From the Guidelines

Subarachnoid hemorrhage (SAH) can cause seizures due to the irritation of the brain tissue by blood in the subarachnoid space.

The exact mechanism of SAH-induced seizures is not fully understood, but it is thought to be related to the irritation of the brain tissue by blood in the subarachnoid space 1.
The blood in the subarachnoid space can cause inflammation and irritation of the surrounding brain tissue, leading to abnormal electrical activity and seizures 1.
Risk factors for seizures in SAH patients include aneurysm location, thickness of the SAH clot, associated intracerebral hematoma, rebleeding, infarction, poor neurological grade, and history of hypertension 1.

Seizures can occur in up to 20% of patients after SAH, most commonly in the first 24 hours 1.
Nonconvulsive status epilepticus is a strong predictor of poor outcome in SAH patients 1.
The use of prophylactic antiepileptic therapy is still commonly used in patients with SAH, although the evidence for its effectiveness is limited 1.

Noncontrast head CT remains the cornerstone of diagnosis of SAH, although its sensitivity decreases over time 1.
Lumbar puncture may be necessary to diagnose SAH if the CT scan is negative 1.
MRI and MRA can be used to obtain more information about the brain and to search for other causes of SAH, although their practical limitations in the emergency setting are significant 1.

From the Research

Seizures in subarachnoid hemorrhage (SAH) patients are associated with impaired brain perfusion and cerebrovascular reactivity status 2
Hyperemia, or increased blood flow, in SAH patients is linked to a higher risk of seizures 2
Cerebral perfusion pressure (CPP) is higher in patients with seizures and ictal-interictal continuum (IIC) compared to controls 2
Supra-optimal CPP precedes increased seizures and IIC in SAH patients, suggesting a potential trigger for seizure activity 2

Seizures after acute brain injury are accompanied by elevated heart rate, blood pressure, and respiratory rate 3
There are trends for rising cerebral perfusion pressure and intracranial pressure after seizure onset 3
Seizure-associated increases in global brain metabolism, partial brain tissue oxygenation, and regional cerebral blood flow (rCBF) do not reach significance, but a trend for a pronounced delayed rCBF rise is seen for surface seizures 3

Higher mean World Federation of Neurological Societies grade on presentation is predictive of seizure 4
Seizure itself is not a significant prognostic predictor after a minimum of one-year follow-up 4
Early mortality, rebleeding, and intracerebral hematoma are similar in both seizure and non-seizure groups 5
Late seizures are infrequent in survivors who had seizures in the acute stage, questioning the necessity for routine, long-term prophylactic anticonvulsants in these patients 5

Seizures occur in 24-26% of SAH patients, often within 24 hours of bleeding 5, 6
The occurrence of early seizures does not correlate with the location of the aneurysm or the prognosis 6
Most remaining seizures occur immediately after rebleeding, with no greater morbidity or mortality compared to all patients who rebled 6