What characterizes a subarachnoid hemorrhage?

A subarachnoid hemorrhage is characterized by bleeding that occurs in the subarachnoid space, which is the area between the arachnoid membrane and the pia mater surrounding the brain. This type of bleeding typically results from the rupture of blood vessels, often associated with conditions such as aneurysms or trauma.

In subarachnoid hemorrhage, patients may present with acute symptoms, such as a sudden onset of a severe headache often described as "the worst headache of my life," followed by neck stiffness, photophobia, or altered consciousness due to the irritation of the meninges and brain. The presence of blood in the cerebrospinal fluid can be confirmed through a lumbar puncture, which analyzes that fluid.

The other choices describe different kinds of hemorrhages or conditions. For instance, bleeding into the brain parenchyma refers to intracerebral hemorrhage, while bleeding into the ventricles pertains to intraventricular hemorrhage. Both of these scenarios involve bleeding in locations that are distinct from the subarachnoid space. Bleeding within the skull without external injury can refer to various intracranial hemorrhages but does not specifically indicate the nature of a subarachnoid hemorrhage.