44 Far Lateral Discectomy Relief of radicular pain secondary to disc herniation lateral to the intravertebral foramen. Far lateral or extraforaminal herniated nucleus pulposus (HNP) are disc herniations lateral to the neuroforamen in the exit or far lateral zones. Ian McNab referred to this area as the hidden zone, as it is hidden from myelography. Prior to the advent of computed axial tomography (CAT) scans and magnetic resonance imaging (MRI), these lesions were often missed. Extraforaminal disc herniations compress the exiting nerve root or dorsal root ganglion superiorly into the pedicle above. The nerve root is less mobile in this area, and its ability to migrate away from disc herniations is less than that of intercanal HNPs. The dorsal root ganglion (DRG) is variable in size and location with respect to the neuroforamen. The DRG is largest in the L5 and S1 levels, being 5 to 6 mm wide and 11 to 13 mm long. Of 150 consecutive disc herniations in our practice, 15 were lateral extraforaminal HNPs. In the literature the incidence is reported at 1 to 11%. CAT, MRI, or discogram CAT. 1. MRI—noninvasive (Fig. 44–1). 2. Sagittal images at pedicle level and lateral can reveal lesion (Fig. 44–2). 3. Discogram CAT (Fig. 44–3) confirms that disc herniation is contiguous with disc space. 4. Diagnostic blocks: extraforaminal nerve root block can confirm diagnosis. Addition of steroids may be therapeutic. 1. Enlarged ganglia 2. Conjoined nerve roots 3. Nerve root tumors 1. Severe radicular pain. 2. May involve nerve roots. 3. L4-L5 most common level (L4 radiculopathy). 4. SLR may be negative; check femoral stretch test. 5. Failure of standard laminotomy to relieve symptoms (wrong level, wrong location at right level. 1. Same as with intracanal HNPs 2. Failed nonoperative management 3. Radicular pain corresponding to the lesion documented on confirmatory imaging studies 4. Progressive weakness Majority of herniation is medial to the pedicle. 1. Direct visualization of pathology. 2. Postoperative instability minimized with preservation of pars interarticularis and the inferior facet joint. 3. Simultaneous laminotomy, and extraforaminal approach is possible if indicated.
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Contraindications to Lateral Approach
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