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

Abstract

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.

Fig 1.

Images reveal arachnoid granulation in a 37-year-old man with postoperative changes of a right temporal lobe oligodendroglioma. A, 3D contrast-enhanced MPRAGE image (13.5/7/1; inversion time, 300 ms; flip angle, 15 degrees) shows a well-circumscribed, round, hypointense focal filling defect (arrowheads) within the right transverse sinus. B, Axial T2-weighted MR image (3700/96) shows that the structure shown in A (arrowheads) is isointense to CSF. C, Unenhanced T1-weighted MR image (627/17) shows that the structure shown in A and B is also isointense to CSF in this image.

Fig 2.

Images from the case of a 40-year-old woman with headaches who had normal results of an MR imaging study. A, Axial source image acquired with a 3D contrast-enhanced MPRAGE sequence shows numerous small filling defects (arrowheads), consistent with arachnoid granulations, aligned along the lateral margin of the superior sagittal sinus. B, Sagittal reconstruction image obtained with a 3D contrast-enhanced MPRAGE imaging sequence shows an array of arachnoid granulations within the superior sagittal sinus.

Fig 3.

Images reveal arachnoid granulations in a 54-year-old man with headaches who had normal results of an MR imaging study. A, Sagittal reconstruction image obtained from 3D contrast-enhanced MPRAGE imaging sequence shows a large CSF-isointense filling defect, consistent with an arachnoid granulation (black arrows), at the junction point of the vein of Galen and straight sinus. Note also the presence of smaller arachnoid granulations within the superior sagittal sinus (white arrowheads). B, Axial T2-weighted MR image shows the defect seen in A as a discrete, focal CSF-isointense filling defect within the straight sinus.

Fig 4.

Image reveals arachnoid granulation in a 55-year-old woman with seizures who had normal results of an MR imaging study. Sagittal reconstruction image obtained with a 3D contrast-enhanced MPRAGE sequence shows a large CSF-isointense pouchlike focal filling defect (arrowheads) in the straight sinus. Note that this structure extends to the adjacent CSF space (asterisk) via the orifice opening to the subarachnoid space (small arrows).

Fig 5.

Images reveal invagination of brain tissue into the dural sinus in a 32-year-old woman with pituitary hormonal abnormalities who had otherwise normal results of an MR imaging examination. A, Source image acquired with a 3D contrast-enhanced MPRAGE sequence shows a focal filling defect in the right transverse sinus (arrowheads) that is isointense to brain parenchyma. B, Reconstruction image obtained in an oblique sagittal plane shows that the structure seen in A is contiguous with brain parenchyma (arrowhead), consistent with invagination of brain tissue into the dural sinus.

Fig 6.

Reconstruction image from a 3D contrast-enhanced MPRAGE image shows relationship of intracranial veins to arachnoid granulation in a 35-year-old man with normal results of an MR imaging study. The posteroinferior cerebellar vein (arrows) is seen to enter into a CSF-isointense structure (arrowheads), consistent with an arachnoid granulation.

Fig 7.

Image reveals association of intracranial veins and arachnoid granulations in a 41-year-old man with normal results of an MR imaging examination. Axial source image acquired with a 3D contrast-enhanced MPRAGE sequence shows multiple venous tributaries (small arrows), including the vein of Labbé (large arrow), entering into an arachnoid granulation (arrowhead) within the transverse sinus.

Fig 8.

Image shows appearance of septum within dural sinus in a 68-year-old woman with normal results of an MR imaging examination. Reconstruction image from a 3D contrast-enhanced MPRAGE image shows a linear structure (arrows), consistent with a septum within the straight sinus.

Fig 9.

Image shows septa within dural sinuses in a 39-year-old man with normal results of an MR imaging study. Axial source image from a 3D contrast-enhanced MPRAGE image shows curvilinear septa (arrows) that have intermediate signal intensity in both transverse sinuses. The septa seen in this study were usually smooth, thin, and not limited to the center of the sinus.

Fig 10.

Comparison of 2D time-of-flight MR venograms and 3D contrast-enhanced MPRAGE images of a 37-year-old woman with postpartum dural sinus thrombosis. A, 2D time-of-flight maximum intensity projection MR venogram shows lack of flow-related enhancement in superior sagittal sinus (arrows) and straight sinus (arrowheads). Note that by using this technique, the thrombosis is inferred by absence of a finding (ie, lack of flow-related enhancement) rather than by direct visualization of the thrombus. B, Sagittal reconstruction image obtained from a 3D contrast-enhanced MPRAGE image directly shows thrombus in the straight sinus and superior sagittal sinus (large arrows). The thrombus is also seen to extend into the adjacent vein of Galen (small arrows), have irregular margins, and produce irregular contrast enhancement of the inferior sagittal sinus (arrowheads), which were findings that were not seen in cases showing arachnoid granulations.

Fig 11.

Comparison of 2D time-of-flight venograms and 3D contrast-enhanced MPRAGE images for evaluating residual thrombosis in a 5-year-old female patient treated for dural sinus thrombosis 1 month before MR imaging. A, Maximum intensity projection 2D time-of-flight MR venogram obtained in a slightly oblique coronal plane shows narrowing of the left transverse sinus and patent sigmoid sinus (arrows). The narrowing at the point of the middle arrow could represent stenosis due to thrombus formation or congenital hypoplasia. Again, the thrombosis is inferred by a negative finding (ie, lack of flow-related enhancement) rather than directly visualized. B, Axial source image from a 3D contrast-enhanced MPRAGE image directly shows thrombus (arrows) in the left transverse sinus. The irregular margin and increased thickness allow this entity to be distinguished from septa within dural sinuses (compare with Fig 9).