ABC/2 Formula for ICH Volume

Why use it

Rapid, validated bedside estimation of ICH volume without specialized volumetric software. Volume guides prognosis (ICH Score), surgical decision-making, and prognostication. Can be performed during initial CT review in the emergency department.

About

The ABC/2 formula estimates the volume of an intracerebral hemorrhage (ICH) from three orthogonal CT measurements. It models the hemorrhage as a spheroid and approximates its volume without the need for specialized software. Volume is a key predictor of outcome in ICH — larger hemorrhages are associated with higher mortality and worse neurological outcomes.

When to use

• Non-contrast CT scan showing intracerebral hemorrhage
• ICH Score calculation (requires volume)
• Pre-surgical decision-making for hematoma evacuation
• Prognostication and goals of care discussions in ICH
• Monitoring hematoma expansion on repeat CT

Formula

Pearls & pitfalls

• The formula assumes an ellipsoid (spheroid) shape: V = π/6 × A × B × C ≈ ABC/2.
• A = greatest hemorrhage diameter on the CT slice with the largest area.
• B = perpendicular diameter on the same slice.
• C = number of CT slices with hemorrhage × slice thickness (in cm).
• ABC/2 overestimates volume by ~5–10% in irregular-shaped hemorrhages (e.g., subdural pattern).
• Hematoma expansion (≥6 mL or ≥33% increase) within first few hours is a key predictor of poor outcome.
• Blood pressure control (SBP < 140 mmHg) within 1 hour helps minimize expansion (AHA/ASA 2022).

Next steps

Volume < 30 mL: Small ICH — generally managed medically. Volume 30–60 mL: Moderate — consider neurosurgical consultation. Volume > 60 mL: Large ICH — very high mortality; neurosurgical evaluation; goals of care discussion. Volume > 100 mL: Near uniformly fatal.

Evidence

Broderick et al. (Stroke 1993) validated ABC/2 against computer-assisted volumetry in 139 patients. Correlation r = 0.96. The formula is the standard for clinical volumetry in major ICH trials including ATACH-2 and INTERACT-2.

References

1. Broderick JP et al. Volume of intracerebral hemorrhage: a powerful and easy-to-use predictor of 30-day mortality. Stroke. 1993;24(7):987-993. — link
2. Huttner HB et al. Hematoma growth and outcome in treated neurocritical care patients with intracerebral hemorrhage. Stroke. 2006;37(6):1421-1425. — link