Not all age-related white matter hyperintensities are the same: a magnetization transfer imaging study

Abstract

Purpose: Our aim was to assess whether presumed histologic heterogeneity of age-related white matter hyperintensities (WMH) is reflected in quantitative magnetization transfer imaging measures.

Materials and methods: From a group of patients participating in a double-blind placebo-controlled multicenter study on the effect of pravastatin (PROSPER), we selected 56 subjects with WMH. WMH were classified as periventricular WMH (PVWMH) and deep WMH (DWMH). PVWMH were subclassified as irregular or smooth, depending on the aspect of their border. Signal intensity of WMH on T1-weighted images was scored as iso- or hypointense. The mean magnetization transfer ratio (MTR) value of different types of WMH was assessed and compared. As a control group, we selected 19 subjects with no or limited WMH.

Results: Mean (SE) MTR of PVWMH (frontal, 31.2% [0.2%]; occipital, 32.2% [0.2%]) was lower than that of DWMH (33.7% [0.5%]). The mean MTR of frontal PVWMH (31.2% [0.2%]) was lower than that of occipital PVWMH (32.2% [0.2%]). Compared with occipital PVWMH, frontal PVWMH more often had a smooth lining (72% frontal versus 8% occipital) and an area with low signal intensity on T1-weighted images (76% frontal versus 35% occipital). MTR did not differ between smooth (31.1% [0.3%]) and irregular (31.6% [0.5%]) PVWMH.

Conclusion: Age-related WMH are heterogeneous, despite their similar appearance on T2-weighted images. By taking into account heterogeneity of age-related WMH, both in terms of etiology and in terms of severity of tissue destruction, one may obtain better understanding on the causes and consequences of these lesions.

Fig 1.

Different types of PVWMH. Examples of frontal PVWMH with a smooth lining (A, right and left) and frontal PVWMH with an irregular lining (B, right and left) and examples of occipital PVWMH with smooth (C, right) and irregular (D, right and left) linings.

Fig 2.

Example of a PVWMH with the characteristic high signal intensity on a T2-weighted image (A) with a low signal intensity on a T1-weighted image (B) (arrow).

Fig 3.

Example of an image from the MTI protocol, obtained with saturation pulse (M_s) and having a proton-attenuation weighted contrast. It clearly shows occipital periventricular white matter hyperintensities as well as deep white matter hyperintensities.

Fig 4.

Mean MTRs with 95% confidence intervals for the 4 different regions in the subjects with white matter hyperintensities.

Fig 5.

Subject (8-year-old) with an obstructive hydrocephalus secondary to infratentorial mass before (A, T1-weighted image; C, T2-weighted image) and after placement of a ventriculoperitoneal shunt (B, T1-weighted image; D, T2-weighted image). Notice the location and lining of the areas with increased signal intensity hypointensities on T1-weighted images in the periventricular white matter before drainage (A), disappearing after drainage (B).