Post Hybrid Cochlear Implant Hearing Loss and Endolymphatic Hydrops

Abstract

Objective To evaluate for potential causes of delayed loss of residual hearing that variably occurs with hybrid cochlear implants. Study design Histopathological evaluation of 29 human temporal bone (HTB) with cochlear implant. Setting The Neurotology and House HTB Laboratory of UCLA (House-UCLA). Subjects and methods HTB from cochlear implant patients from the House-UCLA HTB Laboratory (n = 28) and one courtesy of Massachusetts Eye and Ear Infirmary (MEEI). Histopathological analysis to identify the location of cochleostomy, fibrosis and bone formation in the scala vestibuli and tympani, and endolymphatic hydrops. Spiral ganglion neuron counts were obtained. Statistical analysis compared presence of cochleostomy and location with the histopathological findings. Results Seventeen of 29 bones with fibrosis in the scala vestibule (SV) and tympani had evidence of a cochleostomy involving the SV containing the ductus reunions, all of which had hydrops. Ten of eleven bones had no SV fibrosis, and a cochleostomy limited to the scala tympani, of which all had no hydrops. One HTB had moderate SV fibrosis not involving the ductus reuniens, and was without hydrops. One HTB had a SV cochleostomy but the electrode ruptured Reissner’s membrane, and was without hydrops. Cochleostomy was significantly associated with SV fibrosis and hydrops (p<0.01), those without hydrops had no SV atrophy (p<0.01). Round window insertion was associated with no fibrosis and no hydrops. Conclusion We hypothesize that cochleostomies involving scala vestibuli incite fibrosis, compromising the ductus reuniens, causing hydrops which may cause the delayed loss of residual low frequency hearing in cochlear implant.

Predictive factors for short‐ and long‐term hearing preservation in cochlear implantation with conventional‐length electrodes

“…Animal studies support this notion in that RW insertions have been shown to result in less tissue formation, which correlated with better hearing outcomes . Postmortem temporal bone studies demonstrated that cochleostomy approaches were more likely to result in scala vestibuli fibrosis and endolymphatic hydrops when compared to RW insertions . The authors hypothesized that cochleostomies involving the scala vestibuli result in fibrosis of cochlear scala, leading to endolymphatic hydrops, which may be responsible for delayed hearing loss after cochlear implantation.…”

“…37 Postmortem temporal bone studies demonstrated that cochleostomy approaches were more likely to result in scala vestibuli fibrosis and endolymphatic hydrops when compared to RW insertions. 38 The authors hypothesized that cochleostomies involving the scala vestibuli result in fibrosis of cochlear scala, leading to endolymphatic hydrops, which may be responsible for delayed hearing loss after cochlear implantation. In support of this theory, Quesnel et al described a patient who experienced delayed loss of residual hearing, and was found to have intrascalar fibrous tissue and new bone formation years after a cochleostomy approach.…”

Cochlear implant histopathology

“…If the insertion involves the scala vestibuli it may cause fibrosis and ossification that blocks the ductus reuniens and result in a delayed endolymphatic hydrops because the endolymph passage from the cochlea to the saccule is blocked. 1 There was no relationship between speech understanding and the number of neurons. In fact, there was a slightly reversed association.…”

Challenging aspects of contemporary cochlear implant electrode array design

“…However, cochleostomy and related surgical approaches were found to be more associated with new bone formation and fibrotic tissue encapsulation of the electrode array due to larger initial intracochlear damage than RW, partly because they can lead to unintended involvement of scala vestibuli. 29 , 30 In fact, a direct comparison of perimodiolar arrays (Clarion TM or HiRes90K™) with a lateral wall array (Full-Band Straight) confirmed thickened fibrous capsule at the medial aspect of the electrode array in individuals implanted with a perimodiolar device. 31 This finding was attributed to closer proximity to the modiolus and differences in the shape of electrical field.…”