A Radiological Study on the Topographical Relationships between the Vestibular, Cochlear and Facial Nerves

Abstract

Objective: The purpose of our study was to investigate the topographical relationship between these nerves along their course from the brainstem through the internal acoustic canal IAC in the living human brain using MR imaging. Materials and Methods:We performed three-dimensional gradient echo balanced Fast Field Echo (3D bFFE) sequence oblique parasagittal MR imaging in 73 healthy subjects. The IACs were analyzed from the brainstem end of the IAC to the fundus in contiguous sections. At five levels, the topographical relationships between the facial and vestibulocochlear nerves (VCN) were recorded. In the lateral portions of the IACs where they separated from each other, the relative sizes of the individual nerves were examined. Results:In general, the facial nerve (FN), which is a round structure, is located anteriorly and superiorly to the vestibulocochlear nerve throughout its course. The vestibulocochlear nerve is usually rectangular; however, it was found to be round and at times triangular in shape near the brainstem, before it became crescent-shaped at the porus in 89% of the cases. The superior vestibular nerve kept its posterosuperior position in the canal, and the inferior vestibular nerve (IVN) and the cochlear nerve (CN) travelled inferior to it. The superior and inferior vestibular nerves were divided by the falciform crest in 53% of the cases. The inferior vestibular nerve was the smallest nerve in 52% of the cases, and the cochlear nerve was the largest in 36% of the cases. Conclusion:To the best of our knowledge, this study is the largest in vivo MR study, and most of our findings differ from previous cadaver studies. Determination of these topographical relationships may facilitate our understanding of the complicated physiological relationships between the 7 th and 8 th nerve complexes during surgery in this region.Key Words: Cochlear nerve, Facial nerve, Magnetic Resonance, Topography, Vestibular nerve Özet Amaç: Bizim amacımız, yaşayan insanlarda MR görüntülemeyi kullanarak, bu sinirlerin beyin sapından, internal akustik kanala kadar olan kısmında topografik ilişkilerini araştırmaktır. Gereç ve Yöntem:Yetmiş üç sağlıklı bireyde 3D gradient echo balanced fast field echo (3D bFFE) sekans oblik parasagittal MR inceleme yaptık. İAK, beyin sapından İAK'ın bitimindeki fundusa kadar, ardışık kesitlerle analiz edildi. Beş seviyede fasiyal ve vestibülokoklear sinirin topografik ilişkileri kaydedildi. İAK'ın lateral bölümünde (sinirin kendi içinde bölümlere ayrıldığı kısımda) sinirlerin rölatif boyutları değer-lendirildi. Bulgular:Genel olarak fasiyal sinir, yuvarlak bir yapıda, anterior yerleşimli ve tüm seyri boyunca vestibulokoklear sinirin süperiorundadır. Vestibulokoklear sinir ıklıkla dikdörtgen şeklindedir. Fakat bazen beyin sapına yakın kısımda yuvarlak ve nadiren üçgen şeklinde ve vakaların %89'unda porusda kresentrik yapıdadır. Superior vestibuler sinir kanal içinde posterosüperior pozisyonunu korur ve inferior vestibüler sinir ve koklear sinir superior vestibüler sinirin altından g...

Three-Dimensional Constructive Interference in Steady State (3D CISS) Imaging and Clinical Applications in Brain Pathology

“…Comparing preoperative MRI findings with intraoperative findings, they found a correlation of 74 % between nerve location and intraoperative findings [ 73 ]. 3D CISS images accurately demonstrate the topographical relationship between the tumor and the facial and vestibulocochlear nerves, which is especially useful for the improvement of microsurgery and endoscopic surgery in the internal acoustic canal [ 74 ].…”

Comparative Study between 3D Balanced Fast Field Echo Sequence and 3D Driven Equilibrium Sequence in the Assessment of the Inner Ear Structure and Internal Auditory Canal Nerves

“…MR cisternography using three dimensional (3D) heavily T2-weighted imaging techniques is considered the main imaging modality for identification and assessment of inner ear structures anatomy and pathology as well as for identification of the posterior fossa cranial nerves especially the internal Correspondence to: Dr. Ahmed S. Abdelrahman, E-Mail: dr_ahmedsamy@yahoo.com auditory canal (IAC) cranial nerves [1][2][3][4][5] , so it is considered the modality of choice in preoperative assessment before cochlear implant surgery, giving proper anatomical and pathological information about the integrity of the cochlear nerve and the cochlea which is mandatory before surgery [6] .…”