Which condition results from bleeding in the subarachnoid space?

Subarachnoid hemorrhage is specifically defined as bleeding that occurs in the subarachnoid space, which is the area between the arachnoid mater and the pia mater surrounding the brain. This condition typically arises from the rupture of cerebral aneurysms or arteriovenous malformations, leading to blood leaking into the cerebrospinal fluid.

This presents with classic symptoms such as a sudden severe headache, often described as a "thunderclap" headache, which can be accompanied by other neurological deficits, nausea, vomiting, and changes in consciousness. The identification of subarachnoid hemorrhage is critical, as it can lead to severe complications, including increased intracranial pressure and vasospasm.

In contrast, subdural hematomas occur under the dura mater due to tearing of bridging veins, typically from trauma, and epidural hematomas occur between the dura mater and the skull, often following skull fractures. Pulmonary embolism is an obstruction in the pulmonary artery and is unrelated to bleeding in the central nervous system. Understanding these distinctions helps in diagnosing and managing different types of bleeding in the context of neuroanatomy and trauma.