ICH Volume Calculator (ABC/2 Method)

About the ICH Volume Calculator (ABC/2 Method)

The ICH Volume Calculator uses the ABC/2 method — the most widely used bedside technique for estimating intracerebral hemorrhage volume from non-contrast CT imaging. Developed by Kothari et al. (1996) and validated across numerous studies, this simplified ellipsoid formula provides rapid volume estimation that correlates closely with computer-assisted volumetric analysis (r = 0.93).

Accurate volume measurement matters in acute hemorrhagic stroke because ICH volume is one of the most frequently cited markers of 30-day mortality and functional outcome at the population level. The landmark Hemphill ICH Score incorporates volume at the ≥30 mL threshold, and hemorrhage size is also discussed in common AHA/ASA and trial-based reference frameworks such as STICH II and cerebellar ICH volume thresholds.

This calculator supports both the standard ABC/2 method and the modified ellipsoid formula (4/3πr₁r₂r₃). Enter dimensions directly from CT measurement tools, or derive the C dimension from slice thickness and number of affected slices. The calculator provides volume classification, location-based reference thresholds, hematoma expansion context, and mass-effect context for worksheet or discussion use.

When This Page Helps

Rapid ICH volume estimation is useful because it converts bedside CT measurements into the volume ranges commonly used in scoring systems, prognosis papers, and location-based reference discussions. This calculator removes the need to do the ellipsoid arithmetic by hand while keeping the result in a worksheet-style format.

How to Use the Inputs

1. Select the calculation method — ABC/2 (standard) or ellipsoid formula
2. Measure A: the largest hemorrhage diameter on the CT slice showing the greatest extent
3. Measure B: the diameter perpendicular to A on the same CT slice
4. Enter C directly (craniocaudal extent), or derive it from slice thickness × number of hemorrhage-containing slices ÷ 10
5. Select hemorrhage location (supratentorial vs. infratentorial) for location-specific reference thresholds
6. Review volume classification, context thresholds, and outcome estimates

Example Calculation

Tips & Best Practices

• Always measure A on the CT slice with the largest hemorrhage area, then measure B perpendicular to A on the same slice
• Window/level settings matter — use standard brain window (W:80 L:40) for consistent measurements
• If CTA spot-sign information is available, read it as a separate imaging feature rather than part of the ABC/2 formula itself
• Serial volume measurements are often compared over time when clinicians are tracking expansion on repeat imaging
• Remember that IVH volume is calculated separately and is not included in parenchymal ICH volume
• For irregular hematomas, consider repeating measurements and averaging, or using volumetric software

The ABC/2 Method: History and Validation

The ABC/2 formula was published by Kothari, Brott, Broderick, and colleagues in 1996 as a simplified bedside alternative to time-consuming planimetric volumetric analysis. The method models the hemorrhage as an ellipsoid and uses three orthogonal diameters measured on CT. Its simplicity — requiring only a ruler and basic arithmetic — made it immediately practical for emergency settings.

Validation studies demonstrate strong correlation (r = 0.91-0.95) with gold-standard volumetric measurements across different hemorrhage sizes, locations, and CT scanner types. A large validation study confirmed ABC/2 accuracy within ±5 mL for hematomas under 25 mL, though accuracy decreases for very large or irregularly shaped hemorrhages.

Volume Context by Range

ICH volume is frequently used as one part of early ICH context:

**Small ICH (< 10 mL):** Often associated with lower short-term mortality and less mass effect, although location still matters.

**Medium ICH (10-30 mL):** A broad middle range where outcome varies by location, intraventricular extension, age, and early expansion.

**Large ICH (30-60 mL):** Above the 30 mL threshold used in the ICH Score and many prognosis papers. In the literature, this range is often discussed with location, neurologic status, and mass effect rather than volume alone.

**Massive ICH (> 60 mL):** Associated with very high mortality at the population level and often used as a marker of severe disease burden.

Hematoma Expansion Context

Hematoma expansion is one of the most studied early modifiers of ICH outcome. Trial literature often discusses blood pressure management, reversal of anticoagulation, and CTA spot-sign status alongside baseline volume when clinicians interpret early risk. This calculator does not model those treatment pathways; it only provides the initial volume estimate and broad reference context.

Frequently Asked Questions

• How accurate is the ABC/2 method compared to volumetric software?

  The ABC/2 method correlates with planimetric volumetry at r = 0.93 (Kothari 1996). It slightly overestimates irregular hematomas and underestimates oblong ones, but it remains a common bedside approximation when formal volumetry is not available.

• What volume thresholds are commonly referenced for ICH?

  For supratentorial ICH, the Hemphill ICH Score uses a 30 mL threshold, and STICH II studied lobar hematomas of 10-100 mL with GCS ≥ 9. For cerebellar hemorrhage, values above roughly 15 mL or diameter above 3 cm are often cited in guideline and neurosurgical reference discussions. These thresholds do not replace full imaging and clinical assessment.

• How do I count slices for the C dimension?

  Count all CT slices where the hemorrhage occupies more than 25% of the expected area. Some protocols use >25%, >50%, or >75% area thresholds. The standard Kothari method counts any slice showing hemorrhage.

• What is hematoma expansion and why does it matter?

  Hematoma expansion is usually described as an early increase in hemorrhage volume, often using thresholds such as >33% or >6 mL within 24 hours. It is associated with worse outcomes at the population level, and imaging features such as a CTA spot sign can shift how strongly clinicians worry about it.

• Does the ABC/2 method work for all hemorrhage shapes?

  ABC/2 is most accurate for relatively elliptical hematomas. For very irregular, multilobar, or C-shaped hemorrhages, planimetric volumetry is preferred. Some studies suggest ABC/3 for irregularly shaped ICH.

• What volume thresholds are used in prognostic scores?

  The ICH Score uses 30 mL. The FUNC score uses 30 mL and 60 mL cutoffs. For cerebellar ICH, 15 mL is a commonly cited reference threshold. Generally, each 10 mL increase in ICH volume is associated with higher 30-day mortality at the population level.