Mass effect in the thoracic spine from remnant bone wax: an MR imaging pitfall.

Bone wax used in neurosurgical procedures is a rare cause of complications after surgery. We present a patient who developed paraplegia following thoracic spine surgery. A subsequent MR imaging study demonstrated a signal void that resembled postoperative air but appeared to cause cord compression and proved after a second surgery to represent bone wax. Recognizing the MR imaging and CT characteristics of bone wax is important to prevent mistaking it for residual air in postoperative imaging.