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.