5.2 Subarachnoid Hemorrhage, Aneurysm Clipping/Coiling & Hunt-Hess Grading

Subarachnoid Hemorrhage, Aneurysm Clipping/Coiling & Hunt-Hess Grading

Subarachnoid hemorrhage (SAH) is a devastating and life-threatening neurologic emergency characterized by the rapid extravasation of arterial blood into the subarachnoid space—the delicate area between the arachnoid membrane and the pia mater that closely surrounds the brain and spinal cord. While head trauma is the most common cause of SAH overall, spontaneous (non-traumatic) SAH accounts for approximately 5% to 10% of all strokes and carries an exceptionally high burden of morbidity and mortality.

The vast majority (approximately 85%) of spontaneous SAHs are caused by the sudden rupture of an intracranial saccular (often termed 'berry') aneurysm. Other less common causes include the rupture of arteriovenous malformations (AVMs), bleeding diatheses, intracranial arterial dissections, and sympathomimetic drug abuse (e.g., cocaine or methamphetamine).

Patients experiencing an aneurysmal SAH classically present with a sudden, severe, and catastrophic headache, often described by patients as a "thunderclap" headache or the absolute "worst headache of my life." This distinct clinical hallmark reaches peak intensity within seconds to minutes. It is frequently accompanied by profound nausea, forceful vomiting, photophobia, nuchal rigidity (meningismus), and varying degrees of altered mental status or focal neurological deficits. Seizures may also occur concurrently at the time of presentation. The sudden, explosive increase in intracranial pressure (ICP) resulting from the arterial bleed can occasionally lead to transient loss of consciousness, cardiac arrest, or even sudden death before the patient reaches the hospital.

Diagnostic Evaluation

The initial, definitive diagnostic test of choice for suspected SAH is an emergent non-contrast computed tomography (CT) scan of the head. This imaging modality is highly sensitive if performed within the first 6 to 12 hours after the onset of symptoms. Extravasated blood typically appears as hyperdense (bright white) material heavily filling the basal cisterns, sylvian fissures, and cortical sulci.

If the CT scan is negative or equivocal, but the clinical suspicion remains high based on the patient's presentation, a lumbar puncture (LP) is absolutely mandatory. An LP that reveals an elevated opening pressure, a persistently elevated red blood cell count that does not clear or diminish in successive collection tubes (which rules out a traumatic tap), and the presence of xanthochromia confirms the diagnosis. Xanthochromia is the yellowish discoloration of the cerebrospinal fluid (CSF) caused by bilirubin, an enzymatic breakdown product of hemoglobin, which typically takes up to 12 hours after the hemorrhage to fully develop in the CSF.

Following the confirmation of an SAH, comprehensive vascular imaging, such as CT angiography (CTA) or digital subtraction angiography (DSA), is required immediately to identify the exact source of bleeding, pinpoint the aneurysm's precise anatomical location, accurately measure its size and neck morphology, and strategically plan subsequent definitive treatment. DSA remains the gold standard due to its high spatial resolution.

Clinical Grading Scales

Two primary, universally recognized clinical scales are utilized to grade the severity of the SAH and predict patient prognosis: the Hunt and Hess scale and the World Federation of Neurosurgical Societies (WFNS) grading system. Additionally, the Fisher Scale is exclusively used to evaluate the radiological severity and precisely predict the risk of delayed cerebral ischemia.

The Hunt and Hess scale focuses primarily on the patient's clinical presentation, overall consciousness, and symptomatology upon admission:

• Grade I: Asymptomatic, or presenting with a mild headache and slight nuchal rigidity.
• Grade II: Moderate to severe headache, nuchal rigidity, but no specific neurologic deficit other than a cranial nerve palsy (often CN III or VI).
• Grade III: Drowsiness, confusion, lethargy, or a mild focal neurologic deficit.
• Grade IV: Stupor, moderate to severe hemiparesis, possible early decerebrate rigidity, and vegetative autonomic disturbances.
• Grade V: Deep coma, fixed decerebrate rigidity, and a moribund appearance.

The Fisher Scale grades the amount and distribution of subarachnoid blood directly visualized on the initial non-contrast CT scan to predict the precise likelihood of the patient developing symptomatic cerebral vasospasm and delayed cerebral ischemia:

• Grade 1: No blood detected on the CT scan.
• Grade 2: Diffuse deposition or thin layer with all vertical layers of blood (such as in the interhemispheric fissure, insular cistern, or ambient cistern) measuring less than 1 mm thick.
• Grade 3: Localized dense clots and/or vertical layers of blood measuring 1 mm or greater in thickness.
• Grade 4: Diffuse or no subarachnoid blood present, but with the presence of intracerebral or intraventricular hemorrhage. Notably, patients with Fisher Grade 3 are considered to have the absolute highest risk of developing clinically significant vasospasm due to the thick clots burdening the basal vessels.

Aneurysm Securing: Clipping vs. Coiling

The paramount, overriding objective in the acute management of aneurysmal SAH is the strict prevention of early rebleeding. Rebleeding from an unsecured ruptured aneurysm carries a catastrophic mortality rate of up to 70%, and most commonly occurs within the dangerous window of the first 24 to 48 hours following the initial hemorrhage. Thus, early, definitive securement of the ruptured aneurysm is an absolute imperative. Strict blood pressure control (typically keeping systolic BP strictly below 160 mm Hg) is medically necessary until the aneurysm is successfully secured to actively reduce this risk.

There are two primary, distinct therapeutic modalities to secure a ruptured aneurysm: open microsurgical clipping and endovascular coiling. The choice of procedure depends on a multitude of patient-specific factors, including the patient's clinical grade, age, comorbidities, the exact location, size, and neck morphology of the aneurysm, and the presence of a space-occupying intracerebral hematoma.

Microsurgical Clipping involves performing a craniotomy to surgically access the brain and the aneurysm. The neurosurgeon carefully dissects the delicate arachnoid membranes under microscopic magnification to visualize the parent artery and the aneurysm neck. A specialized, spring-loaded titanium clip is then permanently placed across the neck of the aneurysm to entirely obliterate arterial blood flow into the fragile aneurysm sac while strictly preserving flow within the parent vessel. Clipping is often the strongly preferred approach for patients presenting with large, life-threatening intraparenchymal hematomas requiring concurrent surgical evacuation, for aneurysms with very wide necks (making endovascular treatment exceedingly difficult without flow-diverting stents), or for aneurysms located at major vessel bifurcations (e.g., middle cerebral artery bifurcations) that are anatomically more accessible surgically.

Endovascular Coiling is an advanced, minimally invasive technique where a specialized microcatheter is carefully navigated from the femoral or radial artery, directly up into the complex cerebral circulation, and meticulously placed directly within the aneurysm sac. Tiny, detachable platinum coils are then serially deployed into the aneurysm to completely pack it. This physically promotes blood thrombosis and definitively seals the aneurysm off from the active arterial circulation. The landmark International Subarachnoid Aneurysm Trial (ISAT) demonstrated unequivocally that for aneurysms deemed equally suitable for either clipping or coiling, endovascular coiling was strongly associated with superior functional outcomes and higher rates of independent survival at one year, leading to a massive global paradigm shift towards early endovascular management. Coiling is particularly favored for older, frailer patients, those presenting with poor clinical grades (such as Hunt and Hess IV or V), and aneurysms located deep in the posterior circulation (e.g., basilar tip aneurysms), which are notoriously challenging to access safely via open surgery.

Regardless of the specific modality chosen, all patients require highly specialized, intensive care unit monitoring immediately following the procedure. Vigilant management of external ventricular drains (EVDs) is often critically required if hydrocephalus develops, as the excessive blood products in the subarachnoid space can mechanically obstruct the arachnoid granulations and severely disrupt the normal absorption of cerebrospinal fluid (CSF).