Fig 3. Postoperative axial and sagittal MR images of lumbar spine before and after administration of intravenous contrast media and noncontrast axial CT scan.

A, An axial T1-weighted (TR, 477; TE, 14) MR image shows a signal void gas accumulation in the right anterolateral epidural space compressing the dural sac and displacing the right L5 nerve root to the posterior.

B, An axial postcontrast T1-weighted MR image at the same level with Fig 1A demonstrates granulation tissue enveloping the signal void gas.

C, A sagittal fat saturated T2-weighted (TR, 3500; TE, 120) MR image reveals the signal void gas collection at the level of L4 vertebra inferior endplate. Disk space narrowing and degeneration at the L4-L5 endplates were also observed.

D, An axial CT scan confirms the ovoid cystlike gas occupying the right lateral recess.