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Low- vs High-Grade Glial Neoplasms: MRS, Perfusion, and Diffusion

January 5, 2008
Written by: , Filed in: Neuroradiology
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A recent study was carried out to determine the ability of these techniques alone or in combination to identify the histopathologic grade of glial neoplasms.

The study has shown that for distinguishing low- from high-grade glial tumors, rCBV is the best single parameter, with improvement when NAA/Cr is also considered.

This was a prospective study involving 105 patients with cerebral gliomas who underwent DWI, PWI, and MRS. 87 studies were done preoperatively, and 18 cases of low-grade tumors were imaged after partial resection, simple debulking, or biopsy.

Lesions were grouped according to the level of malignancy; 40 were classified as low grade (grade 2) and 65 as high grade (grades 3 or 4). Conventional MR consisted of FLAIR and pre- and post-contrast T1. DWI was performed with b values of 0 s/mm2 and 1000 s/mm2. PWI images were used to determine relative cerebral blood volume (rCBV) maps.

For each apparent diffusion coefficient (ADC) and rCBV, 8 regions of interest were drawn in each tumor and contralateral normal brain. Ratios of minimum ADC and maximum rCBV values compared with contralateral tissue were calculated. MRS was performed with a single-voxel technique. Analysis was performed of N-acetyl aspartate (NAA), creatine (Cr), choline (Cho), lactate, and lipid.

No lipid was found in the low-grade tumors; in the high-grade tumors, 67.7% had none, 4.6% had trace amounts, and 27.7% had evidence of lipid. For lactate, the values were 81.0%, 14.3%, and 26.2% for the low-grade tumors and 40.0%, 33.8%, and 26.2% for the high-grade tumors, respectively.

Statistically significant differences were seen between the groups for rCBV ratio to normal tissue, measuring an average of 0.98 in low-grade tumors, and 2.35 in high-grade tumors (P <0.0001). Similarly, the NAA/Cr ratio in tumor was 0.69 versus 0.28 (P <0.0001), and the Cho/Cr ratio in tumor was 2.01 versus 2.47 (P <0.05). No significant difference was seen for ADC ratio of tumor to normal tissue. For distinguishing low- from high-grade tumors, rCBV was the best single parameter, with improvement when NAA/Cr was also considered. If a tumor has an rCBV >1.16 and an NAA/Cr ratio <0.44, there is a sensitivity of 87.7% for detecting high-grade tumor and a specificity of 76.2%. An rCBV of >1.16 alone yields a sensitivity of 80% and a specificity of 78.6%, and NAA/Cr <0.44 alone yields rates of 69.2% and 80%, respectively. Conclusions
Multimodal assessment of glial neoplasms with MR perfusion (rCBV) and spectroscopy (NAA/Cr) are most useful in distinguishing low-grade from high-grade tumors.

Reviewer’s Comments
This is another example of a well-written paper with a useful statistical analysis and conclusion. (Reviewer–Yaron Lebovitz, MD

Zonari P, Baraldi P, Crisi G. Multimodal MRI in the Characterization of Glial Neoplasms: The Combined Role of Single-Voxel MR Spectroscopy, Diffusion Imaging and Echo-Planar Perfusion Imaging.
Neuroradiology; 2007; 49: 795-803

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