Haemorrhage Volume Estimation

ABC/2 Formula for Intracerebral Haemorrhage Volume is a fast and simple method for estimating the volume of intracerebral haemorrhage (or any other ellipsoid lesion for that matter) that obviates that need for  software for volumetric 3D analysis.

Background and Purpose

Intracerebral haemorrhage volume is an important predictor of morbidity and mortality and is an important parameter in the calculation of the Intracerebral Haemorrhage (ICH) Score 

The volume of intracerebral hemorrhage (ICH) is a powerful prognostic indicator, correlating strongly with 30-day mortality. Rapid, bedside estimation of hemorrhage volume enables clinicians to assess severity, guide triage decisions, and enrol appropriate patients into clinical trials. The ABC/2 rule offers a validated and efficient method to estimate ICH volume from CT imaging.

The ICH score was developed at the University of California, San Francisco Medical Center (UCSF), with the original study analysing 161 patients presenting with ICH to UCSF between 1997-1998

ABC/2 Formula
ABC intracranial volume
  • A: Maximum haemorrhage diameter on the axial CT slice with largest haemorrhage
  • B: Diameter 90° to A on the same slice
  • C: Cranio-caudal extent of haemorrhage, either:
    • Number of slices with visible haemorrhage × slice thickness (in cm), OR
    • Direct cranio-caudal measurement (in cm) from reformatted views

ICH Volume Estimate (mL or cm³) = A × B × C ÷ 2

Intracerebral Haemorrhage Volume ABC:2
Clinical Utility
  • Requires <1 minute to perform
  • Strong correlation with computerised planimetric measurements (R² = 0.96)
  • High interrater and intrarater reliability (ICC = 0.99)
  • Overestimates volume slightly (mean 1.5±1.3 mL)
Prognostic Significance
  • ICH volume ≥ 30 mL is a component of the ICH Score (worse prognosis)
  • Volume >50–60 mL is associated with high mortality
  • Useful for trial eligibility screening (e.g., STICH criteria)
Mathematical Basis
  • Simplified from the ellipsoid volume formula:
    • True: (4/3)π × (A/2) × (B/2) × (C/2)
    • Approximate: ABC/2 (assumes π ≈ 3)
Limitations
  • Assumes ellipsoid morphology
  • Overestimates volumes in irregular or anticoagulant-related hemorrhages
  • ABC/3 may be proposed for highly irregular shapes (unvalidated)
References

References

Publications

FOAMed

Fellowship Notes

MBBS DDU (Emergency) CCPU. Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Co-creator of the LITFL ECG Library. Twitter: @rob_buttner

Dr James Hayes LITFL author

Educator, magister, munus exemplar, dicata in agro subitis medicina et discrimine cura | FFS |

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