Successful management of peripheral nerve trauma relies on accurate localization of the injury and grading of the severity of nerve injury to determine whether surgical intervention is required. Existing techniques, such as electrodiagnostic studies and conventional imaging modalities, provide important information, but are limited by being unable to distinguish severe nerve lesions in continuity that will recover from those that will not. Diffusion tensor imaging (DTI) and tractography of peripheral nerves provide a novel technique to localize and grade nerve injury, by assessing the integrity of the nerve fibers across the site of nerve injury. Diffusion tensor imaging and tractography also hold promise as markers of early nerve regeneration, prior to clinical and electrodiagnostic evidence of recovery. In the present review, the techniques of peripheral nerve DTI and tractography are discussed with respect to peripheral nerve trauma, with illustrative cases demonstrating potential roles of these novel approaches.
Thomas Anthony Gallagher, Neil G. Simon and Michel Kliot
Bornali Kundu, Amy Penwarden, Joel M. Wood, Thomas A. Gallagher, Matthew J. Andreoli, Jed Voss, Timothy Meier, Veena A. Nair, John S. Kuo, Aaron S. Field, Chad Moritz, M. Elizabeth Meyerand and Vivek Prabhakaran
Functional MRI (fMRI) has the potential to be a useful presurgical planning tool to treat patients with primary brain tumor. In this study the authors retrospectively explored relationships between language-related postoperative outcomes in such patients and multiple factors, including measures estimated from task fMRI maps (proximity of lesion to functional activation area, or lesion-to-activation distance [LAD], and activation-based language lateralization, or lateralization index [LI]) used in the clinical setting for presurgical planning, as well as other factors such as patient age, patient sex, tumor grade, and tumor volume.
Patient information was drawn from a database of patients with brain tumors who had undergone preoperative fMRI-based language mapping of the Broca and Wernicke areas. Patients had performed a battery of tasks, including word-generation tasks and a text-versus-symbols reading task, as part of a clinical fMRI protocol. Individually thresholded task fMRI activation maps had been provided for use in the clinical setting. These clinical imaging maps were used to retrospectively estimate LAD and LI for the Broca and Wernicke areas.
There was a relationship between postoperative language deficits and the proximity between tumor and Broca area activation (the LAD estimate), where shorter LADs were related to the presence of postoperative aphasia. Stratification by tumor location further showed that for posterior tumors within the temporal and parietal lobes, more bilaterally oriented Broca area activation (LI estimate close to 0) and a shorter Wernicke area LAD were associated with increased postoperative aphasia. Furthermore, decreasing LAD was related to decreasing LI for both Broca and Wernicke areas. Preoperative deficits were related to increasing patient age and a shorter Wernicke area LAD.
Overall, LAD and LI, as determined using fMRI in the context of these paradigms, may be useful indicators of postsurgical outcomes. Whereas tumor location may influence postoperative deficits, the results indicated that tumor proximity to an activation area might also interact with how the language network is affected as a whole by the lesion. Although the derivation of LI must be further validated in individual patients by using spatially specific statistical methods, the current results indicated that fMRI is a useful tool for predicting postoperative outcomes in patients with a single brain tumor.
Thomas A. Gallagher, Veena A. Nair, Michael F. Regner, Brittany M. Young, Andrew Radtke, Joshua Pankratz, Ryan L. Holdsworth, Dovile Baniulis, Nicole K. Kornder, Jed Voss, Benjamin P. Austin, Chad Moritz, Mary E. Meyerand and Vivek Prabhakaran
Functional MRI (fMRI) has proven to be an effective component of pretreatment planning in patients harboring a variety of different brain lesions. The authors have recently reported significant relationships concerning distances between brain tumor borders and areas of functional activation (lesion-to-activation distance; LAD) with regard to patient morbidity and mortality. This study further examines the relationship between LAD, focusing on a host of vascular lesions and pre- and posttreatment morbidity.
This study included a sample population of patients with vascular lesions (n = 106), primarily arteriovenous malformations (AVMs) and cavernomas. These patients underwent pretreatment fMRI-based motor mapping (n = 72) or language mapping (n = 84). The impact of LAD and other variables derived from the patient medical record were analyzed with respect to functional deficits in terms of morbidity (weakness and/or aphasia).
In patients with no pretreatment deficits, there was trend for a significant relationship between the Wernicke area LAD and posttreatment language deficits. In patients with or without pretreatment deficits, a trend toward significance was observed between sensorimotor LAD and posttreatment motor deficits. Additionally, lesion type (AVMs or cavernomas) affected posttreatment deficits, with more patients with cavernomas showing posttreatment language deficits than patients with AVMs. However, this difference was not observed for posttreatment motor deficits.
These findings suggest that the proximity of a vascular lesion to sensorimotor and language areas is a relevant parameter in estimating patient prognosis in the perioperative period. Additionally, vascular lesion type and existence of pretreatment deficits play a significant role in outcomes.