Proton chemical shift imaging in normal pressure hydrocephalus

Abstract

Background and purpose: Differentiation of normal pressure hydrocephalus (NPH) from other types of dementia and the selection of appropriate candidates for shunt surgery remain a clinical challenge. The aims of this study were to assess the efficacy of cerebral metabolites depicted by proton chemical shift imaging (1H-CSI) in distinguishing NPH from other dementias and to examine the relationship between metabolite changes and the outcome of shunt surgery.

Methods: 1H-CSI measurements were obtained in nine patients with clinical diagnosis of NPH; six patients with other types of dementia, including Alzheimer and Pick disease; and five control subjects. The 1H-CSI sequence consisted of a double spin-echo sequence with imaging parameters of 2000/135/4-2 (TR/TE/acquisitions). Volumes of interest were selected from a section through the lateral ventricles. The peak areas and ratios of N-acetylaspartate, creatine, choline, and lactate were calculated. In two patients, follow-up 1H-CSI and N-isopropyl (123I)-p-iodoamphetamine brain perfusion imaging were available after treatment with continuous spinal drainage.

Results: Lactate peaks were observed in the lateral ventricles for all patients with NPH (lactate/creatine, 0.23 +/- 0.14) but not for patients with other types of dementia or control subjects. In all cases, we noted no significant differences in the peak ratios in the voxels located at the white matter near the lateral ventricles. In one patient with NPH, intraventricular lactate disappeared and regional CBF recovered after drainage.

Conclusion: The intraventricular lactate level may be useful in differentiating NPH from other types of dementia.

fig 1.

Proton MR spectra (TR/TE, 2000/135) in the patient with NPH. Upper left, axial T1-weighted MR image of the same patient. A box outlines volume of interest, which includes the bodies of lateral ventricles in the hemisphere. Lower left corner shows spectra from the body of the left lateral ventricle and surrounding parenchyma. The spectrum from the voxel of the parenchyma (black arrow) shows normal spectral pattern (upper right). The spectrum from the voxel in the body of left lateral ventricle (white arrow) shows the lactate peak (lower right). NAA, Cho, and Cr peaks also are observed, suggesting that this intraventricular voxel contains periventricular brain tissue

fig 2.

Proton MR spectra (TR/TE, 2000/135) in two patients with NPH. The spectra obtained from periventricular regions (upper row) with the intraventricular spectra (lower row) are shown. Apparent inverted doublet peaks at 1.3 ppm are observed in the intraventricular spectrum of one case (left side) and can be recognized as lactate peaks. In the other case (right side), good qualities of lactate peaks are seen compared with the peaks from the periventricular region in the upper row

fig 3.

Proton MR spectra (TR/TE, 2000/135) before and after continuous spinal drainage in the lateral ventricle of a patient with NPH. The spectra were obtained from a intraventricular voxel (black arrow in VOI). Before treatment, lactate peaks are observed as inverted doublet peaks at 1.3 ppm from the intraventricular voxel of NPH (upper middle). Cho, Cr, and NAA peaks suggest partial volume artifact from periventricular brain tissue. A metabolic image of lactate (upper right) before treatment shows that lactate is confined to the lateral ventricles and surroundings. After treatment, lactate is not observed clearly (lower right). The reduced CBF (upper left) returned to normal after continuous spinal drainage (lower left) at SPECT