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Anatomic Variations in Temporal Bones Affect the Intensity of Nystagmus During Warm Caloric Irrigation

Patki, Aniruddha Uday; Ronen, Ofri; Kaylie, David Marcus; Frank-Ito, Dennis Onyeka; Piker, Erin Gillikin

doi: 10.1097/MAO.0000000000001129

Hypothesis: Anatomic variables within the mastoid will correlate with intensity of caloric responses.

Background: During caloric irrigation, heat is transferred from the external auditory canal to the lateral semicircular canal (LSCC) through aerated mastoid bone. Temporal bone airspace volume and bone volume vary widely but the effect of this variation on caloric irrigation testing is not well characterized. Understanding this effect is necessary to understand how mastoid surgery may alter caloric irrigation results.

Methods: Twenty-two mastoid airspace and bones, as well as LSCC, were reconstructed from computed tomography scans of 11 subjects with normal anatomy who underwent vestibular function evaluation. Respective surface area (SA) and volume (V) of the mastoid airspace, bones, LSCC, and distance from LSCC to tympanic membrane (LSCC-TM) were calculated. In addition, computed values from these anatomic structures were correlated with the maximum velocity of slow phase nystagmus during warm caloric irrigation (MVwarm).

Results: Our results showed that the combined effect of airspace SA:V, bone SA:V, LSCC SA:V, and LSCC-TM distance accounted for 69.5% of the variation in MVwarm. Airspace SA:V (R2 = 0.22) and LSCC SA:V (R2 = 0.02) positively correlated with MVwarm, while bone SA:V (R2 = 0.17) demonstrated an inverse correlation with MVwarm.

Conclusion: Preliminary results from this pilot study suggest that a substantial amount of the variability in MVwarm can be explained by temporal bone anatomy. Results also indicate that the denser the bone, the more heat is transferred to the LSSC, whereas increased airspace serves as an insulator. A larger study is necessary to confirm our findings.

*Department of Surgery, Division of Head and Neck Surgery and Communication Sciences, Duke University Medical Center, Durham, North Carolina, U.S.A.

Department of Otorhinolaryngology/Head and Neck Surgery, Hadassah University Hospital, Jerusalem, Israel

Address correspondence and reprint requests to Dr. Aniruddha Uday Patki, M.D., 40 Duke Medicine Circle, M150, Green Zone, DUMC 2824, Durham, NC 27710; E-mail:

The authors disclose no conflicts of interest.

Copyright © 2016 by Otology & Neurotology, Inc. Image copyright © 2010 Wolters Kluwer Health/Anatomical Chart Company