🧠 Subarachnoid Hemorrhage Volume: Key Points [Neurosurgery Wiki]

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====== 🧠 Subarachnoid Hemorrhage Volume: Key Points ======

Estimating the volume of a subarachnoid hemorrhage (SAH) is trickier than for intraparenchymal or intraventricular bleeds due to its irregular, diffuse distribution in the subarachnoid space. Here’s a comprehensive look at how it's approached:

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===== 🔬 1. Why It's Hard to Measure =====

  * SAH spreads along cisterns, sulci, and fissures, making it non-confluent and irregular.
  * There’s no standard “ABC/2” method for SAH like there is for ICH.

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===== 🧮 2. Methods of Estimation =====

==== A. Visual Grading Systems (most commonly used) ====

**➤ Fisher Scale (Classic)**  
Used to predict vasospasm, not volume per se:

  * Grade 1: No SAH
  * Grade 2: Diffuse thin SAH (<1 mm)
  * Grade 3: Localized clot and/or vertical layer >1 mm
  * Grade 4: Any SAH with intraventricular hemorrhage

**➤ Modified Fisher Scale**  
More detailed, still semiquantitative, and slightly better correlated with vasospasm risk.

==== B. Hijdra Score ====

A more granular scale scoring 10 basal cisterns and sulci from 0 (no blood) to 3 (completely filled with blood), total score 0–30.

==== C. Volumetric Estimation Using Imaging Software ====

Manual or semi-automated segmentation of hyperdensities on CT using tools like:

  * 3D Slicer
  * OsiriX
  * ITK-SNAP

**Pros:**  
→ Results in volume in mL

**Cons:**  
→ Time-consuming  
→ Not routinely done in clinical practice  
→ Mainly used in research

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===== 📊 3. Clinical Reference Values =====

^ SAH Classification ^ Estimated Volume ^ Prognostic Value ^
| Small/localized | < 5 mL | Lower risk |
| Moderate | 5–15 mL | Intermediate risk |
| Large | >15–20 mL | Higher risk of vasospasm, poor outcome |

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===== 🛠️ 4. Radiological AI Tools =====

Some modern centers use AI-based algorithms to:

  * Automatically segment blood in SAH
  * Estimate volumes
  * Correlate with outcome scores

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