In this prospective study, patients were included if there was evidence of mass like lesion at conventional MRI of the brain. The final diagnosis was made from either histopathologic result after surgical resection or biopsy or clinical–radiologic diagnosis. For clinical–radiologic diagnosis, a follow-up MRI after 1 year was used as the reference standard. The following exclusion criteria were applied: patients younger than 16 years of age; patients who had undergone surgery before MRI examination, patients without complete MRI protocol and patients with non-diagnostic DWI, perfusion or MRS sequences due to motion artifacts. Hence, over the course of two years starting December 2013 till December 2015, total patients’ count was 39 adult patients (27 males and 12 females), their age ranged from 16 to 65 years with a mean of 37.6 years ± 17.3. Informed consent was obtained from all patients and the study was approved by the Ethics Committee of our institution.
Imaging techniques and analysis
MR imaging was performed using Siemens Avanto 1.5 MR system with a standard head coil. Each study consisted of axial and coronal T2-weighted turbo spin echo (T2 TSE) utilizing repetition time (TR) of 3000 ms, an echo time (TE) of 120 ms, axial fluid-attenuated inversion recovery (FLAIR) (TR/TE, 8000/138, time of inversion (TI) = 2000 ms), pre-contrast axial, coronal and sagittal T1-weighted spin echo (T1 SE) (550/15), and post contrast conventional axial, sagittal and coronal T1 spin echo (550/15), with 3 mm slice thickness, 0.3 mm gap, 256 × 256 acquisition matrix, and 180 mm field of view (FOV).
DWI was performed in the axial plane, using a T2-weighted, echo-planar spin-echo sequence EPI with the following parameters: TR = 3400 ms, TE = 100 ms, 192 × 192 acquisition matrix, 5 mm slice thickness, 0.3 mm gap and b-value = 0, 500, 1000 s/mm2. The minimum ADC value was measured in the lesion core using a region of interest (ROI) while preferably avoiding cystic and necrotic areas. Standard mean ADC values were calculated automatically and expressed in 10−3 mm2/s. ROIs were also drawn on the contralateral normal-appearing brain parenchyma as a control .
The perfusion weighted imaging (PWI) protocol was performed with a T2-weighted, echo-planar, spin-echo sequence (EPI) using the following parameters: TR = 1480, TE = 30, 128 × 128 acquisition matrix, 5 mm section thickness, no gap, and 50 scans. Gadopentetate dimeglumine contrast medium was injected at a dose of 0.1 mmol/kg using a power injector at a flow rate of 5 ml/s followed by a saline bolus (20 ml). Nineteen images per second were then acquired. Data processing was performed by using an Syngo Neuro Perfusion Evaluation as the analytic program. As the color maps of cerebral blood volume were generated, the maximum CBV in the lesion was calculated by placing the ROI in the solid areas showing the highest color intensity. Data were then compared with those of the ipsilateral or contralateral normal-appearing white matter to measure the relative CBV (rCBV = CBV of the lesion/CBV of normal appearing white matter). CBV of the normal appearing white matter is considered as a reference, lesions with rCBV less than that of the whiter matter is considered hypo perfuse, and above is considered hyper perfused.
Multi-voxel two-dimensional chemical shift imaging (2D CSI) was performed with an echo time of intermediate TE (135 ms) (TR 1,500 ms, FOV 160 mm, acquisition time 7 min 34 s) to evaluate the levels of choline (Cho) 3.36–3.21 ppm, creatine (Cr) 3.15–3.0 ppm, N-acetyl aspartate (NAA) 2.18–2.01 ppm, lactate 1.35 ppm and lipids 1.33–0.9 ppm using a point resolved spectroscopy (PRESS) sequences. The volume of interest size and position were determined by examining the MR images in all three dimensions (sagittal, coronal and transverse planes), the aim is to include the largest portion of the lesion, peri-focal area together with normal contra-lateral brain within the region of interest (only with assessment by multi-voxel 2D CSI) as much as we can and to exclude subcutaneous fat and regions with large variations in magnetic susceptibility. Appropriate automatic shimming achieved by using 4–8-Hz line width, 1-kHz spectral width, Water suppression using chemical shift selective saturation technique (CHESS) were done and the automated software developed by the manufacture spectroscopic data (Syngo neuro spectroscopy evaluation). The metabolite ratios: Cho/Cr, Cho/NAA, NAA/Cr and NAA/Cho were calculated by dividing the metabolite integral values in the same spectrum and it was done automatically by the work station software.
Seventeen cases could be confirmed by pathology. Routinely processed paraffin-embedded tissues were cut and stained with the conventional hematoxylin and eosin stain and reticulin stain. Immunohistochemical analysis was performed for CD20, CD3, pancytokeratin and S-100. Both the primary antibody and the detection kit were purchased from Lab Vision Corporation (Neo Markers, USA). Immunohistochemical staining was performed using an avidin-biotinylated immunoperoxidase methodology.
Follow-up MRI was done for the non-biopsied cases including conventional MRI studies and advanced neuro-imaging for confirmation of the preliminary diagnosis. Patients were considered to have non-neoplastic process if they had regressive or vanishing lesions after treatment documented on MRI at 1 year follow-up.
Statistical analysis of the data was carried out using SPSS version 18. Descriptive statistical analysis was presented as counts and percentages for categorical variables and as mean and standard deviation for continuous variables. For comparison of the quantitative variables between the low-grade glioma and non-neoplastic groups, we applied the Student-t test. A P value < 0.05 was considered statistically significant. We used a receiver operating characteristic analysis curve (ROC) to decide the cutoff between low-grade gliomas and non-neoplastic lesions. We then calculated the accuracy, sensitivity, specificity, positive predictive values (PPV) and negative predictive values (NPV) associated with these cutoff points (all values are presented as %).