The effect of tympanoplasty surgery performed in the lateral head position under general anaesthesia on the optic nerve sheath diameter

During tympanoplasty surgery, the head and neck remain in the lateral position throughout the procedure. This situation may disrupt venous blood flow, compromise cerebral perfusion, and increase intracranial pressure (ICP). Non-invasive measurement of the optic nerve sheath diameter (ONSD) using ultrasonography may enable early diagnosis of changes in ICP. This study investigated the effect of lateral head position on ONSD and thereby on ICP. In this prospective observational study ONSD measurements were taken at three time points following intubation (T1: 5 min in the supine position, T2: at the end of the case in the lateral head position, and T3: 5 min after the patient’s head was restored to the supine position upon completion of the surgery, but prior to the initiation of extubation preparation. ONSD values measured at T2 were found to be 0.658 mm higher than those at T1 ( p < 0.001). At T3, ONSD was found to be 0.260 mm higher compared to T1 ( p < 0.001); however, it showed a decrease of 0.398 mm compared to T2 ( p < 0.001). On the other hand, while the interaction between time units and surgical side (right/left ear), patient age and body mass index was not significant, it was found that ONSD increased significantly as the surgical duration increased ( p = 0.835, p = 0.854, p = 0.973 and p < 0.001, respectively). . This study demonstrates that the lateral head position during tympanoplasty surgery leads to a significant and bilateral increase in ONSD, which serves as an indirect indicator of potential ICP alterations. While ONSD values decrease upon returning to the supine position, they do not fully recover to baseline before extubation. This cumulative increase is independently driven by prolonged surgical duration rather than patient age, BMI, or the operated side. Further research is required to evaluate the long-term clinical and cerebral outcomes of these positional changes. Health Sciences University Bursa Training and Research Hospital Clinical Research Ethics Committee (approval number 2011-KAEK-2025 2020/01–12). ClinicalTrial.gov Identifier: NCT07407972 First registration date 29/01/2026.