Danny R. Rose, Jr., MD
Cerebral venous sinus thrombosis (CVST) is a relatively rare form of stroke that typically affects young individuals. Improved methods of diagnosis and treatment have significantly improved outcomes of CVST, but current indirect noninvasive imaging that relies on visualizing venous flow perturbation can lead to delays that may result in increased morbidity and mortality. Magnetic resonance direct thrombus imaging (MRDTI) may improve upon this through its ability to visualize thrombus directly by exploiting the short T1 relaxation time of methemoglobin within the thrombus. To date there has been little study using this imaging modality in the cerebral venous system. Yang et al. sought to investigate the ability of MRDTI (using a so-called “black-blood MR technique” or “MRBTI”) to detect CVST in a prospective study comparing this technique to traditional diagnostic imaging.
Forty-seven patients with signs and symptoms suspicious for CVST were recruited for the study. All patients received CT, MR and Time of Flight MR venography, with five patients also receiving a contrast enhanced CT venogram as well. Two readers performed a consensus reading of all conventional imaging studies with full clinical and outcome information, with a total of 14 venous segments being assessed for thrombi based on the presence or absence of intraluminal filling defects. MRBTI was performed using 3D variable-flip-angle turbo spin echo on a 3.0T scanner. MRBTI images were randomized and presented to two independent readers who were blinded to the diagnostic/therapeutic management of the patients, clinical information and conventional imaging data. Image quality was rated on a 4 point scale with 4 being excellent with no relevant artifacts. The presence or absence of thrombus was recorded for each of the 14 segments assessed via conventional imaging. Patients with CVST detected by MRBTI were divided into two groups based on duration of clinical onset: ≤ 7 days and between 7-30 days.
With conventional imaging, a total of 116 thrombosed venous segments were identified among 23 patients. MRBTI correctly identified 113 out of 116 segments, resulting in a sensitivity of 97.4%. In 527 out of 531 segments, CVST was ruled out correctly with a specificity of 99.3%. Using patient based parameters MRBTI correctly identified all 23 patients with CVST. One false-positive and zero false-negatives were identified, resulting in a sensitivity of 100% and specificity of 95.8%. There were no issues with image quality—647 of 658 segments (98%) were diagnostic according to the 4 point rating scale, and the overall image quality score was 3.5±0.6. Signal-to-noise and contrast-to-noise ratio, another metric of image quality comparing the signal intensity of the thrombus to that of adjacent tissue, was found to have significant differences in all signal measurements taken.
Utilizing MRBTI in CVST was found to approach the high diagnostic accuracy of conventional imaging in this small prospective study. Patients who stand to benefit most include those with renal impairment, which may serve as a contraindication to contrasted imaging, as well as pregnant patients and others where radiation exposure should be avoided. The utility of MRBTI may also extend to monitoring for thrombus progression/resolution, as this imaging modality is able to calculate thrombus volume as well. One significant limitation of the study that limits its widespread use is the use of a 3.0T MRI, which is seldom found outside of academic institutions and tertiary care centers. Other limitations to this study stem primarily stem from the use of a single center and small sample size, thus validation of this study in a multicenter prospective study with a larger enrollment is crucial.