A diagnosis of SAH is made based on the patient's history and physical examination, together with diagnostic tests. Approximately half of SAH patients have a period of reduced consciousness, including syncope, confusion, convulsions, and/or coma. Patients are often dazed, confused, or drowsy within the first few hours after SAH. In a middle aged adult who complains of a headache and suddenly loses consciousness, SAH should be a prime consideration in the differential diagnosis.
Early computerized tomography (CT) is the cornerstone of SAH diagnosis. CT scans are highly reliable prognostic indicators of the clinical course, especially in predicting the development of vasospasm. The amount and location of blood in the subarachnoid space is predictive of the severity of vasospasms. A computerized tomography (CT) scan without contrast is often done first because contrast could obscure the location of the SAH. More precise 3 dimensional representation in preparation for surgery can be obtained using computerized tomography angiography CTA or magetic resonance angiograpy MRA.
Conventional angiography remains the gold standard to visualize the major cerebral blood vessels and their branches. Angiography is usually done immediately following diagnosis of SAH by a CT scan in patients who are clinically stable. Early angiography assists with a definitive diagnosis and enables the surgical team to plan treatment. If a contrast CT shows negative results and there are no signs of increased ICP, the physician may perform a lumbar puncture to rule out SAH. A lumbar puncture is contraindicated in the presence of increased ICP due to the risk of brain stem herniation and the possibility of causing rebleeding.
Visit to Harvard's website and read about Subarachnoid Hemorrhage of Unknown Etiology Look for the answer to this question:
If a lumbar puncture is done, what substance in the spun sample confirms the diagnosIs of SAH?
The Hunt and Hess SAH classification system is used to describe the severity of the bleed and to predict the most appropriate treatment option. The patient is assigned to a category on admission; changes in the patient's condition can then be monitored according to this baseline.