Ingenuity using 3D-MRI fusion image in evaluation before and after microvascular decompression for hemifacial spasm

Abstract

Background: Hemifacial spasm (HFS) is most often caused by blood vessels touching a facial nerve. In particular, responsible vessels compress the root exit zone (REZ) of the facial nerve. Although we recognize these causes of HFS, it is difficult to evaluate the findings of precise lesion in radiological imaging when vessels compress REZ. Hence, we tried to obtain precise images of pre- and postoperative neuroradiological findings of HFS by creating a fusion image of MR angiography and the REZ of facial nerve extracted by magnetic resonance imaging (MRI) diffusion tensor image (DTI).

Case description: A 52-year-old woman had a 2-year history of HFS on the left side of her face. It was confirmed that the left vertebral artery and anterior inferior cerebellar artery were presented near the facial nerve on MRI. REZ of the facial nerve was visualized using DTI and fusion image was created with vascular components, making it possible to recognize the relationship between compression vessels and REZ of the facial nerve in detail. She underwent microvascular decompression and her HFS completely disappeared. We confirmed that the REZ of the facial nerve was decompressed by MRI imaging, in the same way as before surgery.

Conclusion: We describe that the REZ of facial nerve and compressive vessels was delineated in detail on MRI and this technique is useful for pre- and postoperative evaluation of HFS.

Keywords: Diffusion tensor fusion image; Hemifacial spasm; Magnetic resonance image; Microvascular decompression; Root exit zone.

Figure 1:

Preoperative MRI. MRI SPGR (left side) and T2 drive (right side) images confirmed that the left vertebral artery (black arrow) and anterior inferior cerebellar artery (red arrow) were close to the facial nerve (yellow arrow heads), but the detailed relationship with REZ of facial nerve was difficult to understand. a: left upper, b: right upper, c: left lower, d: rtght lower.

Figure 2:

Depiction of the facial nerve by MRI diffusion tensor image (DTI). We have created 3D images of the facial nerve and brainstem (d: coronal; e: sagittal; and f: axial view) by extracting RExZ and AS (green) and RDP and CP (yellow) of the facial nerve with reference to DTI( a, coronal; b: saggital, c: axial view, blue line: diffusion tensor image) d, e, f: purple: brainstem. g; Preoperative image: the left vertebral artery and anterior inferior cerebellar artery compressed REZ of the left facial nerve (green).

Figure 3:

Intraoperative view. REZ (yellow arrow heads) of facial nerve was decompressed by transposition of the left vertebral artery (black arrows) and interposition of anterior inferior cerebellar artery (red arrows).

Figure 4:

Perioperative fusion images. Brainstem (purple), the AS and RExP parts of the facial nerve called REZ (green), other parts of the facial nerve (yellow) and MRA (preoperative [red] and postoperative [blue] vertebrobasilar system). (a) Postoperative image: vascular compression on REZ has been released. (b) Fusion image of pre- and postoperative examination could allow us to evaluate the extent of decompression easily. Preoperative vascular image (translucent blue), postoperative vascular image (red), and REZ of facial nerve (green).