Normal structures in the intracranial dural sinuses: delineation with 3D contrast-enhanced magnetization prepared rapid acquisition gradient-echo imaging sequence.

BACKGROUND AND PURPOSE The potential pitfalls in the diagnosis of dural sinus thrombosis include the presence of arachnoid granulations, intrasinus fibrotic bands (so-called septa), and hypoplasia or aplasia of the dural sinuses. The purpose of this study was to assess the appearance, distribution, and prevalence of arachnoid granulations and septa in the dural sinuses by using a high resolution 3D contrast-enhanced magnetization prepared rapid acquisition gradient-echo (MPRAGE) imaging sequence. METHODS Conventional MR images and contrast-enhanced MPRAGE images of 100 consecutive patients who had no abnormalities of the dural sinuses were retrospectively reviewed. The incidence, site, number, size, signal intensity, and shape of arachnoid granulations and septa within the sinuses and their relationship with adjacent veins were recorded. RESULTS With 3D contrast-enhanced MPRAGE imaging, 433 round, oval, or lobulated focal filling defects were found in a total of 90 patients. Curvilinear septa were observed in 92 patients. Sixty-nine patients had round, oval, or lobulated defects in the transverse sinus, 59 had such defects in the superior sagittal sinus, and 47 had such defects in the straight sinus. All except two of the above defects were isointense relative to CSF on all images. These structures were presumed to be arachnoid granulations. Of 431 arachnoid granulations, 233 (53.8%) were located in the superior sagittal sinus, 122 (28.1%) in the transverse sinus, and 76 (17.6%) in the straight sinus. One or more veins were seen to enter arachnoid granulations in 414 (96%) instances. CONCLUSION The contrast-enhanced 3D MPRAGE imaging sequence showed a much higher prevalence and a different distribution of arachnoid granulations and septa within dural sinuses than have been observed in previous radiologic studies. Arachnoid granulations were closely related spatially to veins.