Aneurysmal Subarachnoid Hemorrhage (Fisher Scale, WFNS, CTA Spot Sign & Vasospasm Surveillance)

• Seen in adults (40–60 years, female predilection) presenting with hyperacute, catastrophic, explosive headache ('thunderclap headache', 'worst headache of my life'), neck stiffness, photophobia, altered mental status, or sudden collapse.
• Caused by rupture of an intracranial saccular (berry) aneurysm (85% of non-traumatic SAH), commonly located at branch points of the Circle of Willis: anterior communicating artery (ACom, 30–35%), posterior communicating artery (PCom, 25%), or middle cerebral artery (MCA) bifurcation (20%).

Imaging Findings

• Non-Contrast CT Brain (NCCT - Sensitivity >98% within first 12–24 Hours):
• –
  High-attenuation hyperdense acute blood (50–70 HU) casting the basal cisterns, Sylvian fissures, interhemispheric fissure, and cerebral sulci.
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  Hemorrhage Distribution Clues for Aneurysm Location:
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  Interhemispheric fissure / septum pellucidum: Anterior communicating artery (ACom).
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  Ipsilateral Sylvian fissure & middle fossa: Middle cerebral artery (MCA) bifurcation.
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  Suprasellar cistern & ambient cistern: Posterior communicating artery (PCom).
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  Fourth ventricle & prepontine cistern: Basilar tip or PICA aneurysm.
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  **SWI / T2* GRE & FLAIR: Together with FLAIR sulcal hyperintensity, SWI shows dark blooming artifact** within the basal cisterns, Sylvian fissures, and dependent occipital horns, providing >95% sensitivity for subacute or trace SAH when non-contrast CT has normalized.
• –
  DWI / ADC: Essential for detecting secondary delayed cerebral ischemia (DCI) / vasospasm-induced infarction (new wedge-shaped or cortical territories of true diffusion restriction on DWI/ADC typically occurring between days 4 and 14).
• Modified Fisher Grading Scale (Predicting Delayed Cerebral Vasospasm Risk):
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  Grade 1: Minimal or diffuse thin SAH (<1 mm) without intraventricular hemorrhage (IVH) (low vasospasm risk).
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  Grade 2: Minimal or thin SAH (<1 mm) WITH intraventricular hemorrhage (moderate vasospasm risk).
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  Grade 3: Thick cisternal SAH (≥1 mm) WITHOUT intraventricular hemorrhage (high vasospasm risk).
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  Grade 4: Thick cisternal SAH (≥1 mm) WITH intraventricular hemorrhage (highest vasospasm risk).
• World Federation of Neurosurgical Societies (WFNS) Clinical Grading Scale (Correlate with CT Fisher Grade):
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  Grade 1: GCS 15 without focal neurological motor deficit (low risk).
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  Grade 2: GCS 13–14 without focal neurological motor deficit.
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  Grade 3: GCS 13–14 WITH focal neurological motor deficit.
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  Grade 4: GCS 7–12 with or without focal motor deficit (high risk).
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  Grade 5: GCS 3–6 (comatose) with or without focal motor deficit; dictates urgent neurosurgical ICU resuscitation and invasive ICP monitoring.
• CT Angiography (CTA - Definitive First-Line Vascular Investigation):
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  Delineates saccular outpouching, neck-to-dome ratio, parent vessel incorporation, and multiple aneurysms (present in 15–20%).
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  CTA 'Spot Sign' / Active Contrast Extravasation: Demonstrates focal hyperdense contrast pooling (blush) within an associated intraparenchymal or subarachnoid hematoma, indicating active arterial bleeding, impending early re-rupture, and ultra-high early mortality requiring emergent neurovascular securement.
• Key Acute Complications:
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  Acute Obstructive Hydrocephalus: Temporal horn enlargement (>2 mm width) and rounded frontal horns due to blood clogging arachnoid villi or fourth ventricular outlet obstruction.
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  Intraventricular & Intraparenchymal Hemorrhage: Hematoma extending into adjacent brain parenchyma or ventricular system.

Differential Diagnosis

Important Points to Remember

• Diagnostic Pitfall: Assuming a negative non-contrast CT excludes SAH in a patient presenting >24 hours after thunderclap headache! Non-contrast CT sensitivity drops to ~85% at 5 days and ~50% at 1 week as blood hemolyzes. If clinical suspicion is high and CT is normal after 12 hours, lumbar puncture for CSF spectrophotometry (bilirubin / xanthochromia) is mandatory!
• Crucial Review Areas:
• 1.
  Temporal horns of lateral ventricles for acute early hydrocephalus (earliest sign of ventriculomegaly).
• 2.
  Anterior communicating artery, PCom, and MCA bifurcation for the causative aneurysm and any second/multiple aneurysms.
• 3.
  Tip of the basilar artery and PICA origin near the foramen magnum.
• 4.
  Lung bases / cardiac function on scout for neurogenic pulmonary edema and takotsubo cardiomyopathy.
• Case-Specific Radiologist Management:
• 1.
  Immediate Verbal Alert: Direct telephone notification to on-call neurosurgical consultant and neuro-intensive care registrar immediately confirming SAH and acute hydrocephalus.
• 2.
  Immediate Vascular Imaging: Emergency CT Angiography (Circle of Willis CTA from C1 to skull vertex) to identify the bleeding aneurysm for urgent securement; proceed to catheter Digital Subtraction Angiography (DSA) if CTA is equivocal.
• 3.
  External Ventricular Drain (EVD) Triaging: If acute hydrocephalus with temporal horn dilatation is present, facilitate urgent bedside external ventricular drainage by neurosurgery.
• 4.
  Aneurysm Securement Protocol (Coiling vs Clipping): Emergent transfer to Neuro-Intervention / Neurosurgery for definitive occlusion within 24 hours (endovascular detachable platinum coiling [ISAT trial] or surgical clipping) to prevent catastrophic rebleeding (rebleed carries 50–70% mortality).
• 5.
  Vasospasm & Triple-H Protocol: Initiate oral Nimodipine (60 mg every 4 hours for 21 days); daily Transcranial Doppler (TCD) surveillance for delayed cerebral ischemia (peak days 4–14); coordinate endovascular balloon angioplasty or intra-arterial milrinone/verapamil if medically refractory symptomatic vasospasm develops.