Aqueductal stenosis: evaluation with gradient-echo rapid MR imaging.

To assess the utility of gradient echo (GRE) magnetic resonance (MR) imaging in documenting aqueductal patency, spin-echo (SE) and GRE axial images were obtained with a 1.5-T system in 26 patients with aqueductal or periaqueductal lesions and in 26 control subjects. All SE images with a long repetition time (TR) were obtained with first-order gradient moment nulling. GRE imaging was performed with the use of the sequential section acquisition technique called gradient recalled acquisition in the steady state (GRASS), with a TR of 150 msec, an echo time of 14-17 msec, and a flip angle of 50 degrees, so to depict stationary cerebrospinal fluid (CSF) as low intensity and flowing CSF as high intensity. All patent aqueducts were seen as high intensity on GRE images. In 18 of 20 obstructed aqueducts, low intensity was seen within the aqueducts on GRE images. SE images obtained with gradient moment nulling did not allow confident distinction between patent and obstructed aqueducts. It appears that GRE imaging is useful in rapidly assessing aqueductal patency.