BTF Guidelines - Surgical Management of TBI - Post-Traumatic Mass Volume Measurement in Traumatic Brain Injury Patients

Severe TBI Guidelines

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Appendix I
1. Direct volumetric measurement with imaging software using a modern computer tomographic CT scanner is the gold standard. This has been applied only on rare occasions.
2. The "ellipsoid method" was developed to calculate the volume of arteriovenous malformations3. It is based on the concept that the volume of an ellipsoid is approximately one-half of the volume of the parallelepiped (a six-faced polyhedron, all of whose faces are parallelograms lying in pairs of parallel planes) into which it is placed. By measuring three diameters of a given lesion in the arterial phase of an angiogram, a parallelepiped is constructed, and its volume, divided in half, is close to the actual volume of the malformation. By extending this concept from angiography to CT scanning, calculation of space-occupying lesions becomes possible4. The "ABC" method has been described by Kothari et al.2 for the measurement of intracerebral hemorrhages, and is also based on the concept of measuring the volume of an ellipsoid. The formula for an ellipsoid is:
  V_e = 4/3 Π (A/2) (B/2) (C/2)
  where A, B, and C are the three diameters. For Π = 3, the formula becomes V_e = ABC/2
  The volume of an intracerebral hemorrhage can be approximated by following the steps listed below:
  - Identify the CT slice with the largest area of hemorrhage (Slice 1)
  - A: measure the largest diameter, A.
  - B: measure the largest diameter 90° to A on the same slice, B.
  - C: count the number of 10-mm slices.
  - Compare each slice with slice 1.
  - If the hemorrhage is greater than 75% compared with slice 1, count the slice as 1.
  - If the hemorrhage is 25 to 75%, count the slice as 0.5.
  - If the hemorrhage less than 25%, do not count the slice.
  - Add up the total C.
3. More recently, the "Cavalieri direct estimator" method has been introduced1. It breaks down the lesion on the CT scan into a corresponding number of points. The volume of a lesion is the product of the sum of the points that fall into the lesion, the area associated with each point, and the distance between the scan slices. A grid that is used to determine the number of points can be obtained by photocopying a template provided in the original article or by preparing a uniformly spaced point grid by computer4.