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.

Is ventriculomegaly and hindbrain herniation seen before and after prenatal neural tube defect repair associated with a worse functional level than anatomical level at birth?

OBJECTIVE: To determine if the evaluation of the fetal ventricular system and hindbrain herniation (HBH) is associated with motor outcome at birth in prenatally repaired open neural tube defect (NTD). METHODS: Retrospective cohort study of 47 patients with NTD who underwent prenatal repair (17 fetoscopic; 30 open-hysterotomy). At referral and 6 weeks postoperatively, the degree of HBH, ventricular atrial widths and ventricular volume were evaluated by MRI. Head circumference and ventricular atrial widths were measured on ultrasound at referral and during the last ultrasound before delivery. Anatomic level of the lesion (LL) was determined based on the upper bony spinal defect detected by ultrasound. We considered the functional level as worse than anatomical level at birth when the motor level was equal or worse than the anatomical LL. RESULTS: 26% (12/47) of the cases showed worse functional level than anatomical level at birth. Having a HBH below C1 at the time of referral was associated with a worse functional level than anatomical level at birth (OR = 9.7, CI95 [2.2-42.8], p < 0.01). None of the other brain parameters showed a significant association with motor outcomes at birth. CONCLUSIONS: HBH below C1 before surgery was associated with a worse functional level than anatomical level at birth.

In Utero Restoration of Hindbrain Herniation in Fetal Myelomeningocele as Part of Prenatal Regenerative Therapy Program at Mayo Clinic.

OBJECTIVE: To assess our initial experience with prenatal restoration of hindbrain herniation following in utero repair of myelomeningocele (MMC). PATIENTS AND METHODS: Three consecutive patients with prenatally diagnosed MMC (between January 1, 2018 and September 30, 2018) were managed with open in utero surgery. As per institutional review board approval and following a protocol designed at the Mayo Clinic Maternal & Fetal Center, fetal intervention was offered between 19 0/7 and 25 6/7 weeks of gestation. Prenatal improvement of hindbrain herniation was the declared restorative end point. Obstetrical and perinatal outcomes were also assessed. RESULTS: Diagnosis of MMC was confirmed upon referral between 20 and 21 weeks' gestation by using fetal ultrasound and magnetic resonance imaging. In all cases reported here, the spinal defect was lumbosacral with evidence of hindbrain herniation. Open in utero MMC repair was performed between 24 and 25 weeks' gestation with no notable perioperative complications. Postprocedure fetal magnetic resonance imaging performed 6 weeks after in utero repair documented improvement of hindbrain herniation. Deliveries were at 37 weeks by cesarean section without complications. Most recent postnatal follow-ups were unremarkable at both 11 months (baby 1) and 3 months of age (baby 2), with mild ventriculomegaly. Antenatal and postnatal follow-up of baby 3 at 1 month of age was also unremarkable. CONCLUSION: Our study highlights the prenatal restoration of hindbrain herniation following in utero MMC repair in all cases presented here as an example of a prenatal regenerative therapy program in our institution.

Cerebrospinal Fluid Flowmetry in Pediatric Patients with Chiari Malformation I with Surgical Implications.

BACKGROUND: Chiari malformations include a large spectrum of anomalies of hindbrain formation that appear at different stages of development of the central nervous system. Chiari described these malformations as congenital anomalies of the hindbrain characterized by downward elongation of the brain stem and cerebellum into the cervical portion of spinal cord. Much research regarding Chiari malformation I (CMI) has focused on the cerebrospinal fluid (CSF) dynamics rather than the anatomic relationships of the tonsils and brainstem. The aim of the present study was to measure the peak CSF velocity at the foramen magnum and record the changes after foramen magnum decompression in patients with CMI aged <18 years. METHODS: A total of 39 patients with CMI were included during a 2-year period and were analyzed for peak CSF flow velocity with respect to surgical intervention using predefined magnetic resonance imaging protocols and surgical technique. RESULTS: After foramen magnum decompression, the postoperative mean CSF peak flow velocity showed a statistically significant difference compared with the preoperative value. CONCLUSION: Decompression of the foramen magnum was associated with decreased CSF peak velocity in patients with CMI.

Progressive hydrocephalus despite early complete reversal of hindbrain herniation after prenatal open myelomeningocele repair.

OBJECTIVE: Open prenatal myelomeningocele (MMC) repair is typically associated with reversal of in utero hindbrain herniation (HBH) and has been posited to be associated with a reduction in both postoperative prenatal and immediate postnatal hydrocephalus (HCP) risks. However, the long-term postnatal risk of HCP following HBH reversal in these cases has not been well defined. The authors describe the results of a long-term HCP surveillance in a cohort of patients who underwent prenatal MMC repair at their institution. METHODS: A retrospective review of all prenatal MMC repair operations performed at the Mayo Clinic between 2012 and 2017 was conducted. Pertinent data regarding the clinical courses of these patients before and after MMC repair were summarized. Outcomes of interest were occurrences of HBH and HCP and the need for intervention. RESULTS: A total of 9 prenatal MMC repair cases were identified. There were 7 cases in which MRI clearly demonstrated prenatal HBH, and of these 86% (6/7) had evidence of HBH reversal after repair and prior to delivery. After a mean postnatal follow-up of 20 months, there were 3 cases of postnatal HCP requiring intervention. One case that failed to show complete HBH reversal after MMC repair required early ventriculoperitoneal shunting. The other 2 cases were of progressive, gradual-onset HCP despite complete prenatal HBH reversal, requiring endoscopic third ventriculostomy with choroid plexus cauterization at ages 5 and 7 months. CONCLUSIONS: Although prenatal MMC repair can achieve HBH reversal in a majority of well-selected cases, the prevention of postnatal HCP requiring intervention appears not to be predicated on this outcome alone. In fact, it appears that in a subset of cases in which HBH reversal is achieved, patients can experience a progressive, gradual-onset HCP within the 1st year of life. These findings support continued rigorous postnatal surveillance of all prenatal MMC repair patients, irrespective of postoperative HBH outcome.

Enhancing nodular lesions in Chiari II malformations in the setting of persistent hindbrain herniation: case report and literature review.

BACKGROUND: Chiari II malformation includes concomitant cerebellar tonsillar herniation, hydrocephalus, and myelomeningocele. Rarely, pediatric patients with persistent hindbrain herniation develop a new enhancing nodule at the cervicomedullary junction as adults. These new lesions may be suspicious for neoplastic growth, but it remains unclear if neurosurgical intervention is necessary. CASE REPORT: A 27-year-old female patient with history of Chiari II malformation and persistent hindbrain herniation presented with a 3-month history of headache and upper extremity weakness and numbness. Neuroimaging revealed a new enhancing nodule near the cervicomedullary junction suspicious for neoplasm. Following posterior fossa decompression and excision of the enhancing lesion, pathological analysis demonstrated only benign glioneural heterotopia. RESULTS: New enhancing nodules at the cervicomedullary junction in Chiari II malformation are exceedingly rare and are likely benign, reactive changes rather than a neoplastic process. Biopsy or surgical excision of these lesions is likely unnecessary for asymptomatic patients.

Defining, diagnosing, clarifying, and classifying the Chiari I malformations.

PURPOSE: Chiari malformations (CM) have been traditionally classified into four categories: I, II, III, and IV. In light of more recent understandings, variations of the CM have required a modification of this classification. METHODS: This article discusses the presentation, diagnostics, and treatment of the newer forms of hindbrain herniation associated with the CM type I. RESULTS: The CM 1 is a spectrum that includes some patients who do not fall into the exact category of this entity. CONCLUSIONS: While CM have been categorically recognized as discrete and individual conditions, newer classifications such as CM 0 and CM 1.5 exhibit some degree of continuity with CM 1; however, they require distinct and separate classification as symptoms and treatments can vary among these clinical subtypes.

Evaluation of Soft Tissue Hypertrophy at the Retro-Odontoid Space in Patients with Chiari Malformation Type I on Magnetic Resonance Imaging.

INTRODUCTION: Chiari malformation type I (CM-I) is a well-known hindbrain disorder in which the cerebellar tonsils protrude through the foramen magnum. The soft tissues, including the transverse ligament and the tectorial membrane at the retro-odontoid space, can compress the cervicomedullary junction if they become hypertrophic. METHODS: Twenty-two symptomatic patients with CM-I (aged 5-19 years) were treated between 2007 and 2017 at our institute. The retro-odontoid soft tissue was evaluated using T2-weighted magnetic resonance imaging. Anteroposterior (AP) distances and craniocaudal distances of the soft tissue were measured in patients with CM-I and 48 normal control children. Modified clivoaxial angles were also evaluated as the index of ventral compression of the cervicomedullary junction. RESULTS: Of the 18 patients treated with foramen magnum decompression, 16 patients improved postoperatively, whereas the condition of 2 remained unchanged. The AP distances in the CM-I group (6.0 mm) were significantly larger than those in the control group (3.5 mm), whereas there were no apparent differences in the craniocaudal distances. Modified clivoaxial angles were obviously smaller in the CM-I group (131.5°) than in the control group (146.9°). Moreover, the AP distances were significantly reduced postoperatively (5.5 mm), although the other parameters did not change significantly. CONCLUSIONS: The retro-odontoid soft tissue in symptomatic patients with CM-I can be hypertrophic enough to compress the cervicomedullary junction ventrally even if there are no combined osseous anomalies. Foramen magnum decompression works to reduce the hypertrophic changes significantly, suggesting that downward tonsil movement might participate in hypertrophic soft tissue formation at the retro-odontoid space.

Coagulation in hindbrain membrane meningioma patients treated with different injections using acute hypervolemic hemodilution.

The aim of this study was to analyze the changes in coagulation in meningioma patients treated with different injections using the method of acute hypervolemic hemodilution (AHH). One hundred fifty hindbrain membrane meningioma patients were randomly divided into 5 groups, 30 per group. The first group were injected 40ml/time with Danhong after anesthesia induction; the second group were injected with 40ml~60ml/time Kangai and combined with interventional chemotherapy and embolization procedure; the third group of AHH were injected with polygeline 15ml/kg; the fourth group were injected with hydroxyethyl starch (130/0.4) sodium chloride in doses of 15ml/kg; the control group underwent basic treatment for lowering blood pressure and lowering blood fat. The changes of coagulation index were recorded before and after surgery and before and after the injection of different medications. Compared to the control group, for the first group of AHH, after being treated for 10 days and 30 days, the concentrations of bone specific alkaline phosphatase (BALP), bone Gla protein (BGP) and pro-collagen carboxy-terminal propeptide (PICP) were higher than that of the control group, the levels of endotoxin (ET) and C-reactive protein (CRP) were decreased compared to the control group (p less than 0.05); for the second group of AHH, after being treated for 10 days, the index of prothrombin time (PT), activated partial thromboplastin time (APTT), thrombin time (TT), fibrinogen (Fg) were not significantly changed, but the related level of vascular endothelial growth factor (VEGF) significantly decreased (p less than 0.05). Comparing the coagulation function index after surgery in the third and fourth groups, there were no significant changes in mean arterial pressure (MAP) level, heart rate (HR) value presented a low decrease, central venous pressure (CVP) level increased and the level of interleukin IL-6 showed a steady state after increasing. Analyzing the levels of interleukin IL-8 and tumor necrosis factor-α (TNF-α) after surgery, it was seen that in the third group they increased and in the fourth group they decreased (p less than 0.05). Danhong injection improved the coagulation function and microcirculation of patients, Kangai injection and interventional chemotherapy and embolization restrained the appearance of tumor angiogenesis, AHH operation with polygeline injection and hydroxyethyl starch (130/0.4) sodium chloride kept blood flow in normal parameters.

Prenatal surgery for myelomeningocele: review of the literature and future directions.

Open spina bifida or myelomeningocele (MMC) is one of the most common serious congenital malformations. Historically, this condition has been treated with closure of the MMC defect shortly after birth. The goal of postnatal closure is to cover the exposed spinal cord and prevent infection. However, postnatal surgery does not reverse or prevent the neurologic injury seen in MMC, reverse hindbrain herniation, or prevent hydrocephalus. The neurologic defects result from primary incomplete neurulation and secondary chronic prenatal damage to the exposed neural elements through mechanical and chemical trauma. In a hope to reduce the numerous surgical procedures, medical complications, and lifelong disabilities associated with MMC, the proposal of prenatal closure was put forth more than two decades ago. After promising results in animal models and some clinical series, a randomized controlled trial, the Management of Myelomeningocele Study (MOMS), was conducted. The MOMS trial demonstrated that closure during the prenatal period could be performed relatively safely and can result in significant benefit to the child. Specifically, prenatal closure results in improved motor function, reduced hindbrain herniation, and reduced need for a cerebral spinal fluid diversion. Long-term outcomes of the patients in the MOMS trial continues in the MOMS 2 study as these children grow. Additionally, investigations are underway on modifications to the open fetal MMC closure techniques.

Nonsynostotic Posterior Brachycephaly with Hindbrain Herniation.

BACKGROUND: Positional plagiocephaly is the most common cause of cranial asymmetry. The underlying cause of Chiari-1 malformation has many possible theories, and anecdotally some pediatric neurosurgeons have had experience of severe cases of positional brachycephaly with Chiari-1. However, to date, there have been no published cases linking nonsynostotic plagiocephaly with Chiari-1 malformation. CASE DESCRIPTION: An 18-month-old boy presented with a head injury. On examination he had a Glasgow Coma Score of 15 with no focal neurologic deficits, but he was noted to have marked posterior brachycephaly. A computed tomography scan showed a slim left-sided hemispheric acute subdural hematoma with no mass effect, which was treated conservatively. Of note, all of his cranial vault sutures were open, and a diagnosis of incidental positional plagiocephaly was made. Subsequent magnetic resonance imaging as part of a work-up to exclude nonaccidental injury showed a small posterior fossa with a steep tentorium and herniation of the cerebellar tonsils to the level of the body of the second cervical vertebra. CONCLUSIONS: Chronic hindbrain herniation is well reported in cases of craniosynostosis, but to our knowledge this is the first published case associated with nonsynostotic deformational plagiocephaly. We hypothesize that severe posterior plagiocephaly can cause disproportion of the posterior fossa: hindbrain volume ratio and acquired chronic cerebellar herniation. Nevertheless, positional plagiocephaly and Chiari-1 are common entities, and it is possible that the dual diagnoses were coincidental in this case. This report serves to raise awareness of a putative causal relationship between positional plagiocephaly, reduced posterior fossa volume, and hindbrain herniation.

Cerebellar and hindbrain motion in Chiari malformation with and without syringomyelia.

OBJECTIVE: The pathogenesis of syringomyelia associated with Chiari malformation type I (CM-I) is unclear. Theories of pathogenesis suggest the cerebellar tonsils may obstruct CSF flow or alter pressure gradients, or their motion might act as a piston to increase CSF pressure in the spinal subarachnoid space. This study was performed to measure cerebellar tonsillar and hindbrain motion in CM-I and assess the potential contributions to syrinx formation. METHODS: Sixty-four CM-I patients and 25 controls were retrospectively selected from a clinical database, and all subjects had undergone cardiac-gated cine balanced fast-field echo MRI. There were a total of 36 preoperative CM-I scans, which consisted of 15 patients with and 21 patients without syringomyelia. Nineteen patients underwent paired pre- and postoperative imaging. Anteroposterior (AP) and superoinferior (SI) movements of the tip of the cerebellar tonsils, obex, fastigium of the fourth ventricle, pontomedullary junction, and cervicomedullary junction were measured. The distance between the fastigium and tip of the tonsils was used to calculate tonsillar tissue strain (Δi/i0). RESULTS: CM-I patients had significantly greater cerebellar tonsillar motion in both the AP and SI directions than controls (AP +0.34 mm [+136%], p < 0.001; SI +0.49 mm [+163%], p < 0.001). This motion decreased after posterior fossa decompression (AP -0.20 mm [-33%], p = 0.001; SI -0.29 mm [-36%]; p < 0.001), but remained elevated above control levels (AP +56%, p = 0.021; SI +67%, p = 0.015). Similar trends were seen for all other tracked landmarks. There were no significant differences in the magnitude or timing of motion throughout the hindbrain between CM-I patients with and without syringomyelia. Increased tonsillar tissue strain correlated with Valsalva headaches (p = 0.03). CONCLUSIONS: Cerebellar tonsillar motion may be a potential marker of CM-I and may have use in tailoring surgical procedures. The lack of association with syringomyelia suggests that tonsillar motion alone is not the driver of syrinx formation. Tonsillar tissue strain may play a part in the pathophysiology of Valsalva headaches.

Successfully treated symptomatic fusiform basilar artery aneurysm in a patient with hindbrain malformation via inverted Y-stenting.

A double overlapping reverse Y-stent approach to creating flow diversion using traditional open-cell stent technology was evaluated as a treatment option symptomatic fusiform basilar aneurysms. A 36-year-old man with a complex hindbrain malformation presented with acute ocular dysmotility due to a rapidly enlarging fusiform basilar artery aneurysm. The aneurysm was treated by insertion of two stents into the vertebrobasilar system in an inverted Y-configuration from the basilar tip to the V4 segments of the bilateral vertebral arteries, essentially creating flow diversion without using a dedicated flow diversion device. This resulted in immediate symptomatic improvement. The stents remained patent and the aneurysm was obliterated at 6 months follow-up. Furthermore, the patient remained free of associated symptoms at 10 months follow-up. Thus, the double stenting technique can be used instead of a flow diversion device to effectively create flow diversion, promote aneurysm sac thrombosis, and lead to resolution of symptoms in large fusiform basilar artery aneurysms.

Elevated corticosterone in the dorsal hindbrain increases plasma norepinephrine and neuropeptide Y, and recruits a vasopressin response to stress.

Repeated stress and chronically elevated glucocorticoids cause exaggerated cardiovascular responses to novel stress, elevations in baseline blood pressure, and increased risk for cardiovascular disease. We hypothesized that elevated corticosterone (Cort) within the dorsal hindbrain (DHB) would: 1) enhance arterial pressure and neuroendocrine responses to novel and repeated restraint stress, 2) increase c-Fos expression in regions of the brain involved in sympathetic stimulation during stress, and 3) recruit a vasopressin-mediated blood pressure response to acute stress. Small pellets made of 10% Cort were implanted on the surface of the DHB in male Sprague-Dawley rats. Blood pressure was measured by radiotelemetry. Cort concentration was increased in the DHB in Cort-treated compared with Sham-treated rats (60 ± 15 vs. 14 ± 2 ng Cort/g of tissue, P < 0.05). DHB Cort significantly increased the integrated arterial pressure response to 60 min of restraint stress on days 6, 13, and 14 following pellet implantation (e.g., 731 ± 170 vs. 1,204 ± 68 mmHg/60 min in Sham- vs. Cort-treated rats, day 6, P < 0.05). Cort also increased baseline blood pressure by day 15 (99 ± 2 vs. 108 ± 3 mmHg for Sham- vs. Cort-treated rats, P < 0.05) and elevated baseline plasma norepinephrine and neuropeptide Y concentrations. Cort significantly enhanced stress-induced c-Fos expression in vasopressin-expressing neurons in the paraventricular nucleus of the hypothalamus, and blockade of peripheral vasopressin V1 receptors attenuated the effect of DHB Cort to enhance the blood pressure response to restraint. These data indicate that glucocorticoids act within the DHB to produce some of the adverse cardiovascular consequences of chronic stress, in part, by a peripheral vasopressin-dependent mechanism.

Raised intracranial pressure and hydrocephalus following hindbrain decompression for Chiari I malformation: a case series and review of the literature.

OBJECT: Chiari-syringomyelia is a heterogeneous condition that may be treated by decompression of the foramen magnum. Raised intracranial pressure (ICP) and/or hydrocephalus is a rare complication of this treatment. We aim to describe the incidence, clinical presentation, radiographic findings, management and outcome of patients developing raised ICP and/or hydrocephalus after hindbrain decompression for Chiari I malformation. METHODS: Retrospective analysis of 138 consecutive adult and paediatric patients with Chiari I malformation who underwent foramen magnum decompression. RESULTS: The incidence of post-operative symptomatic raised ICP and/or hydrocephalus in this series was 8.7%. Overall, 9 of 12 patients developing raised ICP or hydrocephalus required a VP shunt, an overall incidence of 6.5%. However, 3 of 12 patients were successfully managed with external ventricular drainage or conservatively. Presentation was with headache or CSF wound leak at a median of 13 days post-operatively. Subdural hygromata were observed in five cases in association with hydrocephalus and urgent drainage to relieve mass effect was required in two cases. At a mean follow up of 36 months, 9 of 12 patients were asymptomatic. CONCLUSIONS: There is a risk of requiring a permanent VP shunt associated with decompression for Chiari I even in the absence of ventriculomegaly or signs of raised ICP pre-operatively. Patients presenting with new symptoms or CSF wound leak following FMD mandate investigation to exclude hydrocephalus, raised ICP or subdural hygroma.

Craniovertebral junction abnormalities with hindbrain herniation and syringomyelia: regression of syringomyelia after removal of ventral craniovertebral junction compression.

OBJECT: Hindbrain herniation syndrome, or Chiari malformation Type I (CM-I), occurs frequently with craniovertebral junction (CVJ) abnormalities when there is reduction in the posterior fossa volume. Syringomyelia is often present. Posterior fossa dorsal decompression (PFDD) is typically performed but has adverse results when ventral bone abnormality exists. This paper presents the results of a prospective study on CVJ abnormalities in patients with CM-I and syringomyelia. METHODS: Between 1984 and 2008 (the MR imaging era), 298 patients with CVJ abnormalities and CM-I underwent ventral cervicomedullary decompression. Eighty-four patients had associated syringomyelia (15 with secondary invagination and 69 with primary basilar invagination, os odontoideum, or malunion of fractures). Of these 84 patients with CVJ abnormalities, CM-I, and syringomyelia, 46 had previously undergone PFDD, and 28 had previously undergone PFDD combined with fusion procedures or shunt placements. Of the 84 patients, a cervicothoracic syrinx was observed in 57, thoracic syrinx in 14, and holocord syrinx in 13. Studies included CT, MR imaging, and cine flow studies. All 298 patients who underwent ventral CVJ decompression had irreducible or partially reducible pathology. All 84 with syringomyelia showed brainstem dysfunction, lower cranial nerve symptoms, or myelopathy. RESULTS: Brainstem signs improved in 66 of the 84 patients, myelopathy improved in 58, and syringomyelia regressed in 64. CONCLUSIONS: Neurological improvement and syringomyelia resolution can occur using only ventral cervicomedullary junction decompression in patients with basilar invagination and basilar impression. This is likely due to the relief of neural encroachment and reestablishment of CSF pathways.

Volumetric analysis of syringomyelia following hindbrain decompression for Chiari malformation Type I: syringomyelia resolution follows exponential kinetics.

OBJECT: Resolution of syringomyelia is common following hindbrain decompression for Chiari malformation, yet little is known about the kinetics governing this process. The authors sought to establish the volumetric rate of syringomyelia resolution. METHODS: A retrospective cohort of patients undergoing hindbrain decompression for a Chiari malformation Type I with preoperative cervical or thoracic syringomyelia was identified. Patients were included in the study if they had at least 3 neuroimaging studies that detailed the entirety of their preoperative syringomyelia over a minimum of 6 months postoperatively. The authors reconstructed the MR images in 3 dimensions and calculated the volume of the syringomyelia. They plotted the syringomyelia volume over time and constructed regression models using the method of least squares. The Akaike information criterion and Bayesian information criterion were used to calculate the relative goodness of fit. The coefficients of determination R(2) (unadjusted and adjusted) were calculated to describe the proportion of variability in each individual data set accounted for by the statistical model. RESULTS: Two patients were identified as meeting inclusion criteria. Plots of the least-squares best fit were identified as 4.01459e(-0.0180804)(x) and 13.2556e(-0.00615859)(x). Decay of the syringomyelia followed an exponential model in both patients (R(2) = 0.989582 and 0.948864). CONCLUSIONS: Three-dimensional analysis of syringomyelia resolution over time enables the kinetics to be estimated. This technique is yet to be validated in a large cohort. Because syringomyelia is the final common pathway for a number of different pathological processes, it is possible that this exponential only applies to syringomyelia related to treatment of Chiari malformation Type I.

Acute deterioration of a Chiari I malformation: an uncommon neurosurgical emergency.

OBJECTIVES: Report and discuss acute neurological deterioration of Chiari I malformation (CMI), surgical treatment and timing, clinical outcome and literature review. CASE REPORT: We report a recent case of a 15-year-old girl admitted for an acute neurological deterioration caused by an undiagnosed hindbrain herniation that required an urgent foramen magnum decompression and external ventricular drainage insertion. Moreover, we report and discuss the literature. To the authors' knowledge, this is only the third paediatric patient identified in this setting to be treated for an acute neurological deterioration due to a previous asymptomatic hindbrain herniation. The patient made an uncomplicated recovery and was discharged home on the seventh postoperative day and has remained well at review. DISCUSSION: Acute deterioration of CMI in completely asymptomatic patients in absence of concomitant pathological findings is rarely reported in the literature, and exceptional in children. CONCLUSIONS: CMI is typically treated electively, but as this case illustrates, it can present with rapidly deteriorating neurological signs. Symptoms usually respond well to surgical intervention with rapid improvement.

Accessing the recesses of the fourth ventricle: comparison of tonsillar retraction and resection in the telovelar approach.

OBJECTIVE: To compare the effectiveness of the telovelar approach with tonsillar manipulation for approaching the recesses of the fourth ventricle. METHODS: A telovelar approach was performed in 8 injected cadaveric heads. Areas of exposure were measured for the superolateral and lateral recesses. Horizontal angles were evaluated by targeting the cerebral aqueduct and medial margin of the lateral recess. Quantitative comparisons were made between the telovelar dissections and various tonsillar manipulations. RESULTS: Tonsillar retraction provided a comparable exposure of the superolateral recess with tonsillar resection (26.4 +/- 17.6 vs 25.2 +/- 12.5 mm2, respectively; P = .825). Tonsillar resection significantly increased exposure of the lateral recess compared with tonsillar retraction (31.1 +/- 13.3 vs 20.2 +/- 11.5 mm2, respectively; P = .002). Compared with tonsillar retraction, the horizontal angle to the lateral recess increased after either contralateral tonsillar retraction (22.7 +/- 4.8 vs 36.7 +/- 6.5 degrees) or tonsillar resection (22.7 +/- 4.8 vs 31.5 +/- 7.6 degrees; all adjusted P < .01). The horizontal angle to the cerebral aqueduct increased significantly with tonsillar resection compared with tonsillar retraction (17.6 +/- 2.3 vs 13.2 +/- 2.8 degrees; P < .001) CONCLUSION: Compared with tonsillar retraction, tonsillar resection provides a wider corridor to, and a larger area of exposure of, the cerebral aqueduct and lateral recess. Contralateral tonsillar retraction improves access to the lateral recess by widening the surgical view from the contralateral side.