Relationship between Type of White Matter Tract Affection and Pathological Grade of Pediatric Brain Tumour Assessed by MR Diffusion Tensor Imaging and Fiber Tractography

Abstract
Background: Incorporation of WM fibers within a tumor mass, seen especially in low-grade tumors, and destruction of WM fibers by high-grade tumors can be depicted by MR diffusion tensor imaging and fiber tractography. These features have profound implications for the extent of resection amenable for the individual tumor.
Aim of Study: The purpose of this study is to evaluate the role of MR diffusion tensor imaging and fiber tractography in accurately depicting the relation between the grade and aggressivity of the paediatric brain tumour and the pattern of affection of white matter tracts in their direct vicinity. These information help the neurosurgeons to take a decision about the extent of excision and safety margin around the tumour.
Material and Methods: A total of fifty patients with brain tumors were included in this study using pre-operative contrast-enhanced magnetic resonance imaging and DTI fiber tractog-raphy for preoperative depiction of the relation between white matter tract affection and aggressivity of the tumour.
Diffusion tensor imaging, by improving the recognition and characterization of white matter tracts, offers a glimpse into the brain microstructure at a scale that is not easily accessible with other modalities.
Result: The extent of white matter pathway involvement was clearly identified in all patients by using color-coded DT imaging maps and MR Tractography and was correlated with the pathological grade of the tumour.
Pattern I (not affected) is a rare pattern exclusively found in benign acting tumours. It was seen within 4 cases (17.4%) of the benign acting group only.
Pattern II (displacement) is the most common pattern being detected in 19 cases (82.6%) of the benign acting group and in 15 cases (68.2%) of the malignant acting group.
Pattern III (oedematous) is the second most common type of tract involvement seen within 2 cases (8.7%) of the benign acting group and within 9 cases (40.9%) of the malignant acting group.
Pattern IV (infiltrated and partially disrupted) was seen within 2 cases (8.7%) of the benign acting group and within 7 cases (31.2%) of the malignant acting group.
Pattern V (destroyed) was detected in 3 cases (13.6%) of the malignant group and no cases in the benign acting group.
Conclusion: Diffusion-tensor imaging allowed for the detailed visualization of WM tract affection by the tumour. The most common pattern of affection detected in our study is the displacement pattern with prevalence in the benign acting group of tumours. Destruction pattern was totally confined to the malignant acting lesions. Edema pattern and partial disruption pattern are more prevalent in the malignant acting lesions. Despite some limitations and pitfalls, DTI is currently the only clinically feasible method of demonstrating the white matter tracts in vivo.