Free ICH Volume Calculator

Estimating ICH Volume with the ABC/2 Formula

This free online intracerebral hemorrhage volume calculator uses the ABC/2 (also called the ABC CT) method to estimate the size of a parenchymal bleed from head CT measurements. The tool converts linear dimensions into a volumetric estimate quickly, helping clinicians assess hematoma burden at the bedside. Below we describe the ABC CT formula, explain how to obtain the necessary parameters, and provide guidance on interpreting the results.

ABC CT Parameters and the Core Formula

The ABC/2 approach relies on four straightforward inputs:

• A – the maximum length of the hemorrhage (cm or mm).
• B – the width perpendicular to A on the same CT slice.
• C – the thickness of one CT slice (same units as A and B).
• slices – the number of slices containing hemorrhage, weighted by the percentage of cross‑sectional area involved.

The basic equation is:

$$\text{ICH volume} = \frac{A \times B \times C \times \text{slices}}{2}$$

This form assumes the bleed resembles an ellipsoid. Since the true volume of an ellipsoid is $\frac{4}{3}\pi \times \frac{A}{2} \times \frac{B}{2} \times \frac{C}{2}$, setting $\pi \approx 3$ collapses the expression to the simple ABC/2 shape.

Adjusting for Irregular Hemorrhage Shape

A more refined version of the ABC CT formula introduces a shape factor (SF) to better handle non‑ellipsoid hematomas:

$$\text{ICH volume} = \frac{A \times B \times C \times \text{slices}}{SF}$$

• Use SF = 2 when the hemorrhage appears round or ellipsoid.
• Use SF = 3 when the bleed is irregular, separated, or multinodular.

This adjustment reduces overestimation of volume in complex-shaped bleeds.

Step‑by‑Step Instructions for the Calculator

1. Identify the largest slice: On the axial CT image showing the greatest hemorrhage area, measure the longest diameter (A) and the greatest perpendicular width (B). Keep all lengths in the same unit (cm or mm).
2. Count slices: For each slice in which hemorrhage is visible, estimate the percentage of the slice area occupied:
   • ≥75% → count as 1 slice.
   • 25–75% → count as 0.5 slice.
   • <25% → do not count. Sum these values to obtain slices.
3. Select the slice thickness (C), which is a fixed parameter of the CT protocol (e.g., 2 mm, 5 mm).
4. Choose the shape category – round/ellipsoid (SF = 2) or irregular/multinodular/separated (SF = 3).
5. The calculator then computes the intracerebral hemorrhage volume in mL (equivalent to cm³) or mm³.

Clinical Meaning of the Volume Estimate

A hematoma volume above 50–60 mL is a recognised predictor of poor outcome and often influences decisions about surgical evacuation or aggressive medical therapy. The ICH score, which incorporates volume together with age, Glasgow Coma Scale, infratentorial origin, and intraventricular extension, provides a more complete mortality risk assessment and is available alongside this volume calculator.

Common Causes of Intracerebral Bleeding

Parenchymal hemorrhage can arise from a wide range of conditions:

• Hypertension – chronic elevated blood pressure weakens small arterial walls, making them prone to rupture.
• Anticoagulant therapy – drugs such as warfarin and heparin, often used to prevent clots, increase bleeding risk. (The INR calculator helps monitor coagulation status.)
• Vascular anomalies – arteriovenous malformations and aneurysms.
• Head trauma – contusions, fractures, or penetrating injuries.
• Bleeding disorders – haemophilia, thrombocytopenia, disseminated intravascular coagulation (DIC), sickle cell disease.
• Hypervascular tumours – metastases, angiomas, or primary brain tumours.
• Cerebral amyloid angiopathy – especially in older patients.
• Unknown cause – a substantial proportion of ICHs have no identifiable aetiology.

Worked Example Using the ABC CT Formula

A 65‑year‑old patient presents with acute right‑sided weakness. CT reveals a left basal ganglia hemorrhage. The measurements are:

• A = 5 cm
• B = 3 cm
• C = 0.2 cm (2 mm)
• slices = 40 (weighted)
• Shape = ellipsoid → SF = 2

$$\text{Volume} = \frac{5 \times 3 \times 0.2 \times 40}{2} = \frac{120}{2} = 60 \text{ mL}$$

This volume exceeds the 50 mL threshold, indicating a large hematoma that may warrant urgent neurosurgical opinion.

Important Disclaimer

This ICH volume calculator is intended for educational and clinical decision support only. It does not replace the judgment of a qualified healthcare professional. All results should be interpreted within the full clinical context and discussed with the treating physician.