Author: Tammie L. S. Benzinger, M.D., Ph.D.

Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, USA

Patient History

A 16-year-old boy presented with seizures and was found to have a contrast enhancing mass at the left temporo-occipital lobe.

Sequence details:

Imaging was performed at 3 Tesla MAGNETOM Trio, A Tim System, using 12-channel head coils. A single shot spin-echo echo-planar imaging (EPI) was used for DTI (Diffusion tensor imaging) acquisition with the following parameters: 60 slices without a gap, FOV = 190 mm, phase FOV = 100 %, slice thickness = 2 mm, base resolution = 96, phase resolution = 100 (that makes voxel size = 2 x 2 x 2 mm), phase partial Fourier = 6/8, TR = 9900 msec, TE = 102 msec, average = 1, b-value = 1400 sec/mm2, bandwidth = 1080 Hz, EPI factor = 96, echo spacing = 1 msec. Average ADC map, trace weighted map, FA map, and tensor data were created inline.

Image Findings

Figure 1 (A). DarkFluid T2-weighted image demonstrates focal T2 hyperintensity within the left temporooccipital lobe, displacing the trigone of the left lateral ventricle anteriorly. (B) Susceptibility-weighted imaging (SWI) demonstrates central hemorrhage (signal loss) within the mass. (C) Postcontrast T1-weighted image demonstrates the left temporooccipital enhancing mass. (D) Texture diffusion showing the possible tracts within the slices. (E) and (F) are ADC map and trace-weighted images. (G) Tractography showing the tracts splitting and surrounding the tumor. This suggests a low grade primary glial neoplasm.

Results and discussion

Susceptibility-weighted imaging demonstrated internal hemorrhage within the mass. DTI demonstrated central reduced diffusion and displacement (rather than interruption) of the surrounding axon bundles. Prior to DTI, the differential diagnosis based upon conventional MR imaging would suggest primary glial neoplasm. Displacement, rather than disruption, of the fiber bundles at DTI is suggestive of lower grade neoplasm, which was confirmed at pathology to be a dysembryoplastic neuroepithelial (DNET) tumor. DNETs are pathologically benign cortical lesions that often arise in the temporal lobe. They usually are found in children and young adults with seizures that tend to become refractory to medical treatment. These lesions have many different imaging characteristics.

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