The usefulness of magnetic resonance imaging for sequestered lumbar disc herniation treated with endoscopic surgery.

Forty two patients with sequestered lumbar intervertebral disc herniation were treated by endoscopic surgery with the mobile Endospine system. The herniations and migration were confirmed on magnetic resonance imaging (MRI). The interlamina fenestration and pars interarticularis fenestration approaches were used for intracanal herniations and far lateral lumbar disc herniations (FLLDH) according to the degree of migration as observed on MRI. Sequestered herniations were exposed and removed completely with the mobile endoscopic system for all patients without neurologic complications or dural tears. Intraoperative findings were compared with preoperative MRI results. Of 24 caudal intracanal herniations, 15 had sequestered nuclei located ventrally beneath the dural theca and the transverse nerve root; 5 were between the transverse nerve root and dural theca (axillary); 4 were dorsally located on the nerve root and dural theca. However, preoperative MRI did not clearly display the sequestered nuclei between the transverse nerve root and dural theca (axillary), or the dorsally migrated disc on the nerve root and dural theca. Of 6 cranial intracanal herniations, 5 had free fragments located beneath the dural theca, and 1 dorsal to the dural sac. Of the 2 dorsal herniations, the migrated nucleus adhered to the dural sac was not found on preoperative MRI; in the other case, dorsal migration of nucleus, annulus and endplate around the dural sac was also not observed on preoperative MRI. Among the 10 FLLDH, preoperative MRI showed cranial migration and foraminal obstruction in all patients, with sequestered disc material at the ventral and medial sides of the exiting nerve root, displacing the exiting nerve root and ganglion cranially and dorsally. During the 12 to 48 month postoperative follow-up period, 26 patients had excellent clinical results and 15 patients had good results (Macnab scale). In conclusion, MRI is important for evaluating sequestered lumbar disc herniation, although it has its limitations. Sequestered herniations can be exposed and removed completely with the mobile endoscopic system.