Ostrich (Struthio camelus) syrinx morphology and vocal repertoire across postnatal ontogeny and sex: Implications for understanding vocal evolution in birds.

Vocal production in birds has been the target of considerable research that mostly has focused on phylogenetically well-nested songbirds. Anatomical descriptions and recordings of many non-songbirds have often only focused on a single ontogenetic stage or sex. While basic morphology of the vocal organ (syrinx) of ostrich (Palaeognathae, Struthio camelus) has been known since the 1800s, descriptions of its vocal repertoire and syrinx anatomy since then have been incomplete or inconsistent. New toolkits now enable detailed qualitative description of internal anatomy and meristic data and allow it to be compared to vocal production. Here we describe the anatomy of the syrinx in Struthio camelus for three post-hatching ontogenetic stages and both an adult male and female utilizing dissection and contrast enhanced X-ray computed tomography (diceCT). We find changes in ring geometry and spacing through ontogeny as well as lateral labia thickness. We document a small unpaired, midline, cartilaginous structure, a "pessuliform process" at the tracheobronchial juncture present throughout ontogeny and in both males and females. Investigation of the vocal repertoire of ostriches across ontogeny using a new dataset of 77 recordings led to identification of four vocalizations not previously reported in the literature, including the simultaneous production of a hiss and tonal. We find syrinx morphology largely consistent across ontogeny and in male and female adults. Both are capable of producing long duration tonal calls, but these may be more frequent in male birds. Closed-mouth boom calls remain unique to males. A detailed understanding of diversity in parts of early diverging clades is pivotal in attempting to estimate features of the ancestral syrinx in birds and how avian vocalization evolved.

Predictors of syrinx presentation and outcomes in pediatric Chiari malformation type I: a single institution experience of 218 consecutive syrinx patients.

PURPOSE: Chiari I malformation (CM-I) in pediatric patients can impose substantial neurologic and functional impairment. Additionally, the presence of syrinx is often a harbinger of clinical compromise, but little attention has been devoted to identifying features associated with syrinx development and the clinical impact of syrinx resolution. Therefore, this study aims to identify clinical and radiographic variables associated with preoperative syrinx presence and postoperative syrinx reduction in pediatric patients with CM-I and determine the relationship between postoperative syrinx reduction and clinical symptom improvement. METHODS: The authors performed a retrospective analysis of 435 consecutive pediatric patients who underwent surgical treatment of CM-I from 2001 to 2021 at a single tertiary pediatric medical center. All patients underwent pre- and postoperative MRI, and clinical and radiographic variables were recorded and subject to inferential analysis. RESULTS: Syrinx at presentation was independently associated with symptoms of spinal cord dysfunction at presentation (OR 2.17 (95% CI 1.05-4.48); p = 0.036), scoliosis (OR 5.33 (2.34-10.86); p = 0.001), and greater pB-C2 (posterior basion to C2 distance) measurement length (OR 1.14 (95% CI 1.01-1.30); p = 0.040). Syrinx at presentation was inversely associated with tussive headaches at presentation (OR 0.27 (95% CI 0.16-0.47); p = 0.001) and cranial nerve deficits at presentation (OR 0.49 (95% CI 0.26-0.92); p = 0.025). Postoperatively, patients with radiographic evidence of syrinx improvement had greater rates of symptom improvement (93.1% vs 82.1%; p = 0.049), better CCOS scores (15.4 vs 14.2; p = 0.001), and decreased rates of readmission (6.0% vs 25.0%, p = 0.002) and reoperation (0.5% vs 35.7%; p = 0.001). The difference in syrinx resolution was similar but not statistically significant (10.3% vs 16.7%; p = 0.251). AO joint anomaly (OR 0.20, 95% CI 0.04-0.95; p = 0.026) and foramen magnum diameter (OR 1.12, 95% CI 1.00-1.25; p = 0.049) were the only independent predictors of syrinx improvement, and surgical technique was the only predictor for syrinx resolution (OR 2.44, 95% CI 1.08-5.50; p = 0.031). Patients that underwent tonsil reduction surgery whose syrinx improved had a wider foramen magnum diameter than those whose did not improve (34.3 vs 31.7; p = 0.028). CONCLUSIONS: Radiographic syrinx improvement is associated with greater rates of symptom improvement and less readmissions and reoperations for CM-I. AO joint anomalies and narrower foramen magnums were independent risk factors for the lack of syrinx improvement. These novel insights will help guide preoperative patient counseling, pre- and intraoperative surgical decision-making, and postoperative clinical prognostication in the treatment of pediatric CM-I.

A complicated Chiari type 1 malformation and holocord syrinx as a likely cause for heel pain.

BACKGROUND: Chiari malformations are a rare group of rhomboencephalic abnormalities involving the brain, craniocervical junction and spine. They may manifest in a variety of clinical presentations which relate to the variable involvement of the cerebellum, brainstem, lower cranial nerves, spinal cord and altered CSF flow dynamics. METHOD: We report an unusual case of incidental diagnosis of a type I Chiari malformation with secondary cystic cerebellar tonsillar encephalomalacia and holocord syrinx following investigation of a 5YO girl presenting with heel swelling related to progressive neuropathic osteoarthropathy of the posterior calcaneal body and apophysis. RESULT: The child was treated with decompressive suboccipital craniectomy and C1 laminectomy and tonsillar resection. Cerebellar tonsillar gliosis and cystic degeneration were confirmed on histopathology. Referral for ongoing engagement with occupational and physical therapy. CONCLUSION: Most type I Chiari malformations in the paediatric population are incidental and asymptomatic. Neurological symptoms are typically mild and relate to altered CSF flow dynamics; however, we present a complex case of type I Chiari malformation with an unusual constellation of associated complications.

Natural history of Chiari I malformation with syrinx and dilatation of the central canal in the pediatric population: the CHEO experience.

PURPOSE: Given that syrinx is often considered an indication of surgery in children with Chiari I malformation (CM1), understanding of the natural history of these patients is very challenging. In this study, we investigate the natural history of children with CM1 that have syrinx and/or prominence of the central canal on presentation. METHODS: All pediatric Chiari I patients who had syrinx and/or prominence of the central canal who underwent MR imaging of the head and spine from 2007 to 2020 were reviewed. Patients were divided into 3 groups (early surgery, delayed surgery, and conservative management). We focused on those patients who did not initially undergo surgery and had at least 1 year of clinical follow-up. We assessed if there were any radiological features that would correlate with need for delayed surgical intervention. RESULTS: Thirty-seven patients met the inclusion criteria. Twenty-one patients were female and 16 were male. The mean age at presentation was 8.7 (5.8 SD). Fourteen (38%) patients had early surgical intervention, with a mean of 2.5 months after initial presentation, 8 (16%) had delayed surgery due to new or progressive neurological symptoms and 46% of patients did not require intervention during follow-up. The length of tonsillar herniation and the position of the obex were associated with the need of surgery in patients who were initially treated conservatively. CONCLUSION: In pediatric patients with CM1 with syringomyelia and prominence of the central canal, conservative treatment is initially appropriate when symptoms are absent or mild. Close follow-up of patients with CM1 and dilatation of the central canal who have an obex position below the foramen magnum and greater tonsillar herniation is suggested, as these patients show a trend towards clinical deterioration over time and may require earlier surgical intervention.

Duraplasty using a combination of a pedicled dural flap and collagen matrix in posterior fossa decompression for pediatric Chiari malformation type 1 with syrinx.

PURPOSE: In posterior fossa decompression for pediatric Chiari malformation type 1 (CM-1), duraplasty methods using various dural substitutes have been reported to improve surgical outcomes and minimize postoperative complications. To obtain sufficient posterior fossa decompression without cerebrospinal fluid-related complications, we developed a novel duraplasty technique using a combination of a pedicled dural flap and collagen matrix. The objective of this study was to describe the operative nuances of duraplasty using a combination of a pedicled dural flap and collagen matrix in posterior fossa decompression for pediatric CM-1. METHODS: We reviewed the clinical and radiographic records of 11 consecutive pediatric patients who underwent posterior fossa decompression with duraplasty using a combination of a pedicled dural flap and collagen matrix followed by expansile cranioplasty for CM-1. The largest area of the syrinx and the size of the posterior fossa were calculated. RESULTS: The maximum syrinx area was reduced by a mean of 68.5% ± 27.3% from preoperatively to postoperatively. Four patients (36.4%) had near-complete syrinx resolution (> 90%, grade III reduction), five (45.5%) had 50% to 90% reduction (grade II), and two (18.2%) had < 50% reduction (grade I). The posterior fossa area in the midsagittal section increased by 8.9% from preoperatively to postoperatively. There were no postoperative complications, including cerebrospinal fluid leakage, pseudomeningocele formation, or infection. CONCLUSION: Duraplasty using a combination of a pedicled dural flap and collagen matrix in posterior fossa decompression is a promising safe and effective surgical technique for pediatric CM-1 with syrinx.

Chiari Type 1 Malformation and Syringomyelia in Children: Classification and Treatment Options.

Chiari type 1 malformation (CIM) is defined as tonsillar ectopia of >5 mm, while syringomyelia (SM) is defined as a cerebrospinal fluid (CSF)-filled cavity larger than 3 mm dissecting the spinal cord. Over the last decades, our understanding of these pathologies has grown; however, many controversies still exist almost in every aspect of CIM and SM, including etiology, indication for treatment, timing of treatment, surgical technique, follow-up regime, and outcome. This chapter provides a comprehensive overview on different aspects of CIM and SM and on the still existing controversies, based on the evidence presently available. Future directions for clinical research concerning CIM and SM treatment and outcome are elaborated and discussed as well.

High-fidelity continuum modeling predicts avian voiced sound production.

Voiced sound production is the primary form of acoustic communication in terrestrial vertebrates, particularly birds and mammals, including humans. Developing a causal physics-based model that ultimately links descending vocal motor control to tissue vibration and sound requires embodied approaches that include realistic representations of voice physiology. Here, we first implement and then experimentally test a high-fidelity three-dimensional (3D) continuum model for voiced sound production in birds. Driven by individual-based physiologically quantifiable inputs, combined with noninvasive inverse methods for tissue material parameterization, our model accurately predicts observed key vibratory and acoustic performance traits. These results demonstrate that realistic models lead to accurate predictions and support the continuum model approach as a critical tool toward a causal model of voiced sound production.

Fourth ventricular subarachnoid stent for Chiari malformation type I-associated persistent syringomyelia.

OBJECTIVE: Syringomyelia (syrinx) associated with Chiari malformation type I (CM-I) is commonly managed with posterior fossa decompression, which can lead to resolution in most cases. A persistent syrinx postdecompression is therefore uncommon and challenging to address. In the setting of radiographically adequate decompression with persistent syrinx, the authors prefer placing fourth ventricular subarachnoid stents that span the craniocervical junction particularly when intraoperative observation reveals arachnoid plane scarring. The objective of this study was to evaluate the safety and efficacy of a fourth ventricle stent for CM-I-associated persistent syringomyelia, assess dynamic changes in syrinx dimensions, and report stent-reduction durability, clinical outcomes, and procedure-associated complications. METHODS: The authors performed a single-institution, retrospective review of patients who underwent fourth ventricular subarachnoid stent placement for persistent CM-I-associated syringomyelia following a prior posterior fossa decompression. The authors' institutional Chiari database contains 600 cases with 149 decompressions for CM-I-associated syringomyelia, of which 13 met criteria for inclusion. Data on patient demographics, clinical presentation and outcomes, and MRI findings were collected. The maximal syrinx diameter was estimated by calculating the area of an elliptical cross-section in the largest axial plane from preoperative, immediately postoperative, and late postoperative T2-weighted MR images. RESULTS: All 13 patients experienced a significant decrease in mean syrinx area from the preoperative to the late postoperative MRI (mean syrinx diameter 114.1 ± 81.8 mm2 vs 24.5 ± 23.8 mm2, p < 0.001). The mean time until late postoperative MRI was 19.7 months (range 2.0-70.7 months). The syrinx area reduced on average by 75.0% ± 23.9% at the time of the last postoperative scan. Syrinx resolution was variable, with 4 patients (30.8%) achieving near-complete resolution (> 90%, grade III reduction), 7 patients (50%) having 50%-90% reduction (grade II), and 2 patients (14.3%) having < 50% decrease (grade I). One patient experienced catheter migration into the left brachium pontis with an associated cyst at the tip of the catheter that decreased in size on follow-up imaging. CONCLUSIONS: Placement of fourth ventricular subarachnoid stents spanning the craniocervical junction in patients with persistent CM-I-associated syringomyelia after posterior fossa decompression is a safe therapeutic option and significantly reduced the mean syrinx area, with a greater reductive effect seen over longer follow-up periods.

Minimally invasive foramen magnum decompression using tubular retractors (MIFT) for Chiari I malformations.

BACKGROUND: Chiari malformation type 1 has been traditionally treated with foramen magnum decompression and C1 arch excision with or without duroplasty depending on the surgeon's preference. Each of the various surgical modifications has its advantages and disadvantages. METHODS: We describe a minimally invasive tubular retractor-based approach to achieve bony decompression in these cases. We have had good results comparable to the open approach. CONCLUSIONS: Strict orientation to the midline using soft tissue landmarks in between the muscles and bony landmarks in the deeper planes is important to achieve good surgical results. Operative time decreases with expertise and is comparable to the open technique. Minimal blood loss and decreased hospital stay and an excellent cosmetic scar make this procedure more appealing.

Syringosubarachnoid shunt: insertion technique.

BACKGROUND: Syringomyelia is a rare disorder but its impact on patients' quality of life can be devastating. The exact pathophysiology remains unknown; the syrinx can either be idiopathic or associated with conditions such as Chiari malformation, scoliosis, malignancy, infection and trauma. Several techniques have been described to decompress syringomyelia with distal drainage to the subarachnoid space, pleura or peritoneum. METHOD: We present a modification of the syringosubarachnoid shunt insertion technique with minimal myelotomy and the use of a T shaped shunt which does not require suturing to the pia matter to prevent shunt migration. CONCLUSION: This technique for syringosubarachnoid shunt insertion is likely to prevent shunt migration and scarring whilst minimizing suturing and optimising syrinx decompression.

Impact of tumor-associated syrinx on outcomes following resection of primary ependymomas of the spinal cord.

PURPOSE: To interrogate the association of tumor-associated syrinxes with postoperative neurological and oncological outcomes in patients surgically treated for WHO grade 2 spinal ependymomas. METHODS: Adults treated for primary spinal intramedullary ependymomas between 2000 and 2020 were identified and data were gathered on preoperative neurological exam, radiographic characteristics, operative details, and postoperative neurological outcome. Neurological status was graded on the modified McCormick Scale (MMS). Neurological worsening immediately postoperatively and at last follow-up were defined by ≥ 1 MMS grade deterioration. Decision-tree analyses were also performed to identify independent predictors of new neurological deficits. RESULTS: Seventy patients were identified; mean age 45.4 ± 12.7; 60% male. Forty-eight patients (68.6%) had tumor-associated syrinxes, were more common among males (68.8%) and cervical lesions (68.8 vs. 31.8%; P = 0.005). Postoperatively patients with syrinxes had better MMS (P = 0.035) and were less likely to require a gait aid (39.6 vs. 81.8; P = 0.002). This latter difference persisted to last follow-up (22.9 vs. 59.1%; P = 0.006). On decision-tree analysis the strongest predictors of long-term neurological worsening were advanced age (≥ 63 years) and worse baseline neurological function. Worsened neurological status in the immediate postoperative period was best predicted by thoracic localization, the presence of a hemosiderin cap, and longer craniocaudal extension. CONCLUSION: For spinal ependymomas, tumor-associated syrinxes may portend decreased risk for immediate postoperative neurologic deficits but do not predict long-term neurological outcomes (MMS) or odds of successful gross total resection. Thoracic localization appears to best predict new immediate postoperative deficits, and worse baseline neurological function and advanced age best predict long-term deficits.

Feasibility of rapid spine magnetic resonance evaluation for spinal cord syrinx in the pediatric population.

PURPOSE: This study investigates the feasibility of ultrafast fluid sensitive techniques for evaluation of pediatric spinal cord syrinx. Rapid imaging could obviate the need for sedation, which is often required for children undergoing lengthier standard spine imaging. METHODS: Children undergoing standard spine imaging for Chiari malformation, suspected Chiari malformation, or syrinx were included. Patients who provided informed consent were imaged with rapid acquisition sagittal and axial T2 HASTE spine sequences in addition to standard spine imaging. Standard and rapid spine imaging were then reviewed separately by a pediatric neuroradiologist. The presence or absence of syrinx, syrinx diameter, and length were assessed. The degree of cerebellar tonsillar ectopia, conus position, and evaluation of the filum were also recorded. RESULTS: Seventy-six patients aged 1 month to 18 years (mean 7 years) met the inclusion criteria. The sensitivity and specificity of rapid spine imaging for syrinx was 87.8% and 94.7% respectively. All syrinxes > 2.3 mm in diameter were identified with the rapid spine sequences. There was no statistically significant difference between rapid and standard spine imaging in assessment of syrinx diameter or length. Compared with standard spine imaging, rapid spine sequences demonstrated a 100% sensitivity for low-lying conus and a 98.2% sensitivity for cerebellar tonsillar ectopia. The filum was identified on only 31.6% of the rapid spine studies. CONCLUSION: Rapid T2 imaging demonstrated a high sensitivity for the presence and extent of spinal cord syrinx and may provide an alternative to traditional, lengthier standard spine imaging in selected patients.

Pediatric Chiari I malformation: novel and traditional measurements associated with syrinx and surgery.

PURPOSE: Multiple imaging parameters have been examined to estimate the presence of syrinx and the need for surgery in Chiari I patients (CM1); however, no consistent or definitive criteria have been proposed. The objective of this study was to review existing and identify novel radiological and clinical characteristics of CM1 patients that associate syrinx development and surgical intervention. METHODS: Patients with Chiari I malformation diagnosed on imaging between 0 and 18 years were retrospectively reviewed from January 1, 2007 to February 12, 2020. Participants were included if they had a baseline MRI of the head and spine prior to surgical intervention if required. Forty age-matched controls with cranial imaging were identified for comparison. Imaging parameters and clinical symptoms were recorded. RESULTS: A total of 122 CM1 patients were included in this study. Of the 122 patients, 28 (23%) had syrinx, and 27 (22%) had surgery. The following imaging parameters associated with syrinx and surgical intervention were identified: midbrain length (P < 0.001; P = 0.032), the obex position (P = 0.002; P < 0.001) and medullary kinking (P = 0.041; P < 0.001). Among the clinical features, the presence of overall pain (P = 0.017; P = 0.042), neck pain (P = 0.005; P = 0.027), and sensory dysfunction (P < 0.001) were found to be strongly associated with syrinx and surgery. CONCLUSION: While further investigation is needed, these specific radiological and clinical parameters should be considered when evaluating CM1 patients and may be used to guide further management.

Chiari malformation type 1 presenting as isolated unilateral foot drop with rapid recovery following posterior fossa decompression.

BACKGROUND: Chiari malformation (CM) type 1 is characterized by descent of the cerebellar tonsils resulting from crowding of the posterior fossa. In 30% of cases, it is associated with syringomyelia. When symptomatic, it may result in a classic constellation of symptoms. CASE PRESENTATION: Here we describe a case of a 16-year-old male who presented with isolated, unilateral foot drop due to CM type 1 and holosyrinx. This unique presentation is extremely rare, and we additionally present a review of all other reported cases in the literature. After undergoing posterior fossa decompression with C1 laminectomy and duraplasty, our patient made a complete neurological recovery within 2 weeks postoperatively and his MRI entire spine at 3 months postoperatively demonstrated a nearly complete resolution of the holosyrinx with significant decompression of the foramen magnum. CONCLUSION: This rare presentation highlights the importance of maintaining a broad differential, particularly in pediatric patients, and expediting the workup in order to offer a surgical decompression within 1-2 months of foot weakness to maximize the probability of a full neurological recovery.

Comparison of posterior cranial fossa morphometric measurements in Chiari type I patients with and without syrinx cavity on magnetic resonance imaging.

Purpose: To compare the posterior fossa measurements of Chiari type I malformation (CHM1) patients with and without syrinx and with a control group. Material and methods: The patients with syrinx were divided into 2 groupd according to syrinx width/cord width (S/C) ratios: group 1 - S/C ratio < 50%; group 2 - S/C ratio > 50%. The length of the clivus, the AP length of the foramen magnum, the AP length of the posterior fossa, the perpendicular distance between the McRae line and (a) the splenium of corpus callosum, (b) the pons, and (c) the fastigium of the 160 patients and of the 160 control patients were statistically compared. In addition, the measurements of the patients with and without syrinx, according to the S/C ratio, were statistically compared. Results: Syrinx was present in 59 (36.8 %) of the 160 patients. The S/C ratio was < 50% in 30 (50.9 %) of them, and S/C ratio > 50% in 29 (49.1%) of them. All the measurements in the patient group, except of the AP length of the foramen magnum, were statistically significantly lower than in the control group (p = 0.001). There was no significant difference in the measurements of the patients with syrinx group 1 and the patients without syrinx, but the AP length of posterior fossa was statistically significantly lower in the patients with syrinx group 2 than the patients without syrinx (p = 0.03). Conclusion: The S/C ratio can be a guide to the underlying aetiology.

Long-term outcomes of posterior fossa decompression for Chiari malformation type 1: which patients are most prone to failure?

PURPOSE: The role of an osseous-only posterior fossa decompression (PFD) for Chiari malformation type 1 (CM1) remains controversial. We reviewed long-term outcomes for patients with CM1 undergoing a PFD to evaluate if there was any difference for failure when compared to patients undergoing a PFD with duraplasty (PFDD). METHODS: Consecutive patients surgically treated at a single tertiary pediatric neurosurgery clinic over a 25-year period with at least 5 years of follow-up were evaluated. PFD patients were compared to those that initially received a PFDD. Demographics, surgical indications, surgical approach, outcomes, and complications were reviewed. RESULTS: A total of 60 patients were included in this study of which 25 (41.67%) underwent PFD and 35 (58.33%) underwent PFDD. Mean age at surgery was 7.41 years (range 0.4 to 18 years) with a mean follow-up of 8.23 years (range 5 to 21 years). Those that received a PFD had a lower rate of radiographic syrinx improvement (p = 0.03), especially in the setting of holocord syringes. Failure rate was significantly higher in the PFD group (20% vs 2.90%, p = 0.03). However, complications were significantly higher in the PFDD group (17.14% vs 4.0%, p = 0.04). CONCLUSIONS: PFD provides a safe treatment option with similar clinical improvements and lower post-operative complication rate compared to PFDD, albeit at the cost of greater chance of reoperation, especially in the setting of a holocord syrinx. Patients with a holocord syrinx should be considered for a PFDD as their initial procedure.

Early- and long-term surgical outcomes in 109 children with lipomyelomeningocele.

AIM: To determine the functional outcomes and risk factors for outcomes following surgery for lipomyelomeningocele (LMMC). METHODS: Data from 109 children with LMMC who underwent surgery from January 2008 to December 2017 were retrospectively studied to evaluate functional outcomes and possible risk factors for early- (at discharge from hospital or within 1 month of surgery) and long-term outcomes after surgery. RESULTS: There were 53 boys and 56 girls with median age of 36 months (IQR 12-90 months; range, 4 months to 18 years) at surgery. At presentation, neurological function was normal (asymptomatic group) in 28 (25.7%) children while there was neurological dysfunction (symptomatic group) in 81 (74.3%). Near total or radical excision of lipoma was done in 71 (65.1%) children. Six (5.8%) children had deterioration of neurological function in the post-operative period with recovery of function in three of them. There were no statistically significant risk factors for early outcomes. At a mean follow-up of 62.5 months (IQR 35-82 months; range, 12-146 months), 21 (27.6%) of the 76 symptomatic group children (including 59.3% with incomplete bladder dysfunction) showed improvement, 52 (68.4%) remained the same, while 3 (4%) deteriorated. In 31 children (symptomatic group) who developed symptoms after 1 year of age, early surgery after development of symptoms was associated with better chances of recovery (p = 0.0008). In the asymptomatic group, 23 (88.5%) had normal neurological function at mean follow-up of 57.5 months (IQR 30-77 months; range, 12-141 months) and 3 (11.5%) had neurological deterioration. The mean time to late deterioration (re-tethering) from surgery was 51.3 months (IQR 24-75 months; range, 24-84 months). Presence of syrinx on initial MRI (p = 0.008) and partial resection of the lipoma (p = 0.02) were independent risk factors for delayed deterioration. CONCLUSION: Radical resection of LMMC probably helps in preserving neurological function in > 90% of children at long-term follow-up. Fifty-five percent of children > 2 years of age with incomplete bladder dysfunction regained normal function following surgery. In children who develop symptoms after birth, early surgical intervention can reverse the neurological deficits.

Long-term outcomes for children with an incidentally discovered Chiari malformation type 1: what is the clinical significance?

OBJECTIVES: Chiari malformation type 1 (CM1) is an increasingly common incidental finding on magnetic resonance imaging (MRI). The proportion of children with an incidentally discovered CM1 who upon further evaluation require operative intervention for previously unrecognized signs and symptoms of neurological compromise or significant radiographic findings (syringomyelia) is unclear. An extensive long-term single-institution patient series was evaluated to better clarify the likelihood of surgery in patients who present with an incidentally discovered CM1. METHODS: This study was conducted using prospective data for patients up to 18 years old that were evaluated for a CM1 at a large tertiary pediatric neurosurgery clinic between February 2009 and June 2019. Patients were excluded if they did not have an incidentally discovered CM1 and at least 12 months of clinical follow-up. RESULTS: A total of 218 consecutive patients were included in this study. The mean age at the initial neurosurgical evaluation was 6.5 years (range 5 months to 18.4 years), and the mean duration of clinical follow-up was 40.6 months (range 12 to 114 months). Initial MR imaging was most commonly obtained for the evaluation of seizures (15.1%), nonspecific headaches (not occipital or tussive) (14.7%), trauma (9.6%), and developmental delay (7.8%). Of the patients studied that eventually required surgery, we identified two groups: those operated before 6 months since presentation and those operated after 6 months. A total of 36 patients (16.5%) underwent a decompression with 22 patients (61.1%) receiving surgery within 6 months and the remaining 14 patients (38.9%) beyond 6 months. Patients undergoing early surgery (10.1%) initially presented with a significant syrinx or were noted to have an occult neurological dysfunction, whereas a smaller subset of patients (6.4%) eventually required surgery over time due to the development of new symptoms or a de novo syrinx. Only the presence of syringomyelia was statistically significant for the need of a surgical intervention, while age, sex and degree of tonsillar herniation were not. CONCLUSION: Evaluation of a large group of patients with an incidentally discovered Chiari malformation demonstrated that most patients may be managed conservatively, especially in the absence of syringomyelia. However, there is a subset of patients who will go on to develop a de novo syrinx or neurological symptoms that are new or progressive during follow-up, which should be evaluated by imaging of the brain and spinal cord. The presence of syringomyelia was associated with need for early surgical intervention. However, for patients without syringomyelia, surgical intervention is uncommon but may be delayed up to several years after presentation; therefore, long-term clinical follow-up is recommended.

Are craniocervical angulations or syrinx risk factors for the initiation and progression of scoliosis in Chiari malformation type I?

The pathophysiology behind the instigation and progression of scoliosis in Chiari malformation type I (CMI) patients has not been elucidated yet. This study aims to explore the initiating and progressive factors for scoliosis secondary to CMI. Pediatric patients with CMI were retrospectively reviewed for radiological characteristics of tonsillar herniation, craniocervical anomaly, syrinx morphology, and scoliosis. Subgroup analyses of the presence of syrinx, scoliosis, and curve progression were also performed. A total of 437 CMI patients were included in the study; 62% of the subjects had syrinx, and 25% had scoliosis. In the subgroup analysis of 272 CMI patients with syrinx, 78 of them (29%) had scoliosis, and multiple logistic regression analysis showed that tonsillar herniation ≥ 10 mm (OR 2.13; P = 0.033) and a clivus canal angle ≤ 130° (OR 1.98; P = 0.025) were independent risk factors for scoliosis. In the subgroup analysis of 165 CMI patients without syrinx, 31 of them (19%) had scoliosis, and multiple logistic regression analysis showed that a clivus canal angle ≤ 130° (OR 3.02; P = 0.029) was an independent risk factor for scoliosis. In the subgroup analysis of curve progression for 97 CMI patients with scoliosis, multiple logistic regression analysis showed that anomalies of the craniocervical junction and syrinx were not risk factors for curve progression. Many complex factors including craniocervical angulation, tonsillar herniation, and syrinx might participate in the instigation of scoliosis for CMI patients, and the relationship between craniocervical angulation and scoliosis deserves further study.

Clinical and radiological evaluation of treated Chiari I adult patients: retrospective study from two neurosurgical centers.

Chiari malformation type I (CM1) is a common neurosurgical disorder. It often causes debilitation in the affected patients. CM1 is a herniation of the caudal cerebellum into the spinal canal. This study aimed to evaluate the clinical and radiological outcomes of posterior fossa decompression and duraplasty (PFDD) in treated CM1 patients. In retrospective design, we reviewed the medical records of diagnosed patients with CM1 at two neurosurgical centers spanning 8 years from 2010 to 2017. We selected all CM1 patients who underwent PFDD surgery (n = 72) as the core sample for this study. We used the Chicago Chiari Outcome Scale (CCOS) to evaluate clinical outcomes. Pre- and postoperatively, we assessed the syrinx/cord ratio, the syrinx length, and the improvement of aqueductal stroke volume (ASV) on CSF flow MRIs. The mean value of CCOS was 14.1 ± 2.1. On midsagittal MRIs, the mean regression in ectopia tonsils was 9.4 ± 1.9 mm (i.e., mean pre- and postoperative tonsil herniation was 13.1 ± 3.1 mm and 4.0 ± 1.6 mm, respectively; p < 0.001). On coronal MRIs, the mean regression in ectopia tonsils was 8.4 ± 1.5 mm (i.e., mean pre- and postoperative tonsil herniation was 13.9 ± 2.4 mm and 5.8 ± 1.0 mm, respectively; p < 0.001). A strong positive correlation was observed between clinical improvement and the increase in ASV values. CSF flow MRIs can help in the surgical decision and follow-up of CM1 patients. ASV ≤ 12 µl is a significant predictor for surgical intervention. Full clinical and radiological evaluation utilizing CSF flow MRI are essential. Most syrinx cavities have regressed following PFDD.