Rationale and Objectives
Resting-state (RS) networks, revealed by functional magnetic resonance imaging (fMRI) studies in healthy volunteers, have never been evaluated in anesthetized patients with brain tumors. Our purpose was to examine the presence of residual brain activity on the auditory network during propofol-induced loss of consciousness in patients with brain tumors.
Materials and Methods
Twenty subjects with intracranial masses were prospectively studied by means of intraoperative RS-fMRI acquisitions before any craniectomy. After performing single-subject independent component analysis, spatial maps and time courses were assigned to an auditory RS network template from the literature and compared via spatial regression coefficients.
Results
All fMRI data were of sufficient quality for further postprocessing. In all but two patients, the RS functional activity of the auditory network could be successfully mapped. In almost all patients, contralateral activation of the auditory network was present. No significant difference was found between the mean distance of the RS activity clusters and the lesion periphery for tumors located in the temporal gyri vs. those in other brain regions. The spatial deviation between the activated cluster in our experiment and the template was significantly ( P = 0.04) higher in patients with tumors located in the temporal gyri than in patients with tumors located in other regions.
Conclusions
Propofol-induced anesthesia in patients with intracranial lesions does not alter the blood-oxygenation level-depended signal, and independent component analysis of intraoperative RS-fMRI may allow assessment of the auditory network in a clinical setting.
Introduction
Resting-state functional magnetic resonance imaging (RS-fMRI) acquisitions, based on system-wide coherent blood-oxygenation level dependent (BOLD) signal fluctuations, visualize a set of regions suggesting an underlying functional relationship despite deprivation of external stimuli . In humans, fMRI-visualized RS activity has been shown to be stable throughout light sleep/wake cycles , during light sleep, deep sleep, or sedation , as well as during different levels of consciousness including propofol-induced loss of consciousness . The partial preservation of functional connectivity in the absence of consciousness has been attributed to preserved anatomical connections dissociated from higher cognitive functions .
Thus far, however, these RS networks, revealed by fMRI studies mostly in healthy volunteers, have never been evaluated in anesthetized patients with brain tumors. The present study investigated the feasibility of acquiring whole-brain RS-fMRI measurements in patients with brain tumors by means of intraoperative fMRI during pharmacological modulation of the level of consciousness. The anesthetic drug used was propofol because of its advantage over isoflurane/sevoflurane in keeping low subdural intracranial pressure and arteriovenous oxygen difference while keeping higher cerebral perfusion pressure in patients with brain tumors . Under the proof-of-principle study design, we orientated in the RS activity of the auditory cortex because it has been shown in many studies to be robustly identifiable across healthy subjects and patients , its analysis is relatively simple compared to other networks , and previous works have tested the influence of different anesthetics on its activation in healthy subjects. The auditory network involves the superior temporal gyrus, the transverse temporal gyrus (Heschl’s gyrus), the insula, and the postcentral gyrus. The primary auditory cortex has also known interactions with the angular gyrus, the supramarginal gyrus, Broca’s, and Wernicke’s areas.
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Materials and Methods
Ethics Statement
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Subjects
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Intraoperative MRI
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Anesthesia Protocol
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Image Processing and Data Analysis
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Table 1
Demographics, Clinical Data, and Resting-state BOLD Fluctuations Analysis of the Auditory Network in Our Patient Cohort
Patient (Age/Sex) Tumor Site (Side) z-value Ratio Tumor-Cluster Distance (mm) Template-Cluster Distance (mm) 1 (55/M) Gyrus temporalis medius (R) 13.9 3.9 60.4 15.0 2 (39/F) Gyrus temporalis medius et superior (L) 15.8 4.0 55.2 12.6 3 (23/M) Gyrus temporalis (L) 11.1 1.7 50.5 11.0 4 (27/M) Gyrus temporalis inferior (R) 13.1 7.3 43.9 16.5 5 (19/F) Temporomesial and temporobasal (R) 1.9 2.6 46.5 26.8 6 (33/M) Gyrus temporalis medius et superior (R) 12.0 1.9 29.7 12.8 7 (27/M) Skull base (R) 9.5 3.4 n.a. \* n.a. \* 8 (46/F) Thalamus (R) 3.7 4.2 48.4 13.6 9 (52/F) Skull base (L) 10.3 2.3 n.a. \* n.a. \* 10 (44/M) Gyrus parahippocampalis (L) 9.2 4.9 24.3 12.0 11 (34/M) Gyrus parahippocampalis (L) 14.4 3.2 39.9 14.7 12 (77/F) Gyrus frontalis superior (L) 12.2 0.9 41.2 8.7 13 (30/M) Gyrus frontalis inferior et insula (L) 8.8 6.9 52.8 3.5 14 (30/F) Gyrus frontalis superior et medius (R) 8.6 3.4 18.0 6.3 15 (72/M) Gyrus postcentralis (L) 10.5 2.3 34.1 12.3 16 (48/F) Gyrus postcentralis (L) 9.8 1.8 52.6 12.8 17 (52/F) Gyrus postcentralis (L) 13.0 2.9 60.2 15.7 18 (24/M) Gyrus precentralis (R) 9.1 2.3 32.1 8.2 19 (25/M) Gyrus precentralis (L) 3.2 3.3 60.9 14.1 20 (29/F) Gyrus precentralis (L) 9.6 1.8 53.8 18.5
BOLD, blood-oxygenation level dependent.
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Results
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Discussion
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Conclusions
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