Bicaudate index on magnetic resonance imaging: effects of normal aging.

The bicaudate and bifrontal indices have been used in prior computed tomographic studies to investigate atrophy of the caudate nuclei in patients with Huntington's chorea and cerebral atrophy. However, the relationship between these indices and caudate volume has not been documented previously. In this study, we used high-field magnetic resonance imaging (MRI) to determine the effects of normal aging on the bicaudate and bifrontal indices and to study the relationship between these indices and caudate volume. The subjects were 49 normal volunteers, aged 22 to 82 years, who were without any significant neurologic or psychiatric disorders. Age was positively correlated with bicaudate index (r = .59; P < .0001) and bifrontal index (r = .40; P < .0047). Age was negatively correlated with caudate nuclei volume (r = -.47; P < .0005). Caudate volume was negatively correlated with bicaudate (r = -.27; P < .06) and bifrontal (r = -.31; P < .03) indices. These findings are consistent with prior reports of caudate nuclei degeneration with increasing age. Linear and volumetric caudate measurements with MRI may prove useful in the investigation of caudate nuclei function in the neuromotor decline with normal aging and in disorders such as Huntington's chorea.