Hemorrhages within the brain are called intraparenchymal hemorrhages (IPH). While you should look everywhere in the brain for evidence of traumatic injury, there are specific locations within the brain where IPH may appear after trauma.
The pattern of brain injury is influenced by multiple factors that include the magnitude of the injury, the mix of rotation and linear forces at the time of the injury, and the age of the patient. But, once you know where to look you will be more likely to recognize traumatic hemorrhages, even for subtle findings on computed tomography (CT) images.
The typical locations for intraparenchymal hemorrhages are the corpus callosum, the gray-white matter interface, the midbrain, the inferior frontal and temporal lobes, and the brainstem. Let’s take a look at some of the most common (and the most important) locations that you need to carefully inspect when reading CT images.
Identifying a corpus callosum hemorrhage on a brain CT scan
A common location for a traumatic hemorrhage is the splenium of the corpus callosum. The splenium is the posterior part of the corpus callosum. One reason that this is a common site for a post-traumatic hemorrhage may be its proximity to the posterior falx (falx cerebri).
A hemorrhage within the splenium of the corpus callosum may be subtle on CT but is usually quite evident on magnetic resonance imaging (MRI). In this case, it can be seen on a sagittal T1-weighted image (Fig. 2).
While the posterior falx itself is difficult to see on MRI, its course can be predicted by the location of the inferior sagittal sinus. The splenium of the corpus callosum is adjacent to the posterior margin of the sinus—and therefore adjacent to the posterior falx as well.
As a result of brain trauma, the splenium of the corpus callosum may come into contact with the relatively rigid posterior falx, leading to a traumatic hemorrhagic contusion.
Notably, there is also support for the theory that this injury is the result of shearing forces. Regardless of its cause, look for hemorrhages in the posterior corpus callosum on CT and MRI after head trauma.
Identifying a midbrain hemorrhage on a brain CT scan
Another common site of intraparenchymal brain hemorrhages after trauma is the lateral midbrain. A hemorrhage in the lateral midbrain is less common than a hemorrhage in the corpus callosum, and its presence usually suggests a poor prognosis for the patient.
Just as a splenium injury may be due to its proximity to the falx, a midbrain hemorrhage may be the result of its proximity to the medial edge of the tentorium cerebelli. But, a midbrain hemorrhage may also be the result of distracting forces between the relatively fixed brainstem and the more mobile cerebral hemispheres. Be careful not to mistake a subarachnoid hemorrhage in the ambient cistern for a parenchymal hemorrhage—since they have very different clinical implications!
Using a diffusion-weighted MRI (a technique that involves measuring the random motion of water molecules in a tissue), you may be able to detect an area of restricted diffusion in the midbrain without a hemorrhage. Restricted diffusion in the midbrain can occur as the result of a traumatic brain injury at the level of the midbrain and upper pons.
Coronal reconstruction of a brain CT illustrates the proximity of the midbrain to the medial edge of the tentorium. The midbrain normally resides within the tentorial notch or aperture (the space between the tentorial medial edges).
Identifying an inferior frontal or temporal lobe hemorrhage on a brain CT scan
The inferior frontal lobes are a common site for traumatic brain injury. Damage to this region may be associated with loss of sense of smell in patients, since the olfactory bulbs reside there.
With regard to the skull base, there are three important areas where you should look for abnormalities on head CT in a patient presenting with head trauma:
- Along the inferior frontal lobes
- The tip of the temporal lobes
- The ambient cisterns
Along the inferior frontal lobes, you may be able to note an area of high attenuation from blood products or low attenuation without hemorrhage due to a cortical contusion. The tip of the temporal lobe is also a common site of traumatic hemorrhage. Both sites are prone to injury because of their relationship to the skull.
Brain swelling after trauma may lead to the loss of ambient cisterns on CT images. The absence of ambient cisterns can be difficult to appreciate as you develop your familiarity with head CT. So, it is important to look for the normal ambient cisterns in every head trauma case.
Identifying a brainstem hemorrhage on a brain CT scan
The brainstem is another common location for intraparenchymal traumatic hemorrhage. When an intra-axial hemorrhage is present within the brainstem, a common location is the posterior pons at the midline on a brain CT scan. This finding may indicate a Duret hemorrhage, which follows brain herniation and is thought to be the result of venous compression after herniation of the brain through the tentorial hiatus.
So, we’ve covered several common sites of intraparenchymal hemorrhages in patients who experienced head trauma. Hemorrhages can occur throughout the brain and depending on the mechanism and magnitude of the brain injury, you will find it worthwhile to examine these sites on any brain CT scan of your trauma patients!
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