Use of a machine learning algorithm with a focus on spinopelvic parameters to predict development of symptomatic tethered cord after initial untethering surgery.

OBJECTIVE: Among patients with a history of prior lipomyelomeningocele repair, an association between increased lumbosacral angle (LSA) and cord retethering has been described. The authors sought to build a predictive algorithm to determine which complex tethered cord patients will develop the symptoms of spinal cord retethering after initial surgical repair with a focus on spinopelvic parameters. METHODS: An electronic medical record database was reviewed to identify patients with complex tethered cord (e.g., lipomyelomeningocele, lipomyeloschisis, myelocystocele) who underwent detethering before 12 months of age between January 1, 2008, and June 30, 2022. Descriptive statistics were used to characterize the patient population. The Caret package in R was used to develop a machine learning model that predicted symptom development by using spinopelvic parameters. RESULTS: A total of 72 patients were identified (28/72 [38.9%] were male). The most commonly observed dysraphism was lipomyelomeningocele (41/72 [56.9%]). The mean ± SD age at index MRI was 2.1 ± 2.2 months, at which time 87.5% of patients (63/72) were asymptomatic. The mean ± SD lumbar lordosis at the time of index MRI was 23.8° ± 11.1°, LSA was 36.5° ± 12.3°, sacral inclination was 30.4° ± 11.3°, and sacral slope was 23.0° ± 10.5°. Overall, 39.6% (25/63) of previously asymptomatic patients developed new symptoms during the mean ± SD follow-up period of 44.9 ± 47.2 months. In the recursive partitioning model, patients whose LSA increased at a rate ≥ 5.84°/year remained asymptomatic, whereas those with slower rates of LSA change experienced neurological decline (sensitivity 77.5%, specificity 84.9%, positive predictive value 88.9%, and negative predictive value 70.9%). CONCLUSIONS: This is the first study to build a machine learning algorithm to predict symptom development of spinal cord retethering after initial surgical repair. The authors found that, after initial surgery, patients who demonstrate a slower rate of LSA change per year may be at risk of developing neurological symptoms.

Kyphectomy and sliding growing rod technique in patients with congenital lumbar kyphosis deformity with myelomeningocele.

OBJECTIVE: Neural tube defects are the most common congenital disorders after cardiac anomalies. Lumbar kyphosis deformity is observed in 8-15% of these patients. This deformity severely limits the daily lives of these patients. In our study, we aimed to correct the kyphosis angle of the patients with lumbar kyphosis associated with myelomeningocele (MMC) and allow them to continue their growth without limiting their lung capacity by applying kyphectomy and sliding growing rod technique. PATIENTS AND METHODS: In this study, we retrospectively evaluated 24 patients with congenital lumbar kyphosis deformity associated with MMC, aged between 4 and 9 years, and who applied to Umraniye Training and Research Hospital between the dates of 2018 and 2021. We evaluated preoperative and postoperative kyphosis angles, correction rates, bleeding during operations, operation time, level of instrumentation, number of the resected vertebrae, initial levels of the posterior defects, duration of hospital stays, annual lengthening, and weight of the patients. RESULTS: Mean age was 5.04 (between 4 and 9). Mean preoperative and early postoperative kyphosis angles were 129.8° (87-175°) and 0.79° (- 20-24°), respectively. The kyphotic deformity correction rate was 99.1%. A difference was found regarding kyphosis measurements between preoperative and early period values (p < 0.05). The annual height lengthening of patients was calculated as 0.74 cm/year and 0.77 cm/year between T1-T12 and T1-S1, respectively. Mean preoperative level of hemoglobin (Hgb) was 11.95, postoperative Hgb value was 10.02, and the decrease was significant (p < 0.05). In terms of complications, 50% (12) had broken/loosen screws, 50% (12) had undergone debridement surgery, 37.5% (9) had vacuum-assisted closure therapy, and 33.3% (8) had to get all of their implants removed. CONCLUSION: We believe that our sliding growing rod technique is a new and updated surgical method that can be applied in these patient groups, facilitating the life, rehabilitation process, and daily care of MMC patients with lumbar kyphosis. This technique seems to be a safe and reliable method which preserves lung capacity and allows lengthening.

Intrauterine Correction of Fetal Myelomeningocele Through Minihysterotomy.

Spina bifida is the most common congenital central nervous system anomaly, resulting in lifelong neurologic, urinary, motor, and bowel disability.1 Its most frequent form is myelomeningocele, characterized by spinal cord extrusion into a sac filled with cerebrospinal fluid.1 We report the case of a 28-year-old pregnant female with no comorbidities. At 16 weeks of pregnancy, fetal ultrasound presented ventriculomegaly, cerebellar herniation, and lumbar myelomeningocele. At 22 weeks, intrauterine surgical correction was performed (Video 1). A minihysterotomy spanning approximately 3 cm was performed. The defect was opened, and the neural placode was dissected and released. This was followed by the isolation of the peripheric dura, which was molded into a tube and closed with watertight suture. Finally, the minihysterotomy was sutured and the skin was closed. The pregnancy followed its course with no complications, and the child was born at term with the lesion closed and no necessity of intensive care. Recent studies have demonstrated that infants who undergo open in utero myelomeningocele repair have better neurologic outcomes than those who are treated after birth.1,2 However, maternal morbidity is nonnegligible with the classical open surgery.2 Peralta et al2 propose a modification of the classic 6.0- to 8.0-cm hysterotomy in which the same multilayer correction of the spinal defect is performed through a 2.5- to 3.5-cm hysterotomy. This modification, called minihysterotomy, has been successfully performed outside of its creation center and was associated with reduced risks of preterm delivery and maternal, fetal, and neonatal complications.2,3.

Evaluation of the height of the corpus callosum body region in fetal meningomyelocele malformation.

PURPOSE: To investigate height of the corpus callosum (CC) in order to describe the corpus callosum anomalies in fetuses with meningomyelocele (MMC) and compare these findings with the corpus callosum of healthy fetuses. METHODS: In this study, fetal MRI examinations were performed on 44 fetal MMC malformation cases. As the control group, 34 fetal MRI examinations, which were anatomically normal, were evaluated retrospectively. In the study group, lateral ventricle diameter, the level and diameter of the MMC defect, and CC height were measured. In the control group, CC height and lateral ventricular diameter were measured. RESULTS: The mean CC body height was 1.36 mm in the study group, and 2.48 mm in the control group. The height of the CC body region of the study population was inclined to be thinner compared with the control population (p<0.001). CONCLUSIONS: The fact that the height of the CC body region was found to be thinner in fetal MRI in cases of MMC compared with normal fetuses suggests that various callosal anomalies are uncertain, investigation of additional callosal anomalies may be beneficial in the decision for the continuation of pregnancy, and termination or intrauterine surgery in cases with MMC. Further large case group studies are needed.

Long-Term Imaging Follow-up from the Management of Myelomeningocele Study.

BACKGROUND AND PURPOSE: Short-term results demonstrate that prenatal repair of a myelomeningocele is associated with a reduction in hydrocephalus and an increased likelihood of the reversal of Chiari II malformations compared with postnatal repair. The purpose of this study was to identify the long-term imaging findings at school age among subjects who underwent pre- versus postnatal repair of a myelomeningocele. MATERIALS AND METHODS: A subset of subjects enrolled in the Management of Myelomeningocele Study who underwent either prenatal (n = 66) or postnatal (n = 63) repair of a lumbosacral myelomeningocele and had follow-up brain MR imaging at school age were included. The prevalence of posterior fossa features of Chiari II malformation and supratentorial abnormalities and the change in these findings from fetal to school-age MR imaging were compared between the 2 groups. RESULTS: Prenatal repair of a myelomeningocele was associated with higher rates of normal location of fourth ventricle and lower rates of hindbrain herniation, cerebellar herniation, tectal beaking, brainstem distortion, and kinking at school age compared with postnatal repair (all P < .01). Supratentorial abnormalities, including corpus callosal abnormalities, gyral abnormalities, heterotopia, and hemorrhage, were not significantly different between the 2 groups (all P > .05). The rates of resolution of brainstem kinking, tectal beaking, cerebellar and hindbrain herniation, and normalization of fourth ventricle size from fetal to school age MR imaging were higher among the prenatal compared with postnatal surgery group (all, P < .02). CONCLUSIONS: Prenatal repair of a myelomeningocele is associated with persistent improvement in posterior fossa imaging findings of Chiari II malformation at school age compared with postnatal repair.

Double Lumbar Localization of Myelomeningocele: Case Report.

INTRODUCTION: Myelomeningocele (MMC) is a malformation resulting from the neural tube's failure to close during embryonic development, and the majority of the cases of neural tube defects (NTDs) were prevalent as single location lesions along the spine; however, multiple NTDs (MNTDs) are a very rare condition. Only a few cases of MNTDs were found in the literature. CASE PRESENTATION: We report the case of a 2-month-old male infant prenatally diagnosed with MMC, presented with two unconnected lumbar and lumbosacral epidermal, soft, dome-shaped swellings located on both sides of the midline (paravertebral) covered by intact skin. MRI revealed double MMC at the level of L4-L5, with spinal nerve roots. The patient underwent surgical repair of the defects by replacing the spinal cord and its nerve roots inside the thecal sac and recreating a covering layer around the neural structures to resemble thecal sac. The outcome was favorable, and postoperative head CT scan did not show any complication. CONCLUSION: Our case report is considered the first from Algeria to report the condition and the first to report the occurrence of double lesions in the same spine region. MMC can be associated with neurological deficits or other congenital anomalies, thus it is necessary to thoroughly examine such patients. However, there was no antenatal folic acid deficiency in our case. We recommend antenatal care with adequate folic acid supplementation given that its deficiency during pregnancy is considered a ubiquitous risk factor for the condition. The optimal timing for surgery of MMC cases is 8 ± 5 days. Prenatal intrauterine repair of the condition provides favorable outcomes but carries high fetal and maternal risks. Surgical repair should include the sac removal, the reconstruction of the placode, and the closure of the overlying meninges. With early diagnosis and proper repair of such cases, MMC has good prognosis and favorable outcomes.

The significance of hindbrain herniation reversal following prenatal repair of neural tube defects.

OBJECTIVE: The aim of this study was to determine whether reversal of hindbrain herniation (HBH) on MRI following prenatal repair of neural tube defects (NTDs) is associated with reduced rates of ventriculoperitoneal (VP) shunt placement or endoscopic third ventriculostomy (ETV) within the 1st year of life. METHODS: This is a secondary analysis of prospectively collected data from all patients who had prenatal open repair of a fetal NTD at a single tertiary care center between 2012 and 2020. Patients were offered surgery according to inclusion criteria from the Management of Myelomeningocele Study (MOMS). Patients were excluded if they were lost to follow-up, did not undergo postnatal MRI, or underwent postnatal MRI without a report assessing hindbrain status. Patients with HBH reversal were compared with those without HBH reversal. The primary outcome assessed was surgical CSF diversion (i.e., VP shunt or ETV) within the first 12 months of life. Secondary outcomes included CSF leakage, repair dehiscence, CSF diversion prior to discharge from the neonatal intensive care unit (NICU), and composite neonatal morbidity. Demographic, prenatal sonographic, and operative characteristics as well as outcomes were assessed using standard univariate statistical methods. Multivariate logistic regression models were fit to assess for independent contributions to the primary and secondary outcomes. RESULTS: Following exclusions, 78 patients were available for analysis. Of these patients, 38 (48.7%) had HBH reversal and 40 (51.3%) had persistent HBH on postnatal MRI. Baseline demographic and preoperative ultrasound characteristics were similar between groups. The primary outcome of CSF diversion within the 1st year of life was similar between the two groups (42.1% vs 57.5%, p = 0.17). All secondary outcomes were also similar between groups. Patients who had occurrence of the primary outcome had greater presurgical lateral ventricle width than those who did not (16.1 vs 12.1 mm, p = 0.02) when HBH was reversed, but not when HBH was persistent (12.5 vs 10.7 mm, p = 0.49). In multivariate analysis, presurgical lateral ventricle width was associated with increased rates of CSF diversion before 12 months of life (adjusted OR 1.18, 95% CI 1.03-1.35) and CSF diversion prior to NICU discharge (adjusted OR 1.18, 95% CI 1.02-1.37). CONCLUSIONS: HBH reversal was not associated with decreased rates of CSF diversion in this cohort. Predictive accuracy of the anticipated benefits of prenatal NTD repair may not be augmented by the observation of HBH reversal on MRI.

Development of a simulator for training of fetoscopic myelomeningocele surgery.

OBJECTIVE: To develop a realistic simulation model for laparotomy-assisted fetoscopic spina bifida aperta (SBa) surgery, to be used for training purposes and preoperative planning. METHODS: The predefined general requirement was a realistic model of an exteriorized uterus, allowing all neurosurgical steps of the intervention. The uterus was modelled using ultrasound and MRI images of a 25 weeks' gravid uterus, consisting of flexible polyurethane foam coated with pigmented silicone. The fetal model, contained an opening on the dorsal side for a customizable spinal insert with all the aspects of a SBa, including a cele, placode, and myofascial and skin layer. The model was assessed in a series of validation experiments. RESULTS: Production costs are low, uterus and fetus are reusable. Placental localization and the level and size of the spinal defect are adjustable, enabling case-specific adaptations. All aspects of the simulator were scored close to realistic or higher for both appearance and functional capacities. CONCLUSIONS: This innovative model provides an excellent training opportunity for centers that are starting a fetoscopic SBa repair program. It is the first simulation model with adjustable spinal defect and placental localisation. Further objective validation is required, but the potential for using this model in preoperative planning is promising.

Complex spinal dysraphism: myelomenigocele associated with dorsal bony spur, split cord malformation type I, syringomyelia, lipoma and tethered cord.

Variations in split cord malformation (SCM) are known. However, association of SCM type I with myelomeningocele along with same level dorsal bony spur has not been described previously. We report a 1-year old male child who presented with these findings with associated syringomyelia, lipoma and tethered cord.

Fetal MRI prior to intrauterine surgery of open neural tube defects: What does the radiologist need to know.

The management of myelomeningocele study trial showed significant prognostic improvement in fetal repair before 26 weeks of gestation. Hence, surgery in utero represents the best treatment option for open-neural tube defects (NTDs). Fetal surgery of open-NTDs has specific inclusion and exclusion criteria, which can be adequately studied with fetal MRI. The main concern: the spine (spinal defects other than Myelomeningocele and Myeloschisis, the level of the lesion higher than T1 or lower than S1 and the degree of kyphosis ≥ 30°), the skull/brain (no cerebellum herniation and Chiari II malformation and the presence of any intracranial abnormality unrelated to open NTDs), the uterus (cervix length less than 2 cm, multiple gestations and placental and uterine abnormalities) and any other fetal abnormality not attributed to spinal defect. In this review, we describe the fundamental role of fetal MRI in supporting therapeutic decisions in pre-surgery intrauterine planning through the accurate and comprehensive description of findings, providing a proposal of a structured report. In addition, we describe how post-surgical MRI is important in investigating the effectiveness of surgery and detecting repairing complications.

Ultrasound evaluation of uterine scar thickness after open fetal surgery for myelomeningocele.

PURPOSE: This study aimed to analyse the evolution of uterine scar thickness after open fetal surgery for myelomeningocele (MMC) by ultrasonography, and to establish a cut-off point for uterine scar thickness associated with high-risk of uterine rupture. METHODS: A prospective longitudinal study was conducted with 77 pregnant women who underwent open fetal surgery for MMC between 24 and 27 weeks of gestation. After fetal surgery, ultrasound follow-up was performed once a week, and the scar on the uterine wall was evaluated and its thickness was measured by transabdominal ultrasound. At least five measurements of the uterine scar thickness were performed during pregnancy. A receiver operating characteristics (ROC) curve was constructed to obtain a cut-off point for the thickness of the scar capable of detecting the absence of thinning. Kaplan-Meier curves were constructed to evaluate the probability of thinning during pregnancy follow-up. RESULTS: The mean ± standard deviation of maternal age (years), gestational age at surgery (weeks), gestational age at delivery (weeks), and birth weight (g) were 30.6 ± 4.5, 26.1 ± 0.8, 34.3 ± 1.2 and 2287.4 ± 334.4, respectively. Thinning was observed in 23 patients (29.9%). Pregnant women with no thinning had an average of 17.1 ± 5.2 min longer surgery time than pregnant women with thinning. A decrease of 1.0 mm in the thickness of the uterine scar was associated with an increased likelihood of thinning by 1.81-fold (95% confidence interval [CI]: 1.32-2.47; p < 0.001). The area below the ROC curve was 0.899 (95% CI: 0.806-0.954; p < 0.001), and the cut-off point was ≤ 3.0 mm, which simultaneously presented greater sensitivity and specificity. After 63 days of surgery, the probability of uterine scarring was 50% (95% CI: 58-69). CONCLUSION: A cut-off point of ≤ 3.0 mm in the thickness of the uterine scar after open fetal surgery for MMC may be used during ultrasonography monitoring for decision-making regarding the risk of uterine rupture and indication of caesarean section.

A comparison of MRI appearance and surgical detethering rates between intrauterine and postnatal myelomeningocele closures: a single-center pilot matched cohort study.

INTRODUCTION: Intrauterine myelomeningocele repair (IUMR) and postnatal myelomeningocele repair (PNMR) differ in terms of both setting and surgical technique. A simplified technique in IUMR, in which a dural onlay is used followed by skin closure, has been adopted at our institution. The goal of this study was to compare the rates of clinical tethering in IUMR and PNMR patients, as well as to evaluate the appearance on MRI. METHODS: We conducted a retrospective review of 36 patients with MMC repaired at our institution, with 2:1 PNMR to IUMR matching based on lesion level. A pediatric neuroradiologist blinded to the clinical details reviewed the patients' lumbar spine MRIs for the distance from neural tissue to skin and the presence or absence of a syrinx. An EMR review was then done to evaluate for detethering procedures and need for CSF diversion. RESULTS: Mean age at MRI was 4.0 years and mean age at last follow-up was 6.1 years, with no significant difference between the PNMR and IUMR groups. There was no significant difference between groups in the distance from neural tissue to skin (PNMR 13.5 mm vs IUMR 17.6 mm; p = 0.5). There was no difference in need for detethering operations between groups (PNMR 12.5% vs IUMR 16.7%; RR 0.75; CI 0.1-5.1). CONCLUSIONS: There was no significant difference between postnatal- and intrauterine-repaired myelomeningocele on MRI or in need for detethering operations. These results imply that a more straightforward and time-efficient IUMR closure technique does not lead to an increased rate of tethering when compared to the multilayered PNMR.

Symptomatic Dermal Inclusion Cysts in Infants following Fetal Surgery for Myelomeningocele: Report of Two Cases and Review of the Literature.

INTRODUCTION: It remains unclear if fetal repair of myelomeningocele (MM) is associated with a greater risk of developing symptomatic dermal inclusion cysts (ICs) at the neural placode. We report two infants treated with fetal surgery who developed symptomatic IC at less than 1 year of age, and we discuss the current literature on symptomatic IC in children with MM. CASE PRESENTATION: Two infants underwent fetal MM repair at 24 weeks of gestational age. Case 1 was born at 30 weeks and had two revisions of the MM wound early in life. At 8 months of age, the patient presented with meningismus and imaging findings of an IC, which was resected at the time of presentation. At 3 years of age, this patient was found to have recurrence of the IC after presenting with worsening bladder function and underwent repeat debulking with no recurrence at 6 years of age. Case 2 was born at 32 weeks of gestational age with uncomplicated recovery. At 8 months of age, the patient presented with irritability and fullness at the lumbar repair site. Imaging showed a large IC with restricted diffusion and extension into the subcutaneous tissue; this was resected completely at the time of presentation, see intraoperative photographs. There has been no sign of recurrence at age of 15 months. CONCLUSIONS: Careful monitoring for IC in infancy in MM patients who have had fetal surgery is recommended.

Presentación de un meningocele lumbosacro en un adulto / Case Presentation of a ruptured lumbosacral meningocele in an adult patient

La espina bífida, o mielodisplasia, es una anomalía de origen multifactorial congénita que se presenta con mayor frecuencia durante el desarrollo embrionario. Se produce por el cierre parcial de los pliegues neurales conjuntamente con una fusión defectuosa de los arcos vertebrales. Su clínica es variable e incluye una serie de manifestaciones como expresión del compromiso neurológico. El diagnóstico se basa en la presencia de las manifestaciones clínicas ayudado de estudios imagenológicos. La corrección quirúrgica del defecto es la conducta terapéutica que se preconiza como adecuada. Se presenta el caso de una paciente de 34 años de edad con mielomeningocele no corregido en edad infantil que se presenta con complicaciones infecciosas y secuelas neurológicas. Se administró esquema de antibioticoterapia con varios antibióticos de amplio espectro, y se decidió intervenir quirúrgicamente, con lo que se logró el cierre del orificio comunicante de la región espinal con el exterior. Además, se reconstruyó la zona aledaña al mielomeningocele para evitar posible sepsis del Sistema Nervioso Central. La paciente tuvo una evolución favorable y fue dada de alta hospitalaria a los 7 días posteriores a la intervención quirúrgica sin secuelas neurológicas(AU)

Spine bifida, or myelodysplasia, is a multifactorial congenital anomaly that occurs most frequently during embryonic development. It is produced by the partial closure of the neural folds together with a defective fusion of the vertebral arches. Its clinic is variable and includes a series of manifestations as an expression of neurological compromise. The diagnosis is based on the presence of clinical manifestations, aided by imaging studies. Surgical correction of the defect is the therapeutic conduct that is recommended as adequate. This report presents the case of a 34-year-old patient with uncorrected myelomeningocele in childhood who presented with infectious and neurological sequelae complications(AU)

The Construction of a Predictive Composite Index for Decision-Making of CSF Diversion Surgery in Pediatric Patients following Prenatal Myelomeningocele Repair.

BACKGROUND AND PURPOSE: There is a wide range of clinical and radiographic factors affecting individual surgeons' ultimate decision for CSF diversion for pediatric patients following prenatal myelomeningocele repair. Our aim was to construct a composite index (CSF diversion surgery index) that integrates conventional clinical measures and neuroimaging biomarkers to predict CSF diversion surgery in these pediatric patients. MATERIALS AND METHODS: This was a secondary retrospective analysis of data from 33 patients with prenatal myelomeningocele repair (including 14 who ultimately required CSF diversion surgery). Potential independent variables, including the Management of Myelomeningocele Study Index (a dichotomized variable based on the shunt-placement criteria from the Management of Myelomeningocele Study), postnatal DTI measures (fractional anisotropy and mean diffusivity in the genu of the corpus callosum and the posterior limb of internal capsule), fronto-occipital horn ratio at the time of DTI, gestational ages, and sex, were evaluated using stepwise logistic regression analysis to identify the most important predictors. RESULTS: The CSF diversion surgery index model showed that the Management of Myelomeningocele Study Index and fractional anisotropy in the genu of the corpus callosum were significant predictors (P < .05) of CSF diversion surgery. The predictive value of the CSF diversion surgery index was also affected by fractional anisotropy in the posterior limb of the internal capsule and sex with marginal effect (.05

.10). The overall CSF diversion surgery index model fit the data well with statistical significance (eg, likelihood ratio: P < .001), with the performance (sensitivity = 78.6%; specificity = 86.5%, overall accuracy = 84.8%) superior to all individual indices in sensitivity and overall accuracy, and most of the individual indices in specificity. CONCLUSIONS: The CSF diversion surgery index model outperformed all single predictor models and, with additional validation, may potentially be developed and incorporated into a sensitive and robust clinical tool to assist clinicians in hydrocephalus management.

Myelomeningocele as an anomaly of secondary neurulation.

PURPOSE: Myelomeningocele (MMC) is the representative entity of open neural tube defects resulting from an error during primary neurulation. However, cases of MMC in the region of the secondary neural tube (below the junction of S1 and S2 vertebrae) are sometimes encountered. We aimed to analyze the clinical features of atypical "low-lying" MMC in comparison to the typical MMC and suggest possible pathoembryogenesis. METHODS: From 1986 to 2020, 95 MMC patients were treated in our institute. A retrospective review of the radiological and clinical information was performed. We defined "low-lying" MMCs as those with fascia or lamina defects below the S1-2 interspinous ligament. RESULTS: Thirty-one out of the 95 MMC patients were identified as having low-lying MMC. The percentage of low-lying MMC within the entire MMC group increased dramatically (19% from 1990 to 1999 and 48% from 2000 to 2020). Thirty-nine percent of the low-lying MMCs were associated with hydrocephalus, and 36% showed the Chiari malformation. Clean intermittent catheterization was being performed by 52% of the patients and 46% had a motor weakness. The proportions of hydrocephalus, neurological symptoms, and the number of related procedures in the low-lying MMC were substantially lower than the typical MMC in our cohort and the literature. CONCLUSIONS: We present cases of atypical MMC occurring in the region of secondary neurulation. These cases provide clues that secondary neurulation may lead to open neural defects. Future experiments with animal models supporting what we have seen in the clinics will greatly enhance the understanding of the developmental process of neurulation and the corresponding anomalies.

Retained Medullary Cord Associated with Terminal Myelocystocele and Intramedullary Arachnoid Cyst.

INTRODUCTION: The retained medullary cord (RMC) is a newly defined entity of closed spinal dysraphism that is thought to originate from regression failure of the medullary cord during the last phase of secondary neurulation. The terminal myelocystocele (TMC) is an unusual type of closed spinal dysraphism, characterized by localized cystic dilatation of the terminal part of the central canal that then herniates through a posterior spinal bifida. The co-occurrence of RMC and TMC is extremely rare. CASE PRESENTATION: We treated a baby girl with a huge sacrococcygeal meningocele-like sac with two components. Untethering surgery and repair surgery for the sac revealed that RMC, associated with intramedullary arachnoid cyst (IMAC), was terminated at the bottom of the rostral cyst, forming the septum of the two cystic components, and the caudal cyst was TMC derived from the central canal-like ependymal lining lumen (CC-LELL) of the RMC at the septum. IMAC within the RMC communicated with TMC, and both contained xanthochromic fluid with the same properties. CONCLUSION: We speculated that the mass effect of the coexistent IMAC impeded the flow of cerebrospinal fluid in the CC-LELL within the RMC and eventually formed a huge TMC. In surgical strategies for such complex pathologies, it is important to identify the electrophysiological border between the functional cord and nonfunctional RMC and the severe RMC to untether the cord, as with a typical or simple RMC.