Clinical features of conjoined lumbosacral nerve roots versus lumbar intervertebral disc herniations

Abstract

Unidentified nerve root anomalies, conjoined nerve root (CNR) being the most common, may account for some failed spinal surgical procedures as well as intraoperative neural injury. Previous studies have failed to clinically discern CNR from herniated discs and found their surgical outcomes as being inferior. A comparative study of CNR and disc herniations was undertaken. Between 2002 and 2008, 16 consecutive patients were diagnosed intraoperatively with CNR. These patients were matched 1:2 with 32 patients diagnosed with intervertebral disc herniations. Matching was done according to age (within 5 years), gender and level of pathology. Surgery for patients with CNR or disc herniations consisted of routine microsurgical techniques with microdiscectomy, hemilaminotomy, hemilaminectomy and foraminotomy as indicated. Outcomes were measured using the Oswestry Disability Index and the Short Form-36 Questionnaire. Clinical presentation, imaging studies and surgical outcomes were compared between the groups. Conjoined nerve root's incidence in this study was 5.8% of microdiscectomies performed. The S1 nerve root was mainly involved (69%), followed by L5 (31%). Patients with CNR tended to present with nerve root claudication (44%) compared to the radiculopathy accompanying disc herniations (75%). Neurologic deficit was less prevalent among patients with CNR. Nerve root tension tests were not helpful in distinguishing between the etiologies. Radiologist's suspicion threshold for nerve root anomalies was low (0%) and no coronal reconstructions were obtained. The surgeon's clinical suspicion accurately predicted 40% of the CNRs. Surgical outcomes did not differ between the cohorts regarding the rate of postoperative improvement, but CNR patients showed a trend toward having mildly worse long-term outcomes. Suspecting CNRs preoperatively is beneficial for appropriate treatment and avoiding the risk of intraoperative neural injury. With nerve root claudication and imaging suggestive of a "disc herniation", the surgeon should be alert to the differential diagnosis of a CNR. Treatment is directed at obtaining adequate decompression by laminectomy and foraminotomy to relieve the lateral recess stenosis. Outcomes can be expected to be similar to routine disc herniations.