Novel Grading System of Sigmoid Sinus Dehiscence for Radiologic Evaluation of Pulsatile Tinnitus

Background: There is no consensus on the prevalence of sigmoid sinus dehiscence, with each study offering various definitions and mechanisms of symptoms. Patients who undergo resurfacing surgery for sigmoid sinus dehiscence do so for the defining symptom of pulsatile tinnitus that they experience. Few studies have considered the prevalence of this bony abnormality in asymptomatic populations and those that have find disparate results ranging from 1 to 18%. Understanding a nonpulsatile tinnitus population’s prevalence of sigmoid sinus dehiscence will clarify how distinct this abnormality is to pulsatile tinnitus patients and which types of sigmoid sinus dehiscence are less prevalent in nonsymptomatic patients and more likely to be contributing to symptoms. This study analyzes a cohort of patients without pulsatile tinnitus to characterize the prevalence and types of sigmoid sinus wall anomalies in a nonsymptomatic cohort. In this analysis, a grading system is developed to standardize sigmoid sinus dehiscence.

Methods: In this retrospective study, temporal bone CT scans of 91 patients without pulsatile tinnitus at a single institution were analyzed for sigmoid sinus dehiscence. The dehiscence was divided into three grades: grade 1 indicating a micro dehiscence of <3.5 mm with an opening to the mastoid air cells, grade 2 indicating a major dehiscence of >3.5 mm with an opening to the mastoid air cells, and grade 3 indicating a sigmoid sinus wall dehiscence that significantly opens directly to the underlying tissue rather than into the mastoid air cells. Dehiscences were measured for their greatest distances.

Results: In nonsymptomatic patients, sigmoid sinus dehiscence occurred in 34% of the cohort. Of these dehiscences, 75% were grade 1 and 25% were grade 2. The range of dehiscence measurements for grade 1 dehiscences was 0.9 to 3.4 mm. The range of dehiscence measurements for grade 2 was 4 to 7.5 mm. There were no cases of grade 3 dehiscence among this cohort.

Conclusion: Sigmoid sinus dehiscence occurred in over a third of our nonsymptomatic cohort. While all grades of sigmoid sinus dehiscence may currently be treated surgically, it is important to consider that a large portion of nonpulsatile tinnitus patients may have these sigmoid sinus anomalies asymptomatically. This grading system allows for the standardization of sigmoid sinus dehiscence definition and severity in future studies. Grade 3 dehiscences were completely absent in this cohort of nonpulsatile tinnitus patients. This type of significant dehiscence through the temporal bone leaving the underlying tissue exposed with no bony covering over the sinus is rare and less likely an incidental finding. Larger cohort studies are necessary and should consider which grades of dehiscence are most common in patients with pulsatile tinnitus, particularly in patients undergoing sigmoid sinus wall reconstruction to clarify which grades of sigmoid sinus wall anomaly are most responsive to surgical repair.

No conflict of interest has been declared by the author(s).