Background
Endoscopic surgery has demonstrated its effectiveness against disc herniations. However, there are limitations in its use in removing a highly up-migrated lumbar disc in hidden zone. This study aimed to introduce the biportal endoscopic approach for the treatment of a highly up-migrated lumbar disc and to report the preliminary surgical outcomes.
Methods
This study included 28 patients with a highly up-migrated lumbar disc who underwent biportal endoscopic surgery through one-level above contralateral corridor for disc removal. Patients were re-evaluated by postoperative MRI to confirm the successful removal of ruptured fragments. Simple X-ray was obtained for assessing the development of spinal instability. Back and leg pain were evaluated using Visual Analog Scale (VAS) scores. The satisfaction rate of clinical outcomes was assessed using the modified MacNab criteria.
Results
The mean age of patients was 62.3 years, and the mean follow-up period was 21.4 months. Compared to preoperative scores, VAS scores of back and leg pain significantly improved. At the final follow-up, two patients had unfavorable outcome due to the presence of residual leg pain. There was no new development of segmental instability or spondylolisthesis.
Conclusions
Biportal endoscopic approach with one-level above contralateral corridor may be an alternative treatment method for a highly up-migrated lumbar disc, with advantages including direct visualization of the hidden zone from the tail of ruptured fragment to the ruptured site, preservation of the facet joint and pars interarticularis.

Spinal subdural hematoma (SDH) is a rare complication after spinal surgery. Only a few cases are reported on spinal SDH following open lumbar spinal decompression or fusion surgery. Moreover, there has been no case report on spinal SDH following percutaneous transforaminal endoscopic lumbar discectomy. We report a case of spinal SDH following endoscopic discectomy, review the literature of this complication and discuss the etiology to it and methods to prevent it. A 63-year-old woman presented with severe radiating pain. Pain was not improved with conservative management. Lumbar magnetic resonance imaging (MRI) was checked and revealed right L3-4 ruptured disc with severe L4 root compression. Percutaneous transforaminal endoscopic decompression was performed and the pain subsided promptly after the endoscopic procedure. On 7th post-operative day, pain on Rt. buttock, anterior thigh was deteriorated severely, more than in pre-operatively. Deteriorated pain was not controlled by oral medications and epidural block. Repeat MRI showed no definite recurrence of disc herniation at decompressed level but spinal SDH, severely compressing cauda equina was seen on T12-sacral area. Spinal SDH is a rare complication following spine surgery, including percutaneous endoscopic surgery. A spine surgeon should be aware of the possibility of spinal subdural hematoma, having severe sequel.