Extreme lateral disc herniation: diagnosis by computed tomographic scanning.

Extreme lateral disc herniation with compression of the nerve root as it exits through the foramen has been a recognized entity for a number of years. Until recently, this diagnosis was made infrequently except at the time of operation. Reported here are 12 cases of root compression from disc herniation at the level of the pedicle or farther laterally in the foramen (extreme lateral disc herniation). Diagnosis and localization of the root compression were determined preoperatively in 11 of 12 cases based on the computed tomographic (CT) scan appearance of the lesion. Myelography was performed in 9 cases and was interpreted as normal in 6 and abnormal in 3 instances. In each of the 3 abnormal studies, the actual abnormality was at a different level than that predicted by the myelogram. The clinical presentations in these patients were not distinct except that a positive straight leg raising test was present in only 7 of 12. Preoperative knowledge of the site of nerve root compression as delineated by CT scanning was essential in planning the operative procedure. It prevented unnecessary exploration of uninvolved levels and directed the surgeon to the far lateral site of the herniation. Illustrative examples are presented.