Unexpected Resection of Gray Ramus Communicans During Endoscopic Lumbar Surgery: A Report of Two Cases.

Encountering nerve-like structures that do not correspond to the typical course of the spinal nerve root during endoscopic lumbar discectomy is rare. We describe two cases in which fine nerve-like fibers were identified during posterolateral full-endoscopic lumbar discectomy using the outside-in technique and were subsequently confirmed histologically as neural tissue. Both patients underwent surgery for L3/4 foraminal disc herniation. During the removal of the fat tissue overlying the disc, thin, vine-like, whitish fibers were observed. No abnormalities were detected on motor evoked potentials (MEPs) or somatosensory evoked potentials (SEPs), and we did not identify any continuous central neural bundle. In case 1, a preoperative fast imaging employing steady-state acquisition (FIESTA) MRI obtained 10 years earlier, before lumbar fusion, showed a fine branch arising from the L3 nerve root and coursing toward the disc, consistent with the intraoperative findings. Histopathology revealed ganglion-like structures in case 1 and predominantly unmyelinated nerve fibers in case 2. Histological examination revealed axonal structures clearly demonstrated by neurofilament staining, while Klüver-Barrera staining was negative, indicating the absence of myelinated fibers. These findings suggested that the excised fibers consisted predominantly of unmyelinated nerve fibers, consistent with a gray rami communicantes. We review these anatomical findings and emphasize the need for awareness of such branches to prevent inadvertent nerve resection during endoscopic lumbar surgery.