Advanced intraoperative MRI in pediatric brain tumor surgery

Abstract

Introduction: In the pediatric brain tumor surgery setting, intraoperative MRI (ioMRI) provides "real-time" imaging, allowing for evaluation of the extent of resection and detection of complications. The use of advanced MRI sequences could potentially provide additional physiological information that may aid in the preservation of healthy brain regions. This review aims to determine the added value of advanced imaging in ioMRI for pediatric brain tumor surgery compared to conventional imaging. Methods: Our systematic literature search identified relevant articles on PubMed using keywords associated with pediatrics, ioMRI, and brain tumors. The literature search was extended using the snowball technique to gather more information on advanced MRI techniques, their technical background, their use in adult ioMRI, and their use in routine pediatric brain tumor care. Results: The available literature was sparse and demonstrated that advanced sequences were used to reconstruct fibers to prevent damage to important structures, provide information on relative cerebral blood flow or abnormal metabolites, or to indicate the onset of hemorrhage or ischemic infarcts. The explorative literature search revealed developments within each advanced MRI field, such as multi-shell diffusion MRI, arterial spin labeling, and amide-proton transfer-weighted imaging, that have been studied in adult ioMRI but have not yet been applied in pediatrics. These techniques could have the potential to provide more accurate fiber tractography, information on intraoperative cerebral perfusion, and to match gadolinium-based T1w images without using a contrast agent. Conclusion: The potential added value of advanced MRI in the intraoperative setting for pediatric brain tumors is to prevent damage to important structures, to provide additional physiological or metabolic information, or to indicate the onset of postoperative changes. Current developments within various advanced ioMRI sequences are promising with regard to providing in-depth tissue information.

Keywords: advanced MRI; intraoperative MRI; pediatric brain tumor patients; postoperative changes; surgical anatomy.

FIGURE 1

Study flowchart.

FIGURE 2

Neurosurgical cases demonstrating the added value of advanced MRI. (A) Preoperative images of a 10-year-old girl with a diffuse midline glioma (H3K27 mt) originating from the left posterior thalamus and mesencephalon and expanding into the atrium of the left ventricle. Left: the transverse T1-weighted contrast-enhanced image shows enhancement of the tumor (yellow outline). Center: the coronal fractional anisotropy color-coded map (single-shell diffusion MRI, 16 directions) shows left-right asymmetry demonstrating the displacement of fibers caused by the tumor (yellow outline). The white circles depict the arcuate fasciculus, and the red ovals depict the corticospinal tracts. Solid lines depict the unaffected side, and the dashed lines show the affected side. Right: reconstruction of the corticospinal tract 1), arcuate fasciculus 2), tumor 3), and optic radiation 4). A parietal surgical approach posterior to the arcuate fasciculus and superior to the optic radiation 5) was chosen for tumor mass reduction and histopathological diagnosis. (B) Preoperative images of a 17-year-old girl with neurofibromatosis type 1 and a space-occupying lesion in the fourth ventricle. Left: the sagittal T1-weighted contrast-enhanced images. The differential diagnosis was pilocytic astrocytoma or high-grade glioma. Center: transverse T1-weighted contrast-enhanced image. Right: the hyperperfusion (white arrow) of the unquantified arterial spin labeling image makes diagnosing a high-grade glioma more probable. Histopathological examination revealed a high-grade glioma with pilocytic features. (C) Preoperative images of a 17-year-old boy with a pilocytic astrocytoma. Left: sagittal T1-weighted contrast-enhanced image. Center: transverse T1-weighted contrast-enhanced image. Right: amide-proton transfer-weighted (APTw) image. Note the hyperintense region (white arrow) that matches the contrast enhancement on T1-weighted contrast-enhanced image. The red outer rim (yellow arrow) of the APTw image is likely caused by susceptibility-weighted air-tissue artifacts. Ethical approval from the local medical ethics committee was obtained for this study.