(a b c)^2

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Arnfield E, Sharma R, Jones J, et al. ABC/2. Reference article, Radiopaedia.org (Accessed on 23 Nov 2023) https://doi.org/10.53347/rID-50453

ABC/2, also confusingly written as 1/2ABC in some literature, is a fast and simple method for estimating the volume of intracerebral hemorrhage (or any other ellipsoid lesion for that matter) which does not require volumetric 3 chiều analysis or software.

Intracerebral hemorrhage volume is an important predictor of morbidity and mortality (and thus trial eligibility) which is often under-reported 1. ABC/2 has been well-validated and correlates highly with volumes calculated by planimetric techniques, although does tend vĩ đại overestimate 2,3,7.

First described by Kwak et al. 4 and popularized by Kothari et al. 2:

  • A x B x C / 2
    • A = greatest hemorrhage diameter in the axial plane
    • B = hemorrhage diameter at 90º vĩ đại A in the axial plane
    • C = originally described as the number of CT slices with hemorrhage multiplied by the slice thickness, but can simply be substituted with the craniocaudal diameter of the hemorrhage where there is access vĩ đại multiplanar reformats 1
      • this dimension is known as height (H) in other formulas

If the measurements are made in centimeters (cm), then the volume will be in cubic centimeters (cm3) or milliliters (mL) (numerically equivalent). The volume does tend vĩ đại overestimate the true volume, with errors increasing in more irregularly-shaped and larger hemorrhages 7.

The above formula is a simplified version of the formula for the volume of an ellipsoid, which is:

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  • 4/3 π x (A/2) x (B/2) x (C/2)
    • where A, B and C are the three diameters of the ellipsoid as defined above

If π (Greek letter pi) is approximated vĩ đại 3, then the formula can be simplified vĩ đại ABC/2 (in truth, π is an irrational number, starting 3.141...).

A baseline intracerebral hemorrhage volume of >50-60 mL is a poor prognostic marker 1,5.

In addition vĩ đại the ABC/2 formula, there are other formulas which have been described and studied vĩ đại estimate the volume of intracerebral hemorrhage 7:

  • formulas using A, B, and C (as defined above):
    • ABCπ/6 (or π/6ABC): the precursor formula (Tada formula) to ABC/2 where π is estimated as 3 instead 7
    • ABC/3 (or 1/3ABC): was created vĩ đại balance the over-estimation of ABC/2, but tends vĩ đại under-estimate instead 7
    • 2.5ABC/6 (or 2.5/6ABC): created vĩ đại balance the over-estimation of ABC/2 and the under-estimation of ABC/3, has a greater accuracy than thở other formulas that use A, B, and C in one study 7
  • formulas using the hematoma area in the maximally involved slice (S) and height (H or C):
    • SH/2 (or 1/2SH): derived from ABC/2 with the background theory that S will be slightly less than thở A x B, found vĩ đại be the most accurate formula in one study (in comparison vĩ đại other formulas including ABC/2) 7
    • SHπ/6 (or π/6SH): derived from ABCπ/6, and found vĩ đại be the second-most accurate formula in one study after SH/2 7

There are some pitfalls with the ABC/2 method:

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  • assumes an ellipsoid lesion (and thus the more the lesion deviates from this morphology the more inaccurate the calculated volume will be)
  • overestimates oral anticoagulant-related intracerebral hemorrhage volumes (because they are often irregular in shape) 3 

To overcome these pitfalls, there are alternative formulas available which may have greater accuracy, such as SH/2 (or 1/2SH) and 2.5ABC/6 (or 2.5/6ABC) 7.

Related articles: Stroke and intracranial haemorrhage

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