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ICH Volume by ABC/2

A fast bedside estimate of intraparenchymal hemorrhage volume that approximates the ellipsoid formula. Volume (mL) ≈ (A × B × C) / 2, where A, B, and C are the three orthogonal diameters of the hematoma in centimeters. Validated against planimetric volumes for spontaneous ICH.
reviewed 2026-07-01

Method (measure on CT)

  • A = greatest hemorrhage diameter (cm) on the axial slice with the largest area
  • B = diameter perpendicular to A on that same slice (cm)B is measured in-plane, at 90° to A on the same axial image.
  • C = number of slices with hemorrhage × slice thickness (cm) — the craniocaudal dimensionUse the slice-weighting rule: count a slice as 1 if the hemorrhage area on it is >75% of the largest slice, 0.5 if 25–75%, and 0 if <25%. Multiply the resulting count by slice thickness in cm.
  • Volume (mL) = (A × B × C) / 2
  • Keep all three measurements in centimeters so the result is in milliliters

Reporting must state

  • Estimated hematoma volume in mL and the location (lobar, basal ganglia, thalamic, pontine, cerebellar)
  • Intraventricular extension (IVH) and hydrocephalusIVH and hydrocephalus independently worsen prognosis and may prompt EVD placement.
  • Midline shift and herniation
  • Spot sign on CTA and any interval expansion vs prior — predictors of hematoma growth
  • Cerebellar hemorrhage ≥3 cm or with brainstem compression / hydrocephalus — neurosurgical emergency

C = (slice-weighted number of slices with clot) × slice thickness, in cm.

Estimated volume

Enter A, B, and C in centimeters to estimate the hematoma volume.

ABC/2 worked reference

Formula: Volume (mL) = (A × B × C) / 2, all diameters in cm.

A

Largest axial diameter of the clot (cm).

B

Perpendicular diameter on the same slice (cm).

C

Approximate vertical extent = (number of slices with clot, slice-weighted) × slice thickness (cm).

Example

A = 4 cm, B = 3 cm, C = 5 cm → (4 × 3 × 5) / 2 = 30 mL.

Thresholds (context)

Supratentorial ICH >30 mL and/or reduced GCS carries high mortality; volume feeds prognostic scores (e.g., ICH score).

  • ABC/2 assumes an ellipsoid shape and overestimates the volume of irregular, multilobular, or separated hematomas — for these, planimetric/volumetric software is more accurate.
  • The /2 denominator derives from the ellipsoid volume (4/3·π·(A/2)(B/2)(C/2) ≈ ABC/2 when π ≈ 3). Do not confuse this with the /3 form some authors use for very irregular clots.
  • Best validated for spontaneous intraparenchymal hemorrhage; subdural and epidural crescentic/lentiform collections are not well modeled by ABC/2.

Sources

  • Kothari RU, et al. The ABCs of Measuring Intracerebral Hemorrhage Volumes. Stroke. 1996;27(8):1304-1305.

Educational reference for clinicians — not medical advice. Verify against the primary source before acting on it; guidelines change. Final decisions rest with the interpreting physician and your institution's protocols.