ABC2-SPH worked example: a 19 ml putaminal ICH
A worked ABC/2 example is the same three measurements you would take on a scan, written slowly so the arithmetic is not the mystery. Measure the longest length of the hematoma on the largest slice (A), the width at ninety degrees on that slice (B), and the extent in the third direction — often slice thickness times the number of slices where the bleed is seen (C). Multiply A × B × C. Divide by two. The unit is centimetres, the result is millilitres, roughly. This is an estimate used at the bedside. It is not a lab assay. Different eyes, different windows, different C.
Suppose, for teaching only, A is 4 cm, B is 3 cm, and C is 3 cm. 4 × 3 × 3 = 36. Half of 36 is 18. You would say «about 18 ml on ABC/2». Change C by one slice and the number moves. That is why we say about. Real scans are messier than this rectangle. Irregular bleeds make C the sloppy letter. The formula still helps people talk. It does not replace the radiologist’s report.
Where people slip the arithmetic
Mixing centimetres and millimetres. Counting every faint smear as a full slice. Measuring A and B on different slices. Forgetting the divide by two and doubling the scare. If you are a family member, you do not need to measure. If you are learning the score, write the three numbers before you multiply. Circle the unit. Then halve. Then stop. Do not «adjust» because the number feels too small or too large. That adjustment is how estimates become stories.
- Same unit for A, B and C. Centimetres.
- A and B on the largest slice, at right angles.
- C is the third direction, honestly counted, not hoped.
- Multiply, then divide by two. Not the other way round.
- Teaching numbers are teaching numbers. Not someone’s scan.
| Step | Do | Slip |
|---|---|---|
| A, B | Largest slice, perpendicular | Two different slices |
| C | Honest third extent | Counting haze as full slices |
| Arithmetic | ABC, then /2 | Forgetting the half |
| Language | «About» | A false precision to two decimals |
The risk of treating 18.0 as truth
A neat number photographs well in a note. An irregular bleed does not care. If the clinical picture and the estimate fight, the picture wins until someone re-measures or repeats the scan. Do not carry a worked example into a family’s room as if it were their relative. Teach the steps. Leave their millilitres to their team.
What a neat number is not allowed to become
A, B and C in centimetres, the product, then half: say about, count C honestly, and do not invent a decimal. ABC/2 is a shared ruler so people can talk. It is not a verdict and not a photograph of the future. The next sentence in the room still belongs to the patient, not to the arithmetic, however tidy the scrap of paper looks.