ICH Volume Calculator - ABC/2 Bedside CT Estimate

The ICH volume calculator estimates the size of an intracerebral hemorrhage from a non-contrast head CT using the Kothari 1996 ABC/2 bedside method. It is built for clinicians, students, and researchers who already have a CT slice in front of them and need a quick mL number to compare against published severity thresholds, the Hemphill ICH score, and surgical candidacy cut points.

• • Bedside severity check: convert admission CT measurements into a single mL number that can be matched against the 30 mL cutoff used in the Hemphill ICH score.
• • Repeat-scan tracking: compare admission and follow-up CT measurements to flag hematoma expansion in patients being watched on a neuro ICU pathway.
• • Teaching and registry work: walk trainees through the ABC/2 method, partial-slice accounting, and the round-versus-irregular shape choice, or produce an estimate that can be cross-checked against planimetric software in audit and protocol-screening work.

The bedside estimate is most useful when the CT is already loaded and the question is whether the bleed has crossed a published threshold. It is not a substitute for planimetric software on a PACS workstation, and it is not a clinical decision tool.

The Hemphill 2001 ICH score uses 30 mL as the volume factor in the five-component bedside grade, so the mL readback from this calculator is the value the score expects when admission CT measurements are added up.

The ICH volume calculator applies the Kothari 1996 ABC/2 formula. A is the greatest hemorrhage diameter on the CT slice that shows the most blood, B is the diameter 90 degrees to A on the same slice, and C is the number of CT slices with hemorrhage multiplied by the slice thickness. The product is divided by 2 for a round or ellipsoid hematoma, or by 3 for a separated, multinodular, or irregular bleed.

• A (length): Greatest hemorrhage diameter on the CT slice with the most blood, in centimeters.
• B (width): Diameter 90 degrees to A on the same CT slice, in centimeters.
• C (slice thickness): Thickness of one CT slice in centimeters. A 5 mm slice is entered as 0.5, not 5.
• slices: Number of CT slices showing blood. Full slices (>=75% blood) count as 1, partial slices (25-75%) count as 0.5.
• shape factor: Divisor in the formula: 2 for round or ellipsoid, 3 for separated, multinodular, or irregular hematoma.

Partial-slice accounting is built in: a slice with 25% to 75% blood is treated as half a slice, and a slice with less than 25% blood is treated as zero. The Kothari paper validated the formula against planimetric measurement with R^2 = 0.96.

According to Kothari et al., Stroke 1996, intracerebral hemorrhage volume can be estimated at the bedside in under one minute with the formula ABC/2, where A is the greatest hemorrhage diameter, B is the diameter 90 degrees to A, and C is the number of CT slices with hemorrhage multiplied by the slice thickness.

Because chronic hypertension is the largest single risk factor for spontaneous ICH, a working mL number pairs naturally with a Blood Pressure Calculator that puts the admission blood pressure in front of the same clinical picture.

Four concepts are enough to read the result correctly. They cover the geometric model behind ABC/2, slice counting, prognostic thresholds, and the shape factor.

Reading the result panel as a set, rather than a single mL number, is the most accurate way to use the calculator. The mL readback, effective slice count, shape factor, and prognostic band together describe how the estimate was built.

The companion ICH Score Calculator takes the mL readback and turns it into the per-factor points of the Hemphill 2001 score, which is the bedside severity grading built around the same 30 mL hematoma threshold.

The form mirrors the published ABC/2 steps. A short worked pass through the inputs keeps the same logic the user would use on a PACS caliper.

1. 1 Pick the CT slice with the most blood: scroll through the non-contrast head CT and choose the axial slice where the hemorrhage looks largest. That slice drives A and B.
2. 2 Measure A and B in centimeters: place the caliper across the longest blood diameter for A, then rotate 90 degrees for B. Round to one decimal place because CT calipers are not more precise than that.
3. 3 Enter the slice thickness in centimeters: use 0.5 for a 5 mm reconstruction, 0.2 for a 2 mm reconstruction, and 1.0 for a 1 cm reconstruction. Entering 5 instead of 0.5 is a common ten-fold error.
4. 4 Count full and partial slices: count slices where blood covers at least 75% of the slice as full slices, slices with 25% to 75% as partial slices, and ignore slices with less than 25% blood.
5. 5 Pick the hematoma shape: choose round or ellipsoid for a single contiguous bleed, and separated, multinodular, or irregular for a bleed that breaks into separate pockets.
6. 6 Read the mL number with the prognostic band: use the mL readback and the prognostic band together. The mL is the bedside number, and the band is the published threshold it is being compared against.

A 65-year-old with a right basal ganglia hemorrhage has A = 4.5 cm, B = 3.2 cm, a 0.5 cm (5 mm) reconstruction, 12 slices with at least 75% blood, and 2 partial slices. Volume = 4.5 x 3.2 x 0.5 x 13 / 2 = 46.8 mL, just below the 50 mL AHA/ASA 2022 poor-outcome band.

When the bedside volume is ready, the ICH Calculator adds the GCS band, age band, intraventricular hemorrhage flag, and infratentorial origin flag to convert the mL readback into the full 0 to 6 Hemphill total.

A bedside ICH volume number is most useful when it can be compared to published thresholds without doing the arithmetic in the reader's head.

• • Published bedside method: the same ABC/2 formula Kothari validated against planimetric software in 1996, with the published 0.96 correlation.
• • Partial-slice accounting: full and partial slices are combined as the original paper describes, with the effective slice count returned so the user can see how the volume was assembled.
• • Shape factor included: round or ellipsoid and separated, multinodular, or irregular hematomas use the two published divisors, with the chosen factor shown next to the mL readback.
• • Prognostic band labeling: the result panel labels the volume as below 30 mL, at or above 30 mL, or at or above 50 mL, matching the Hemphill 2001 cutoff and the AHA/ASA 2022 surgical discussion band.

The calculator is not a clinical decision tool and does not replace planimetric software. Its job is to put a defensible bedside number beside the published thresholds so the comparison is a glance, not a calculation.

A bedside mL number also fits a wider acute-cardiovascular workflow, and the HEART Score Calculator applies a similar rapid severity grading pattern to chest pain using admission history, ECG, age, and troponin.

Three small changes to the inputs can move the result by tens of milliliters, especially when slices are thin or the hematoma is irregular.

• • ABC/2 is a bedside estimate and can diverge from planimetric software on irregular or separated bleeds, where the ellipsoid approximation is the weakest.
• • The 30 mL and 50 to 60 mL thresholds are prognostic and severity markers, not surgical decisions. The AHA/ASA 2022 guideline does not set a single volume cut point for surgery.

The most common bedside error is a slice thickness entered in millimeters instead of centimeters. A 5 mm slice typed as 5 produces a 25-fold overestimate, enough to cross both thresholds by itself.

According to AHA/ASA 2022 ICH guideline, hematoma volume is a powerful prognostic factor, with the 30 mL threshold used in the ICH score and larger volumes in the 50 to 60 mL range associated with poor outcome.

According to Broderick et al., Stroke 1993, admission hematoma volume is a powerful and easy-to-use predictor of 30-day mortality after spontaneous intracerebral hemorrhage, and a volume of 30 mL or more has been used as a key cutoff in bedside severity scoring since that work.