Classic Herniated Nucleus Pulposus HNP

APLD is efficacious only for patients whose herniations are still contained by the annulus or posterior longitudinal ligament, and this is the most important factor that has prevented the more widespread use of the procedure. Therefore effort must be expended to determine which patients are appropriate for this type of procedure. Magnetic resonance imaging (MRI) can be extremely helpful in excluding obviously migrated fragments and large disc extrusions. Herniations with smooth obtuse margins (Figure 8.1) are generally contained. Hernia-tions with acute angulations or irregular shapes are more likely extruded. Although the intact annular fibers on an MR image are sometimes evidence of a contained herniation, there can be exceptions to this criterion.

An absolute contraindication of APLD is the migration of a disc fragment. When small degrees of migration are present (<3 mm), the possibility of a good result from APLD is not precluded. In cases such as this, the epicenter of the herniation can still be at the disc level. Until recently, this criterion had always been assumed to be valid based on common sense although never proven by data. In a French study comparing chymopapain with APLD, 50% of the patients treated with APLD had fragments that had migrated more than 3 mm from the disc space. The success rate for APLD in this report was approximately 43%, proving the importance of this criterion.10

It is now clear that perhaps the most definitive procedure for selecting patients for APLD is the computed tomography (CT) discogram. This procedure demonstrates complete tears of the annulus and posterior longitudinal ligament (Figure 8.2), indicated by free flow of contrast medium into the epidural space, thus indicating the herniations that are extruded. A CT discogram also allows the assessment of the size of the rent in the annulus that is communicating with the hernia-tion. Castro et al.11 have shown this to be valuable information. When the rent is narrow, which gives a mushroom effect to the herniation, it is naturally more difficult to transmit a pressure difference through such an annular tear. The result of the procedure is then in doubt; a 50% success rate is reported in patients with this finding. When the neck of the herniation is wide (Figure 8.3), with room for transmission of the pressure difference or actual retraction of the herniation back through the rent in the annulus, an excellent success rate (>80%) was reported. At our own institution, by this criterion, we had an 88% success rate.

Besides the characterization of the herniation on imaging studies, a number of associated radiographic findings should be considered when one is evaluating patients for APLD. Patients with degenerative facet disease should be carefully evaluated prior to APLD. These patients often have associated back pain that is likely to persist after a successful APLD. A facet nerve block prior to a percutaneous discec-

Scan Hernia Nukleus Pulposus

Figure 8.1. (A) Axial MR image showing contained HNP and a small central contained herniation with smooth obtuse margins. This patient would be a good candidate for a percutaneous discectomy. Such individuals often have back pain that can respond only to disc decompression. (B) Sagittal MR image showing contained HNP; L4-5 disc herniation is noted. The epicenter of the HNP is at the level of the disc space, and there is no evidence for an extruded fragment. (C) Axial CT scan showing contained HNP.

Figure 8.1. (A) Axial MR image showing contained HNP and a small central contained herniation with smooth obtuse margins. This patient would be a good candidate for a percutaneous discectomy. Such individuals often have back pain that can respond only to disc decompression. (B) Sagittal MR image showing contained HNP; L4-5 disc herniation is noted. The epicenter of the HNP is at the level of the disc space, and there is no evidence for an extruded fragment. (C) Axial CT scan showing contained HNP.

Figure 8.2. Axial view of a CT discogram showing contrast medium (arrow) that has ex-travasated into the epidural space. This patient had an extruded fragment and would not have responded to a percutaneous discectomy.

tomy can help disclose what portions of a patient's symptoms are related to a facet syndrome.

Clinically, patients who are candidates for APLD have the classic symptoms of a radiculopathy with sciatica (i.e., leg pain greater than back pain) and the classic neurological findings of wasting, weakness,

Figure 8.2. Axial view of a CT discogram showing contrast medium (arrow) that has ex-travasated into the epidural space. This patient had an extruded fragment and would not have responded to a percutaneous discectomy.

Scan Hernia Nukleus Pulposus
Figure 8.3. Axial view of a CT discogram showing a tear in the annulus with a wide neck (arrows) communicating with the HNP.
Bulging Disk

sensory and reflex changes, as well as a positive straight leg raising. APLD is not a procedure for patients with vague or equivocal symptoms and bulging discs. The percentage of patients who would be expected to fit into the high success category for APLD is approximately 5 to 10% of the overall herniated disc population that finally comes to surgery. With such low morbidity associated with APLD, however, what level of potential success (80%?, 60%?, 50%?) is acceptable to allow the procedure to be carried out on a more widespread basis? Now that APLD is no longer considered experimental, I usually give the patient the benefit of the doubt and the decision-making power to have the procedure even if a lower success rate might be expected. Such an instance occurs during discography when contrast material flows behind the posterior longitudinal ligament, indicating a complete tear of the annulus but not a complete extrusion. In our experience, these patients have approximately a 50% chance of success. When we encounter this situation we now give the patient the option to proceed with APLD even with the lower success rate. In fact, no patient has ever refused the 50:50 chance of avoiding an open discectomy.

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