FIGURE 1.

A-P, Serial CT axial images at the C6 spinal segment before A through H and after I through P craniocervical decompression for a patient with Chiari I malformation associated with cervicothoracic syringomyelia. Images A and I were obtained without contrast and the other images were obtained at these hourly intervals after intrathecal contrast administration (CT myelography), 0.5 B, J, 2 C, K, 4 D, L, 6 E, M, 8 F, N, 10 G, O, 22 H, P h. The black arrowhead A indicates the syrinx. The myelogram dye concentration decreases more slowly from the subarachnoid space (F, black large arrow) before compared to after surgery (N, white arrowhead). Similarly, the dye concentration decreases more slowly in the syrinx before surgery (H, small black arrow) compared to after surgery (P, small white arrow). Q and R, Hounsfield units in this patient were measured in the spinal subarachnoid space (SAS), spinal cord (SC), and syrinx from the serial CT axial images and graphs were drawn of the mean and standard deviation of pixel values (error bars) in these regions of interest at each time point. The graphs confirm the visual impression that myelogram dye concentration decreases more slowly from the subarachnoid space before Q compared to after surgery R and that dye concentration decreases more slowly in the syrinx before surgery Q compared to after surgery R.