29 Idiopathic Spinal Cord Herniation Abstract Idiopathic spinal cord herniation (ISCH) is a relatively rare disorder causing patients to present with thoracic myelopathy. The disorder is characterized by herniation of the spinal cord through a ventral dural defect. Diagnostic workup should include magnetic resonance imaging (MRI) of the thoracic spine, which typically reveals anterior displacement and kinking of the spinal cord. Computed tomography myelography is useful in distinguishing between ISCH and an arachnoid cyst. The goals of operative management are to halt progressive neurologic decline and preserve spinal cord function. Two main surgical strategies are used to treat patients with ISCH. The first technique involves repairing the defect primarily, either with sutures or with a dural patch. The second technique consists of widening the dural defect. Postoperative improvement in motor function can be expected in 68% of all cases, stabilization of neurologic function in 19% of all cases, and neurologic deterioration in 7%. Close postoperative clinical follow-up is recommended to monitor patients for possible spinal cord tethering or reherniation. Keywords: dural defect, idiopathic spinal cord herniation, myelopathy, thoracic spinal cord herniation, thoracic spine Clinical Pearls • Magnetic resonance imaging is critical to the diagnosis of idiopathic spinal cord herniation, and findings typically include anterior displacement of the spinal cord, with kinking or beaking. • Before ventral intradural exploration, bilateral dentate ligament release is recommended to detether the spinal cord, which allows it to be manipulated more safely. • Close postoperative clinical follow-up is recommended to monitor patients for possible spinal cord tethering or reherniation. Idiopathic spinal cord herniation (ISCH) is a relatively rare disorder that was first described in 1974 by Wortzman et al.1 The disorder is characterized by herniation of the spinal cord through a ventral dural defect. Strangulation of the spinal cord occurs because of the constricting edges of the dural defect, which typically leads to progressive myelopathic symptoms. The rarity of ISCH has made it challenging to elicit the incidence, natural history, and optimal treatment of the disease. Groen et al2 performed a meta-analysis of 126 case reports to better characterize this disorder. The mean age of patients was 51 years, and women were more affected than men, with a male-to-female ratio of 1:1.8. In this meta-analysis, ISCH was most typically found between the T3 and T7 levels and never occurred in the cervical or lumbar region. Brown–Séquard syndrome was present in 66% of the patients, paraparesis in 30%, isolated sensory deficit in 3%, and isolated motor deficit in 1%. The anatomic proximity between the corticospinal tracts and anterior horn of the spinal cord and the ventral dural defect likely underlies the predisposition for motor deficits. The etiology of the dural defect and the spinal cord herniation is unknown, but there are several mechanisms proposed in the medical literature. Intraoperative findings by Watanabe et al3 and Nakazawa et al4 of a cavity formed by duplicated membranes led them to hypothesize that a congenital duplication of the dura matter is partly the cause of ISCH.3,4 Alternative theories include acquisition of a dural defect secondary to trauma, degenerative disc herniation,5 inflammatory process,6 and pressure-induced erosion from an intradural arachnoid cyst.7 Chronic cerebrospinal fluid (CSF) pulsations and negative extradural thoracic pressure likely contribute to the gradual displacement of a portion of the spinal cord through the dural defect.8 Adhesions then form between the defect of the dural edges and the herniated segment of the spinal cord, leading to progressive strangulation of the cord ( Magnetic resonance imaging (MRI) is critical to the diagnosis of ISCH, as evidenced by the paucity of cases reported in the literature prior to 1990. MRI findings typically include anterior displacement of the spinal cord, with kinking or beaking ( Computed tomography myelography is another imaging modality used to differentiate between ISCH and an arachnoid cyst. Visualization of the dural defect with contrast or visualization of the spinal cord herniation through the defect may be observed ( Although there are reports of nonoperative management and spontaneous resolution of ISCH,9 there is a general consensus that symptomatic ISCH warrants operative intervention. The purpose of operative management is to halt progressive neurologic decline and preserve function. Most operative techniques described in published reports are performed via a posterior approach. The goals of surgery are to reduce the herniated spinal cord and prevent recurrence of herniation. There are two main strategies to achieving these goals. The first is to repair the defect primarily with sutures or a dural patch.8 The second strategy is to widen the dural defect.3 Proponents of the latter technique believe that widening the defect relieves the strangulation with less manipulation of the spinal cord, compared with repairing the defect with sutures or a patch. Critics of this technique believe that closure of the dural defect is necessary to prevent reherniation, reduce the spinal cord to its natural position, and restore normal CSF flow. There is insufficient evidence to suggest that one strategy is superior to the other; however, the preference at our institution is to repair the defect when feasible.
29.1 Introduction
29.2 Pathogenesis
Fig. 29.1).
29.3 Diagnostic Workup
Fig. 29.2). Spinal cord atrophy and T2 signal change may also be seen on MRI. The most common misdiagnosis of ISCH is an intradural arachnoid cyst; however, there are subtle differences between the two on MRI that will aid in diagnosis. Higher kink angles and the disappearance of CSF ventral to the spinal cord are findings that favor ISCH, whereas vertebral scalloping and alterations in CSF flow are suggestive of an arachnoid cyst.9
Fig. 29.3). A lack of contrast filling dorsal to the spinal cord suggests a loculated arachnoid cyst.
29.4 Operative Management
Thoracic Key
Fastest Thoracic Insight Engine
