Task-Based and Resting-State Functional MRI in Observing Eloquent Cerebral Areas Personalized for Epilepsy and Surgical Oncology Patients: A Review of the Current Evidence

Abstract

Functional magnetic resonance imaging (fMRI) is among the newest techniques of advanced neuroimaging that offer the opportunity for neuroradiologists, neurophysiologists, neuro-oncologists, and neurosurgeons to pre-operatively plan and manage different types of brain lesions. Furthermore, it plays a fundamental role in the personalized evaluation of patients with brain tumors or patients with an epileptic focus for preoperative planning. While the implementation of task-based fMRI has increased in recent years, the existing resources and evidence related to this technique are limited. We have, therefore, conducted a comprehensive review of the available resources to compile a detailed resource for physicians who specialize in managing patients with brain tumors and seizure disorders. This review contributes to the existing literature because it highlights the lack of studies on fMRI and its precise role and applicability in observing eloquent cerebral areas in surgical oncology and epilepsy patients, which we believe is underreported. Taking these considerations into account would help to better understand the role of this advanced neuroimaging technique and, ultimately, improve patient life expectancy and quality of life.

Keywords: brain tumor; epilepsy surgery; functional neuroimaging; neurophysiology; seizures.

Figure 1

Contrasting experimental fMRI designs distinguish between various tasks-related signals: (A) the solid, green line represents the block design, wherein the task block represents a prolonged period of a repetitive paradigm separated by rest; (B) the dashed, yellow line represents the event-related task trials that exhibit different conditions presented in a random sequence; (C) mixed-type design with transient activities (trials) presented throughout the sustained activity (task block).

Figure 2

An exemplary fMRI of a healthy volunteer showing an intraparenchymal area of activation in the precentral gyrus (hand knob area).

Figure 3

An exemplary fMRI of a patient with a left frontal lobe mass at the precentral gyrus (hand knob area) showing lateral displacement of the parenchymal associated with hand activation. Additional activation in the medial cerebral cortex of the left paracentral sulcus just anterior to the left paracentral lobule represents the supplementary motor area (SMA).

Figure 4

Functional localization of Broca’s and Wernicke’s areas using verbal fluency (red) and verb generation (blue) paradigms in a control patient.

Figure 5

fMRI of activation in Broca’s area as an indicator of a left hemispheric language dominance area using verbal fluency (red) and verb generation (blue) paradigms in a patient with left temporal lobe mass. In addition, there is a superior displacement of the parenchymal area associated with language activation.

Figure 6

Stimuli for visual field mapping and construction of functional field maps (FFMaps). Retinotopic mapping stimuli consist of an expanding black and white checkerboard ring (A) or a rotating checkerboard wedge (B). The patient was asked to stare at the yellow dot in the center while the rings of flickering stimuli were outside of his/her visual field (A) to separate the signal from the fovea from the periphery of the visual field.