Cerebral Inflow and Outflow Discrepancies in Severe Sudden Sensorineural Hearing Loss

The aim of this study is to evaluate whether cerebral inflow and outflow abnormalities, assessed by the means of a validated ultrasound model, could be associated with Sudden Sensorineural Hearing Loss (SSNHL). According to Clark, a total of 42 patients affected by severe SSNHL and 19 healthy volunteers matched by gender without any history of sudden hearing impairment have been included in this study. Patients and controls underwent EchocolorDoppler assessment of brain hemodynamics. All subjects affected by SSNHL were also assessed with Auditory Brainstem Responses (ABR) and Magnetic Resonance Imaging (MRI) in order to exclude retrocochlear pathology. The head inflow through the common carotid artery was practically equivalent between groups, but at the level of the carotid bifurcation, the external carotid artery showed a highly significant flow rate in SSNHL 5.4±2 vs 3.9±1.1 ml/s in controls (p=0.01). The brain inflow was similar between patients and controls, but interestingly the flow rate of the vertebral artery was significantly reduced in SSNHL 1.6±0.8 vs 2.8±0.9 ml/s (p=0.01). The brain outflow was found significantly restricted at the level of the jugular outlet 6.6±6 vs 9.9±6 ml/s (p=0.002); consequently, the collateral flow index was significantly increased in SSNHL (p=0.001). The present study shows a discrepant distribution of the brain inflow which seems to penalize the posterior segments of the Willis polygon in patients affected by severe SSNHL. In addition, our study confirms the presence of chronic cerebrospinal venous insufficiency in SSNHL with significant activation of venous collateral circulation.