Predictive value of fractional anisotropy of the arcuate fasciculus for the functional recovery of language after brain tumor resection: A preliminary study
Introduction
Modern in vivo neuroimaging and intraoperative cortical and subcortical stimulation studies have supported the role of subcortical language networks in language function [1], [2], [3]. The arcuate fasciculus is a subcortical association fiber tract that can be categorized as part of the superior longitudinal fasciculus [4]. The tract may connect Broca's speech area of the inferior frontal gyrus with Wernicke's speech area of the superior temporal gyrus in the dominant hemisphere, and classically has been recognized to have important roles in conduction aphasia [5], [6], [7], [8], [9], [10]. A recent lesion-mapping study in stroke patients found that lesions in the left arcuate fasciculus could be a predictor for impaired speech production [11].
While brain tumors are located in the perisylvian region, the arcuate fasciculus tends to be affected by the tumor mass or tumor invasion. Thus, language function can be impaired due to network disturbance. In case that the tracts are not destroyed but rather compressed and functionally suppressed by the tumor, they can be restored after tumor resection. In such conditions with possible restoration, aiming for postoperative recovery of the language functions, not only the cortical language areas but also subcortical association fiber tracts including the arcuate fasciculus, in proximity to the tumor, should be preserved [12], [13], [14], [15], [16]. However, to date, it remains difficult to identify whether the tracts can recover after surgery and to predict language deficit prognoses.
In the present study, we evaluated the preoperative state of the arcuate fasciculus as a predictive factor for possible improvement and recovery of language functions after tumor resection by using diffusion tensor imaging (DTI) tractography. DTI measures the diffusion anisotropy of water molecules often reported as fractional anisotropy (FA), which can be a microstructural indicator useful to demonstrate and evaluate the status of the white matter fiber tracts [17]. Then we focused on the FA of the arcuate fasciculus because the FA could be considered as a surrogate marker of white matter integrity.
Section snippets
Patient profiles and language functions
Twelve right-handed patients who underwent surgical resection of newly diagnosed supratentorial brain tumors at the Department of Neurosurgery of Kanazawa University Hospital were examined in this study. Handedness was assessed in every patient by using the Edinburgh handedness inventory to exclude left-handed patients. All tumors were located in the left frontal, left temporal, or left parietal lobes and were not located in the occipital lobe. Patient age at the time of admission ranged from
Results
In each patient, both arcuate fasciculi could be reconstructed in tractography in the preoperative MR study (data not shown). None of the 12 patients had complications that affected postoperative examinations, and WAB examinations were successfully performed within 12 days postoperatively. The total WAB score evaluated both pre- and postoperatively, ΔWAB score and preoperative average FA value of both arcuate fasciculi, and the relative FA values are summarized in Table 1. Representative cases
Fractional anisotropy and brain tumors
Recently, the number of studies that evaluate preoperative DTI tractography of white matter association fibers in patients with brain tumors has increased [18], [19], [20], [21], [22]. The tumor can affect fiber tracts and related functional regions by shifting them from expected anatomical locations as well as by destroying their integrity due to tumor invasion. With the effects of tumor angiogenesis, the tumor invasion tends to result in the development of edematous parenchyma around the
Conclusion
The preoperative relative FA of the left dominant hemisphere arcuate fasciculus that is affected by compression or tumor invasion could be a predictive marker for postoperative language improvement and recovery. Patients with preoperative highly increasing relative FA have a high possibility of language recovery in the short term, after relief of compression following tumor resection. In such condition, meticulous surgical excision with minimal damages to adjacent parenchyma should be performed
Conflict of interest
None.
Acknowledgements
This work was partly supported by the Japanese Society for the Promotion of Science (Grants-in-aid for scientific research C, Hayashi; Grants-in-aid for young scientist B, Kinoshita).
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