Role of diffusion tensor magnetic resonance tractography in predicting the extent of resection in glioma surgery

Abstract

Diffusion tensor imaging (DTI) tractography enables the in vivo visualization of the course of white matter tracts inside or around a tumor, and it provides the surgeon with important information in resection planning. This study is aimed at assessing the ability of preoperative DTI tractography in predicting the extent of the resection achievable in surgical removal of gliomas. Patients with low-grade gliomas (LGGs; 46) and high-grade gliomas (HGGs; 27) were studied using a 3T scanner according to a protocol including a morphological study (T2, fluid-attenuated inversion-recovery, T1 sequences) and DTI acquisitions (b = 1000 s/mm(2), 32 gradient directions). Preoperative tractography was performed off-line on the basis of a streamline algorithm, by reconstructing the inferior fronto-occipital (IFO), the superior longitudinal fascicle (SLF), and the corticospinal tract (CST). For each patient, the relationship between each bundle reconstructed and the lesion was analyzed. Initial and residual tumor volumes were measured on preoperative and postoperative 3D fluid-attenuated inversion-recovery images for LGGs and postcontrast T1-weighted scans for HGGs. The presence of intact fascicles was predictive of a better surgical outcome, because these cases showed a higher probability of total resection than did subtotal and partial resection. The presence of infiltrated or displaced CST or infiltrated IFO was predictive of a lower probability of total resection, especially for tumors with preoperative volume <100 cm(3). DTI tractography can thus be considered to be a promising tool for estimating preoperatively the degree of radicality to be reached by surgical resection. This information will aid clinicians in identifying patients who will mostly benefit from surgery.

Fig. 1.

(A) A case of a left frontal oligodendroglioma infiltrating the left CST (magenta) both at the level of the subcortical white matter of the precentral gyrus and at the level of the centrum semiovale. Color maps show a reduction of anisotropy due to the presence of the lesion. Preoperative tumor volume was 29 cm³. (B) Postoperative MR shows a residual lesion in the area of deep infiltration of the fascicle. Involvement of CST is predictive of worse surgical outcome, as in patients with infiltrated CST it is less likely to obtain total resection (see Table 1).

Fig. 2.

(A) A case of a left temporal oligodendroglioma with a deep nodule infiltrating the left IFO (cyan) at a posterior level where it passes from the occipital lobe to the external/extreme capsule. Color maps show a reduction of anisotropy due to the presence of the lesion; tractography shows a narrowing of the fascicle if compared to the contralateral normal IFO. Preoperative tumor volume was 27.5 cm³. (B) Postoperative MR shows the persistence of the deep nodule, resulting in a subtotal resection. Infiltration of IFO is predictive of worse surgical outcome, because in these patients total resection is less likely than is partial resection (see Table 1).

Fig. 3.

(A) Preoperative volume is associated with surgical outcome, as partial resection is more likely to be obtained in larger tumors, whereas total and subtotal resection is more likely to be obtained in smaller tumors (volume, <100 cm³). A detail of the graph is showed in (B): damaged fascicles are more likely to be found in larger tumors, whereas intact fascicles are more likely to be found in smaller tumors, and the size of 100 cm³ appears as a possible threshold.

Fig. 4.

Expected probability of total resection. (A) The presence of intact fascicles guarantees an high probability of total resection, and those cases are concentrated in the region of small tumors. As concerns with the cases that showed damaged fascicles, the probability of total resection is substantially lower and decreases with preoperative volume. (B and C) A similar pattern is found for infiltrated CST and displaced CST, as the cases with damaged CST show a low probability of total resection, which decreases rapidly to zero as the volume increases, whereas cases with intact CST have a higher probability of total resection, which appears high for small tumors. (D) Also in cases with infiltrated IFO the probability of total resection is higher when the fascicle is not damaged.