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Characteristics of Dysembryoplastic Neuroepithelial Tumors With MR Spectroscopy, Diffusion-Weighted Imaging, and Perfusion-Weighted Imaging

January 7, 2008
Written by: , Filed in: Neuroradiology, Pediatric Radiology
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Background
Dysembryoplastic neuroepithelial tumors (DNTs) are benign, generally seizure-inducing cortical-based tumors that generally present around age <20 years. Following surgical resection, recurrence is very rare. On CT, the tumors are usually hypodense and may have calcifications. MR characteristics are typically low on T1 and high on T2, occasionally with a multicystic appearance without surrounding edema. One third of tumors enhance and may have an appearance similar to an enlarged gyrus, with remodeling of the overlying calvarium. Imaging appearance can be similar to that of other low-grade glial tumors such as diffuse astrocytoma and ganglioglioma. The objective of a recent study was to determine/describe characteristics of MR spectroscopy (MRS), diffusion-weighted imaging (DWI), and perfusion-weighted imaging (PWI) of DNTs. The results show that dysembryoplastic neuroepithelial tumors (DNTs) demonstrate ml/Cr on MR spectroscopy and apparent diffusion coefficients to be significantly higher than in normal parenchyma. Cerebral blood volume is lower than in normal parenchyma.. Participants The retrospective study included 22 patients with pathologically proven DNT and 14 control patients. Methodology
MRI was performed with T1, double echo, FLAIR, and 3D gradient echo postcontrast T1. DWI was performed with b values of 0 and 1000. MRS was performed as multivoxel technique. PWI consisted of a 10-slice slab to cover the entire lesion. Cerebral blood volume (CBV) was assessed.

The lowest apparent diffusion coefficient (ADC) and highest CBV values of 5 regions of interest were recorded for each area. Relative CBVs (rCBVs) were assessed by dividing the CBV value by the normal contralateral tissue.

Results
All DNTs were supratentorial lesions. Of 22 lesions, 10 were in temporal lobes, 8 in frontal lobes, and 4 in parietal lobes. All involved cortical and subcortical regions with slight mass effect on either adjacent parenchyma or cerebrospinal fluid spaces. Margins were well defined in 18 and poorly defined in 4. Mean size was 39 +/- 18.6 mm.

In all, T1 was hypointense and T2 was hyperintense without peritumoral edema.

Six of 22 lesions had a cystic appearance and in 4 (18.2%), MRI demonstrated prominent enhancement. In 6 (27.3), adjacent cortex was dysplastic, appearing abnormally sulcated, isointense to cortex on T1, and slightly hyperintense on T2.

In pathological specimens, 16 demonstrated cortical dysplasia. MRS demonstrated similar NAA/Cho, NAA/Cr, Cho/Cr, and NAA/Cho+CR to normal brain.

However, ml/Cr and ADC were significantly higher than in normal parenchyma (P <0.001). rCBVs were lower than those in normal parenchyma (P <0.001), even in contrast-enhanced areas. The highest correlation with diagnosis of DNT was with ADC, followed by rCBV and ml/Cr. Reviewer’s Comments
DNTs demonstrate characteristic features on MRS, ADC values, and PWI, with rCBVs lower than those in brain parenchyma and elevated ADC values. MRS demonstrates a small decrease in NAA and an increase in ml/Cr. These values may be useful in differentiating these lesions from other low-grade neoplasms.

Author: Yaron Lebovitz, MD

Reference:
Bulakbasi N, Kocaoglu M, et al. Dysembryoplastic Neuroepithelial Tumors: Proton MR Spectroscopy, Diffusion and Perfusion Characteristics.

Neuroradiology; 2007; 49 (October): 805-812

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