Lumbar diskal cyst containing intervertebral disk materials.

The diskal cyst is a relatively new clinical entity and develops clinical symptoms of a unilateral single nerve root lesion. Although many cases of diskal cyst have been reported, the pathogenesis of diskal cyst remains unclear, and several theories regarding the pathogenesis have been proposed. This article presents 2 cases of diskal cyst communicating with an adjacent herniated disk. Magnetic resonance imaging findings showed diskal cysts in the epidural space of the lumbar spine. Surgical resection was performed, and apparent connections between the corresponding disk and cysts were found. Histopathologic examinations of the cyst wall demonstrated cartilaginous tissue including nucleus pulposus and annulus fibrosis. These patient's symptoms improved remarkably postoperatively, and there was no recurrence of diskal cyst.The hypothesis supported by many authors is hemorrhage from the epidural venous plexus. Diskal cysts arise first from an underlying intervertebral disk injury that causes an annulus fibrosis fissure in the posterior intervertebral disk. Hemorrhage from the epidural venous plexus with a rich blood flow then occurs in the space between the peridural membrane and vertebral body. However, in our cases, we confirmed that the diskal cyst could have developed from the resorption process of an intervertebral disk herniation. Only 5 cases of diskal cyst demonstrating the presence of cartilaginous tissue in the cyst have been reported. Our 2 cases are rare and support the hypothesis of resorption of intervertebral disk herniation.