🧠 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:
🔬 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.
🧮 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
📊 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 |
🛠️ 4. Radiological AI Tools
Some modern centers use AI-based algorithms to:
- Automatically segment blood in SAH
- Estimate volumes
- Correlate with outcome scores