Tinnitus refers to the perception of sound in the absence of any external auditory stimulus. It can be divided into two categories: subjective and objective tinnitus. Objective tinnitus is further classified into vascular and non-vascular tinnitus, based on its origin. Vascular tinnitus, also referred to as pulsatile tinnitus (PT), accounts for about 10% of all tinnitus cases [1]. Up to 92% of PT cases have identifiable underlying causes [2], offering the possibility of symptom relief through surgical intervention. The causes of PT include significant vascular wall abnormalities in the temporal bones [3,4]. There are three potential mechanisms that explain how these anomalies cause PT: (1) turbulence in blood flow due to alterations in vascular hemodynamics [5,6], (2) vibration of a dehiscent vascular wall in the absence of turbulent flow [7,8], and (3) third-window lesions in the inner ear causing abnormal sound perception [9,10]. Among the various vascular wall abnormalities, sigmoid sinus abnormalities are the most common identifiable cause of PT of venous origin, with a prevalence of approximately 20% in PT patients [8,11,12].

An accurate diagnosis of the underlying anatomical abnormality is critically important before proceeding with surgery for the treatment of PT. This can be achieved through a combination of history-taking, physical examination, audiologic tests, laboratory tests, imaging examination, ultrasonography, and the water occlusion test (WOT) [13]. The aim of this study was to analyze the outcomes of surgery for PT and to evaluate the efficacy of the WOT as a powerful additional tool in diagnostic process, when used in conjunction with temporal bone computed tomography (TBCT) to determine the optimal surgical modality for vascular wall anomalies causing PT.

In this study, we observed a high success rate of SS-R in patients with PT originating from sigmoid sinus variants. Of the 26 patients enrolled in the study, 21 (80.76%) showed a significant improvement in symptoms post-surgery. Additionally, the study aimed to validate the prognostic value of the WOT, a method previously published by our research group [13], by analyzing the surgical outcomes of SS-R in PT patients based on the WOT results. However, five patients exhibited no change in surgical outcomes, despite preoperative diagnosis using TBCT, intraoperative findings, and the WOT. The first patient (no. 6 in Table 1), who had preoperative TBCT and intraoperative findings of SS-Deh and SS-Div underwent SS-R alone, which resulted in no change in outcome. In this patient, the WOT result was partial, suggesting that her SS-Div significantly impacted her PT symptoms. Therefore, reshaping the sigmoid sinus to reduce turbulence in the SS-Div or obliterating it with a periosteal flap might be necessary to achieve successful surgical outcomes. As previously reported, partial results in the WOT, which support the impact of SS-Div on symptoms, occur because water occlusion of the EAC only reduces sound coming from the venous sinus dehiscence but does not affect, or even amplifies, turbulence sounds originating from SS-Div, PMEV, or an arteriovenous fistula [13]. In more detail, pulsatile sound from the venous sinus dehiscent site is transmitted to the tympanic membrane through air transmission (air pulsation mechanism), while pulsatile sound from turbulent blood flow can be directly transmitted to the cochlea through bone conduction (turbulence conduction mechanism). Given that water occlusion of the EAC only affects the movement of the tympanic membrane, SS-Deh and HJB-Deh may show positive results in the WOT, whereas SS-Div, PMEV, and arteriovenous fistula may show partial or negative results in the WOT.

The mastoid emissary vein (MEV) is a normal venous structure connecting the extracranial venous system and sigmoid sinus [17] that is found in the majority of the population and typically has no significant clinical features [18]. Kim et al. [19] reported that the prevalence of MEV was 74% on the left side and 81% on the right side, and the mean mastoid emissary foramen diameter was 1.73 mm. Forte et al. [20] measured the internal foramina of sigmoid sinuses in 50 normal cadaver skulls and reported that 60% had diameters smaller than 2 mm and 85% had diameters smaller than 3.5 mm [18]. Although most MEVs do not display significant clinical features, those with a diameter large enough to cause turbulence could potentially contribute to PT. In our study, TBCT revealed six cases of PMEV, with a mean diameter of 2.72 mm. Among them, two patients (no. 15 and 16 in Table 1) had only PMEV contributing to PT, with diameters of 2.59 mm and 2.4 mm respectively, and their WOT results were both partial. One patient underwent only SS-R and the other underwent SS-R with emissary vein ligation surgery. Their surgical outcomes were both stable; however, their THI scores varied, with one increasing by 100% and the other decreasing by 97%. Based on this intriguing result, we suggest that a confirmed diagnosis of PMEV, obtained through various diagnostic tools including the WOT, should be managed with emissary vein ligation surgery to alleviate symptoms.

One patient (No. 13 in Table 1), who showed SS-Deh, HJB-Deh, and PMEV on TBCT preoperatively, was confirmed to have a thin SS plate and HJB-Deh intraoperatively. Based on the positive WOT results in this patient, only SS-R and HJB-R were performed. The surgical outcome was stable, with a reduction of 14.2% in VAS LD and 58.2% in THI. However, the evaluation of the surgical outcome in this patient was limited due to the onset of mild conductive hearing loss post-surgery, likely caused by a minor disturbance of air conduction associated with the resurfacing materials. The final patient (no. 26 in Table 1), who exhibited SS-Deh in preoperative TBCT and was found to have a thin SS plate during surgery, demonstrated negative WOT results. The unchanging outcome of the surgery in this patient underscores the clinical prognostic value and significance of WOT once more.

Based on an analysis of 10 cases that showed discrepancies between preoperative TBCT and intraoperative surgical findings, as well as five cases with consistent results, we acknowledge the limitations of using TBCT and intraoperative findings to diagnose anatomical abnormalities. This is particularly relevant when predicting the surgical outcomes of PT. Therefore, we propose that a comprehensive diagnostic evaluation for PT, which includes preoperative TBCT, WOT, and intraoperative findings, may be essential in identifying the best surgical approaches and ensuring successful surgical results. Although the prior report primarily highlighted the diagnostic significance of a new WOT based on potential PT mechanisms [13], our study aims to underscore the importance of WOT in deciding surgical procedures, in conjunction with surgical findings and outcomes.

Our study has certain limitations that should be acknowledged and addressed in future research. Firstly, our study was retrospective in nature, with a relatively small sample size, and all surgeries were conducted by a single surgeon at one institution. Future research should be prospective, encompassing a larger sample size, and should include data from SS-R operations performed by multiple surgeons across various hospitals, all using the same method. Secondly, we only analyzed subjective outcomes when evaluating the surgical results in this study. Objective outcomes, such as those provided by Lee et al. [21] should be considered in the analysis of PT. Finally, the evaluation of the surgical management efficacy of PMEV in this study may have been limited due to the inclusion of only one patient. To evaluate surgical outcomes, we need data from a larger number of patients with PMEV causing PT who have undergone emissary vein ligation surgery.