Diffusion tensor imaging of the corticospinal tract before and after mass resection as correlated with clinical motor findings: preliminary data

Abstract

Background and purpose: The role of diffusion tensor imaging (DTI) in neurosurgical planning and follow-up is currently being defined and needs clinical validation. To that end, we sought correlations between preoperative and postoperative DTI and clinical motor deficits in patients with space-occupying lesions involving the corticospinal tract (CST).

Methods: DTI findings in four patients with masses near the CST and not involving motor cortex were retrospectively reviewed and compared with contralateral motor strength. CST involvement was determined from anisotropy and eigenvector directional color maps. The CST was considered involved if it was substantially deviated or had decreased anisotropy. Interpretations of the DTIs were blinded to assessments of motor strength, and vice versa.

Results: Of the four patients with potential CST involvement before surgery, DTI confirmed CST involvement in three, all of whom had preoperative motor deficits. The patient without CST involvement on DTI had no motor deficit. After surgery, DTI showed CST preservation and normalization of the position and/or anisotropy in two of the three patients with preoperative deficits, and both of those patients had improvement in motor strength. The other patient with preoperative deficits had evidence of wallerian degeneration on DTI and had only equivocal clinical improvement.

Conclusion: Preoperative CST involvement, as determined on DTI, was predictive of the presence or absence of motor deficits, and postoperative CST normalization on DTI was predictive of clinical improvement. Further study is warranted to define the role of DTI in planning tumor resections and predicting postoperative motor function.

Fig 1.

Patient 1. Preoperative (A–C) and postoperative (D–F) axial images of a right thalamic pilocytic astrocytoma: contrast-enhanced T1-weighted images (A and D), T2-weighted images (B and E), and directional color maps (C and F). Before surgery, DTI reveals decreased FA (diminished blue in C) and posteromedial displacement of the right PLIC (arrow in C). After surgery, DTI shows persistently decreased FA and displacement of the right PLIC (arrowhead in F).

Fig 2.

Patient 2. Preoperative (A–C) and postoperative (D–F) axial images of a left frontal pilocytic astrocytoma: contrast-enhanced T1-weighted images (A and D), T2-weighted images (B and E), and directional color maps (C and F). Before surgery, DTI reveals decreased FA (diminished blue in C) and posteromedial displacement of the left PLIC (arrow in C). After surgery, DTI shows both restored FA (normal blue in F) and normal positioning of the left PLIC.

Fig 3.

Patient 3. Preoperative (A–C) and postoperative (D–F) axial images of a left thalamic ganglioglioma: contrast-enhanced T1-weighted images (A and D), T2-weighted images (B and E), and directional color maps (C and F). Before surgery, DTI reveals lateral displacement of the left PLIC (arrow in C); after surgery, DTI shows that the position has returned to normal.

Fig 4.

Patient 4. Preoperative (A–C) and postoperative (D–F) axial images of the right striatal hemorrhagic cavernous angioma: contrast-enhanced T1-weighted images (A and D), T2-weighted images (B and E), and directional color maps (C and F). Before surgery, DTI reveals only slight displacement of the right PLIC. After surgery, DTI shows a preserved right PLIC.

Fig 5.

Patient 1. Axial images of the brainstem. Before (A) and after (C) surgery, conventional T2-weighted images show subtle blunting of the right ventral surface of the pons (arrow). Preoperative (B) and postoperative (D) DTI reveals marked diminution of the CST in the right ventral pons, consistent with wallerian degeneration (arrowhead).