The Effect of Transverse Sinus Stenosis Caused by Arachnoid Granulation on Patients with Venous Pulsatile Tinnitus: A Multiphysics Interaction Simulation Investigation.

This study aimed to investigate the effect of the transverse sinus (TS) stenosis (TSS) position caused by arachnoid granulation on patients with venous pulsatile tinnitus (VPT) and to further identify the types of TSS that are of therapeutic significance for patients. Multiphysics interaction models of six patients with moderate TSS caused by arachnoid granulation and virtual stent placement in TSS were reconstructed, including three patients with TSS located in the middle segment of the TS (group 1) and three patients with TTS in the middle and proximal involvement segment of the TS (group 2). The transient multiphysics interaction simulation method was applied to elucidate the differences in biomechanical and acoustic parameters between the two groups. The results revealed that the blood flow pattern at the TS and sigmoid sinus junction was significantly changed depending on the stenosis position. Preoperative patients had increased blood flow in the TSS region and TSS downstream where the blood flow impacted the vessel wall. In group 1, the postoperative blood flow pattern, average wall pressure, vessel wall vibration, and sound pressure level of the three patients were comparable to the preoperative state. However, the postoperative blood flow velocity decreased in group 2. The postoperative average wall pressure, vessel wall vibration, and sound pressure level of the three patients were significantly improved compared with the preoperative state. Intravascular intervention therapy should be considered for patients with moderate TSS caused by arachnoid granulations in the middle and proximal involvement segment of the TS. TSS might not be considered the cause of VPT symptoms in patients with moderate TSS caused by arachnoid granulation in the middle segment of the TS.

Fluid-structure interaction study on the causes of mending material damage after sigmoid sinus wall reconstruction.

BACKGROUND AND OBJECTIVE: Sigmoid Sinus (SS) Wall Reconstruction (SSWR) is the mainstream treatment for pulsatile tinnitus (PT), but it has a high risk of recurrence. The damage of mending material is the key cause of recurrence, and its hemodynamic mechanism is still unclear. The purpose of this study was to investigate the hemodynamic causes of mending material breakage. METHODS: In this study, six patient-specific geometric models were reconstructed based on the data of the computed tomography angiography (CTA). The transient fluid-structure coupling method was performed to clarify the hemodynamic state of sigmoid sinus and the biomechanical state of the mending material. The distribution of stress and displacement and the flow pattern were calculated to evaluate the hemodynamic and biomechanics difference at the mending material area. RESULTS: The area of blood flow impact in some patients (2/6) was consistent with the damaged location of the mending material. The average stress (6/6) and average displacement (6/6) of damaged mending material were higher than those of complete mending material. All (6/6) patients showed that the high-stress and high-displacement proportion of the DMM region was higher than that of the CMM region. Moreover, the average stress fluctuation (6/6) and average displacement (6/6) fluctuation degree of damaged mending material is larger than that of complete mending material. CONCLUSIONS: The impact of blood and the uneven stress and displacement fluctuation of the mending material may be the causes of mending material damage. High stress and high displacement might be the key causes of the mending material damage.

Multiphysics Interaction Analysis of the Therapeutic Effects of the Sigmoid Sinus Wall Reconstruction in Patients with Venous Pulsatile Tinnitus.

Sigmoid sinus wall dehiscence (SSWD) is an important etiology of venous pulsatile tinnitus (VPT) and is treated by sigmoid sinus wall reconstruction (SSWR). This study aimed to investigate the therapeutic effects of the different degrees of SSWR and the prognostic effect in patients with VPT. Personalized models of three patients with SSWD (control), 3/4SSWD, 1/2SSWD, 1/4SSWD, and 0SSWD were reconstructed. A multiphysics interaction approach was applied to elucidate the biomechanical and acoustic changes. Results revealed that after SSWR, the average pressure of venous vessel on the SSWD region reduced by 33.70 ± 12.53%, 35.86 ± 12.39%, and 39.70 ± 12.45% (mean ± SD) in three patients with 3/4SSWD, 1/2SSWD, and 1/4SSWD. The maximum displacement of the SSWR region reduced by 25.91 ± 30.20%, 37.20 ± 31.47%, 52.60 ± 34.66%, and 79.35 ± 18.13% (mean ± SD) in three patients with 3/4SSWD, 1/2SSWD, 1/4SSWD, and 0SSWD, with a magnitude approximately 10-3 times that of the venous vessel in the SSWD region. The sound pressure level at the tympanum reduced by 23.72 ± 1.91%, 31.03 ± 14.40%, 45.62 ± 19.11%, and 128.46 ± 15.46% (mean ± SD). The SSWR region was still loaded with high stress in comparison to the surrounding region. The SSWR region of the temporal bone effectively shielded the high wall pressure and blocked the transmission of venous vessel vibration to the inner ear. Patients with inadequate SSWR still had residual VPT symptoms despite the remission of VPT symptoms. Complete SSWR could completely solve VPT issues. High-stress distribution of the SSWR region may be the cause of the recurrence of VPT symptoms.

Effects of Different Degrees of Extraluminal Compression on Hemodynamics in a Prominent Transverse-Sigmoid Sinus Junction.

OBJECTIVES: To simulate hemodynamic changes after extraluminal compression in pulsatile tinnitus (PT) patients with a prominent transverse-sigmoid sinus junction (PTSJ). METHODS: One patient-specific case was reconstructed based on computed tomography venography (CTV) images of a PT patient. The compression degree served as a new index in this study. Cases with 10, 20, 30, 40, 50, 60, 70, 80, and 90% of the compression degree of the control subject were constructed. Steady-state computational fluid dynamics (CFD) were assessed. The wall pressure distribution, wall maximum pressure (P max ) and flow pattern (velocity streamlines and velocity vector) of the PTSJ were calculated to evaluate hemodynamic differences among all cases. RESULTS: With increasing compression, the wall pressure at the compression point and downstream of the PTSJ decreased but increased upstream. When the compression degree exceeded 70%, the upstream pressure increased significantly. Above 50% compression, the blood flow pattern downstream of the sigmoid sinus tended to spiral, especially after 80% compression. Beyond 60% compression, the blood flow pattern under the compression axis became more medial. CONCLUSION: Mechanical compression of PTSJ changes wall pressure and blood flow patterns. The degree of compression should be carefully observed to avoid possible complications or reoccurrence.

Hemodynamics study on the relationship between the sigmoid sinus wall dehiscence and the blood flow pattern of the transverse sinus and sigmoid sinus junction.

Sigmoid sinus wall dehiscence (SSWD) is a common pathophysiology of patients with pulsatile tinnitus (PT). However, the pathological mechanism of SSWD is unclear. This study aimed to investigate the relationship between the position of the SSWD and blood flow pattern of the transverse sinus and sigmoid sinus (TS-SS) junction. The impact of the blood flow was hypothesized to be the pathological mechanism of SSWD. Twenty patients and two healthy volunteers were analyzed retrospectively, and transient computer fluid dynamics was used to verify this hypothesis. A 4D flow magnetic resonance imaging experiment was performed to validate the numerical simulation. The position of high-velocity blood flow impacting the vessel wall (17/20) was consistent with SSWD. In healthy volunteers, the temporal bone was thin where the blood flow impacted the blood vessel wall. The average wall shear stress (20/20) and pressure (18/20) of the SSWD area (peak) were higher than those of sigmoid sinus wall anomalies (the contact area between the vessel wall and the temporal bone at the TS-SS junction). The average wall pressure percentage differences of 16/20, 11/20, and 4/20 patients were more than 5%, 10%, and 20%, respectively. The average wall shear stress percentage differences of 20/20, 18/20, and 16/20 patients were more than 5%, 10%, and 20%, respectively. In brief, the blood flow of the TS-SS junction impacted the vessel wall and increased wall pressure, which might be an important pathological mechanism of SSWD. This study could serve as a basis for the diagnosis and SSWD resurfacing surgery of patients with PT induced by SSWD.

Hemodynamic mechanism of pulsatile tinnitus caused by venous diverticulum treated with coil embolization.

BACKGROUND AND OBJECTIVE: Coil embolization has become a new treatment method for pulsatile tinnitus (PT) caused by sigmoid sinus diverticulum (SSD). Although this therapy has achieved good results in clinical reports, the hemodynamic mechanism of coils in the treatment of PT in SSD remained unclear. METHODS: Finite element method (FEM) and computational fluid dynamics (CFD) were combined to explore the hemodynamic mechanism of coil embolization in SSD treatment. Three personalized geometric models of sigmoid sinus were established according to the CTA data of patients. Coil model were established by FEM, and the hemodynamic differences of SSD before and after coiling were compared by transient CFD method. RESULTS: Velocity streamlines disappeared in the SSD after coiling. At the peak time (t1 = 0.22 s), the SSD-average velocity decreased in every patient. The average value of the decreased in three patients was 0.154 ± 0.028 m/s (mean ± SD). Wall average pressure (Pavg) also showed a decline in every patient. Average of decrements of three patients was 17.69 ± 4.91 Pa (mean ± SD). Average WSS (WSSavg) was also reduced in every patient. The average value of WSS drop was 9.74 ± 3.02 Pa (mean ± SD). After coiling, the proportion of low-velocity region in the sigmoid sinus cortical plate dehiscence (SSCPD) area increased. Average of increments was 22.1 ± 5.36% (mean ± SD). CONCLUSIONS: A reduction in SSD-average velocity, wall pressure, and WSS were the short-term hemodynamic mechanism of coil embolization for PT. Coil embolization increased the proportion of low-velocity region in the SSCPD area, thereby creating a hemodynamic environment that easily produced thrombus and protects blood vessels from the impact of blood flow. This phenomenon was the long-term effect of coil embolization.

Effect of Emissary Vein on Hemodynamics of the Transverse- Sigmoid Sinus Junction.

Objective: To investigate the effect of the blood flow direction and afflux location of emissary veins (EVs) on the hemodynamics of the transverse-sigmoid sinus (TS-SS) junction. Methods: A patient-specific geometric model was constructed using computed tomography venography (CTV) and 4D flow MR data from a venous pulsatile tinnitus (PT) patient. New EV models were assembled with the afflux at the superior, middle and inferior portions of the SS from the original model, and inlet and outlet directions were applied. Computational fluid dynamics (CFD) simulation was performed to analyze the wall pressure and flow pattern of the TS-SS junction in each condition. Results: Compared to the model without EVs, the wall pressure was greatly increased in models with inlet flow and greatly decreased in models with outlet flow. The more closely the EV approached the TS-SS, the larger the pressure in models with inlet flow, and the smaller the pressure in models with outlet flow. The flow streamline in the lateral part of the TS-SS junction was smooth in all models. The streamlines in the medial part were regular spirals in outlet models and chaotic in inlet models. The streamlines showed no obvious changes regardless of afflux location. The velocity at the TS-SS junction of inlet models were uniform, medium-low flow rate, while in control and outlet models were the lateral high flow rate and the central low flow rate. Conclusion: The flow direction and afflux location of EVs affect the hemodynamics of the TS-SS junction, which may influence the severity of PT.

Multiphysics coupling numerical simulation of flow-diverting stents in the treatment of patients with pulsatile tinnitus.

Patients with pulsatile tinnitus (PT) have unstable treatment effects after resurfacing surgery. Flow-diverting stents (FDS) are proposed as a potential method for the treatment of PT, but the therapeutic effect is not clear. This study aimed to investigate the efficacy of FDS in the treatment of patients with PT induced by sigmoid sinus diverticulum (SSD) and sigmoid sinus wall dehiscence (SSWD). In addition, we aimed to explore the treatment mechanism of PT. Transient-state multiphysics coupling numerical simulation method based on computed tomography angiography of five patients was used to clarify the biomechanical and acoustic states before and after FDS placement. FDS was placed to prevent the blood flow from impacting the vessel wall in the SSD and SSWD areas. Low blood flow velocity (<0.0391 m/s), high relative residence time (>10 Pa-1 ), and low wall shear stress of SSD might lead to thrombosis after FDS placement. The average pressure on the SSWD area of each patient decreased by 13.77%, 18.82%, 29.23%, 19.03%, and 11.20%. The average displacement of the vessel wall on the SSWD area showed acute pulsation and decreased by 15.29%, 14.64%, 30.22%, 41.03%, and 21.28%. The average sound pressure level at the tympanum decreased by 14.01%, 9.33%, 17.66%, 18.88%, and 25.18%, respectively. In brief, FDS was placed to avoid blood flow impacting vessels and reduce the vibration of vessels in the short term, thereby attenuating the degree of PT. The long-term prognosis was that the SSWD area was blocked after SSD thrombosis. Therefore, FDS might be an effective method for the treatment of PT induced by SSD and SSWD. This study would provide a theoretical basis for the treatment of PT and an exploration of FDS design in the treatment of PT.

Hemodynamic study of the therapeutic effects of the different degrees of sigmoid sinus diverticulum reconstruction on patients.

Sigmoid sinus diverticulum (SSD) is a common pathophysiology of pulsatile tinnitus (PT) and mainly treated by SSD reconstruction surgery. The degree of reconstruction is an important indicator of SSD reconstruction surgery, but its impact on the effect of SSD reconstruction is unclear. This study aimed to clarify the effect of the degree of SSD reconstruction on diverticulum reconstruction surgical treatment. One patient-specific case (control subject) was reconstructed based on the computed tomography angiography (CTA) images of patients with PT. The SSD reconstruction degree was used as a new index in this study. And the case of 30% (case 1), 60% (case 2), and 100% (case 3) of the diverticulum reconstruction degree of control subject were constructed. Transient-state computational fluid dynamics was performed. Wall pressure distribution, wall average pressure (Pavg) of SSD, flow pattern (velocity streamlines and velocity vector), wall shear stress (WSS) and averaged WSS (WSSavg) were calculated and used in evaluating the hemodynamic differences among the DRD cases. Results demonstrated that change in SSD pressure was not linear with increase in DRD. The DRD that reached 60% of the original diverticulum was effective. At the peak point of the inlet boundary condition (T1 = 0.22s), the Pavg of SSD had a nonlinear change (control subject, 126.967 Pa vs. case 1, 126.274 Pa vs. case 2, 106.897 Pa vs. case 3, 94.116 Pa). Flow vorticity decreased gradually, and the smoothness of the streamlines increased with DRD. WSSavg slightly changed with increasing DRD. The high-speed flow blood hit the diverticulum entrance and then swirled to hit the area of the sigmoid sinus wall abnormal. It was concluded that flow patterns related to PT differ with DRD. In diverticulum reconstruction surgery, there is a threshold value, and only when the DRD exceeds this value (60% or 70% or 80%), it will have a noticeable effect. In this study, DRD should at least reach 60% of the original diverticulum. When DRD is insufficient, hemodynamic change in the diverticulum is small, and the PT may have remained. SSD may be caused by high-speed blood flow.

Hemodynamic study on the different therapeutic effects of SSWD resurfacing surgery on patients with pulsatile tinnitus.

Sigmoid sinus wall anomalies (SSWA) are a common pathophysiology of pulsatile tinnitus (PT) and usually treated by sigmoid sinus wall dehiscence (SSWD) resurfacing surgery. However, symptoms of tinnitus remain unrelieved after surgery in some patients with PT, and even new tinnitus appears. The cause of the difference in therapeutic effects is unclear. In this study, eight patient-specific SSWA geometric models were reconstructed on the basis of computed tomography angiography, including four cases of postoperative rehabilitation (group 1, 1-4 cases) and four cases of non-rehabilitation (group 2, 5-8 cases). Transient-state computational fluid dynamics (CFD) was performed to clarify the SS blood flow pattern and hemodynamic states. The wall pressure distribution on SSWA area, pressure difference, and flow pattern in SS were calculated to evaluate the hemodynamic changes of rehabilitation and non-rehabilitation patients before and after surgery. The difference of hemodynamics between these patients was statistically analyzed. The accuracy of CFD simulation was evaluated by cross validating the numerical and particle image velocimetry experimental results. Results showed that the SSWA area in patients with PT was loaded with high pressure. No difference was found in the hemodynamic characteristics between the two groups pre- and postoperation. When the average pressure (Pavg) and time-average Pavg (TAPavg) on the SSWA area were studied, the TAPavg difference pre- and postoperation between the two groups was found significant (p = 0.0021). The TAPavg difference had a negative change in postoperative rehabilitation patients (case 1, -44.49 Pa vs. case 2, -15.85 Pa vs. case 3, -25.88 Pa vs. case 4, -16.58 Pa). The postoperative TAPavg of non-rehabilitation patients was higher than the preoperative one (case 5, 24.70 Pa vs. case 6, 28.56 Pa vs. case 7, 5.81 Pa vs. case 8, 13.04 Pa). The velocity streamlines in the SS with rehabilitation became smoother and more regular than that without rehabilitation. By contrast, the velocity streamlines in SS without rehabilitation showed increased twisting and curling. No difference was found in time-average volume-averaged vorticity (TAVavgV) between the two groups. Therefore, the high pressure of the vessel wall on SSWA area was one of the causes of PT. The variation of SSWA wall pressure difference before and after PT was the cause of the difference in therapeutic effects after SSWD resurfacing surgery. In patients with SSWA, disordered blood flow in SS was another cause of PT. SSWD repair may relieve tinnitus to some extent, but blood flow disorders may still arise.