Hemorrhage within the brain parenchyma may be caused by a number of different etiologies, with several of them shown in the adjacent image. It may be hard to identify the exact cause of the hemorrhage based on a non contrast CT alone. In the absence of trauma, patients may need further work up with a CT angiogram looking for a vascular malformation or with an MRI looking for an underlying mass.

In this example we see an extra-axial hematoma adjacent to the right frontal and parietal lobes (blue arrows). This hematoma is located above the dura. We notice here that the hematoma:

• Does not cross sutures/ is bound by sutures
• Is lens shaped
• With several foci of air (green arrows)
• With an associated skull fracture (orange arrow)
• Is likely caused by injury to the middle menigneal artery or potentially injury to a dural venous sinus.
• Requires emergent neurosurgical consultation.

Here we see an extra-axial hemorrhage adjacent to the left frontal lobe (blue arrows). We notice in this example that the hematoma

• Does not cross midline
• Crosses sutures
• Is shaped like a crescent
• Is most likely the result of injury to a bridging vein

The most common cause of subarachnoid hemorrhage is trauma with blood products seen in a peripheral sulcal distribution. However, when subarachnoid hemorrhage is seen filling the basilar cisterns like we seen in this example, the distribution is in a pattern most consistent with a ruptured aneurysm. The next appropriate step is to perform a CT Angiogram to evaluate for an underlying associated aneurysm.