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Hypothesis: A tissue response in the form of foreign body or a hypersensitivity reaction to cochlear implantation is common and may be one possible cause of a soft failure of cochlear implantation.

Background: After a successful cochlear implantation, delayed failure may occur. The causes of a "soft" failure, that is, one in which device malfunction cannot be proven, are unknown.

Methods: The histopathology of the temporal bones of a patient who, in life, had experienced a soft failure after cochlear implantation was described. In addition, the temporal bones of 8 other subjects who, in life, had undergone cochlear implantation were studied for evidence of a foreign body or hypersensitivity reaction.

Results: In the case report, a necrotizing granulomatous giant cell reaction surrounded the cochlear implant electrode track through the mastoid and the middle ear and into the cochlea in both ears. There was osteolysis of the cribrose area, otic capsule, and bone between the facial nerve and the cochlea and destruction of the organ of Corti and spiral ganglion. In the additional 8 cases studied, a similar, although less pronounced, foreign body or hypersensitivity reaction was seen in 6 (75%) of the cases.

Conclusion: A foreign body or hypersensitivity reaction in the form of giant cells and lymphocytic cell infiltration is common after cochlear implantation and may be one possible cause of soft failure.

(C) 2008 Otology & Neurotology, Inc.