Assessment of the corticospinal tract alterations before and after resection of brainstem lesions using Diffusion Tensor Imaging (DTI) and tractography at 3 T

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Abstract

The purpose of the study was to investigate the role of Diffusion Tensor Imaging (DTI) and Diffusion Tensor Tractography (DTT) on the corticospinal tract alterations due to space occupying lesions in the brainstem before and after surgical resection. Pre- and post-surgical DTI data were acquired in 14 patients undergoing surgical resection of brainstem lesions. Patterns of corticospinal tract (CST) alteration on DTT were compared with the neurological exams of the patients pre- and post-operatively. DTT, especially in 3D movie format, seemed very helpful for evaluating the relationship of the lesions with the corticospinal tracts for surgical approach. None of the patients developed additional motor deficit related to surgery except one patient who presented with cerebellar ataxia after surgery. All of the patients with normal CST on DTT presented without motor deficit on neurological exam. The sensitivity, specificity, positive predictive and negative predictive values of DTT before surgery were 100%, 63.6%, 42.9% and 100%, and the corresponding values after surgery were 100%, 96%, 75% and 100% respectively. Although it has low specificity before surgery, DTT is a potentially useful technique in evaluating the effects of brainstem lesions and surgical resection on the relevant corticospinal tracts with high negative predictive value and higher specificity after surgery.

Introduction

Neurosurgical management of a space occupying lesion in the brainstem includes biopsy for diagnosis and/or possible maximum resection of the lesion for treatment. New developments in microsurgery and radiology, especially along with the experience gained from fiber dissection techniques of the brainstem are important stages in the improvement of brainstem surgery [1], [2]. The presence of major motor and sensory pathways in the brainstem still makes it a challenging area for neurosurgeons. Delineating the status of individual white matter tracts in relation to the lesion is essential for pre-operative evaluation and surgical planning. White matter tracts, gray matter nuclei and sometimes even tumors appear relatively homogeneous and may not be easily differentiated on conventional MRI. DTI from which FA maps and Diffusion Tensor Tractography (DTT) images are generated reveals improved tissue contrast between corticospinal tracts, gray matter nuclei and lesion [3], [4], [5], [6], [7], [8], [9], [10]. DTT has also been found to be very useful in treatment planning of brain and brainstem lesions [3], [11], [12], [13], [14].

DTT was introduced into Neuroradiology practice more than a decade ago, but it has not been widely included in the routine clinical protocols yet. One of the main reasons for this lag is that the technique is user-dependent and often requires extensive manual post-processing.

In addition, there has not yet been a gold standard or in vivo validation method to test its robustness or reliability [15], [16].

Although the color FA maps contain the directionality information of the tracts, DTT has obvious strength by visualization even in 3D movie format of the entire tract prior to surgery to guide the neurosurgeon. While the color in FA maps does change by the changing direction of the tract, the color of DTT can be fixed for the visualization purposes. Also the DTT can be visualized over the clinical MR images to help in the anatomical localization of the tract.

The purpose of this study was to investigate the role of DTI and DTT and to test the reliability and robustness of the technique in brainstem lesions by using it before and after surgical resection.

Section snippets

Methods

The study was approved by the local Institutional Review Board at Yeditepe University Hospital. Fourteen patients with a brainstem lesion (six cavernomas, five glial tumors, one hemangioblastoma, one mixed glial tumor and one metastasis) were included in the study. Table 1 shows the demographic information, diagnosis, location and size of the brainstem lesions.

Results

Neurological exams before surgery revealed MRC Grade 5 (no motor deficits) in 22 CSTs, MRC Grade 4 in five CSTs and MRC Grade 3 in one CST (Table 3). There was no patient with MRC Grade 2 or 1. Some of the patients also had various combinations of sensory and cranial nerve deficits but these symptoms were not discussed in this study's scope.

All patients without motor deficit before surgery also had normal motor neurological exams after surgery. There was no additional motor deficit detected in

Discussion

DTT demonstrating the white matter tracts is needed for pre-surgical planning and favorable post-surgical outcomes in the surgical treatment of supratentorial brain lesions [4], [9], [14], [19], [20], [21]. Wu et al. in their 4-year long prospective study found that DTI-based functional neuro-navigation contributes to maximal safe resection of cerebral gliomas and decreases post-operative motor deficits and increases high-quality survival [22].

However, up to date there have been only a limited

Conclusion

DTT is a promising technique in evaluating patients with brainstem lesions with high sensitivity and negative predictive values although it has relatively high false positive results especially before surgery. Technical improvements and further clinical studies are still needed to increase the accuracy of DTT.

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    Preliminary version of this study was presented as a scientific paper at RSNA 2007 Chicago, IL.

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