1.5-T GRASS imaging of benign extradural disease

The authors compared gradient recalled acquisition in a steady state (GRASS) with standard spin-echo sequences and CT myelography in 31 patients with surgically confirmed disease at 45 spinal levels (23 lumbar, four thoracic, 18 cervical). GRASS was highly accurate in identifying the level, causative agent (disk vs bone), and severity of spinal canal compromise at all levels operated on. GRASS detected 16 of 18 sites of foraminal encroachment (89%), demonstrated accurately the degree of foraminal narrowing in 78% (14/18), and correctly differentiated bone from soft-tissue foraminal narrowing in 67% (12/18). In five instances, the entity (disk vs bone) responsible for foraminal stenosis was correctly diagnosed only with CT myelography. The noninvasive nature, sensitivity, ease of interpretation, and shorter acquisition time of GRASS MR imaging make it the preferred screening examination. However, CT myelography more reliably defines the cause and degree of foraminal stenosis