Regional Brain Tissue Displacement and Strain is Elevated in Subjects with Chiari Malformation Type I Compared to Healthy Controls: A Study Using DENSE MRI.

While the degree of cerebellar tonsillar descent is considered the primary radiologic marker of Chiari malformation type I (CMI), biomechanical forces acting on the brain tissue in CMI subjects are less studied and poorly understood. In this study, regional brain tissue displacement and principal strains in 43 CMI subjects and 25 controls were quantified using a magnetic resonance imaging (MRI) methodology known as displacement encoding with stimulated echoes (DENSE). Measurements from MRI were obtained for seven different brain regions-the brainstem, cerebellum, cingulate gyrus, corpus callosum, frontal lobe, occipital lobe, and parietal lobe. Mean displacements in the cerebellum and brainstem were found to be 106 and 64% higher, respectively, for CMI subjects than controls (p < .001). Mean compression and extension strains in the cerebellum were 52 and 50% higher, respectively, in CMI subjects (p < .001). Brainstem mean extension strain was 41% higher in CMI subjects (p < .001), but no significant difference in compression strain was observed. The other brain structures revealed no significant differences between CMI and controls. These findings demonstrate that brain tissue displacement and strain in the cerebellum and brainstem might represent two new biomarkers to distinguish between CMI subjects and controls.

The 270° Circumferential Microsurgical Decompression of the Foramen Magnum in Adult Chiari Malformation Type I: Single Surgeon Series of 130 Patients with Syringomyelia, Neurologic, and Headache Outcomes.

OBJECTIVE: Chiari malformation type I (CM-I) is a craniocervical junction disorder associated with descent of the cerebellar tonsils >5 mm. The prevalence of CM-I is common, including 0.5%-3.5% in the general population, 0.56%-0.77% on magnetic resonance imaging, and 0.62% in anatomic dissection studies. We sought to measure our surgical outcomes related to resolution/improvement of headaches, neurologic outcomes, and syringomyelia compared with reported adult CM-I studies from 2000-2019. METHODS: From December 2003 to June 2018, the first author (K.I.A.) performed 270° circumferential decompression on adult (>18 years) patients with CM-I. At admission and follow-up, all parameters were numerically evaluated; headaches were self-reported on the visual analog scale, neurologic condition was evaluated using Karnofsky Performance Status and European Myelopathy Score, and syrinx width (if present) was measured on magnetic resonance imaging by grades I-IV. All parameters were analyzed, compared, and statistically tested. We compared results with our previously reported and updated systematic review of operative adult CM-I studies (studies from 2000 to 2019). RESULTS: In our series, 118/121 (98%) experienced headache improvements and 100% experienced neurologic improvements. Complete syrinx resolution was experienced by 35/43 (81%); 8 (19%) showed significant improvement. In data from reported studies (2000-2019), only 79% experienced headache resolution, 77% improvement of neurologic status, and 74% resolution/improvement of syrinx (mean). CONCLUSIONS: Our modified 270° circumferential microsurgical foramen magnum decompression for adult CM-I appears to be beneficial in improvement of outcomes, namely in resolution of the syrinx, neurologic symptoms, and headaches. We also confirm the association of body mass index with CM-I. Further studies are needed to confirm our results.

Two cases of persistent falcine and occipital sinuses.

BACKGROUND: The coexistence of falcine and occipital sinuses is rare and its natural course has not been reported. CASE REPORTS: Two patients with persistent falcine and occipital sinuses are described. Both patients had straight sinuses. In one, both the transverse and sigmoid sinuses were hypoplastic and the patient had an acquired Chiari I malformation. The other patient had no other venous anomalies and had a normal posterior cranial fossa. CONCLUSION: The coexistence of falcine and occipital sinuses can lead to an acquired Chiari I malformation. These cases suggest the importance of checking other venous and brain anomalies in this situation.

Outcomes of Dura Splitting Decompression Versus Posterior Fossa Decompression With Duraplasty in the Treatment of Chiari I Malformation: A Systematic Review and Meta-analysis.

BACKGROUND: Surgery is the definitive treatment option for symptomatic Chiari malformation I (CMI), but there is no clear consensus as to the preferred surgical method. This study aimed to quantitatively assess and compare the effect and safety of dura splitting decompression (DSD) and posterior fossa decompression with duraplasty (PFDD) in treating patients with CMI. METHODS: A literature search of EMBASE, MEDLINE, PubMed, Cochrane Library, and Web of Science databases was conducted. References from January 1990 to September 2020 were retrieved. We only included papers containing original data, comparing the use of DSD and PFDD in CMI patients. RESULTS: Overall, 11 relevant studies were identified, wherein 443 patients treated for CMI by DSD were compared with 261 patients treated by PFDD. No difference was observed between PFDD and PFD in terms of clinical improvement (P = 0.69), syringomyelia improvement (P = 0.90), or reoperation (P = 0.22). DSD was associated with shorter operation durations (P = 0.0007), shorter length of stay (P = 0.0007), and shorter overall postoperative complications (P < 0.0001) (especially cerebrospinal fluid [CSF] leak [P = 0.005], meningitis [P = 0.002], and pseudomeningocele [P = 0.002]), as compared with PFDD. CONCLUSIONS: This study confirmed that dura splitting decompression has clinical and syringomyelia improvement outcomes comparable to posterior fossa decompression with duraplasty. Compared with PFDD, DSD not only significantly shortened the operation time and length of stay, but also significantly reduced the overall complication rate, especially those related to incidence of CSF-related complications. More evidence from advanced multicenter studies are needed to require to validate the findings.

Is C1-C2 Reduction and Fixation A Good Choice in the Treatment of Recurrent Chiari-Like Symptoms With Syringomyelia?

BACKGROUND: Foramen magnum decompression (FMD) is the first-choice treatment for Chiari malformation (CM). However, it has been suggested that cerebellar herniation and syringomyelia occur as a natural protective event to prevent neural damage caused by atlantoaxial instability. It is argued that treating instability is the main treatment. Positive results of atlantoaxial fusion have been reported in the literature, but there are no studies including the results of atlantoaxial fusion as the second treatment in patients in whom classical decompression failed. In our study, we report the results of these patients to help in the selection of treatment and we present our treatment algorithm for CM with syringomyelia. METHODS: Thirteen patients who had undergone FMD and duraplasty due to CM and syringomyelia in our clinics and who had recovered clinically and radiologically but had recurrent complaints during long-term follow-up were evaluated. C1-C2 distraction and fusion were performed. We evaluated these patients radiologically and clinically. RESULTS: The mean age of the 13 patients was found to be 32.4 years. Male to female ratio was 6:7. The complaints recurred after an average of 2.1 years. Also, 3 cases were presented with their clinical characteristics and radiologic findings. CONCLUSIONS: FMD may fail even with duraplasty, and treatment of CM in recurrent cases is still controversial. Recently, atlantoaxial instability has been reported to be the main pathology of CM, and the cure for pathology is to treat instability. Recurrent CMs with syringomyelia in which FMD has failed should be treated by atlantoaxial fixation.

Management of Chiari malformation type I and syringomyelia during pregnancy and delivery.

OBJECTIVE: Although a recurrent question in clinical practice, the management of Chiari malformation type I (CMI) and/or syringomyelia during pregnancy and delivery is still debated. The aim of this study was to investigate the modalities of delivery and anesthesia in women presenting with CMI and/or syringomyelia at a national reference center, and to question their potential role in the natural history of these conditions. STUDY DESIGN: We conducted a retrospective cohort study using a standardized questionnaire, a customized clinical severity score and data from medical records. RESULTS: 83 patients were included in the final analysis: 32 had CMI without syringomyelia, 27 had CMI with syringomyelia and 24 had non-foraminal syringomyelia. Most patients (55/83) were not diagnosed at the time of their pregnancy, 12 had surgery before being pregnant and 16 were diagnosed but not operated. Most women underwent vaginal delivery (62 %) and neuraxial (i.e. epidural or spinal) anesthesia (69 %). However, the proportion of cesarean procedures increased to 53.6 % and even 83.3 % when considering only patients already diagnosed or operated on, respectively. Nonetheless, neither vaginal compared to cesarean delivery (change in clinically severity score: -1.5 ± 0.4 versus -0.9 ± 0.4, p = 0.4) nor neuraxial compared to general anesthesia (-1.2 ± 0.3 versus -1.5 ± 0.6, p = 0.7) were associated with increased clinical deterioration. CONCLUSION: Although individual evaluation is mandatory, this study supports that neither delivery nor anesthesia modalities affect the natural history for the vast majority of patients with CMI and/or syringomyelia.

The Perplexity Surrounding Chiari Malformations - Are We Any Wiser Now?

Chiari malformations are a diverse group of abnormalities of the brain, craniovertebral junction, and the spine. Chiari 0, I, and 1.5 malformations, likely a spectrum of the same malformation with increasing severity, are due to the inadequacy of the para-axial mesoderm, which leads to insufficient development of occipital somites. Chiari II malformation is possibly due to nonclosure of the caudal end of the neuropore, with similar pathogenesis in the rostral end, which causes a Chiari III malformation. There have been significant developments in the understanding of this complex entity owing to insights into the pathogenesis and advancements in imaging modalities and neurosurgical techniques. This article aims to review the different types and pathophysiology of the Chiari malformations, along with a description of the various associated abnormalities. We also highlight the role of ante- and postnatal imaging, with a focus on the newer techniques in the presurgical evaluation, with a brief mention of the surgical procedures and the associated postsurgical complications.

Severe Cerebellar Degeneration and Chiari I Malformation - Speculative pathophysiology based on a systematic review.

BACKGROUND: Symptomatic Chiari Type I Malformation (CM) is treated with posterior fossa decompression with or without duroplasty. We have noticed some cases with concomitant severe cerebellar ataxia due to cerebellar atrophy. The aim of this study is to review the literature of CM associated with severe cerebellar atrophy and discuss its potential physiopathology. METHODS: A systematic literature review in the Pubmed Database was performed using the following key-terms: "cerebellar atrophy Chiari", and "cerebellar degeneration Chiari". Articles reporting the presence of cerebellar degeneration/atrophy associated with CM were included. RESULTS: We found only six studies directly discussing the association of cerebellar atrophy with CM, with a total of seven cases. We added one case of our own practice for additional discussion. Only speculative causes were described to justify cerebellar atrophy. The potential causes of cerebellar atrophy were diffuse cerebellar ischemia from chronic compression of small vessels (the most mentioned speculative cause), chronic raised intracranial pressure due to CSF block, chronic venous hypertension, and association with platybasia with ventral compression of the brainstem resulting in injury of the inferior olivary nuclei leading to mutual trophic effects in the cerebellum. Additionally, it is not impossible to rule out a degenerative cause for cerebellar atrophy without a causative reason. CONCLUSIONS: Severe cerebellar atrophy is found in some patients with CM. Although chronic ischemia due to compression is the most presumed cause, other etiologies were proposed. The real reasons for cerebellar degeneration are not known. Further studies are necessary.

The SHORE Score: A Novel Predictive Tool for Improvement After Decompression Surgery in Adult Chiari Malformation Type I.

BACKGROUND: A practical scoring system predicting significant improvement after surgical decompression in adult Chiari malformation type I (CM-1) based on validated outcome measures is lacking. We aimed to develop a simple score and improvement calculator to facilitate the decision making process in symptomatic CM-1 patients. METHODS: We evaluated adult CM-1 patients who presented to our institution between September 2006 and September 2018 and underwent surgical decompression. Previously treated patients were excluded. Univariable analysis and multivariable logistic regression were conducted to derive an optimal model predictive of improvement on last follow-up as measured by the Chicago Chiari Outcome Scale. A score was derived using the beta coefficients of the model, and predictive performance was assessed using receiver operating curves with bootstrap validation. Finally, a web-based improvement calculator was deployed. RESULTS: The surgical cohort consisted of 149 adult CM-1 patients, of which 100 (67%) experienced significant clinical improvement (Chicago Chiari Outcome Scale ≥14) after a mean follow-up of 1.9 years. The final model predictive of significant clinical improvement consisted of headache with Valsalva (odds ratio [OR] = 2.39; P = 0.030), nonwhite race (OR = 2.57; P = 0.041), absence of visual symptoms (OR = 2.59; P = 0.015), syrinx absence (OR = 1.59; P = 0.315), and increased odontoid retroflexion (OR = 2.82; P = 0.009). The score was termed SHORE, which summarizes the model's predictive factors, each assigned 1 point. The model had an area under the curve of 0.754 with an optimism-correct value of 0.721. A calculator was deployed under: https://jhuspine2.shinyapps.io/SHORE_score/. CONCLUSIONS: The score and calculator can serve as supplements to clinical decision making by providing realistic and personalized expectations of postoperative outcome.

Management of Chiari I Deformity in Children and Adolescents: A Report from the Consensus Taskforce of the Brazilian Society of Pediatric Neurosurgery

Much controversy remains on the current management of Chiari I deformity (CID) in children, with many clinical, surgical and ethic-legal implications. The Brazilian Society of Pediatric Neurosurgery (SBNPed, in the Portuguese acronym) has put together a panel of experts to analyze updated published data on the medical literature about this matter and come up with several recommendations for pediatric neurosurgeons and allied health professionals when dealing with CID. Their conclusions are reported herein, along with the respective scientific background.

A Combinatorial Approach with Cerebellar Tonsil Suspension to Treating Symptomatic Chiari Malformation Type I in Adults: A Retrospective Study.

BACKGROUND: Primary Chiari malformations (CMs) are congenital defects of the skull base and brain. Among the 4 CM types, type I (CM-I) occurs most frequently and may cause somatosensorimotor, autonomic and vision symptoms. Presently, posterior fossa decompression alone (PFD) or with duraplasty (PFDD) and cerebellar tonsil (CbT) shrinkage tactics are standard treatments, albeit inherent issues. There has been no report on devising CbT suspension (CTS) to manage CM-I. OBJECTIVES: 1) To design a CTS protocol that can be used with CbT coagulation (CTC) and PFDD; 2) to evaluate the regimen for feasibility, safety, and efficacy in a retrospective study; and 3) to obtain data for planning prospective studies to validate PFDD + CTC + CTS as a novel approach to treating adult CM-I. METHODS: PFDD + CTC + CTS (n = 17), PFDD + CTC (n = 13), and PFDD (n = 12) were performed for 42 adult patients (age range, 18-55 years; female:male = 27:15) following a balanced study design. Neck Disability Index (NDI), Chicago Chiari Outcome Scale (CCOS), and /magnetic resonance imaging/computed tomography were used to determine postsurgery outcomes for approximately 20 months. RESULTS: Comparing to PFDD + CTC or PFDD, patients receiving PFDD + CTC +CTS operation exhibited significantly improved group average NDI (10.72 ± 3.95%; P = 0.007), CbT elevation distance (7.06 ± 2.42 mm; P < 0.001, Kruskal-Wallis test; 55.7 ± 25.4% higher than the presurgery level; P < 0.001, analysis of variance), and syringomyelia syrinx retraction (P = 0.009, analysis of variance). CONCLUSIONS: The PFDD + CTC + CTS regimen appeared to be safe and potentially more efficacious in patients with CM-I evaluated for the period, relative to PFDD + CTC or PFDD treatment. Future prospective studies were warranted.

Severe Cerebellar Degeneration and Chiari I Malformation - Speculative pathophysiology based on a systematic review

SUMMARY BACKGROUND Symptomatic Chiari Type I Malformation (CM) is treated with posterior fossa decompression with or without duroplasty. We have noticed some cases with concomitant severe cerebellar ataxia due to cerebellar atrophy. The aim of this study is to review the literature of CM associated with severe cerebellar atrophy and discuss its potential physiopathology. METHODS A systematic literature review in the Pubmed Database was performed using the following key-terms: "cerebellar atrophy Chiari", and "cerebellar degeneration Chiari". Articles reporting the presence of cerebellar degeneration/atrophy associated with CM were included. RESULTS We found only six studies directly discussing the association of cerebellar atrophy with CM, with a total of seven cases. We added one case of our own practice for additional discussion. Only speculative causes were described to justify cerebellar atrophy. The potential causes of cerebellar atrophy were diffuse cerebellar ischemia from chronic compression of small vessels (the most mentioned speculative cause), chronic raised intracranial pressure due to CSF block, chronic venous hypertension, and association with platybasia with ventral compression of the brainstem resulting in injury of the inferior olivary nuclei leading to mutual trophic effects in the cerebellum. Additionally, it is not impossible to rule out a degenerative cause for cerebellar atrophy without a causative reason. CONCLUSIONS Severe cerebellar atrophy is found in some patients with CM. Although chronic ischemia due to compression is the most presumed cause, other etiologies were proposed. The real reasons for cerebellar degeneration are not known. Further studies are necessary.

RESUMO OBJETIVO A Malformação de Chiari (MC) tipo I sintomática é tratada através da descompressão da fossa posterior com ou sem duroplastia. Observamos alguns casos com ataxia cerebelar grave concomitante devido à atrofia cerebelar. O objetivo deste estudo é revisar a literatura sobre MC associada à atrofia cerebelar grave e discutir sua possível fisiopatologia. METODOLOGIA Conduzimos uma revisão sistemática da literatura no banco de dados Pubmed utilizando as seguintes palavras-chave: "cerebellar atrophy Chiari", e "cerebellar degeneration Chiari". Artigos sobre a presença de degeneração/atrofia cerebelar associada à MC foram incluídos. RESULTADOS Encontramos apenas seis estudos que discutiam diretamente a associação entre atrofia cerebelar e MC, com um total de sete casos. Nós adicionamos um caso da nossa própria prática para ampliar a discussão. Apenas causas especulativas foram descritas para justificar a atrofia cerebelar, entre elas: isquemia cerebelar difusa devido à compressão crônica de pequenos vasos (a causa especulativa mais citada), pressão intracraniana elevada crônica devido ao bloqueio de LCR, hipertensão venosa crônica e associação com platibasia com compressão ventral do tronco cerebral, resultando em lesão do núcleo olivar inferior e levando a efeitos tróficos mútuos no cerebelo. Além disso, não é possível descartar uma causa degenerativa para atrofia cerebelar sem motivos claros. CONCLUSÃO A atrofia cerebelar grave é encontrada em alguns pacientes com MC. A isquemia crônica causada por compressão é a causa mais apontada como suspeita, porém outras etiologias foram propostas. As reais causas da degeneração cerebelar não são conhecidas. Mais estudos são necessários.

Arnold-Chiari malformation type I and the posterior dislocation of the odontoid process aggravate prolonged weaning in a patient with severe viral pneumonia: a case report.

BACKGROUND: Prolonged and difficult weaning is associated with higher rates of complications and mortality. Therefore, it is important to identify the associated factors. CASE PRESENTATION: We describe our experience with a 37-year-old man diagnosed with severe viral pneumonia (influenza A). He presented with acute respiratory failure type I on admission. During intubation, his blood pressure and heart rate decreased, and epinephrine and norepinephrine were administered. Although his clinical condition improved 8 days after intensive care unit (ICU) admission, he experienced difficulty weaning. He remained conscious but had a poor spontaneous cough with sputum production and weak limb muscle strength. His cough reflex was absent during bronchoscopic sputum suction, and he used abdominal breathing during the T-tube test. Magnetic resonance imaging revealed an Arnold-Chiari malformation type I, posterior dislocation of the odontoid process, and syringomyelia, with compression and deformation of the medulla and high cervical cord. The patient was successfully weaned from the ventilator at 20 days after ICU admission. CONCLUSIONS: Arnold-Chiari malformation type I and posterior dislocation of the odontoid process, which aggravate medullary compression and increase the risk of cervical nerve injury, might be a rare factor affecting prolonged weaning in critical illness.

The Retroverted Dens: A Review of its Anatomy, Terminology, and Clinical Significance.

BACKGROUND: Little attention has been given to the retroverted dens within the existing medical literature. However, this finding can have a clinical impact, especially in patients with Chiari malformation type I (CM1), as it can have consequences for further treatment. METHODS: Using standard search engines, we performed a literature review of anatomical, radiologic, and clinical studies as well as pathologic and surgical considerations related to the retroverted dens. Key words for our search included retroverted dens; retroflexed dens; odontoid retroflexion; posterior inclination; and tilted dens. RESULTS: A retroverted dens is most commonly found in the pediatric population in relation to CM1. Research has demonstrated that high degree of dens angulation can result in significant anterior brain stem compression with the need for both anterior and posterior decompression in patients with symptomatic CM1. CONCLUSIONS: A greater degree of dens angulation can lead to neurologic symptoms secondary to spinomedullary compression. Therefore, correct measurements are essential as such findings can influence presurgical planning.

Somatosensory and motor evoked potentials during correction surgery of scoliosis in neurologically asymptomatic Chiari malformation-associated scoliosis: A comparison with idiopathic scoliosis.

OBJECTIVES: To analyze the somatosensory evoked potentials (SEPs) and motor evoked potentials (MEPs) in neurologically asymptomatic Chiari malformation-associated scoliosis (CMS) patients with and without syringomyelia as compared with those in idiopathic scoliosis (IS) ones, and to identify whether the deformities have impacts on the neurophysiological monitoring. PATIENTS AND METHODS: This study included neurologically asymptomatic CMS patients undergoing posterior correction surgery between January 2010 and January 2016. IS patients were involved as control group and a subgroup of age- and height-matched IS patients were selected. The age, standing height and Cobb angles of main curve were measured. The SEPs latency and amplitude, MEPs amplitude, and the rate of abnormal SEPs pathologic change were compared between CMS and IS patients using independent-sample t-test and Chi-square test. RESULTS: Sixty CMS patients and 210 IS patients were included. There was no difference between CMS patients and IS or matched IS patients in SEPs latency and amplitude, MEPs amplitude or rate of abnormal SEPs (p > 0.05). Forty-eight CMS patients concurrent with syringomyelia were associated with higher Cobb angle of main curve and lower SEPs amplitude than those without syringomyelia (p < 0.05). No significant difference was found between CMS patients with and without syringomyelia in age, height, SEPs latency, MEPs amplitude or rate of abnormal SEPs (p > 0.05). CONCLUSION: Neurologically asymptomatic CMS patients showed similar absolute values of neurophysiological monitoring with IS patients. The syringomyelia in CMS indicated more severe curvature and lower SEPs amplitude even after posterior fossa decompression.

Clinical and radiological outcomes of arachnoid-preseving suboccipital decompression for adult chiari I malformation with and without syringomyelia.

OBJECTIVE: To share our experience related to clinic and radiologic outcomes of patients with Chiari I malformation. PATIENTS AND METHODS: This retrospective study evaluated surgical outcome of 48 patients who underwent posterior fossa decompression and duraplasty with arachnoid-preservation technique February 2010 and February 2019. Clinic and radiologic outcomes at long-term follow-up were provided. RESULTS: Surgery led to satisfactory outcomes in both clinic and radiologic measures. The majority of patients (66.7%) in the follow-up period informed us that their symptoms significantly improved. In 14 patients (29.2%), the symptoms were gone totally and no complaining was reported to us. Syringomyelia was encountered in 21 patients (43.7%) on pre-operative MRI. During long-term, significant improvement (syrinx segments were remarkably reduced in diameter) in syrinx size was noted in 16 of the 21 patients (76.1%). In 5 of the 21 patients (23.8), complete improvement, that is, syrinxes were totally collapsed, was seen. Surgery-related complications occurred in a total of 5 patients (10.4%). CONCLUSION: In our experience, we found decompressive craniectomy wide enough with duraplasty without arachnoid opening is safe and successful in patients with CIM. Complication rate is low and arachnoid preserving technique should be performed by experienced neurosurgeons.

Hydrocephalus and Chiari malformation pathophysiology in FGFR2-related faciocraniosynostosis: A review.

BACKGROUND: Patients with syndromic faciocraniosynostosis due to the mutation of the fibroblast growth factor receptor (FGFR) 2 gene present premature fusion of the coronal sutures and of the cranial base synchondrosis. Cerebrospinal fluid (CSF) circulation disorders and cerebellar tonsil prolapse are frequent findings in faciocraniosynostosis. OBJECTIVE: We reviewed the medical literature on the pathophysiological mechanisms of CSF disorders such as hydrocephalus and of cerebellar tonsil prolapse in FGFR2-related faciocraniosynostosis. DISCUSSION: Different pathophysiological theories have been proposed, but none elucidated all the symptoms present in Apert, Crouzon and Pfeiffer syndromes. The first theory that addressed CSF circulation disruption was the constrictive theory (cephalocranial disproportion): cerebellum and brain stem are constricted by the small volume of the posterior fossa. The second theory proposed venous hyperpressure due to jugular foramens stenosis. The most recent theory proposed a pressure differential between CSF in the posterior fossa and in the vertebral canal, due to foramen magnum stenosis.

The Chiari I malformation.

As with many pathologies, the course of our understanding of the Chiari I malformation (CIM) has developed extensively over time. The early descriptions of the Chiari malformations by Hans Chiari in 1891 opened the door for future classification and research on this topic. However, even over a long timeframe, our understanding of the pathophysiology and, more importantly, treatment, remained in its infancy. As recently as the 1970s, CIM was not discussed in popular neurology textbooks. Syringomyelia is listed as a degenerative disorder with no satisfactory treatment. Radiation therapy was considered an option in treatment, and surgery was thought to play no role. During the last 40 years, equivalent to the duration of a neurosurgical career, our understanding of the pathophysiology and natural history of CIM, coupled with modern MRI, has improved the treatment paradigm for this patient population. More importantly, it has given us evidence confirming that CIM is a disorder responsive to surgical intervention, giving patients once thought to be destined for lifelong disability a comparatively normal life after treatment. The purpose of this article is to offer a review of CIM and its important associated entities. The authors will discuss the evolution in understanding of the Chiari malformation and, importantly, distinguish between symptomatic CIM and asymptomatic tonsillar ectopia, based on imaging and presenting symptomatology. They will discuss techniques for surgical intervention, expected outcomes, and complications after surgery. Proper patient selection for surgery based on appropriate symptomatology is tantamount to achieving good surgical outcomes in this population, separating those who can be helped by surgery from those who are unlikely to improve. While our knowledge of the Chiari malformations continues to improve through the efforts of clinical and basic science researchers, surgeons, and patients, our current understanding of these entities represents a monumental improvement in patient care over a relatively short time period.

Role of sleep study in children with Chiari malformation and sleep disordered breathing.

PURPOSE: Chiari malformation incorporate numerous forms of congenital or acquired cerebellar herniation through the foramen magnum. This may lead to brain stem, high spinal cord and cranial nerve compression resulting in obstructive and central apneas. This review highlights he high prevalence of sleep-disordered breathing in this population and the importance of refering these patients for sleep studies as part of their workup. METHODS: A review of the literature was performed through a PubMed and EMBASE search of original articles and reviews using the key words "chiari" "chiari malformation" "hindbrain herniation" "sleep disordered breathing" "obstructive sleep apnea" "central sleep apnea" "sleep study" and "foramen magnum decompression". DISCUSSION: We highlight the pathophysiology of sleep disordered breathing in patients with Chiari malformation, how it can be diagnosed and what the treatment options are. CONCLUSIONS: Sleep-disordered breathing is highly prevalent in patients with CM1. Clinicians caring for these patients should be aware of this and prioritise sleep diagnostic testing to allow for early diagnosis and management particularly in the presence of neurological symptoms and specific brain MRI pointers.

Intraoperative neurophysiological monitoring in paediatric Chiari surgery-help or hindrance?

INTRODUCTION: The role of intraoperative neurophysiological monitoring (IONM) during surgery for Chiari I malformation has not been fully elucidated. Questions remain regarding its utility as an adjunct to foramen magnum decompression surgery, specifically, does IONM improve the safety profile of foramen magnum decompression surgery and can IONM parameters help in intraoperative surgical decision-making. This study aimed to describe a single institution experience of IOM during paediatric Chiari I surgery. METHODS: The methodology comprised a retrospective review of prospectively collected electronic neurosurgical departmental operative database. Inclusion criteria were children under 16 years of age who had undergone foramen magnum decompression for Chiari I malformation with IONM. In addition to basic demographic data, details pertaining to presenting features and post-operative outcomes were obtained. These included primary symptoms of Chiari I malformation and indications for surgery. MRI findings, including the presence of syringomyelia on pre-and post-operative imaging, were reviewed. Details of the surgical technique for each patient were recorded. Only patients with either serial brainstem auditory evoked potential (BAEP) and/or upper limb somatosensory evoked potential (SSEP) recordings were included. Two time points were used for the purposes of analysing IONM data; initial baseline before skin incision and final at the time of skin closure. RESULTS: Thirty-seven children underwent foramen magnum decompression (FMD) with IONM. Mean age was 10.5 years (range 1-16 years) with a male:female ratio 13:24. The commonest clinical features on presentation included headaches (15) and scoliosis (13). Twenty-four patients had evidence of associated syringomyelia (24/37 = 64.9%). A reduction in the SSEP latency was observed in all patients. SSEP amplitude was more variable, with a decrease seen in 18 patients and an increase observed in 12 patients. BAEP recordings decreased in 13 patients and increased in 4 patients. There were no adverse neurological events following surgery; the primary symptom was resolved or improved in all patients at 3-month follow-up. Resolution or improvement in syringomyelia was observed in 19/24 cases. CONCLUSIONS: Our data shows that FMD for Chiari malformation (CM) is associated with changes in SSEPs and BAEPs. However, we did not identify a definite link between clinical outcomes and IONM, nor did syrinx outcome correlate with IONM. There may be a role for IONM in CM surgery but more robust data with better-defined parameters are required to further understand the impact of IONM in CM surgery.