Which type of sequestration does not penetrate the PLL?

Which type of sequestration does not penetrate the PLL?

• A. Subligamentous sequestration
• B. Transligamentous sequestration
• C. Sequestration without PLL penetration
• D. Extrusion

Answer: (A)

The important idea is how the fragment relates to the posterior longitudinal ligament (PLL). In a sequestration, the disc fragment is free, but whether the PLL is breached changes the subtype. If the fragment stays beneath the PLL and the ligament remains intact, this is called subligamentous sequestration. It does not penetrate the PLL because the fragment remains under it in the posterior epidural space. In contrast, when the fragment penetrates the PLL, that’s a transligamentous sequestration. Extrusion describes material that has moved through the annulus fibrosus and often through the PLL, sometimes with a residual stalk back to the parent disc. So the type that does not penetrate the PLL is subligamentous sequestration.

The important idea is how the fragment relates to the posterior longitudinal ligament (PLL). In a sequestration, the disc fragment is free, but whether the PLL is breached changes the subtype. If the fragment stays beneath the PLL and the ligament remains intact, this is called subligamentous sequestration. It does not penetrate the PLL because the fragment remains under it in the posterior epidural space.

In contrast, when the fragment penetrates the PLL, that’s a transligamentous sequestration. Extrusion describes material that has moved through the annulus fibrosus and often through the PLL, sometimes with a residual stalk back to the parent disc. So the type that does not penetrate the PLL is subligamentous sequestration.