Bicaudate Index

Diagram showing the method for measuring the bicaudate index (A / B). A = the width of the frontal horns at the level of the caudate nuclei; B = the diameter of the brain at the same level.





The bicaudate index is a commonly used linear measure of the lateral ventricles. To account for the natural changes in the size of ventricles with aging, BCI is then divided by the upper limits of ‘normal’ for age to calculate the relative bicaudate index.

Diagnosis of hydrocephalus is established when RBCI is >1. Normative values determined from subjects without neurological disease, in the mid to late 1970s.


Divide the width of the frontal horns, at the level of the caudate nuclei, by the corresponding diameter of the brain. Perform measurement on the cut which included the Foramen of Monro.  If the foramen of Monroe is in between two cute, use mean value for of the two cuts.


Bicaudate index plotted against age. The density ellipsoid includes 95% of the data points.



Normal BCI values, stratified by age group, in a cohort of SAH patients without co-existing hydrocephalus.




Gijn, Jan van et al. “Acute Hydrocephalus After Aneurysmal Subarachnoid Hemorrhage”. Journal of Neurosurgery 63.3 (1985): 355-362.

Dupont, Stefan and Alejandro A Rabinstein. “CT Evaluation Of Lateral Ventricular Dilatation After Subarachnoid Hemorrhage: Baseline Bicaudate Index Balues”. Neurological Research 35.2 (2013): 103-106.



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