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.

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Intraradicular lumbar disc herniation is a rare complication of disc disease that is generally diagnosed only during surgery. The mechanism for herniated disc penetration into the intradural space is not known with certainty, but adhesion between the radicular dura and the posterior longitudinal ligament was suggested as the most important condition. The authors report the first case of an intraradicular lumbar disc herniation without subdural penetration; the disc hernia was lodged between the two radicular dura layers. The patient, a 34-year-old soldier, was admitted with a 12-month history of low back pain and episodic left sciatica. Neurologic examination showed a positive straight leg raising test on the left side without sensory, motor or sphincter disturbances. Spinal CT scan and MRI exploration revealed a left posterolateral osteophyte formation at the L5-S1 level with an irregular large disc herniation, which migrated superiorly. An intradural extension was suspected. A left L5 hemilaminectomy and S1 foraminotomy were performed. The exploration revealed a large fragment of disc material located between the inner and outer layers of the left S1 radicular dura. The mass was extirpated without cerebrospinal fluid outflow. The postoperative course was uneventful. Radicular interdural lumbar disc herniation should be suspected when a swollen, hard and immobile nerve root is present intraoperatively.

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