Microanatomy Around the Facial Nerve Pathway for Microvascular Decompression Surgery Investigated with Correlative Light Microscopy and Block-Face Imaging

Facial nerve in skullbase tumors: imaging and clinical relevance

Facial nerve, the 7th cranial nerve, is a mixed nerve composed of sensory and motor fibers, and its main branch is situated in the cerebellopontine angle. Facial nerve dysfunction is a debilitating phenomenon that can occur in skullbase tumors and Bell's pals. Recovery of the facial nerve dysfunction after surgery for skullbase tumors can be disappointing, but is usually favorable in Bell's palsy. Advances in magnetic resonance imaging (MRI) allow to visualize the facial nerve and its course in the cerebellopontine angle, also when a large tumor is present and compresses the nerve. Here, we describe the anatomical, neurochemical and clinical aspects of the facial nerve and highlight the recent progress in visualizing the facial nerve with MRI.

Correlative microscopy and block-face imaging (CoMBI): a 3D imaging method with wide applicability in the field of biological science

Correlative microscopy and block-face imaging (CoMBI) is an imaging method, which is characterized by the ability to obtain both serial block-face images as a 3-dimentional (3D) dataset and sections for 2-dimentional (2D) light microscopic analysis. These 3D and 2D morphological data can be correlated with each other to facilitate data interpretation. CoMBI is an easy-to-install and low-cost 3D imaging method since its system can be assembled by the researcher using a regular microtome, consumer digital camera, and some self-made devices, and its installation and instruction manuals are open-source. After the first release of CoMBI method from our laboratory, CoMBI systems have been installed in more than a dozen laboratories and are used for 3D analysis of various biological specimens. Typical application of CoMBI is 3D anatomical analysis using the natural color and contrast of the specimen. We have been using CoMBI for analyzing human brain to obtain the fine 3D anatomy as a reference to determine the causes of neurological diseases and to improve the effectiveness of surgery. Recently, we have been using CoMBI for detecting the colors of chromogens, which are used for labeling specific molecules. Mouse embryos colored with X-gal, a conventional chromogen for detecting LacZ products, were imaged using CoMBI, and the 3D distribution of X-gal was successfully visualized. Thus, CoMBI can now be used for many purposes, including 3D anatomical analysis, 2D microscopy using sections, and 3D distribution of specific molecules. These suggest that CoMBI should be more widely used in the field of biological research.

Reoperation for residual or recurrent hemifacial spasm after microvascular decompression

PURPOSE

Microvascular decompression (MVD) surgery is the only potential curative method for hemifacial spasm (HFS). Little attention is paid to those recurrent/residual HFS cases. We want to study the potential etiology of those recurrent/residual HFS cases and evaluate the value of reoperation.

METHODS

We retrospectively reviewed reoperation hemifacial spasm patients in our hospital. Intraoperative videos or images were carefully reviewed, and the etiology of recurrent/residual HFS is roughly divided into three categories. Intraoperative findings, surgical outcomes, and complications were carefully studied to assess the value of reoperation for recurrent/residual HFS patients.

RESULTS

A total of 28 cases were included in our case series. Twenty-three of them are recurrent HFS cases, and 5 of them are residual HFS cases. The mean follow-up duration is 24.96 months. There are seventeen patients with missed culprit vessels or insufficient decompression of root exit zone (REZ), eight patients with Teflon adhesion, and three patients with improper application of decompression materials in our case series. The final reoperation outcome with 17 excellent, seven good, and four fair, respectively. Eight (28.57%) of them experienced long-term complications after reoperation.

CONCLUSION

Re-operation for recurrent/residual HFS is an effective therapy and can achieve a higher cure rate. However, the complication rate is higher compared to the first MVD surgery. Accurately identifying REZ and proper decompression strategies to deal with the culprit vessels are very important for surgical success.

TRIAL REGISTRATION NUMBER

UIN: researchregistry7603. Date of registration: Jan. 31st, 2022 "retrospectively registered".

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

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.

Correlative microscopy and block-face imaging (CoMBI) method for both paraffin-embedded and frozen specimens

Correlative microscopy and block-face imaging (CoMBI), a method that we previously developed, is characterized by the ability to correlate between serial block-face images as 3-dimensional (3D) datasets and sections as 2-dimensional (2D) microscopic images. CoMBI has been performed for the morphological analyses of various biological specimens, and its use is expanding. However, the conventional CoMBI system utilizes a cryostat, which limits its compatibility to only frozen blocks and the resolution of the block-face image. We developed a new CoMBI system that can be applied to not only frozen blocks but also paraffin blocks, and it has an improved magnification for block-face imaging. The new system, called CoMBI-S, comprises sliding-type sectioning devices and imaging devices, and it conducts block slicing and block-face imaging automatically. Sections can also be collected and processed for microscopy as required. We also developed sample preparation methods for improving the qualities of the block-face images and 3D rendered volumes. We successfully obtained correlative 3D datasets and 2D microscopic images of zebrafish, mice, and fruit flies, which were paraffin-embedded or frozen. In addition, the 3D datasets at the highest magnification could depict a single neuron and bile canaliculus.

Fully endoscopic microvascular decompression of the hemifacial spasm: our experience

PURPOSE

Microvascular decompression (MVD) surgery has been accepted as a potentially curative method for hemifacial spasm (HFS). The primary cause of failure of MVD is incomplete decompression of the offending vessel due to inadequate visualization. This study is aimed at evaluating the benefit of endoscopic visualization and the value of fully endoscopic MVD.

METHODS

From March 2016 to March 2018, 45 HFS patients underwent fully endoscopic MVD in our department. From opening the dura to preparing to close, the assistant held the endoscope and the surgeon operated. Abnormal muscle response (AMR) and brainstem auditory evoked potentials (BAEP) were monitored. For every patient, the offending vessel was transposed or interposed and achieved complete decompression. AMR was used to evaluate the adequacy of decompression at the end of the surgery. The intra-operative findings and postoperative outcomes and complications were analyzed.

RESULTS

Immediately after surgeries, 39 patients (86.7%) achieved excellent result; 2 cases (4.4%) had good result. So the postoperative effective rate was 91.1% (41/45). During 12-36 month follow-up, the outcomes were excellent in 42 cases (93.3%) and good in 2 cases (4.4%), and the effective rate reached to 97.8% (44/45). No recurrence was noted. The postoperative complications were found in 2 patients (4.4%). One patient (2.2%) showed delayed facial palsy on the tenth day but was fully recovered 1 month later. Intracranial infection was noticed in 1 patient (2.2%) and was cured by using intravenous antibiotics for 2 weeks. There was no hearing impairment, hoarseness, or other complications.

CONCLUSIONS

Fully endoscopic MVD is both safe and effective in the treatment of HFS. Electrophysiological monitoring is helpful to gain a good result and reduce hearing impairment.