Brain tumors may alter WM tracts by displacement, infiltration, or disruption. Precise depiction of the relationship of a brain tumor to its surrounding WM tracts is of crucial importance to plan surgery and determine the extent of tumor resection. The use of DTI tractography can contribute substantially to preoperative planning by confirmation of integrity and location of displaced WM tracts. If preoperative imaging demonstrated that a WM tract was intact but displaced by tumor to a new location (pattern II), surgical approach can be adapted to preserve the displaced tract during resection. Meanwhile, if specific WM tracts were shown by imaging to be disrupted by tumor (pattern V), gross total resection can be attempted without concern for these WM tracts [9, 11].
This prospective study analyzed the impact of DTI tractography in preoperative planning and predicting surgical outcome in patients with gliomas. Twenty patients with glioma were included.
In the present study, preoperative DTI showed non-affection of WM tracts, displacement, edema, infiltration, and disruption in 10%, 75%, 55%, 60%, and 20% of cases, respectively. The frequencies of detected patterns differ than those reported by Zhukov et al. [12], Dubey et al. [13], and Khan et al. [10]. Zhukov et al. [12] identified DTI patterns in 29 patients with brain tumor pathologies of different grades. They detected intact pyramidal tract in 41.1%, displacement in 24.1%, and infiltration in 34.5% of cases. Dubey et al. [13] studied 34 patients with brain tumor pathologies of different grades. They observed displacement in 52.9%, invasion in 32.3%, and disruption in 11.7% of patients. Khan et al. [10] reported in a series of 128 patients with brain gliomas and metastasis that displacement, infiltration, and disruption were detected in 32.8%, 25%, and 42.2% of cases, respectively. These differences could be attributed to variations in tumor type, grade and studied WM tracts.
Displacement and infiltration of the WM tract were detected in higher percentage of high-grade gliomas compared to low-grade tumors, though the difference did not reach statistical significance except in infiltration pattern (p = 0.018). These findings are in accordance with previous studies which concluded that high-grade tumors are associated with displacement or destruction of WM fiber tracts [10, 12, 13].
The extent of resection was planned according to the degree of involvement of WM tract, where complete resection was performed only in the absence of infiltration. In patients who had tumors infiltrating the WM tracts, subtotal resection was only achievable. This method of planning the surgical procedure was stated by previous studies [13,14,15,16,17]. Previous studies showed that the use of DTI resulted in change of the surgical approach in 16 to 47% of patients and a change in the extent of resection in 64 to 80% [10, 16, 17].
The incorporation of DTI and tractography has been associated with improvement of neurological outcome. Postoperative neurological examination during follow-up showed that cognitive function, motor power, and vision deteriorated after surgery in 3 (15%), 2 (10%), and 1 (5%) patients, respectively. Improvement in motor power was observed in 7 (35%) patients. Overall, 70% of patients had no neurological deficit after surgery. This percentage is slightly lower than those reported by previous studies which ranged from 76 to 88.9% [10, 15,16,17].
We were unable to evaluate the association between the pattern of WM tract involvement and neurological outcome after surgery due to the presence of combined patterns in patients. However, Khan et al. [10] assessed this relationship and found that improvement was associated with displacement while deterioration was more frequent with disruption pattern, though no statistical significance was elicited.
Comparison of pre- and postoperative DTI in our series of patients demonstrated postoperative improvement in displaced and edematous patterns, while infiltrative and disruptive patterns showed higher percentage of cases without normalization of fibers position or FA improvement. This improvement in parameters of DTI after surgery is attributed to the considerable reorganization of brain structures which may occur following surgical resection. Such changes can be detected using DTI as reported in the literature [18,19,20,21,22].
Normalization of position and FA after surgery was observed in all low-grade cases, except for one case with displaced pattern in which only partial FA improvement occurred. Normalization of position and partial FA improvement occurred at high-grade and—to less extent—low-grade lesions. The lack of fiber tract position or FA improvement was confined to high-grade lesions. However, the postoperative DTI and tractography changes were not significantly associated with tumor grade.
Our results indicated that reorganization of tracts is more likely to occur in tumors with displaced or edematous patterns compared to the infiltrated and disruptive patterns. There is a paucity of studies which evaluated the potential effect of tumor grade or preoperative DTI pattern on postoperative DTI changes.
Though DTI demonstrated its importance and utility in management of brain tumors, the technique still suffers from some limitations. DTI is a user-defined process. Consequently, the results can vary depending on the chosen parameters such as FA threshold, angular threshold, step length, and numbers of sampling in a voxel length. Moreover, tracked volumes may differ according to the size and locations of the seed regions of interest (ROIs).
Other important limitation of low number of cases is the difficulty to follow and bring the same patients before and after operation; moreover, some of them suffer neurological insult, in addition to COVID-19 pandemic sequelae .Also our study was designed with inclusion criteria including patients harbored different grads of gliomas only and not other brain space occupying lesions .
