ICH Volume Calculator

The ABC/2 formula estimates intracranial hemorrhage volume from CT scans. A is the longest diameter of the hemorrhage on the largest slice, B is the diameter perpendicular to A on the same slice, and C is the height (number of hemorrhagic slices × slice thickness). The product A × B × C is divided by 2 for regular bleeds, 3 for irregular, or 4 for very irregular shapes.

In the ABC formula, A stands for the longest diameter of the hemorrhage on the largest CT slice, B is the diameter perpendicular to A measured on the same slice, and C represents the height of the hemorrhage calculated as the number of slices containing blood multiplied by the slice thickness. Together they approximate the three axes of an ellipsoid.

The divisor accounts for the shape of the hemorrhage. A regular or round bleed closely resembles an ellipsoid, so the standard divisor is 2 (giving the classic ABC/2 formula). Irregular or heterogeneous bleeds are divided by 3, and very irregular or separated bleeds are divided by 4 to avoid overestimating volume.

The ABC/2 method is a validated, widely used bedside estimation tool that correlates well with planimetric (manual) volumetrics. Studies show it tends to slightly overestimate volumes for irregular hematomas but is sufficiently accurate for clinical decision-making, particularly in acute settings where speed matters.

Generally, an ICH volume greater than 30 mL is associated with significant morbidity, and volumes above 60 mL carry a very high 30-day mortality. Volumes over 30 mL in the posterior fossa are often considered surgical thresholds. These cutoffs are guidelines — clinical context, location, and patient factors all influence prognosis.

The most common causes include hypertension (affecting deep structures like the basal ganglia, thalamus, and pons), cerebral amyloid angiopathy (lobar bleeds in older patients), anticoagulation therapy, arteriovenous malformations, tumors, and venous sinus thrombosis. Identifying the cause is important for treatment and preventing recurrence.

The ABC/2 method was specifically developed for intraparenchymal hemorrhage. While some clinicians apply modified versions to subdural hematomas, the shape assumptions differ significantly. For crescent-shaped subdural hematomas, dedicated volume formulas or software-based measurements are more appropriate.

ICH volume is a raw measurement (in mL) of how large the bleed is, estimated from CT dimensions. The ICH Score is a clinical grading tool (0–6) that incorporates volume (≥30 mL vs. <30 mL), Glasgow Coma Scale, hemorrhage location, intraventricular extension, and patient age to predict 30-day mortality. Volume is one component of the score.