Differentiation of transverse sinus thrombosis from congenitally atretic cerebral transverse sinus with CT.

BACKGROUND AND PURPOSE: Transverse sinus thrombosis can have nonspecific clinical and radiographic signs. We hypothesized that the novel "sigmoid notch sign" (on head CT) can help differentiate transverse sinus thrombosis from a congenitally atretic sinus among individuals with absent signal in 1 transverse sinus by MR venography.

METHODS

We retrospectively evaluated 53 subjects with a unilaterally absent transverse sinus signal on MR venography. Eleven had true transverse sinus thrombosis and 42 had an atretic transverse sinus. Reviewers were trained in the sigmoid notch sign: "positive" if 1 of the sigmoid notches was asymmetrically smaller than the other, consistent with a congenitally absent transverse sinus on that side. This sign was scored on CT scans by 2 blinded reviewers to determine if signal dropout was clot or atretic sinus. A consensus rating was reached when the reviewers disagreed. Characteristics of the sigmoid notch sign as a diagnostic test were compared with a gold standard of full chart review by an independent reviewer.

RESULTS

Each reviewer had a sensitivity of 91% (detecting 10 of 11 clots based on a negative sigmoid notch sign) and specificity of 71% to 81%; consensus specificity increased to 86% (36 of 42 individuals with an atretic sinus had a positive notch sign, detecting atretic sinuses based on presence of the sign).

CONCLUSIONS

Asymmetries of the sigmoid notches on noncontrast brain CT is a very sensitive and specific measure of differentiating transverse sinus thrombosis from an atretic transverse sinus when absence of transverse sinus flow is visualized on MR venography.