Changes of Fractional Anisotropy and Apparent Diffusion Coefficient in Patients with Idiopathic Normal Pressure Hydrocep
Since ventricular dilation and periventricular abnormal intensities are commonly seen in patients with idiopathic normal pressure hydrocephalus (INPH) on magnetic resonance imaging (MRI), dysfunction of white matter may have an important role in the mecha
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Abstract Since ventricular dilation and periventricular abnormal intensities are commonly seen in patients with idiopathic normal pressure hydrocephalus (INPH) on magnetic resonance imaging (MRI), dysfunction of white matter may have an important role in the mechanism causing symptoms of INPH. To clarify the pathophysiology of INPH, we analyzed axonal water dynamics using diffusion tensor MRI. Thirty-six patients with possible INPH were included. Regional fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were measured in several white matter regions before and 24 h after a cerebrospinal fluid tap test (CSF-TT). The patients were divided into two groups: patients who showed significant improvements in neurological status after the CSF-TT (positive, n = 17) and those with no neurological improvement (negative, n = 19). After CSF-TT, ADC values were significantly decreased in the frontal periventricular region and the body of the corpus callosum in the positive group (p < 0.05), whereas no significant change was shown in the negative group. FA values were significantly increased in the body of the corpus callosum in both groups after CSF-TT (p < 0.05). After CSF-TT, water molecules at the extracellular space could move to the intraventricular space, resulting in decreased ADC values. This suggests that changes of water dynamics in white matter may have a role in the mechanism causing symptoms of INPH.
K. Demura, M. Mase (), T. Osawa, and K. Yamada Department of Neurosurgery, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan e-mail: [email protected]
Keywords Idiopathic normal pressure hydrocephalus • Diffusion tensor imaging • Fractional anisotropy • Apparent diffusion coefficient • Tap test
Introduction The diagnosis of idiopathic normal pressure hydrocephalus (INPH) is sometimes difficult, and many patients are inaccurately diagnosed as suffering from Alzheimer’s disease or Parkinson’s disease. Recently, the cerebrospinal fluid tap test (CSF-TT) has come to be considered an essential diagnostic test because of its simplicity and high specificity to estimate shunt efficacy. The diffusion tensor MR (magnetic resonance) imaging (DTI) technique is based on the characteristics of barriers, including the myelin sheath and cell membrane, which restrict diffusion of water into brain tissue. As a consequence, water molecules diffuse faster along axonal paths than across them. Fractional anisotropy (FA) is a measure of the directionality of diffusion. Isotropic diffusion of water in multiple directions is measured by the apparent diffusion coefficient (ADC). In general, measures of diffusivity, such as ADC, are inversely related to FA [8, 9]. In INPH patients, since ventricular dilation and periventricular abnormal intensities are commonly seen on MR images, dysfunction of white matter involving axonal fibers may have an important role in the causative mechanism of symptoms [5, 14]. But the mechanism of INPH symptoms remains unclear. To investigate the pathophysiology, we
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