Ultrahigh-field imaging (7 Tesla) in DNET: Unmasking microstructural imaging characteristics - A case report

Abstract

Commercial ultrahigh-field 7 Tesla (T) MRI has been approved for clinical brain imaging, including applications in epilepsy and brain tumors. Increasing magnetic field strength offers significant advantages over lower-field MRI due to improved spatial resolution, signal-to-noise ratio, and contrast-to-noise ratio. These improvements provide better anatomical delineation and gray-white matter tissue-contrast differentiation. We present a case of a presumed dysembryoplastic neuroepithelial tumor (DNET) imaged at 7 T MRI of the second generation, which revealed an unprecedented level of detail of the complex and intricate tumor architecture. Insights of its different components correlate closely with its known histopathological features. These tumors are unique among low-grade neoplasms due to their distinct clinical presentation, imaging features, and histopathological architecture. DNETs are rare, typically occurring in young patients with refractory epilepsy, and are classified by their well-defined histological subtypes. We review the various MRI patterns of DNET, which have been shown to correlate with histological subtypes and the extent of the epileptogenic zone. Complete tumor resection is essential for long-term control and recurrence prevention, emphasizing the importance of precise preoperative visualization of the tumor and its surrounding tissue. In this case, 7 T images demonstrated superior lesion conspicuity and clearer boundaries, highlighting the advantages of ultrahigh-field MRI in defining the full extent of the lesion. Although 7 T MRI is not yet widely available, it has started to gain an important role in the management of epilepsy, particularly for cases requiring detailed structural analysis.

Keywords: 7T MRI; Drug-resistant epilepsy; Dysembryoplastic neuroepithelial tumor; Focal cortical dysplasia; Satellite lesion.

Fig. 1

Brain MRI at 7 T shows enlarged left posterior frontoinsular gyri containing a well-demarcated, multinodular mass. A, coronal T1-weighted image reveals a markedly hypointense intracortical mass (zoomed box). B, coronal high-resolution T2-weighted image (2 mm slice thickness) and C, T2 FLAIR-weighted image confirm the pseudocystic nature of the mass, showing hyperintense signal of the left mass (zoomed boxes). D, post-Gadolinium T1-weighted image shows no contrast enhancement. E, F, diffusion tensor imaging (DTI) tractography of the arcuate fasciculus shows displacement of the white matter fibers due to the mass effect of the tumor, with no evidence of fiber infiltration. The lesion's distinct intracortical, pseudocystic appearance, along with the clinical context, strongly suggests a diagnosis of dysembryoplastic neuroepithelial tumor (DNET).

Fig. 2

Insights into the microarchitecture of DNET from an axial zoomed view. Comparison of ultrahigh-resolution 7 T (in-plane resolution up to 0.15 x 0.15 mm²) vs 3 T MRI (in-plane resolution of 0.43 x 0.43 mm²). A and C, axial T2-weighted images at 7 T (contiguous slices); B, axial T2-weighted image at 3 T at the same slice as A. The improved spatial resolution at 7 T, with a precision down to micrometers, provided an unprecedented level of detail of the “bubble-like” septa and allowed for precise delineation of the tumor's extent at a submillimetric scale. C, noted microarchitecture in an axial T2-weighted image at 7 T; D, graphical representation of the classic histopathological components a DNET as described by Dupont-Daumas in 1988 , showcasing the complex form of DNET (multinodular architecture and adjacent dysplastic cortex). The tumor's radiological microarchitecture closely mirrors the histopathological components, where we can also see a columnar pattern, and clear visualization of cystic nodules and well delimitation of the cortical dysplastic rim from normal cortex (arrowhead).