The video on the left is a contiguous series of CT slices showing the lumbosacral spine of a 7 month old infant. You can look at this video frame by frame and, starting at frame 37, try to identify the pathology indicated by the turquoise questionmark. A big hint is provided by the adjacent movie of a 3D reconstruction (called volume rendering) of these CTs. The answer will be revealed when you click on the drop-down arrow below the video.