Unilateral Nonvisualization of a Transverse Dural Sinus on Phase-Contrast MRV: Frequency and Differentiation from Sinus Thrombosis on Noncontrast MRI

DISCUSSION

To the best of our knowledge, for the first time, our results show that DWI signal abnormality, both T2* blooming artifacts and hyperintense signal, can be a powerful diagnostic tool for the clarification of equivocal findings of TST+ on noncontrast MRVs, with a sensitivity of 93.8% and a specificity of 100% and interrater reliability of κ = 0.86. While most prior work described much lower sensitivities for the detection of DST with DWI sequences, these studies did not assess T2* blooming artifacts on DWI.^12,22 However, our results are supported in prior work by Yildiz et al²³ on cortical vein thrombosis, which demonstrated sensitivities of up to 84% on DWI if both hyperintense signal and T2* blooming artifacts were assessed. It is possible that our higher sensitivity for DWI is because the current study aims to clarify a specific diagnostic conundrum in a much larger anatomic structure (TS) on PC-MRV and due to our assessment of both DWI hyperintense signal and T2* blooming artifacts. Thus, in the setting of NVTS on PC-MRV, DWI signal abnormality is virtually diagnostic for TST+, with the interrater reliability ranging from substantial to almost perfect agreement in the acute-to-subacute setting. This may prove to be a powerful tool in overcoming the limitations of commonly used noncontrast MRV (such as 2D-TOF, 3 D-TOF, and PC-MRV) when the use of gadolinium contrast is contraindicated for criterion standard CE-MRV techniques.

The fairly low sensitivity and variable specificity of individual T1, T2, FLAIR, and GRE sequences in the detection of DST has been previously documented, and our results support the earlier findings. For example, prior work in detecting DST in all major dural venous sinuses by Sadigh et al²² found that for 1 reviewer, the sensitivity and specificity, respectively, of T1 noncontrast was 55% and 55%; for T2, they were 58% and 97%; for FLAIR, they were 67% and 62%; for GRE, they were 67% and 62%; and for DWI (high signal only), they were 25% and 93%. The above sensitivities are similar to those reported in the current study focusing on the TS: For example, the sensitivity for the detection of TST+ is 62.5% for T2 and 68.8% for FLAIR. The much higher specificity in our cohort may be secondary to increased pretest probability for TST+, given that our analysis was limited to patients with abnormal findings on PC-MRV. As discussed above, the prominent difference between the current report and previously reported DWI sensitivities is presumed secondary to the inclusion of T2* blooming artifacts on DWI as abnormal in the current study.

A combination of all MRI– sequences (excluding DWI) results in an improved sensitivity of 87.5% and a decreased specificity of 92.9%, similar to that reported in a large series of 429 patients in which standard MR imaging sequences, including postcontrast sequences, had a combined sensitivity of 79.2% and specificity of 89.9% for the detection of DST (including the superior sagittal, sigmoid, and transverse sinuses).¹²

T1, T2, and FLAIR had false-negative rates up to 40%, thought to be likely secondary to previously described signal characteristics of acute thrombus, which can mimic normal flow voids, in the dural sinuses, reviewed by Bonneville²⁴ in 2014, and have been described as a factor underlying the false-negative results in noncontrast MRV-DST detection. We observed that GRE T2* blooming artifacts alone detected only 8/16 (50%) cases of TST+. This is also presumed to be due to changes in T2* signal during the evolution from the acute-to-subacute phase,²⁴ supporting T2* blooming artifacts being sensitive for acute thrombus but less so for subacute-to-chronic thrombi (as characterized by T1, T2, and FLAIR hyperintense TS signal). However, at least 2 prior studies have reported that GRE is highly sensitive to not only acute but also subacute thrombosis (also characterized by T1, T2, and FLAIR hyperintense signal), though not for chronic DST.^25,26 Of note, Altinkaya et al²⁶ has demonstrated that the sensitivity of GRE for TST+ and sigmoid sinus thrombosis is decreased due to artifacts from the skull base, potentially explaining the discrepancy between the prior studies and the current study, which specifically focused on the TS.

Fifty-six of 192 (29.2%) PC-MRVs without TST+ demonstrated NVTS. Of these, the left TS was NV 23.4% of the time and was considered smaller versus the right TS in 24.0% of cases. The right TS was NV in 5.7% of cases and was considered smaller versus the left TS in 3.1% of cases. These findings are concordant with reports across multiple imaging modalities showing that the left and right TSs are hypoplastic in 39%–60% and 6%–14% of patients, respectively.^27⇓-29 The percentages reported in the current work are lower than of those previously reported, likely secondary to our strict criteria of NV as >50% nonvisualized relative to the contralateral side.

Our limited dataset demonstrates no association with hypoplastic TS and TST+, in disagreement with a recent case-control report correlating TS hypoplasia and increased relative risk for TST+.²⁸ However, an earlier study described the opposite finding that the dominant TS was more likely to thrombose, suggesting that more work will be needed in the future to elucidate whether there is a correlation between TST+ and TS size.³⁰

This study has several limitations. First, the study inclusion criteria of patients who had PC-MRV, noncontrast MR imaging, and MPRAGE+ performed within 24 hours of each other meant that not all patients with TST+ were selected. Thus, the true prevalence of the disease, positive predictive value, negative predictive value, and accuracy could not be calculated, potentially decreasing the generalizability of the results and introducing unforeseen selection bias. Second, because the study was designed specifically to assess the utility of standard MR imaging sequences in the diagnosis of TS thrombosis in a subset of patients with presumed higher pretest probability based on abnormal noncontrast MRV findings, we did not perform an analysis of patients with normal MRV imaging findings. While it is known that conventional MR imaging sequences result in false-positive detection for DST (specificity of 14%–89.9%), a comparison of conventional MR imaging sequence performance in patients without NVTS for detection of TS thrombosis in the current study with prior work could have yielded information on population differences and selection biases.^12,22

Third, although MPRAGE+ is superior to PC-MRV and MRI– in the diagnosis of TST and is thus established as the diagnostic criterion standard for TST+ in this study, some authors have shown that MPRAGE+ demonstrates decreased sensitivity compared with CE-MRV.^9,10 This lowered sensitivity has been theorized to be from the time delay following gadolinium administration to image acquisition, causing enhancement of subacute thrombus, thus resulting in false-negative findings. This outcome could result in underreporting of true TST+ in our study and decreases the sensitivity and specificity of noncontrast MR imaging sequences for thrombus detection. Future work using CE-MRV as the diagnostic criterion standard may be required. Fourth, because the diagnosis of DST of the superior sagittal sinus, internal cerebral veins, vein of Galen, and straight sinus is typically less of a diagnostic challenge on noncontrast MRV due to significantly fewer anatomic variations versus the TS, this study did not assess venous anatomy or MRI– signal on the remainder of the dural venous sinuses, limiting the generalizability of the results to DST other than TST+. Finally, our selection criteria excluded patients with known chronic TST+, and our current findings cannot necessarily be extended to the detection of chronic thrombosis. Future work is needed to assess the clinical utility of DWI for thrombi in the more chronic phase.