Novel grading system of sigmoid sinus dehiscence for radiologic evaluation of pulsatile tinnitus

Background: Sigmoid sinus dehiscence (SSD) is an important etiology of pulsatile tinnitus (PT) though there is currently no consensus on the prevalence of SSD in non-PT populations. This study establishes a grading system of SSD and analyzes a non-PT cohort for prevalence of SSD. Methods: In this retrospective study temporal bone CT scans of 91 patients without PT were analyzed for SSD. 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 opening directly to the underlying tissue. Results: In patients without PT, SSD occurred in 34% of the cohort. Of these, 75% were Grade 1 and 25% were Grade 2. The range of dehiscence measurements for Grade 1 dehiscences was 0.9?3.4 mm. The range of dehiscence measurements for Grade 2 was 4?7.5 mm. There were no cases of Grade 3 dehiscence among this cohort. Conclusions: SSD occurred in over a third of our non-symptomatic cohort. While all grades of SSD may currently be treated surgically, a large portion of non-PT patients may have these sigmoid sinus anomalies asymptomatically. This grading system allows for the standardization of SSD definition and severity in future studies. Grade 3 dehiscences were completely absent in this cohort of non-PT patients. ? 2021 Published by Elsevier Ltd.