Subarachnoid hemorrhage is characterized by which of the following?

Subarachnoid hemorrhage occurs when there is bleeding into the space surrounding the brain, specifically within the subarachnoid space, which is filled with cerebrospinal fluid (CSF). The most definitive characteristic of this condition is the presence of blood in the cerebrospinal fluid. This can be identified through a lumbar puncture where the CSF is analyzed. In cases of subarachnoid hemorrhage, the CSF may appear bloody or xanthochromic (yellowish), indicating the breakdown of red blood cells.

The other options, while related to neurological conditions, do not specifically describe subarachnoid hemorrhage. For instance, excessive spinal fluid production is more characteristic of conditions like idiopathic intracranial hypertension. Difficulty in moving limbs can be a symptom of various neurological disorders but does not specifically indicate subarachnoid hemorrhage. Similarly, inflammation of the meninges refers to meningitis, not subarachnoid hemorrhage. Thus, the presence of blood in the cerebrospinal fluid is the hallmark of subarachnoid hemorrhage, making it the correct answer in this context.