Differentiation of brain abscesses from necrotic glioblastomas and cystic metastatic brain tumors with diffusion tensor imaging

Abstract

Background and purpose: The differentiation of abscesses from glioblastomas and metastases may not always be possible on the basis of DWI. Our hypothesis was that differences in diffusion properties as detected by DTI allow differentiation of abscess from glioblastomas and metastasis. Furthermore, diagnostic performance of tensor metrics quantifying anisotropy or tensor shapes is better than that of ADC in measuring mean diffusivity for this purpose.

Materials and methods: DTI was performed in 15 abscesses, 15 necrotic glioblastomas, and 26 cystic metastases. In each lesion, manually segmented into 4 regions of interest (ie, cystic cavity, enhancing rim, and immediate [edema most adjacent to the enhancing rim] and distant zones of edema), FA, ADC, C(l), C(p), and C(s) values were measured and statistically compared among groups and evaluated with ROC curve analysis. The presence of a hyperintense FA rim (a rim of edematous tissue that was hyperintense on the FA map) was assessed visually.

Results: Abscess was significantly different from glioblastoma for all tensor metrics measured in the cystic cavity and immediate zone of edema and for all except C(l) in the enhancing rim. Abscess was significantly different from metastasis for all tensor metrics measured in the cystic cavity and enhancing rim and for FA, ADC, and C(l) in immediate zone of edema. The incidence of a hyperintense FA rim was significantly higher in glioblastoma and metastasis compared with abscess. The 3 tensor metrics with the highest performance in differentiating abscess from glioblastoma and metastasis were FA, C(l), and C(s) of the cystic cavity.

Conclusions: DTI is able to differentiate abscess from glioblastoma and metastasis. FA, C(l), and C(s) outperformed ADC in diagnostic performance comparisons.

Fig 1.

An example of how the regions of interest were segmented in a left frontal glioblastoma. Four regions of interest (ie, enhancing rim [B and G], cystic cavity [C and H], and immediate [D and I] and distant zones of edema [E and J]) were segmented with contrast-enhanced MPRAGE and T2-weighted images (upper panel) and then were overlaid on FA maps (lower panel). Note that there is a rim of high FA in the immediate zone of edema (arrows in F, G, and J). A circular region of interest is placed on the contralateral NAWM (B and G).

Fig 2.

Visual assessment for the presence of a hyperintense FA rim in the immediate zone of edema. The upper panel shows the contrast-enhanced MPRAGE image, FA, and FA with scattered regions of interest representing the enhancing rim of a metastatic brain tumor (from left to right); the lower panel shows the corresponding images from a brain abscess. A hyperintense FA rim is present in the immediate zone of edema surrounding the metastatic tumor (arrow) but absent from that of the abscess.