MRI myelogram

A 50-year-old female. Sagittal fat-suppressed T2W imaging (a) displays subtle arched hyperintensities in the interspinous epidural space at the lumbar level (arrows), termed the “Dinosaur tail sign”, which may reflect a subtle amount of CSF leakage. MR myelography (b) shows this sign at L2-3 to L4-5 (arrows). This sign is stronger on post-contrast HT2-FLAIR images (c) than on pre-contrast images (d), and is more conspicuous, particularly at T12-L1 and L1-2 (arrows). Epidural fluid collection, which is observed dorsal and ventral to the dural sac as a hypointense line (b, small arrows), is also more clearly visible. Each image in the lower row (e-h) shows the magnification of the lumbosacral traditional area in the upper row (a-d). On fat-suppressed T2W images (e), epidural venous plexuses (arrowheads) are more hypointense than epidural fluid collection (arrows) ventral to the dura mater (small arrows). MR myelography (f) shows that epidural venous plexuses (arrowheads) are more hypointense than epidural fluid collection (arrows), indicating stronger contrast between veins and fluid than on fat-suppressed T2W images. Of note, post-contrast HT2-FLAIR imaging (g) showed no or the weaker enhancement of veins (arrowheads) than that of CSF leaks (arrows). These venous structures are mildly hyperintense on pre-contrast HT2-FLAIR images (h, arrowheads).