Ingenuity using 3D-MRI fusion image in evaluation before and after microvascular decompression for hemifacial spasm
- Department of Neurosurgery, Yamagata City Hospital Saiseikan, Yamagata, Japan.
- Department of Emergency Medicine, Yamagata City Hospital Saiseikan, Yamagata, Japan.
Atsushi Kuge, Department of Emergency Medicine, Neurosurgery, Yamagata City Hospital Saiseikan, Yamagata, Japan.
DOI:10.25259/SNI_1015_2021Copyright: © 2022 Surgical Neurology International This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-Share Alike 4.0 License, which allows others to remix, transform, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms.
How to cite this article: Kenshi Sano1, Atsushi Kuge1,2, Rei Kondo1, Tetsu Yamaki1, Kazuki Nakamura1, Shinjiro Saito1, Yukihiko Sonoda1. Ingenuity using 3D-MRI fusion image in evaluation before and after microvascular decompression for hemifacial spasm. 20-May-2022;13:209
How to cite this URL: Kenshi Sano1, Atsushi Kuge1,2, Rei Kondo1, Tetsu Yamaki1, Kazuki Nakamura1, Shinjiro Saito1, Yukihiko Sonoda1. Ingenuity using 3D-MRI fusion image in evaluation before and after microvascular decompression for hemifacial spasm. 20-May-2022;13:209. Available from: https://surgicalneurologyint.com/surgicalint-articles/11607/
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
Hemifacial spasm (HFS) has been reported to be related to vascular compression of the facial nerve at its root exit zone (REZ) in the majority of patients.[
Facial nerve anatomy
Campos-Benitez and Kaufmann classified the facial nerve into four segments based on their location and their relationship to myelination; route exit point (RExP), attachment segment (AS), root detachment position (RDP), and cisternal portion (CP).[
We performed pre-/postoperative MRI using a 3.0T MR imager (MRI, Achieva 3.0T TX Quasar, Philips) with parameters (T2-weighted image three-dimensional drive: echo time [TE] 2.8 ms, repetition time [TR] 1.45 ms, flip angle 90, band width 11.0, field of view [FOV] 13 cm, reconstruction slice thickness 0.6 mm, matrix 240*432, and number of excitations 1.00, MR angiography [MRA]: TR 25 ms, TE 3.45 ms, FOV 23 cm, reconstruction slice thickness 1.1 mm, matrix 512*512, and number of excitations 1.00).
For diffusion tensor image (DTI), we used a single-shot spin echo sequence (TR 3000 ms, TE 63 ms, and FOV 224 mm) and marked facial nerve in volume date after the facial nerve fiber tracking.
We used the SYNAPSE VINCENT medical imaging system (Fujifilm Medical, Tokyo, Japan) for 3D visualization. We extracted the desired structure from the preoperative T2 drive and pre- and postoperative MRA. The vascular and brainstem models were visualized using surface rendering with automatic thresholding. Because the facial nerve has a very fine structure and it was difficult to extract it automatically, we manually extracted the 2D image. The AS and RExP parts of the facial nerve touch the brainstem with the same signal value, we extended 10 mm after contacting the brain stem in the direction of the medulla oblongata. In extracting the facial nerve, we referred to DTI. In this way, we were able to create separate 3D models by color coding for easy identification.
A 52-year-old woman with intractable left HFS for 2 years was admitted for operation. She previously underwent botulinum toxin injections twice, resulting in only temporary improvement. MRI T2 drive and SPGR images confirmed that the left vertebral artery (VA) and anterior inferior cerebellar artery (AICA) were close to the facial nerve, but the detailed relationship with the REZ of the facial nerve was difficult to understand [
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.
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).
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).
HFS is caused by the compression of the facial nerve by blood vessels located at the AS or RExZ. Histologically, the central myelin and the peripheral myelin suggest that the latter is more resistant to vascular contact.[
The previous reports attempted preoperative simulations using 3D images to ascertain the exact locations of complexly intertwined arteries. Shigematsu et al. and Ishimori et al. used virtual endoscopic imaging and they could recognize vessels containing the parenchyma of the pons.[
We consider that there are the three points to understand the exact compression site and devise a preoperative simulation.
Extraction of facial nerve
We had extracted the facial nerve by the following procedure based on the heavily T2 images with reference to the above anatomical features of the facial nerve. The CISS sequence used to extract the facial nerve (called the Philips T2 drive at our center) has excellent spatial resolution. Therefore, various detailed anatomical structures could be analyzed.[
Facial nerve DTI
We referred to the findings of facial nerve tractography to extract the facial nerve more accurately. DTI is an MRI technique based on the principle that water molecule diffusion is anisotropic in white matter tracts.[
Fusion image with facial nerve and offending vessels pre- and post-MVD
We performed the MVD with transposition in all cases and then confirmed that the offending artery was separated from the facial nerve in intraoperative findings. By creating fusion images pre- and post-MVD, it was possible to easily understand the minute changes in transposition of the offending vessels. In the previous reports, it was challenging to neuroimage for the precise identification of the pathologic contact between the nerves and vessels.[
We extracted the RExZ and AS of facial nerve with a 3D model by MRA and DTI and created a fusion image of the pre-/postoperative artery and nerve. It was considered to be useful in facilitating postoperative evaluation.
For this type of study, formal consent is not required. This article does not contain any studies with human participants performed by any of the authors.
The authors certify that they have obtained all appropriate patient consent.
There are no conflicts of interest.
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