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Benjamin P. C. Wei, MB,BS, PhD; Robert K. Shepherd, PhD; Roy M. Robins-Browne, MB, BCh, PhD, FRCPath, FRCPA, FASM; Graeme M. Clark, MB, MS, PhD, FRCS(Edin), FRCS(Eng), FRACS; Stephen J. O’Leary, MB,BS, PhD, FRACS

Arch Otolaryngol Head Neck Surg. 2007;133(3):250-259.

Objective  To examine the risk of pneumococcal meningitis in healthy rats that received a severe surgical trauma to the modiolus and osseous spiral lamina or the standard insertion technique for acute cochlear implantation.

Design  Interventional animal studies.

Subjects  Fifty-four otologically normal adult Hooded-Wistar rats.

Interventions  Fifty-four rats (18 of which received a cochleostomy alone; 18, a cochleostomy and acute cochlear implantation using standard surgical techniques; and 18, a cochleostomy followed by severe inner ear trauma) were infected 4 weeks after surgery with Streptococcus pneumoniae via 3 different routes (hematogenous, middle ear, and inner ear) to represent all potential routes of bacterial infection from the upper respiratory tract to the meninges in cochlear implant recipients with meningitis.

Results  Severe trauma to the osseous spiral lamina and modiolus increased the risk of pneumococcal meningitis when the bacteria were given via the middle or inner ear (Fisher exact test, P<.05). However, the risk of meningitis did not change when the bacteria were given via the hematogenous route. Acute electrode insertion did not alter the risk of subsequent pneumococcal meningitis for any route of infection.

Conclusions  Severe inner ear surgical trauma to the osseous spiral lamina and modiolus can increase the risk of pneumococcal meningitis. Therefore, every effort should be made to ensure that cochlear implant design and insertion technique cause minimal trauma to the bony structures of the inner ear to reduce the risk of pneumococcal meningitis.

Author Affiliations: Bionic Ear Institute (Drs Wei, Shepherd, Clark, and O’Leary) and Departments of Otolaryngology (Drs Wei, Shepherd, and O’Leary) and Microbiology and Immunology (Dr Robins-Browne), University of Melbourne, Melbourne, Australia.

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