Cochlear Implantation through the Middle Fossa Approach: A Review of Related Temporal Bone Studies and Reported Cases

Abstract Introduction Middle fossa approach has been suggested as an alternative for patients in whom other routes of electrode insertion are contraindicated. Even though there are temporal bone studies about the feasibility of introducing the cochlear implant through the middle fossa, until now, very few studies have described results when cochlear implant surgery is done through this approach. Objective The objective of this study is to review a series of temporal bone studies related to cochlear implantation through the middle fossa and the results obtained by different surgical groups after cochlear implantation through this approach. Data Sources PubMed, MD consult and Ovid-SP databases. Data Synthesis A total of 8 human cadaveric temporal bone studies and 6 studies reporting cochlear implant surgery through the middle fossa approach met the inclusion criteria. Temporal bone studies show that it is feasible to perform cochlear implantation through this route. So far, only two surgical groups have performed cochlear implantation through the middle fossa with a total of 15 implanted patients. One group entered the cochlea in the most upper part of the basal turn, inserting the implant in the direction of the middle and apical turns; meanwhile, the other group inserted the implant in the apical turn directed in a retrograde fashion to the middle and basal turns. Results obtained in both groups were similar. Conclusions Themiddle fossa approach is a good alternative for cochlear implantation when other routes of electrode insertion are contraindicated.

Microanatomical Study of the Extradural Middle Fossa Approach for Preventing Cochlear Damage

OBJECTIVE: The objective is to describe the relationship of anatomical landmark required for the middle fossa approach to preservation of hearing. METHODS: Dissection of 16 fixed human cadaveric heads was performed. we identified a rhomboid-shaped middle fossa landmarks that serve as a guide to minimize cochlea injury. The points of this construct are as follows ; 1) the junction of the greater superficial petrosal nerve and the trigeminal nerve ; 2) the lateral edge of the porus trigemius ; 3) the intersection of the petrous ridge and arcuate eminence ; and 4) the intersection of the lines extended along the axes of the greater superficial petrosal nerve and arcuate eminence. Mean, minimum, and maximum measurements of all distances were determined. RESULTS: The average cochlea-geniculate ganglion distance measured in the dissected specimens was 3.0+/-0.8mm with a range of 1.2 to 4.1mm. The average cochlea-petrous carotid genu distance was 2.9+/-0.9mm with a range of 1.2 to 4.0mm. The average cochlea-internal acoustic meatus distance measured in the dissected specimens was 9.0+/-0.5mm with a range of 7.8-10.9mm. The average cochlea-mandibular nerve distance measured was 9.4+/-0.4mm with a range of 7.6-11.3mm. CONCLUSION: The middle fossa approach requires special knowledge of the anantomy to reduce the risk of damage to cochlea. It is important that the surgeon understand the surgical anantomy. The present study describes the simple geometric construct that proposes to assist in locating the cochlea.

Facial Nerve Decompression via Middle Fossa Approach: Report of Three Cases

OBJECTIVE: Several conservative treatments have been tried in peripheral facial nerve paralysis, because 80% of patients recover spontaneously. Surgical decompression may be helpful to the residual, medically intractable patients. We present here our experiences of facial nerve decompression via middle fossa approach, which seems to be one of good surgical therapeutic options for medically refractory peripheral facial nerve paralysis. METHOD:Three cases of medically intractable peripheral type facial paralysis were microscopically operated via middle cranial fossa approach to decompress the labyrinthine segment of the facial nerve and geniculate ganglion by searching landmarks of middle meningeal artery, greater superficial petrosal nerve and facial hiatus. RESULTS: After operation, two cases of Bell's palsy improved substantially and one case of post-traumatic facial paralysis improved partially. CONCLUSION: This report is presented to describe the surgical facial nerve decompression via middle fossa for early control of peripheral type facial paralysis. Surgical decompression of edematous peripherally paralysed facial nerve could be preferred to conservative treatment in some patients although more surgical experience should be required.

Surgical Anatomy for the Extended Middle Fossa Approach / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: The extended middle fossa approach is an essential method in approaching the internal acoustic canal and the cerebellopontine angle while preserving the hearing function. This work attempted to establish some anatomical landmarks in the petrous apex as it relates to the extended middle fossa approach. MATERIALS AND METHODS: We dissected 49 human skulls of Korean origin by using the extended middle fossa approach. RESULTS: Internal acoustic canal (IAC) was identified in an attempt to find reliable distances and angles to be used in the extended middle fossa approach. In addition, the dimensions of the fundus of IAC and IAC as well as the extension ranges were obtained. CONCLUSION: The extended middle fossa approach is a good method in approaching the internal acoustic canal and cerebellopontine angle. In this study, we have established anatomical landmarks for using this approach in the human skulls of Korean origin.

A Case of Facial Nerve Schwannoma Extending into the Middle Cranial Fossa / 대한이비인후과학회지

Schwannomas of the facial nerve are uncommon tumors, accounting for about 0.8% of all intrapetrous mass lesion.1-3) Very rarely do these lesions acts as expansile tumors of the petrous bone that extend to involve the intracranial cavity.1-10) Recently we experienced 1 case of facial nerve schwannoma unusually extending into middle cranial fossa which was removed by transcochlear and middle fossa approach. So we report the case with review of literature.

An Experience of Early Surgical Intervention for Neurofibromatosis Type II / 대한이비인후과학회지

Neurofibromatosis type II(NF2) is clinically characterized by the presence of bilateral vestibular schwannomas. The exclusive goal in management of NF2 patients is hearing preservation. It has been controversial to determine whether to wait and see or to try early surgical management for hearing preservation. The authors experienced a case of vestibular schwannoma in association with NF2, which was partially removed and decompressed via middle fossa approach with hearing preservation. Based on our experience, we recommend a new strategy for hearing preservation on early surgical intervention of vestibular schwannoma. The criterias of the patient include (1) bilateral normal or serviceable hearing: (2) small sized tumorand: (3) young age. We suggest that the early surgical intervention including decompression may be considered for the hearing preservation especially on the favorable side to approach.

Morphometric Study of the Extradural Middle Cranial Fossa for Transpetrosal Surgery

As an attempt to better understand the microanatomy during transpetrosal surgery and to determine the limitation of extradural middle fossa approach, 16 adults human cadaveric skull base speciments were dissected at the region of petroclivus and posterior cavernous sinus. The important landmarks chosen for this study included the following: a petrosigmoid intersection, arcuate eminence, foramen spinosum, foramen ovale, hiatus of greater superficial petrosal nerve (GSPN), porus acousticus internus, geniculate ganglion, cochlea and petrous portion of internal carotid artery(ICA). The resultant data are as follows: the length between the petrosigmoid intersection and the arcuate eminence was 23.1mm+/-1.9(20.1-26.5). The depth covering geniculate ganglion was 1.3mm+/-0.3(0.8-1.8). The length between the geniculate ganglion and the hiatus of GSPN as well as cochlea were 4.6mm+/-1.1(3.5-7.1) and 0.9mm+/-0.2(0.7-1.2) respectively. The whole length of the GSPN exposed the middle cranial fossa was 11.0mm+/-0.8(9.3-12.5). The diameter f the petrous portion of ICA was 5.9mm+/-0.2(5.5-6.4). The length of the horizontal segment of the petrous ICA that can be exposed for anastomosis was 10.8mm+/-0.9(9.0-12.3). The distance between geniculate ganglion and porus acousticus showed a sighificant difference in all measurements to be compared with right and left side(p<0.05). The angle between the internal acoustic meatus and GSPN correlated inversely to the length of horizontal segment of pertrous ICA(r=-0.54, p<0.05). Morphometric analysis and their correlation between bony landmarks and structures within the pyramid helped to decide the angle and direction from which bone removal could be accomplished more safely during transpetrosal surgery, including the middle fossa approach.