Clin Exp Otorhinolaryngol.  2019 Nov;12(4):392-398. 10.21053/ceo.2018.01921.

Intratympanic Gentamicin Versus Labyrinthectomy: Inner Ear Sensitivity to Gentamicin and Impact on the Contralateral Labyrinth

• Kontorinis G
• Tailor H
• Gaggini M
• Crowther J

• KMID: 2462735
• DOI: http://doi.org/10.21053/ceo.2018.01921

Abstract

OBJECTIVES
To investigate the impact of labyrinthectomy and intratympanic (IT) gentamicin injections on the contralateral labyrinth, we also assessed the response of each individual semicircular canal to each IT gentamicin application.
METHODS
We performed a pilot observational study on tertiary, referral, academic settings. Thirteen patients with unilateral vestibular pathology were organized into two groups, group I (seven patients) receiving IT gentamicin and group II undergoing labyrinthectomy (six patients). All patients underwent six-canal video-head-impulse test in predetermined time intervals. Patients receiving gentamicin were additionally tested 3 to 5 days after every sequential injection, until all ipsilateral canals were ablated, to determine the order of response to gentamicin. We recorded the vestibular-ocular reflex gains and the presence of covert/overt saccades for each canal.
RESULTS
The posttreatment ipsilateral gains were abnormal. No patient from the gentamicin group developed abnormal contralateral responses, while patients undergoing labyrinthectomy had abnormal contralateral responses from at least one canal, even several months posttreatment. Finally, the lateral semicircular canal was the first one to be affected by IT gentamicin followed by the posterior canal: the superior canal was ablated last.
CONCLUSION
In our study, labyrinthectomy had an impact on the responses recorded from the contralateral ear, while IT gentamicin ablated the ipsilateral labyrinthine function without affecting the contralateral responses, possibly because of a milder, more gradual impact. We also show for the first time the order that IT gentamicin application affects the semicircular canals, with the lateral being the first to be affected.

Keyword

Gentamicin; Head Impulse Test; Inner Ear; Semicircular Canals; Vestibular-Ocular Reflex

MeSH Terms

Ear
Ear, Inner*
Gentamicins*
Head Impulse Test
Humans
Observational Study
Pathology
Referral and Consultation
Reflex
Saccades
Semicircular Canals
Gentamicins

Figure

• 

  Fig. 1. Reduced (abnormal) vestibular-ocular reflex gain in the right lateral and posterior semicircular canals following the first intratympanic gentamicin injection (A) and additional abnormal gain in the right superior canal after the second injection (B); the contralateral responses stay normal. The long dotted arrows point the overt and the short ones the covert saccades as seen on the raw data; the abnormal gain can be seen on the plot. LA, left anterior; RA, right anterior; LL, left lateral; RL, right lateral; LP, left posterior; RP, right posterior.

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