Which description fits subligamentous extrusion?

Which description fits subligamentous extrusion?

• A. Herniation that penetrates the PLL
• B. Herniation that does not penetrate the PLL
• C. A free disc fragment in the epidural space
• D. Herniation that remains attached to the host disc after crossing annulus

Answer: (B)

This concept hinges on where the herniated disc material sits relative to the posterior longitudinal ligament (PLL). Subligamentous extrusion describes disc material that has breached the annulus but remains beneath the PLL, extending into the posterior epidural space without tearing through the PLL itself. In other words, the herniation does not penetrate the PLL. If the material had penetrated the PLL, it would be transligamentous extrusion. A free fragment in the epidural space would be sequestration, not an extrusion. And while extrusion can involve material that stays attached to the parent disc after crossing the annulus, subligamentous extrusion is specifically about not crossing the PLL.

This concept hinges on where the herniated disc material sits relative to the posterior longitudinal ligament (PLL). Subligamentous extrusion describes disc material that has breached the annulus but remains beneath the PLL, extending into the posterior epidural space without tearing through the PLL itself. In other words, the herniation does not penetrate the PLL.

If the material had penetrated the PLL, it would be transligamentous extrusion. A free fragment in the epidural space would be sequestration, not an extrusion. And while extrusion can involve material that stays attached to the parent disc after crossing the annulus, subligamentous extrusion is specifically about not crossing the PLL.