Large arachnoid granulations involving the dorsal superior sagittal sinus: findings on MR imaging and MR venography

Abstract

Background and purpose: Large arachnoid granulations (AG) within the dorsal superior sagittal sinus (SSS) have been incompletely characterized and can be confused with pathology. This report reviews the characteristics of these anatomic structures to establish common imaging features that allow differentiation from pathology.

Materials and methods: Twelve cases of large AG in the dorsal SSS are presented, identified by MR imaging. Signal intensity characteristics, size, location, venographic appearance, and association with adjacent venous and osseous structures were documented.

Results: A defect in the dura of the SSS was seen in all of the cases communicating with the subjacent subarachnoid space. The average size of the AG was 8.1 x 9.4 x 10.0 mm (range, 4-19 mm). Ten produced calvarial remodeling, and 11 were in the direct vicinity of the lambda. On T2-weighted images, all were hyperintense to the brain. On T1-weighted images, 8 were hypointense and 4 were hypointense with mixed areas of isointense signal intensity. All of the AGs were associated with cortical venous structures entering the sinus. On MR venography, AGs appeared as focal protrusions into the sinus, displacing, distorting, and narrowing the sinus lumen. Seven patients had headache without other visible cause on MR imaging, and 4 were initially interpreted as thrombosis or tumor.

Conclusion: Large AGs can occur in the dorsal SSS. They are well-defined projections of the subarachnoid space into the sinus, can cause luminal narrowing and calvarial remodeling, and have typical signal intensity characteristics, position, and morphology differentiating them from other pathology. Association with patient symptoms is uncertain.

Fig 1.

Sagittal images from cases 1, 2, 3, 4, 6, and 7 demonstrating the typical position of the dorsal SSS AG identified in this study (arrows). Case 3, Sagittal reconstruction of FSPGR postcontrast T1-weighted image (3T); case 6, sagittal reconstructed image from 2-mm axial FSE T2-WI (3T); all others, sagittal FSE T2-weighted images.

Fig 2.

Case 4, 1.5T, axial T1WI (A), FLAIR (B), T2WI (C), DWI (D), and postcontrast T1WI (E and F). Typical appearance on multiple pulse sequences. Note the large AG with associated defect in the dura (arrows, C) along the rightward margin of the SSS. Note intrinsic vessels, which appear to be displaced cortical veins or channels (arrows, E and F). There is focal calvarial remodeling.

Fig 3.

Case 3, 3T. Axial acquired TOF-MRV (A), CE-MRV (B), and segmented volume-rendered FSPGR sequence after contrast (C).Note multilumen SSS, intrinsic vessels (arrows, B and C), thin AG base along the SSS (arrowhead, C), and adjacent cortical vein (*C).