Posterior epidural migration of a lumbar disc fragment: a series of 6 cases

Object The migration of a lumbar intervertebral disc fragment to the posterior epidural space is a rare complication of lumbar disc herniation (LDH), mostly diagnosed intraoperatively. The authors describe a series of 6 patients with a posterior epidural migration of a lumbar intervertebral disc fragment (PEMLIF) and provide a systematic review of the literature. Methods The authors undertook a retrospective case series of patients with PEMLIF who underwent surgery for LDH between February 2007 and June 2010. In 6 (1.04%) of 572 patients a diagnosis of PEMLIF was established. In addition, a systematic review of the literature produced 41 additional cases reported since 1973. The authors analyzed epidemiological, clinical, and imaging features, as well as surgical treatment and outcome of this infrequent form of LDH. Results This study represents the largest case series to analyze the distinguishing features of PEMLIF. Including the authors' cases, 37 male (78.72%) and 10 female (21.28%) patients (mean age 54.08 years) appear in the literature. Although the predominant clinical disturbance was related to cauda equina compression in 22 patients (46.80%), 19 patients (40.42%) presented with typical symptoms of sciatica or anterior thigh pain. In 27 patients (57.44%), PEMLIFs were localized at high lumbar levels. Magnetic resonance imaging was used in 36 cases. The PEMLIF appeared iso- to hypointense on T1-weighted imaging and had a variable intensity on T2-weighted imaging. After administration of Gd, 85.71% of lesions exhibited a peripheral ring. The preoperative diagnosis was never related to PEMLIF in 68% of cases. The PEMLIF was totally resected in all patients. An additional discectomy was performed in 31 patients (65.95%). Information was incomplete in 1 case. Of the remaining 46 patients, all improved postoperatively: total recovery was achieved in 33 cases (71.74%), subtotal recovery in 2 cases (4.35%), and improvement in 11 cases (23.91%). The postoperative outcome appeared not to depend on the duration or the degree of preoperative neurological deficits or the size of disc fragment. Conclusions The migration of a lumbar intervertebral disc fragment to the posterior epidural space is a rare event, occurring in an advanced working-age population. Clinical presentation is indistinguishable from the typical LDH, but overall cauda equina symptoms are far more common. High lumbar levels are more affected. Magnetic resonance imaging characteristics are difficult to differentiate from those of other entities. Ring enhancement after Gd administration is common. Outcomes in patients with cauda equina symptoms appear better than those in patients with standard ventral compression.