MR Venous Flow in Sigmoid Sinus Diverticulum

Abstract

Background and purpose: Case reports demonstrate that coiling of a sigmoid sinus diverticulum can treat pulsatile tinnitus. We hypothesized that MR imaging 4D flow and computational fluid dynamics would reveal distinct blood flow patterns in the venous outflow tract in these patients.

Materials and methods: Patients with pulsatile tinnitus of suspected venous etiology underwent MR imaging at 3T, using venous phase contrast-enhanced MR angiography, 4D flow, and 2D phase contrast. The contrast-enhanced MRA contours were evaluated to determine the presence and extent of a sigmoid sinus diverticulum. Computational fluid dynamics analysis was performed using the 4D flow inlet flow and the luminal contours from contrast-enhanced MRA as boundary conditions. In addition, computational fluid dynamics was performed for the expected post treatment conditions by smoothing the venous geometry to exclude the sigmoid sinus diverticulum from the anatomic boundary conditions. Streamlines were generated from the 4D flow and computational fluid dynamics velocity maps, and flow patterns were examined for the presence of rotational components.

Results: Twenty-five patients with pulsatile tinnitus of suspected venous etiology and 10 control subjects were enrolled. Five (20%) of the symptomatic subjects had sigmoid sinus diverticula, all associated with an upstream stenosis. In each of these patients, but none of the controls, a stenosis-related flow jet was directed toward the opening of the sigmoid sinus diverticulum with rotational flow patterns in the sigmoid sinus diverticulum and parent sigmoid sinus on both 4D flow and computational fluid dynamics.

Conclusions: Consistent patterns of blood flow can be visualized in a sigmoid sinus diverticulum and the parent sinus using 4D flow and computational fluid dynamics. Strong components of rotational blood flow were seen in subjects with sigmoid sinus diverticula that were absent in controls.

Fig 1.

MRA isosurface MIP rendering, CFD-predicted flow fields, and 4D-flow MR imaging from 6 subjects. The first subject is a control subject. The other 5 are subjects clinically suspected of having a venous cause for pulsatile tinnitus who were found to have a sigmoid sinus diverticulum on MRA. The following observations are made in symptomatic subjects with a sigmoid diverticulum: 1) high velocity flow jet in an upstream stenosis in the transverse sinus directed at the SSD opening; 2) a flow jet into the SSD along the long axis of the SSD, either anteriorly or laterally directed; 3) a vortex of flow in the SSD; and 4) a strong vortex component of flow in the sigmoid sinus from the SSD. In the control subject, none of these flow components were present.

Fig 2.

MRA, CFD simulation, and 4D-flow MR imaging from subject 2 before and after surgical exclusion of her sigmoid sinus diverticulum, which resulted in resolution of symptoms. There was an absence of flow in the SSD as well as lack of a vortex in the downstream sigmoid sinus. Only the SSD was excluded from the CFD flow domain. Thus, the flow jet through the proximal stenosis is unchanged.