Clinical History
A 63-year-old female patient presented with a 5-month severe right-sided buttock and lateral thigh pain, despite anti-inflammatory treatment and physiotherapy. There was pain deterioration during the past 2 weeks and bladder dysfunction during the past 30 hours. Clinical examination revealed reduced sensation, knee reflexes, and hip flexion on the right.
Imaging Findings
The urgent MR imaging examination showed an ovoid-shape lesion in the right posterior epidural space at the level of L2-L3, compressing and displacing the dural sac anteriorly and to the left (Fig. 1). The lesion showed peripheral enhancement after contrast administration. The patient improved immediately after surgery but a new cauda equina syndrome appeared on the 3d postoperative day. The urgent MR imaging examination showed a large epidural haematoma (Fig. 2), which was drained surgically.
Discussion
A. Disc herniation is defined as a rupture of the fibrous annulus with protrusion of the nucleus pulposus. The displacement of disk material away from the original site of sequestration is described as migration. The posterior epidural migration is extremely rare [1, 2]. Structures as the sagittal midline septum, peridural membrane, nerve roots, dura, epidural vascular structures and epidural fat are hypothesized to prevent migration. Structural insufficiency in these barriers may be a cause of posterior migration. An obtuse angle formed by the nerve root and the dural sac may be a high risk for posterior migration [3]. Other conditions predisposing to posterior migration are heavy labour, traction, spinal manipulation or spinal hypermobility [1].
B. Typically, posterior migration is clinically expected to produce significant neurological symptoms due to the interaction of the disk fragment with the neural structures [4]. However, the clinical picture ranges from asymptomatic patients to acute or chronic low back pain, myelopathy and rarely cauda equina syndrome [3]. Clinical examination and history may show tenderness on palpation of the lower lumbar spine with radiating pain to the lateral site of thigh, paresthesias, reduced strength scores, decreased reflexes at knee or ankle, steppage gait, bladder or bowel symptoms. Many of these were present in our case. The fact that patients with typical disc herniation symptoms had finally a neoplasia, emphasize the importance of imaging [4].
C. The method of choice is considered to be MR imaging, with gadolinium administration. Fragments are shown as posterior epidural mass compressing the dural sac, hypointense on T1-w and hyperintense on T2-w images in most of the cases. The migration fragment displaces the epidural fat posteriorly. The fragment may cause an inflammation with granulation tissue and neovascularization, causing a ring enhancement on contrast enhanced MR images, which is indicative of lumbar disc herniation [2, 3].
D. Surgical removal of the disk fragment is the proper therapy. A hemi- or complete laminectomy may be performed. Surgery should be performed urgently in the presence of cauda equina syndrome [3]. For patients with less severe neurological deficits, conservative treatment could be the first treatment option. The fragment may be reabsorbed or migrate from its original position [1]. The impact of imaging is important for the preoperative diagnosis.
E. Migration of a ruptured disc herniation should be included in the differential diagnosis of lesions located in the posterior epidural space. MR imaging is required to preoperatively distinguish migrated disc material from tumour.
Differential Diagnosis List
Posterior epidural migration of lumbar disk fragment.
Epidural abscess
Metastatic tumour
Haematoma
Synovial cyst from the facet joint
Hypertrophic ligamentum flavum
Meningioma
Final Diagnosis
Posterior epidural migration of lumbar disk fragment.
