Comparison of Canine and Feline Meningiomas Using the Apparent Diffusion Coefficient and Fractional Anisotropy

Abstract

Meningiomas are the most common intracranial tumor in dogs and cats, and their surgical resection is often performed because they are present on the brain surface. Typical meningiomas show comparatively characteristic magnetic resonance imaging findings that lead to clinical diagnosis; however, it is necessary to capture not only macroscopic changes but also microstructural changes to devise a strategy for surgical resection and/or quality of removal. To visualize such microstructural changes, diffusion-weighted imaging (DWI) and diffusion tensor imaging (DTI) have been used in human medicine. The aim of this retrospective study was to investigate the different characteristics of the apparent diffusion coefficient (ADC) from DWI and fractional anisotropy (FA) from DTI of meningioma between dogs and cats. Statistical analyses were performed to compare ADC and FA values between the intratumoral or peritumoral regions and normal-appearing white matter (NAWM) among 13 dogs (13 lesions, but 12 each in ADC and FA analysis) and six cats (seven lesions). The NAWM of cats had a significantly lower ADC and higher FA compared to dogs. Therefore, for a comparison between dogs and cats, we used ADC and FA ratios that were calculated by dividing the subject (intra- or peritumoral) ADC and FA values by those of NAWM on the contralateral side. Regarding the intratumoral region, feline meningiomas showed a significantly lower ADC ratio and higher FA ratio than canine meningiomas. This study suggested that ADC and FA may be able to distinguish a meningioma that is solid and easy to detach, like as typical feline meningiomas.

Keywords: cats; diffusion tensor imaging; diffusion-weighted imaging; dogs; magnetic resonance imaging; meningioma.

Figure 1

An example of apparent diffusion coefficient (ADC) and fractional anisotropy (FA) measurements in a cat (Cat 1). Localizing transverse T2-weighted imaging (T2WI) and T1-weighted imaging with contrast enhancement (CE-T1WI) with superimposed ADC and FA color maps. The upper row shows the intratumoral region (“revolver technique”), the middle row shows the peritumoral regions, and the lower row shows the contralateral normal-appearing white matter region. T2WI (A), CE-T1WI (B) of the tumor area, and T2WI (rostral from A and B) of the normal-appearing white matter area (C). Regions of interest (circles) were placed on the ADC maps (D–F) and FA maps (G–I) as in the figure.

Figure 2

An example of apparent diffusion coefficient (ADC) and fractional anisotropy (FA) measurements in a dog (Dog 6). Order of images is same as Figure 1. T2WI (A), CE-T1WI (B) of the tumor area, and T2WI (caudal from A and B) of the normal-appearing white matter area (C). Regions of interest (circles) were placed on the ADC maps (D–F) and FA maps (G–I) as in the figure.

Figure 3

Boxplots comparing canine and feline meningiomas for apparent diffusion coefficient (ADC) values in the intratumoral [small regions of interest (ROIs) and large ROIs] and peritumoral areas, and in the contralateral normal-appearing white matter (as an internal standard). The middle line and upper/lower box edges of each box represent the median and upper/lower quartiles, respectively. Both the end of upper/lower whiskers show the maximum/minimum values. Statistical analyses were performed using the Mann–Whitney U test. *p < 0.05, ***p < 0.0001.

Figure 4

Boxplots comparing canine and feline meningiomas for fractional anisotropy (FA) values in the intratumoral [small regions of interest (ROIs) and large ROIs] and peritumoral areas, and in the contralateral normal-appearing white matter (as an internal standard). The middle line and upper/lower box edges of each box represent the median and upper/lower quartiles, respectively. Both the end of upper/lower whiskers show the maximum/minimum values. Statistical analyses were performed using the Mann–Whitney U test. *p < 0.05, **p < 0.005.

Figure 5

Boxplots comparing canine and feline meningiomas for the apparent diffusion coefficient (ADC) ratio in the intratumoral [small regions of interest (ROIs) and large ROIs] and peritumoral areas. The ADC ratio was calculated by dividing the intratumoral and peritumoral values by the value of the contralateral normal-appearing white matter. The middle line and upper/lower box edges of each box represent the median and upper/lower quartiles, respectively. Both the end of upper/lower whiskers show the maximum/minimum values. Statistical analyses were performed using the Mann–Whitney U test. ***p < 0.0001.

Figure 6

Boxplots comparing canine and feline meningiomas for the fractional anisotropy (FA) ratio in the intratumoral [small regions of interest (ROIs) and large ROIs] and peritumoral areas. The FA ratio was calculated by dividing the intratumoral and peritumoral values by the value of the contralateral normal-appearing white matter. The middle line and upper/lower box edges of each box represent the median and upper/lower quartiles, respectively. Both the end of upper/lower whiskers show the maximum/minimum values. Statistical analyses were performed using the Mann–Whitney U test. **p < 0.005.