Intervertebral disk material: criteria for determining probable prolapse.

To develop histologic criteria that allow distinction of prolapsed from nonprolapsed intervertebral disk material, we reviewed the histologic features of curetted fibrocartilage from 100 consecutive patients having documented disk prolapse into the spinal canal and contrasted our findings to those in 40 intervertebral disks removed at autopsy from 20 patients without prolapse. Neovascularization, occurring at the edges of fibrocartilage fragments, was present in 50% of prolapsed disk specimens and in none of the control autopsy disks (p = 0.0004). Other histologic features sometimes used as evidence of degeneration and/or prolapse (i.e., fibrillation, chondrocyte "cloning," and granular change) were not helpful in distinguishing prolapsed from nonprolapsed control disks. Although this indicator was only 50% sensitive in our series, we propose that edge neovascularization of the fibrocartilage fragments is the only reliable histologic clue that intervertebral disk prolapse has occurred.