Tethered spinal cord among individuals with myelomeningocele: an analysis of the National Spina Bifida Patient Registry

OBJECTIVE The aims of this study were to review the National Spina Bifida Patient Registry (NSBPR) data set to study the rates of tethered spinal cord release (TCR) among patients with myelomeningocele and variability between centers, to compare TCR rates between males and females, and to study the relationships between TCR rates and other condition-specific characteristics. METHODS The NSBPR registry was queried to identify all patients with myelomeningocele. TCR rates were calculated over time using survival analyses; rates between centers and between males and females were compared. Cox proportional hazards models were constructed to identify relationships between TCR rates and sex, functional lesion level, ambulation status, treated hydrocephalus, and prior Chiari decompression. RESULTS Of 6339 patients with information about their operations, 1366 (21.5%) underwent TCR, with significant variability between centers. The majority (75.8%) underwent a single TCR. The annual TCR rate was linear between birth and 13 years (1.8%/year) but declined sharply from 14 to 21 years (0.7%/year). There was no period of time at which the TCR rate accelerated. There were no significant differences in TCR rates between males and females. TCR rate was not related to functional lesion level but was lower among nonambulators compared with community ambulators (p = 0.005) and among those with treated hydrocephalus (HR 0.30, p < 0.001), and higher among those having prior Chiari decompression (HR 1.71, p < 0.001). CONCLUSIONS These results extend the results of prior single-institution studies, demonstrate significant treatment variability between institutions, and challenge the traditional concept that tethering is related to spinal cord stretching due to spinal growth.

Neurosurgery guidelines for the care of people with spina bifida

Myelomeningocele (MMC) arises from an early neural developmental anomaly and results in a variety of structural abnormalities and associated functional neurologic deficits. As such, neurologic issues are central to virtually all clinical problems. Neurosurgical intervention strives to correct or improve these defects and prevent secondary complications. These interventions include closure of the open myelomeningocele and management (across the life span) of hydrocephalus, the Chiari II malformation (C2M) and tethered spinal cord (TSC). The development of pre-natal closure techniques and reports of improved outcome with in-utero closure (IUMC) have revolutionized the neurosurgical approach to myelomeningocele. Controversies remain surrounding patient selection, maternal risks, technique of IUMC (endoscopic vs. open) and long-term outcomes. However, real gains include reduced rates of hydrocephalus, modestly improved motor capabilities and reduction in C2M morbidity. For many decades, the cornerstone of treatment of hydrocephalus for many decades has been the placement and support of ventricular shunts. Endoscopic third ventriculostomy (ETV) with or without choroid plexus coagulation (ETV/CPC) is an appealing alternate strategy that avoids the morbidity and complications associated with shunts. The exact criteria for ETV-CPC candidacy and best metrics for outcome analysis remain active areas of debate and controversy. Similarly, neurosurgical management C2M, has centered upon the indications and clinical thresholds for performing posterior fossa surgical decompression. Tethered spinal cord management incorporates the diagnosis and surgical management of adhesions formed at the initial closure site, the consequent longitudinal traction related stress on the cord and the resulting neurologic signs and symptoms.

Determination of Fetal Spinal Cord Measurement for Every Gestation Age

Background and Hypothesis: Tethered spinal cord is challenging to identify in fetuses. If untreated, tethered spinal cord can result in neurologic weakness and sensory loss in the lower half of the body. The goal of this study is to develop a library of normal ratios of the position of the conus medullaris relative to the spinal canal from normal fetal magnetic resonance imaging (MRI) examinations at each gestation age. This will allow for early identification of tethered spinal cord and timely intervention. We hypothesize that the ratios will decrease throughout pregnancy as the level of the conus medullaris rises. Experimental Design or Project Methods: In this pilot study, a retrospective review of fetal MRIs from patients between 20-38 weeks gestation age were examined. Exclusion criteria included fetuses with fetal spinal or central nervous system anomalies, VACTERL, ventral wall defects, scoliosis, and sacrococcygeal teratoma. The length from the fetal obex to the conus medullaris was measured and defined as the spinal cord length. The length of the obex to the caudal thecal sac was defined as the spinal canal length. The ratio of the spinal cord length to the spinal canal length was calculated. The ratios at each gestation age were compared using ANOVA (p < 0.05). Results: A total of 225 patients were reviewed. We observed a statistically significant decreasing trend in fetal spinal ratios from 20-38 weeks of gestation age. The average ratio at 20 weeks gestation age is 0.756 and at 38 weeks is 0.696. Conclusion and Potential Impact: This retrospective pilot study of fetal MRIs will establish reference values for the ratio of spinal cord to spinal canal lengths at progressing gestation ages. Ultimately, these ratios can establish normal values for identification of tethered spinal cord during the fetal period, thereby allowing early intervention to mitigate complications.

Surgical volume of simple tethered spinal cord releases: review of a large pediatric neurosurgical service experience

OBJECTIVEThe aim of this study was to retrospectively review, from a single busy pediatric neurosurgical service, a consecutive series of patients who had undergone surgery for a simple tethered spinal cord, which was defined by a thickened or fatty filum terminale with a normal conus. The hope was to contribute to benchmark data regarding the expected frequency of surgery for this condition.METHODSThe authors reviewed the electronic medical records of every patient with diagnosed simple tethered spinal cord, defined on spinal MRI as a thickened (> 2 mm in diameter) or fatty filum terminale, and who had undergone primary filum section at Boston Children’s Hospital between 2005 and 2011.RESULTSA total of 208 patients met the study inclusion criteria. At the time of surgery, patients ranged in age from 0.4 to 19.8 years. One hundred forty-four (69%) patients were symptomatic with one or more of the following: bowel/bladder dysfunction, 94 (45%); neurological dysfunction, 49 (24%); scoliosis, 44 (21%); or back pain, 44 (21%). Sixty-four (31%) patients were asymptomatic and were operated on prophylactically when filum pathology was discovered during the course of a workup for clinical syndromes such as anorectal anomalies and/or suspicious cutaneous lesions. No patients in this series were operated on if they had normal MRI studies, defined as a conus tip no lower than L3 and no distal tethering lesion visualized. Over the study period, approximately 1000 major surgical cases were performed in the department every year, only 30 of which were simple detethering procedures, representing well under 5% of the service’s operative volume and approximately 5 cases per surgeon per year. Clinical follow-up, available at a postoperative interval of 6.6 ± 3.8 years, demonstrated that approximately 80% of patients symptomatic with bowel or bladder involvement or neurological dysfunction had improvement or relief of their symptoms and that none of the patients treated prophylactically experienced new-onset symptoms that could be related to spinal tethering.CONCLUSIONSSimple detethering procedures were relatively uncommon in an active, well-established pediatric neurosurgical service and represented less than 5% of the service’s total case volume per year with an average of 5 cases per surgeon per year. No patients with normal MRI studies were operated on during the study period.