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).
Conclusion—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.
Thrombosis of the cerebral dural venous sinuses is an uncommon but potentially devastating cause of stroke, which has a predilection for women and the young. It occurs in 3 to 4 people per 1 000 000 population, and an estimated 86% of cases involve the transverse sinuses.1 The diagnosis of transverse sinus venous thrombosis, however, can be difficult to make given its nonspecific clinical signs and the lack of specificity of MR venograms (MRVs) alone.2 Autopsy and cerebral angiographic studies have consistently shown that a dominant transverse sinus is common, most commonly on the left.2–4 Only 37% to 50% of patients studied have equally sized transverse sinuses.2–4 In 1 study, 22% of normal subjects had 1 transverse sinus, which did not opacify at all by conventional angiography.3 Therefore, it is not uncommon to see dropout on MRV of 1 transverse sinus, suggesting occlusion due to thrombus, when congenital atresia may instead exist.
Standard noncontrast CT of the brain can give a clue to whether a transverse sinus is occluded by clot. Narrowing of the sigmoid plate notch on CT can suggest congenital narrowing or sinus atresia as opposed to clot as a cause of decreased flow.5 This asymmetry in sigmoid plate notches, however, has not been studied in any systematic way as a method to differentiate atretic from occluded sinuses. We hypothesized that, among individuals with absent signal of a transverse sinus on MRV, comparison of the sigmoid notches on noncontrast brain CT can differentiate transverse sinus clot from a congenitally atretic sinus.
The Johns Hopkins Institutional Review Board approved this study. Subjects were selected based on either a sequential review of MRV scans from stroke inpatients or selection by International Classification of Diseases, 9th Revision codes after hospital discharge from Johns Hopkins Hospital or Johns Hopkins Bayview Medical Center from 2007 to 2010. The final data set consisted of individuals with absent signal on MRV in 1 of the transverse sinuses. We oversampled individuals with transverse sinus clot, so our sample does not represent the true prevalence of transverse sinus thrombosis.
A total of 53 patients were included in the study. A blinded investigator (R.H.L.) reviewed all available historical, diagnostic, and imaging studies and then classified each subject as either having clot in the transverse sinus (n=11) or having an atretic sinus (n=43). This complete data review was considered the gold standard for adjudicating transverse sinus clot versus congenital sinus atresia.
A “positive” sigmoid notch sign was defined as an asymmetrically smaller sigmoid notch on the side of MRV loss of transverse sinus signal (Figure). A single slice of each subject's brain CT scan at the level of the sigmoid plate with clear visualization of the bilateral sigmoid notches through which the transverse sinus runs (Figure) was selected and marked with the side of abnormal transverse sinus on MRV. The blinded neurologists adjudicated each CT as having a negative (consistent with transverse sinus thrombosis) or positive sigmoid notch sign (sigmoid sinus congenital atresia) on the side of MRV signal dropout. The blinded reviewers were not given access to any other imaging studies, and their assessment was entirely due to visual estimation from the image, but they could ask for an additional CT slice from the same scan if needed. In the case of disagreement, a consensus rating was made by the reviewers.
Interrater reliability was calculated using a κ statistic. Sensitivity and specificity were calculated relative to the gold standard as were false-positive and -negative rates. Secondary analyses repeated analyses for right versus left signal dropout.
Of the 53 subjects, 11 had venous clot and 42 had an atretic sinus by the gold standard. Of the 11 subjects with clot, 1 subject had a right-sided clot and an atretic left transverse sinus. Another subject had both atresia and clot on the left. Seven of the 11 subjects with clot had right-sided clot. Overall MRV signal dropout was identified on the right for 19 (35.9%) of the 53 patients and the majority of atretic sinuses occurred on the left.
Each blinded neurologist had a sensitivity of 91% (detecting 10 of 11 clots based on a negative sigmoid notch sign). Specificity was 71% for 1 reviewer (identifying a positive sign in 30 of 42 atretic sinus cases) and 81% for the other (a positive sign in 34 of 42 cases). Cohen κ was 0.60. The consensus sensitivity was 91% and specificity was 86%. The false-positive rate was 14.3% (proportion of individuals with atretic sinus who had a negative sigmoid notch sign, suggesting presence of a thrombus), and the false-negative rate was 9.1% (Table 1). Sensitivity and specificity improved to 100% and 92%, respectively, in the 19 cases in which MRV dropout was on the right side (Table 2).
The diagnosis of cerebral sinus thrombosis can be difficult given its nonspecific clinical presentation. Due to the potential seriousness of this diagnosis, a screening tool that is both rapid and highly sensitive to the presence of venous clot is needed. MRV flow studies often overcall occlusion, and a congenitally atretic transverse sinus may appear identical in appearance to a transverse sinus thrombosis. Four-vessel cerebral angiography, the current gold standard in diagnosing thrombosis, can be time-consuming and carries potential risk.
The sigmoid notch sign, as described in this study, is a highly sensitive and specific measure of differentiating clot from atretic sinus when dropout of the transverse sinus is visualized on MRV. With the addition of the sigmoid notch sign on CT (which was likely already obtained, so is cost-effective) to the rest of the clinical presentation, an immediate decision can be made as to whether this is likely a clot requiring anticoagulation or simply an atretic sinus. This technique can be used by specialist or nonspecialist neurologists.
This study is limited by our relatively small sample size, because true transverse clot thrombosis is a relatively rare finding. In addition, our gold standard was based on review of all available records but in the majority of cases did not include cerebral angiography. However, we are confident that our final gold standard classifications were accurate because they were based on the entire set of brain MR images and medical records available. In addition, although the number of patients with thrombosis was especially low, the sample used to calculate specificity is larger with a narrower CI. This allows a clinician to “rule out” a clot with fairly high confidence if there is an asymmetrically smaller sigmoid notch on the same side as absent signal on an MRV.
The sigmoid notch sign, a simple and quick tool, is highly sensitive and specific. This makes it potentially useful to neurologists, in conjunction with clinical judgment, for diagnosis of transverse sinus venous thrombosis when dropout of flow is seen on MRV. Further studies are needed to evaluate its use prospectively and in comparison with conventional angiography.
Sources of Funding
Dr Gottesman is supported by the National Institute on Aging (National Institute of Neurological Disorders and Stroke) RO1 AG040282-01.
- Received March 2, 2012.
- Accepted March 22, 2012.
- © 2012 American Heart Association, Inc.