Lumbar synovial cysts eroding bone.

Synovial or ganglion cysts are uncommon lesions that may occur within the spinal canal. Over 50 reported cases have demonstrated a preponderant incidence at the L4-L5 level in association with degenerative hypertrophic facet changes ( 1, 2). The typical computed tomography (CT) appearance is that of an epidural lowdensity lesion adjacent to the degenerated facet joint that may or may not have a dense periphery. Magnetic resonance (MR) imaging signal characteristics are variable (1). Bony involvement by these cysts has been described in the long bones (3, 4). This report presents two cases of lumbar synovial (ganglion) cysts in which there were lucent bony changes in the adjacent laminae mimicking an epidural tumor.