Ectopic arachnoid granulations: MR imaging and clinical findings

Abstract

In this study, we aimed to describe the MR imaging findings of arachnoid granulations (AGs) which are located away from the dural sinuses, namely the ectopic arachnoid granulations (EAGs), and aid in their differentiation from lytic lesions. We investigated EAGs in 20 patients (11 men and 9 women). 13 of our patients had single EAG, and 7 patients had 2 or more EAGs, with a total number of 32. The AGs which had a multilobulated appearance were accepted as single. EAGs were located adjacent to occipital (n=22, 68.75 %), frontal (n=5, 15.6 %), and temporal (n=4, 12.5 %) bones. One of them was present in the fronto-parietal region (3.1 %). 31 EAGs were isointense to cerebrospinal fluid (CSF) on T1-weighted, T2-weighted, FLAIR and PD images, whereas 1 EAG was hyperintense to CSF and mildly hypointense to gray matter on T1-weighted, FLAIR and PD images. Diffusion-weighted imaging (DWI) was performed for the latter, which appeared isointense relative to CSF on these images. No contrast enhancement was observed on postcontrast series. Multiple fine vascular structures were present in 18 of EAGs (56.2 %). Visible vascular structures were absent in 14 of them. We suggest, EAG might be one of the many etiologic factors of headache. © Universitätsverlag Ulm GmbH 2007.