Herniation of the spinal cord, or displacement of the cord outside the dura, is so rare that only 13 cases have been reported in the literature. The authors report a new case of spontaneous herniation of the spinal cord in a 38-year-old man who presented with lower left limb paresis and Brown-Séquard syndrome, with a T-8 sensory level. Displacement of the spinal cord was noted on computerized tomography following myelography and on magnetic resonance imaging. The herniated cord was confirmed at operation and reduced intradurally. Postoperatively, the patient showed complete neurological recovery. Based on a review of the literature, herniation of the spinal cord may be classified as spontaneous, iatrogenic, or traumatic. At cervical levels, the spinal cord has herniated into an iatrogenic pseudomeningocele located dorsally. At thoracic levels, spinal cord herniations were reported to be in a preexisting extradural arachnoid cyst located ventrally. The authors propose a pathogenesis for spinal cord herniation based on abnormal positioning of the spinal cord in the dural sleeve and the known anteroposterior movements of the cord that occur with cardiac and respiratory pulsations. The presence of a dural defect situated on the concavity of the spinal curvature is a prerequisite for this rare condition. As adhesions develop between the cord and the edges of the dural defect, cerebrospinal fluid pulsations push the cord into a preexisting cyst. The authors suggest modifying the classification by Nabors, et al., of spinal meningeal cysts to include this mechanism of spinal cord herniation. This diagnosis should also be considered in the differential diagnosis of myelopathy in the absence of a mass lesion.

INCE Mixter and Barr 21 first described herniated lumbar intervertebral disc-induced nerve root compression, numerous operative approaches have been used for treatment. Neural compromise caused by a herniated disc outside the confines of the spinal canal is more readily recognized by using computerized tomography and magnetic resonance imaging. Such herniations have been characterized as foraminal, 8 extraforaminal, 15 extreme-lateral, 1,23 far-lateral, 19 and extracanalicular 25 disc prolapse. We prefer the term "extraforaminal" because the boundaries of the neural foramen can be readily identified on computerized tomography and magnetic resonance images, and because extraforaminal lesions are distinct from intraspinal-foraminal, foraminal, and foraminal-extraforaminal lesions.The clinical and radiological characteristics of extraforaminal lesions have been reported. 1,8,10,14,23 Currently two surgical approaches commonly used for the treatment of this type of disc herniation are 1) a conventional approach via a midline laminotomy/fenestration, or one of its modifications, and 2) a paramedian approach. Removal of a truly extraforaminal herniated disc via the midline approach necessitates sacrificing a significant portion, if not all, of the facet joint. The paramedian approach, however, which is performed at the level of the facet joint, provides a more direct route to this lesion. Although several Materials and Methods Anatomical StudiesTwenty-four lumbar extraforaminal disc spaces were studied in three human cadavers. In one cadaver predissection, the arteries and Object. Familiarity with the microsurgical anatomy of the far-lateral compartment is essential for operating in patients with far-lateral discs. In this report the authors address the microsurgical anatomy studied in 24 extraforaminal lumbar disc spaces in three cadavers.Methods. Cadaveric dissections confirmed the authors' operative experience in which they found an arterial arcade to be associated with the nerve trunk. The main trunk of the lumbar artery was located lateral to the exiting nerve root in the region of intervertebral foramen. The trunk of the lumbar spinal nerve descending from the level above was 7 mm (Ϯ 3 mm [standard deviation]) lateral to the lumbar artery.Conclusions. Clarification of the microsurgical anatomy of the far-lateral compartment confirmed the authors' clinical impression that the optimum approach to far-lateral discs is via the inferomedial quadrant of the extraforaminal compartment. In this quadrant, exposure of the main nerve root can be facilitated by dividing the posterior primary ramus and a newly described arterial arcade that envelops the nerve trunk. Once this arcade is divided, the nerve can be retracted with relative ease and safety, and the disc can be removed more easily. KEY WORDS • spine • lumbar intervertebral disc • microsurgery • anatomical study • surgical approachS