninges.  These appear sickle shaped with the inner wall of the collection essentially parallel to the bone, hence it has been referred to as banana shaped.


These illustrations beautifully demonstrate in a pictorial fashion the location of blood in the different types of collections (Courtesy of Click on link for further information -


Extra-dural haematomas almost always occur in the context of trauma, with 95% having an associated underlying fracture.  Sub-durals can occur in traumatic and non-traumatic circumstances, with fractures uncommonly associated.


CT can also assist in aging the extra-axial collection, especially in the case of subdural haematomas into being: hyperacute, acute, subacute or chronic depending on the attenuation value and its density in relation to the adjacent brain parenchyma.





Images and text contributed by

Dr Ian Bickle, Department of Radiology,RIPAS Hospital.

All images are copyrighted and property of RIPAS Hospital.