Endolymphatic Duct Status During Middle Fossa Dissection of the Internal Auditory Canal: A Human Temporal Bone Radiographic Study

Abstract

Successful hearing preservation after acoustic neuroma resection is sometimes complicated by delayed hearing deterioration. The middle fossa approach appears to offer superior long-term hearing results when compared to the retrosigmoid surgical approach. The goal of this study is to investigate the hypothesis that internal auditory canal (IAC) drilling during middle fossa acoustic neuroma removal is associated with a lower incidence of endolymphatic duct (ELD) injury, a potential cause of delayed hearing loss (HL) known to accompany retrosigmoid hearing preservation dissection techniques. A human temporal bone anatomic and radiographic study complemented with a literature review. Twenty human temporal bones were analyzed with high-resolution multislice computed tomography (HRMCT) and subjected to standard extended middle fossa IAC dissection with labyrinthine preservation and follow-up HRMCT for analyses of the ELD. Zero of 20 (0%) temporal bones were found to have violation of the ELD with preservation of the labyrinthine structures and the endolymphatic sac. Reviews of human and animal studies indicate that injury to the ELD may create endolymphatic hydrops, a known cause of hearing deterioration. The ELD is not vulnerable to injury during IAC dissection using the middle fossa approach. A previous radiographic study has shown that the ELD is violated in 24% of temporal bones during retrosigmoid dissection of the IAC. These findings support and may help explain other outcome studies that show that long-term hearing results are superior with the use of the middle fossa approach when compared to results following retrosigmoid dissection.