How Is Subarachnoid Hemorrhage Diagnosed? Tests, Criteria & Process
Subarachnoid Hemorrhage diagnosis relies on MRI brain with/without contrast (preferred), CT head (emergency setting), Electroencephalogram (EEG). Learn the full diagnostic pathway, clinical criteria, differential workup, and what to expect at your evaluation.
Updated March 27, 2026
Subarachnoid Hemorrhage is diagnosed using MRI brain with/without contrast (preferred), CT head (emergency setting), Electroencephalogram (EEG) and targeted clinical evaluation. Subarachnoid hemorrhage is bleeding into the subarachnoid space surrounding the brain, most often caused by a ruptured cerebral aneurysm. It classically presents with a sudden, severe thunderclap headache described as the worst headache of life, accompanied by nausea, vomiting, and neck stiffness.
Clinical Context
The diagnostic process for Subarachnoid Hemorrhage begins with Detailed neurological history and examination, followed by brain imaging and targeted investigation based on presentation. Key investigations include MRI brain with/without contrast (preferred), CT head (emergency setting), Electroencephalogram (EEG), Lumbar puncture and CSF analysis. The gold standard is: MRI brain for structural lesions; EEG for seizure disorders; lumbar puncture for CNS infection and subarachnoid haemorrhage. Clinical guidelines from NICE Neurology / AAN define the diagnostic criteria and recommended investigation pathway.
Clinical Pathway
Subarachnoid Hemorrhage — Full Condition GuideCondition HubSubarachnoid Hemorrhage — Differential DiagnosisDifferentialSubarachnoid Hemorrhage — Treatment PathwaysTreatmentSubarachnoid Hemorrhage — Prognosis & OutlookPrognosisFrequently Asked Questions
How Is Subarachnoid Hemorrhage Diagnosed? Tests, Criteria & Process?+
Subarachnoid Hemorrhage is diagnosed using MRI brain with/without contrast (preferred), CT head (emergency setting), Electroencephalogram (EEG) and targeted clinical evaluation. Subarachnoid hemorrhage is bleeding into the subarachnoid space surrounding the brain, most often caused by a ruptured cerebral aneurysm. It classically presents with a sudden, severe thunderclap headache described as the worst headache of life, accompanied by nausea, vomiting, and neck stiffness.
How do doctors test for subarachnoid hemorrhage?+
The main tests used to diagnose Subarachnoid Hemorrhage include MRI brain with/without contrast (preferred), CT head (emergency setting), Electroencephalogram (EEG). Your doctor will select investigations based on your symptoms, clinical findings, and risk factors.
How long does it take to diagnose Subarachnoid Hemorrhage?+
The time to diagnosis varies. Some cases are identified within hours using clinical presentation and blood tests; others require weeks, repeated investigations, or specialist referral.
Can Subarachnoid Hemorrhage be missed on initial testing?+
Yes — Subarachnoid Hemorrhage can be missed if initial tests are negative or if the presentation is atypical. If clinical suspicion remains high, repeat testing or specialist referral is appropriate.
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