Idiopathic spinal cord herniation (ISCH) is an infrequent condition that can cause progressive myelopathy leading to severe neurological dysfunction.1–6 This condition is characterized by ventral displacement of the spinal cord across a defect in the dura, either congenital or acquired, resulting in vascular compromise and adhesion that subsequently results in injury to the spinal cord.5,6 Since its first description in the English literature by Wortzman and colleagues in 1974, ISCH has slowly become a more readily diagnosed entity with the availability of magnetic resonance imaging (MRI) along with increased awareness in the associated signs and symptoms.7–18
Here we describe a case of ISCH, which provides 2 valuable additions to the currently available literature on this disorder. First, this case demonstrates the presence of a transdural herniated disk fragment, a previously hypothesized etiology of the dural defect present with ISCH.5,6 Second, a video demonstrating the dural graft sling technique for repair of the dural defect is presented to assist surgeons not familiar with the surgical management of this rare entity.
CLINICAL CASE AND OPERATIVE TECHNIQUE
A 50-year-old male with a history of multiple lumbar spine surgeries presented with new-onset and progressive myelopathy. MRIs of his spinal axis (Fig. 1A) demonstrated ventral displacement of the spinal cord, in the midthoracic region, in the pattern characteristic of ISCH. A computed tomography (CT) myelogram (Fig. 1B) was also consistent with this diagnosis. Given the neurological dysfunction present, the decision was made to perform a laminectomy and intradural exploration to repair of the suspected dural defect.
Following induction of general anesthesia and prone positioning on a radiolucent Jackson Frame, localizing fluoroscopy was performed to determine the level of interest. A complete thoracic laminectomy centered primarily at T (thoracic) 7 was carried out in the standard fashion, with partial laminectomies also performed at the inferior portion of T6, and superior T8. Ultrasound was used before performing a durotomy to evaluate the spinal cord position. This confirmed localization with a ventral displacement of the spinal cord at the center of our dural exposure. After opening and retracting the dura with tacking sutures, microdissection around the spinal cord was performed demonstrating a focal protrusion of the spinal cord through a ventral dural defect that appeared partial thickness in nature. The dentate ligaments were transected bilaterally to allow manipulation and gentle rotation of the spinal cord. Once the spinal cord was mobilized a small desiccated herniated disk fragment was noted at the base of the dural defect, which was resected. A strip of latex surgical glove was cut and passed under the spinal cord. This was used to elevate the cord out of the defect. A small Duragen Plus (Integra LifeSciences Co., Plainsboro, NJ) pledget was placed in the defect after which a thin Gor-tex (WL Gore & Associates Inc., Flagstaff, AZ) pericardial patch was then cut to the appropriate size and positioned under the spinal cord to prevent it from reherniating into the defect. The graft was then sutured to the sides of the thecal sac before closing the dura. This technique is demonstrated in the Supplemental Video (Supplemental Digital Content 1, http://links.lww.com/CLINSPINE/A117). The wound was closed in layers in with absorbable sutures.
The patient’s postoperative course was uneventful and he was discharged home on postoperative day 3. His myelopathy improved rapidly over the course of the next several weeks and a postoperative MRI showed the spinal cord positioned centrally within the thecal sac (Fig. 1C). At last follow-up, his neurological symptoms have resolved though he continues to have mild nondisabling back pain.
ISCH is a rare cause of myelopathy, that occurs secondary to an anterior dural defect which allows the spinal cord to descend into the resulting cavity.19 The first report of ISCH was by Wortzman and colleagues in 1974. Since that time, the number of published cases have markedly increased, especially with the advent of MRI.20 In general, ISCH most frequently occurs in the thoracic spine. The unique features of the thoracic spine, which may predispose to this condition, compared with other spinal segments, include the anterior positioning of the thoracic spinal cord, the kyphosis of the thoracic spine, and the anterior physiologic movements of the spinal cord due to cardiac, pulmonary, and flexion and extension movements.19
ISCH most commonly presents with pathology at the T4–T5 level, in women (67/33, female to male ratio), during the sixth decade of life (with a range of 22–78 y).21 Although the etiology remains debatable, there are 3 types of defects described by Aizawa et al22 which include: a pseduomeningocele or epidural cyst, a full-thickness dural defect, and a defect in the layer of duplicated ventral dura. Any clinical or historic injury may precipitate a tear in the dura that grows over time. Alternatively, it has also been proposed that a herniated and calcified disk abutting the dura may initiate thinning, erosion, and eventual compromise or rupture of the dura.22 In this patient, it was noted that the dura appeared, in fact, to be duplicated and a herniated disk fragment was noted within the ventral dural defect perhaps giving credence to this potential mechanism of dural defect formation.
Thoracic myelopathy in a Brown-Séquard syndrome pattern is the most frequently cited presentation if ISCH. Additional manifestations include the full range of neurological signs and symptoms that one might expect from thoracic myelopathy. These signs and symptoms can include gait dysfunction, sphincter, and sexual disturbances, progressive paraparesis, and sensory loss.21
Currently, MRI is the most common imaging modality utilized in making the diagnosis of ISCH. Specifically, one can note on sagittal MRI the ventral angulation of the thoracic spinal cord along with enlargement subarachnoid space behind, giving it a “delta” configuration. One should also be cognizant of posterior compressive arachnoid cysts, which can appear similar to ISCH, and be better defined by phase-contrast MRI which allows for visualization of the dorsal pulsatile cerebrospinal fluid flow. Alternatively a CT myelogram can be performed to support the diagnosis of ISCH, by demonstrating ventral displacement of the spinal cord without a contrast block or defect that could indicate the presence of an arachnoid cyst which does not communicate with the subarachnoid space. A CT myelogram may also be a useful alternative in those with contraindications to MRI.2,23,24
Surgical management is recommended in symptomatic patients with ISCH to prevent further neurological deterioration. Three surgical techniques have been described: use of primary sutures to close the dural defect,6,25–27 use of a dural graft sling to repair the defect3,23,28–34 and enlargement of the dural defect.1,22,35,36
A meta‑analysis by Groen et al37 looked at surgical results of 121 ISCH patients. They demonstrated that 73% had neurological improvement, 20% being unchanged, and 7% with a neurological decline. A more recent review of the literature by Summers et al38 showed that 74% of a patient diagnosed (119/159) with ISCH that underwent surgery demonstrated clinical improvement postoperatively. Overall, 18% showed no clinical changes, and 8% demonstrated worsening postoperative exam findings.38 Subsequent case reports demonstrate a similar theme of improvement with surgical management. These reports spanning from 1974 to 2015 are summarized in Table 1. Unfortunately, detailed reporting of the techniques employed in individual cases has not uniformly been carried out. Therefore, while all 3 of the described surgical approaches to ISCH appear relatively safe and effective, drawing conclusions regarding the optimal mode of surgical repair is not possible at this time.
Although ISCH is a rare clinical condition that causes thoracic myelopathy, patients managed with surgery generally, though not universally, have a favorable neurological outcome. The case presented demonstrates the transdural extension of a herniated thoracic disk as a potential cause for dural defect formation. The associated surgical technique video demonstrates the dural sling technique for the treatment of this rare disorder.
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