Intradural Herniation of Lumbar Intervertebral Discs

IN THE 30 years since the classic report of Mixter and Barr dealing with herniation of the intervertebral disc,⁶ much has been written about the clinical manifestations and natural course of this disease process. A survey of the literature on this subject, which represents the experience of neurosurgeons dealing with several thousand cases of herniated intervertebral discs, indicates that an extradural free fragment of nucleus pulposus is not a particularly common finding at operation. Uncommon to the point of being a medical curiosity is the free fragment which has penetrated through the annulus fibrosus, the posterior longitudinal ligament, the dura mater and the arachnoid, and at operation is found to lie in the subarachnoid space among the roots of the cauda equina. Of the more than 1,000 patients who have undergone a surgical operation for disease of the lumbar intervertebral disc at this hospital during the past 12 years,