Odontoid process inclination in normal adults and in an adult population with Chiari malformation Type I

Geometric morphometric analysis of the brainstem and cerebellum in Chiari I malformation

Background

Chiari I malformation (CMI) is characterized by inferior descent of the cerebellar tonsils through the foramen magnum and is associated with headache and neck pain. Many morphometric research efforts have aimed to describe CMI anatomy in the midsagittal plane using classical measurement techniques such as linear dimensions and angles. These methods are less frequently applied to parasagittal features and may fall short in quantifying more intricate anatomy with fewer distinct homologous landmarks.

Methods

Landmark-based geometric morphometric techniques were used to asses CMI morphology in five anatomical planes of interest.

Results

Significant shape differences between CMI and age/sex-matched controls were found in the midsagittal (Pseudo-F = 5.4841, p = 0.001) and axial planes through the rostral medulla (Pseudo-F = 7.6319, p = 0.001). In addition to tonsillar descent, CMI principal component 1 (PC1) scores in the midsagittal protocol were associated with marked anterior concavity of the brainstem and generalized verticality of the cerebellum with anterior rotation of its anterior lobe. In the axial medulla/cerebellum protocol, CMI PC1 scores were associated with greater anterior-posterior (A-P) dimension with loss of medial-lateral (M-L) dimension.

Discussion

These results suggest that CMI is associated with greater curvature of the brainstem and spinal cord, which may perturb normal neural activities and disrupt cerebrospinal fluid movements. Previous reports on the A-P diameter of the posterior fossa in CMI have conflicted; our findings of greater A-P cerebellar dimensionality with concomitant loss of width alludes to the possibility that more caudal aspects of the posterior cranial fossa are more bowl-like (homogenous in axial dimensions) and less trough-like or elongated in the M-L direction.

Magnetic Resonance Imaging-Related Anatomic and Functional Parameters for the Diagnosis and Prognosis of Chiari Malformation Type I: A Systematic Review and Meta-analysis

OBJECTIVE

Imaging parameters of Chiari malformation type I (CMI) development are not well established. This study aimed to collect evidence of general or specific imaging measurements in patients with CMI, analyze indicators that may assist in determining the severity of CMI, and guide its diagnosis and treatment.

METHODS

A comprehensive search was conducted across various databases including the Cochrane Library, PubMed, MEDLINE, Scopus, and Embase, covering the period from January 2002 to October 2023, following predefined inclusion criteria. Meta-analyses were performed using RevMan (ver. 5.4). We performed a quantitative summary and systematic analysis of the included studies. This study was registered in the PROSPERO (International Prospective Register of Systematic Reviews) prior to initiation (CRD42023415454).

RESULTS

Thirty-three studies met our inclusion criteria. The findings indicated that out of the 14 parameters examined, 6 (clivus length, basal angle, Boogard's angle, supraocciput lengths, posterior cranial fossa [PCF] height, and volume) exhibited significant differences between the CMI group and the control group. Furthermore, apart from certain anatomical parameters that hold prognostic value for CMI, functional parameters like tonsillar movement, obex displacement, and cerebrospinal fluid dynamics serve as valuable indicators for guiding the clinical management of the disease.

CONCLUSION

We collated and established a set of linear, angular, and area measurements deemed essential for diagnosing CMI. However, more indicators can only be analyzed descriptively for various reasons, particularly in prognostic prediction. We posit that the systematic assessment of patients' PCF morphology, volume, and other parameters at a 3-dimensional level holds promising clinical application prospects.

Retroflexed dens in paediatric Chiari 1 patients and implications: Single centre retrospective study

INTRODUCTION

Chiari 1 malformation and hind brain hernia can be associated with skull base and craniocervical anomalies. One of the more recently associated anomalies is a retroverted or retroflexed odontoid process or dens. We conducted a retrospective study of our operated symptomatic and conservatively managed asymptomatic Chiari cohort to assess the impact of dens retroflexion on rate of revision or cerebrospinal fluid diversion following primary foramen magnum decompression (FMD).

METHODS

We undertook a retrospective study of all foramen magnum decompression (FMD) cases for Chiari type 1 malformation performed over a 15-year period in a single tertiary paediatric neurosurgical unit. For comparison, non-operated asymptomatic Chiari cases were considered as reference cohort. Information gathered included: demographics, age, sex, length of cerebellar tonsils below McRae's line, pB-C2 distance (a line drawn perpendicular to one drawn between the basion and the posterior aspect of the C2 body), angle of retroflexion (angle formed between a line drawn through the odontoid synchondrosis and its intersection with a line drawn from the tip of the odontoid process) and angle of retroversion (angle formed between the line drawn from the base of C2 and its intersection with a line drawn from the tip of the odontoid process). Grade of retroflexion was measured using pre-operative mid-sagittal MR images and classified as grade 0 (> 90°), grade 1 (85°-89°); grade 2 (80°-84°) and grade 3 (< 80°). The rates for redo surgery or need for cerebrospinal fluid (CSF) diversion were obtained from clinical records and compared in the operated and non-operated groups.

RESULTS

One hundred twenty-six Chiari 1 patients were included in this study with adequate imaging. Sixty-five patients were in the non-operated asymptomatic cohort with 61 patients in the operated symptomatic cohort. Mean age of non-operated cohort was 10.2 years with M:F ratio (30:35). Mean cerebellar tonsillar length below McRae's line was 10.3 mm. 7.7% of this cohort had associated syrinx. Mean angles of retroversion and retroflexion were 76 and 78°, respectively. Retroflexion grades included (9.2% grade 1, 35% grade 2 and 52.3% grade 3). pB-C2 distance was 6.8 mm. Mean age of operated cohort was 11.3 years, with M:F ratio (21:40). Mean cerebellar tonsillar length below McRae's line was 15 mm. 45.9% of this cohort had associated syrinx. Mean angles of retroversion and retroflexion were 73 and 74.5°, respectively. Retroflexion grades included (4.9% grade 1, 16.5% grade 2 and 78.6% grade 3). pB-C2 distance was 6.9 mm. No association was identified between retroflexion grade and rate of revision or CSF diversion following primary foramen magnum decompression.

CONCLUSION

The operated Chiari 1 cohort had more retroflexed dens, longer tonsils and associated syrinx compared to the non-operated asymptomatic cohort.

Ehlers-Danlos syndrome-associated craniocervical instability with cervicomedullary syndrome: Comparing outcome of craniocervical fusion with occipital bone versus occipital condyle fixation

Introduction:

Ehlers–Danlos syndrome (EDS) predisposes to craniocervical instability (CCI) with resulting cranial settling and cervicomedullary syndrome due to ligamentous laxity. This study investigates possible differences in radiographic outcomes and operative complication rate between two surgical techniques in patients with EDS and CCI undergoing craniocervical fusion (CCF): occipital bone (OB) versus occipital condyle (OC) fixation.

Methods:

A retrospective search of the institutional operative database between January 07, 2017, and December 31, 2019, was conducted to identify EDS patients who underwent CCF with either OB (Group OB) or OC (Group OC) fixation. For each patient, pre- and post-operative radiographic measurements and operative complications were extracted and compared between groups (OB vs. OC): pB-C2, clivoaxial angle (CXA), tonsillar descent, C2C7 sagittal Cobb angle, C2 long axis, and operative complications.

Results:

Of a total of 26 patients, 13 underwent OV and 13 underwent OC fixation. Eighty-five percent of the patients underwent OC underwent fusion from occiput to C2, while the remaining 15% fusion from occiput to C3. Radiographic outcome in the OC versus OB group was preoperative measurements were similar between OC and OB group: pB-C2 8.8 mm (1.5, 6–11) versus 8.3 mm (1.7, 4–9.6), P = 0.43; CXA 128.2° (5.4, 122–136) versus 131.9° (6.8,122–141), P = 0.41; tonsillar descent 6.2 mm (4.8, 0–15) versus 2.9 mm (3.4, 0–8), P = 0.05; C2 long axis 75.2° (6.7, 58–85) versus 67.2° (21.4, 1–80), P = 0.21; postoperative change of CXA + 14.4° (8.8, 0–30) versus 16.2° (12.4, −4–38), P = 0.43; change of pB-C2 − 2.6 mm (1.8, −-5.3 to 0) versus − 1.2 mm (4, −4.6–8), P = 0.26; and postoperative C2C7 sagittal Cobb angle − 2.6° (19.5, −43–39) versus − 2.6° (11.4, −21–12). Operative complications were seen in 1 out of 13 patients (8%) versus 2 out of 13 patients (16%), P = 1.

Conclusions:

In EDS, patients with CCI undergoing CCF radiographic and clinical outcome were similar between those with OC versus OB fixation. Both techniques resulted in sufficient correction of pB-C2 and CXA measurements with a low complication rate.

Chiari 1.5 malformation, accessory odontoid synchondrosis, and ventral compression: case report

The pathogenesis of Chiari 1 malformations has been explained in several different ways, but extensive evidence suggests a relationship between loss of volume within the posterior cranial fossa and Chiari 1 presentations. It is important to be able to differentiate Chiari 1.5 from Chiari 1 malformations as they have similar clinical presentations, but the latter have progressed further and are characterized by caudal herniations of the brain stem through the foramen magnum. Despite the similarities of presentation, Chiari 1.5 malformations have greater rates of complications following posterior decompression surgeries, which are typically performed to relieve ventral compression. An improved understanding of the odontoid synchondroses could lead to better understanding of Chiari malformations and lead to improved treatment of patients with these presentations. Here we present a rare case of an accessory odontoid synchondrosis in a patient with a Chiari 1.5 malformation and ventral compression.

Posterior Fossa Decompression and superficial durotomy rather than complete durotomy and duraplasty in the management of Chiari 1

Objective: We aimed to evaluate the effectiveness and reliability of posterior fossa decompression (PFD) and superficial durotomy in patients who underwent surgery for Chiari malformation type 1 (CM1).Materials and Methods: Our study included 54 patients with the diagnosis of CM1 who had surgery between January 2012 and June 2019. The patients were divided into two groups according to the surgical technique applied. Group 1 included 10 patients who underwent classic PFD and duraplasty, and Group 2 included 44 patients who underwent PFD and superficial durotomy surgery. Pre- and postoperative clinical signs and symptoms of each patient were recorded. Simultaneously, morphometric measurements were compared from computed tomography (CT) and magnetic resonance (MRI) images taken pre- and postoperatively. The data of the two groups were compared.Results: Of the 54 patients, 18 were male, and the mean age was 37.51 ± 15.14. A statistically significant difference was found between the pre- and postoperative morphometric measurements of the subarachnoid distance, craniocervical angle, syringomyelia, and hydrocephalus at the cerebellum level in Group 2 patients who underwent PFD and superficial durotomy surgery (p < 0.05). When morphometric measurements and clinical signs and symptoms of both groups were compared, no significant difference was found (p > 0.05). There was a 92% improvement in clinical signs and symptoms postoperatively. The complications seen in Group 1 decreased to a minimum in Group 2.Conclusion: We believe that a minimally invasive surgical method is superior to avoid major complications. We also found PFD and superficial durotomy shorten the duration of the patient's hospital stayAbbreviations: C1: cervical vertebra 1C2: cervical vertebra 2CM: Chiari malformationCM1: Chiari malformation type 1CSF: cerebrospinal fluidCT: computed tomographyMRI: magnetic resonance imagingPFD: posterior fossa decompressionUSG: ultrasonography.

Chiari malformation type I and basilar invagination originating from atlantoaxial instability: a literature review and critical analysis

Introduction

Recently, a novel hypothesis has been proposed concerning the origin of craniovertebral junction (CVJ) abnormalities. Commonly found in patients with these entities, atlantoaxial instability has been suspected to cause both Chiari malformation type I and basilar invagination, which renders the tried and tested surgical decompression strategy ineffective. In turn, C1-2 fusion is proposed as a single solution for all CVJ abnormalities, and a revised definition of atlantoaxial instability sees patients both with and without radiographic evidence of instability undergo fusion, instead relying on the intraoperative assessment of the atlantoaxial joints to confirm instability.

Methods

The authors conducted a comprehensive narrative review of literature and evidence covering this recently emerged hypothesis. The proposed pathomechanisms are discussed and contextualized with published literature.

Conclusion

The existing evidence is evaluated for supporting or opposing sole posterior C1-2 fusion in patients with CVJ abnormalities and compared with reported outcomes for conventional surgical strategies such as posterior fossa decompression, occipitocervical fusion, and anterior decompression. At present, there is insufficient evidence supporting the hypothesis of atlantoaxial instability being the common progenitor for CVJ abnormalities. Abolishing tried and tested surgical procedures in favor of a single universal approach would thus be unwarranted.

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.

Clinical utility of 2-D anatomic measurements in predicting cough-associated headache in Chiari I malformation

PURPOSE

Cough-associated headache (CAH) is the most distinctive symptom of patients with Chiari I malformation (CMI) and indicates clinically significant disease. We determined the clinical utility of simple 2D anatomic measurements performed on a PACS workstation by assessing their diagnostic accuracy in predicting CAH in CMI patients.

METHODS

Seventy-two consecutive CMI patients (cerebellar tonsillar herniation > 5 mm) with headache seen by neurosurgeons over 6 years were included. Sagittal T1 images were used by two readers to measure: extent of tonsillar herniation, lengths of the clivus and supra-occiput, McRae and pB-C2 lines, as well as clivus-canal, odontoid retroversion, and skull base angles. Neurosurgery notes were reviewed to determine presence of CAH. Mann-Whitney test was used to compare measurements between patients with and without CAH. Predictive accuracy was assessed by receiver operating characteristic (ROC) curve.

RESULTS

47/72 (65.3%) CMI patients reported CAH. Tonsillar herniation with CAH (10.2 mm, 7-14 mm; median, interquartile range) was significantly greater than those without CAH (7.9 mm, 6.3-10.9 mm; p = 0.02). Tonsillar herniation ≥ 10 mm showed sensitivity and specificity of 51% and 68%, and tonsillar herniation > 14 mm showed sensitivity and specificity of 30% and 100%, respectively, for predicting CAH. Other 2D measurements showed no statistically significant differences.

CONCLUSIONS

Among the 2D measurements used, only the extent of tonsillar herniation is different between CMI patients with and without CAH. Although CMI is diagnosed with tonsillar herniation of only 5 mm, we found that a much higher extent of herniation is needed to be predictive of CAH.

Impact of imaging modality, age, and gender on craniocervical junction angles in adults without structural pathology

Context:

Multiple angles of the craniocervical junction (CCJ) are associated with pathological conditions and surgical outcomes, including the clivo-axial angle (CXA), clival slope (CS), and sagittal axis (XS). However, there are varying normative ranges reported and a paucity of data analyzing the effects of imaging modality, age, and gender on these angles.

Setting and Design:

A retrospective review of computed tomographic (CT) and magnetic resonance imaging (MRI) scans in fifty adults without CCJ pathology from 2014 to 2019.

Methods:

Age, gender, indication, and hours between scans were recorded. Two-blinded observers measured all angles. Analysis between angles from the same patient was performed using the Wilcoxon signed-rank test. Multivariable linear regression was used to test for associations between average angles and age or gender.

Results:

Average age and time between scans were 41.3 and 14.3 h, respectively, with 94% performed due to trauma. On CT, average CXA, CS, and XS were 162.1°, 118.4°, and 81.3°, respectively. On MRI, they were 159.8°, 117.2°, 85.3°, respectively. There were statistically significant differences between CXA and XS (P < 0.01) based on imaging modality. On CT, there was a significant increase in XS by 1.93°° and decrease in CS by 1.88°° and on MRI, there was a significant increase in CXA by 1.93°° and decrease in CS by 2.75°° corresponding with a 10-year advancement of age. Gender did not have an effect.

Conclusion:

There are significant differences in angular measurements of the CCJ between CT and MRI from the same patient, as well as changes in normative values based on age.

Quantification of changes in brain morphology following posterior fossa decompression surgery in women treated for Chiari malformation type 1

PURPOSE

While 84% of patients surgically treated for Chiari malformation type 1 (CM1) demonstrate improved quality of life after posterior fossa decompression surgery, there are many risks associated with this surgery. Surgical planning to identify candidates likely to improve postoperatively may benefit from an improved understanding of morphological changes after decompression surgery. To evaluate these changes, we quantified 59 morphological parameters on 42 CM1 adult female patients before and after CM1 decompression surgery.

METHODS

Fifty-nine morphological parameters in the posterior cranial fossa, cranio-cervical, and intracranial regions in the midsagittal plane were evaluated using 42 T1-weighted magnetic resonance images of female CM1 patients before and after surgery, and 42 healthy female controls. Morphological differences before and after surgery were compared through the development of a technique to establish the opisthion location, a key reference point not present after surgery.

RESULTS

In addition to the expected reduction of the cranio-caudal dimension of the cerebellum, objective analyses showed a significant increase in the area of the cerebrospinal fluid spaces, posterior (6×) and inferior (2.6×) to the cerebellum (+ 112 ± 102 and + 140 ± 127 mm2, respectively). This increased area was primarily impacted by an average reduction in the occipital bone length of 24.5 ± 7.3 mm following surgery. Based on multiple angles, results demonstrated a 2°-4° anterior rotation of the cerebellum after surgery.

CONCLUSION

Our results show that decompression surgery results in significant changes in the cerebellum and cerebrospinal fluid spaces. Further investigation should determine how these morphological changes impact clinical outcomes.

The clinical efficacy study of treatment to Chiari malformation type I with syringomyelia under the minimally invasive surgery of resection of Submeningeal cerebellar Tonsillar Herniation and reconstruction of Cisterna magna

Purpose

Discuss the clinical efficacy of treatment to Chiari malformation type I with syringomyelia under the minimally invasive surgery of resection of Submeningeal Cerebellar Tonsillar Herniation and reconstruction of Cisterna magna.

Methods

130 Chiari malformation type I with syringomyelia patients, divided into treatment group, literature group and control group, were collected to be treated under the monitoring of ultrasound in the surgery.

Results

6 months after operation, the lesions were decreased or disappeared, the symptoms were relieved obviously. According to MRI and Mimics 17.0 software, the volumes of Cisterna magna increased distinctly (P < 0.001), the proportions of brain in foramen magnum region were decreased (P < 0.001). Assessed by CCOS scale and Tator methods, the improvement rates of treatment group were 97.7% and 94.6%, the literature group and control group were 82.2% and 77.8%, respectively.

Conclusion

The efficacy of Chiari malformation type I with syringomyelia under the minimally invasive surgery of resection of Submeningeal Cerebellar Tonsillar Herniation and reconstruction of Cisterna magna is remarkable, and the complications are fewer. This surgery emphasizes recovery of tonsil of cerebellum and reconstruction of Cisterna magna and the circulation path of cerebrospinal fluid, which is a safe and efficient treatment.

Significance of Modified Clivoaxial Angles in the Treatment of Adult Chiari Malformation Type I

OBJECTIVE

To investigate the influence of modified clivoaxial angle (MCAA) on the surgical planning and outcome in adult patients with Chiari malformation type I.

METHODS

Clinical data of 268 adult patients undergoing posterior fossa decompression without (PFD) or with duraplasty (PFDD) or with resection of tonsils (RT) for Chiari malformation type I over 10 years were reviewed retrospectively, with outcome evaluated by Chicago Chiari Outcome Scale (CCOS) score. By means of receiver operating characteristic curve, the threshold of MCAA was calculated to stratify the patients.

RESULTS

MCAA was positively correlated with CCOS score. In the MCAA ≤ 127° group (n = 57) with severe ventral cervicomedullary compression (VCMC), CCOS score of PFD, PFDD, and RT was 11.00, 11.06, and 12.42 (P < 0.05), respectively. In the 127° < MCAA ≤ 138° group (n = 87) with moderate VCMC, CCOS score of PFD, PFDD, and RT was 11.71, 12.72, and 13.00 (P < 0.01), respectively. In the MCAA > 138° group (n = 124) with mild or no VCMC, CCOS score of PFD, PFDD, and RT was 13.19, 13.90, and 13.67 (P < 0.05), respectively. The mean MCAA increased by 4.4° postoperatively (P < 0.05), which was positively associated with syringomyelia shrinkage.

CONCLUSIONS

MCAA may play a role in guiding the surgical treatment and predicting the prognosis in adult CMI patients. The larger the MCAA, the less invasive surgery is preferred with higher CCOS. PFDD should be the first choice in patients with mild or no VCMC (MCAA >138°) and RT in patients with moderate VCMC (127° < MCAA ≤ 138°). For patients with severe VCMC (MCAA ≤ 127°), RT could be considered as the primary surgery with awareness of the possible insufficiency of posterior decompression alone.

Predictive value of posterior cranial fossa morphology in the decompression of Chiari malformation type I: A retrospective observational study

Posterior fossa decompression (PFD) is the standard procedure for the treatment of Chiari malformation type I (CMI). Although most patients have satisfactory surgical outcomes, some show no improvement or even a worsening of symptoms. Patient selection is thought to account for these different surgical outcomes. Our aim was to evaluate the predictive value of the preoperative posterior cranial fossa (PCF) morphology on the efficacy of PFD.Data from 39 CMI patients with CMI-related symptoms who underwent occipital foramen enlargement + C-1 laminectomy + enlarged duraplasty were retrospectively collected from January 2011 to May 2018. The patients were divided into improved and unimproved groups according to the modified Chicago Chiari Outcome Scale. Demographic information and clinical history, including preoperative comorbidities and clinical manifestations, were recorded for the 2 groups and compared. PCF morphology was assessed based on 13 linear, 8 angular, 4 areal parameters and 4 ratios related to these liner and areal parameters. The data were then analyzed statistically.Of the 39 patients with CMI, 24 showed improvement after PFD (61.5%), whereas the remaining 15 patients showed no improvement (38.5%). The preoperative symptoms lasted 1 to 240 months, with a median of 24 months. The follow-up period ranged from 2 to 82 months, with a median of 27 months. The improved and unimproved groups differed significantly with regard to upper limb numbness (OR = 10, P = .02) and upper limb weakness (OR = 4.86, P = .02). The 2 groups did not differ significantly with regard to any morphological parameters such as tonsillar descent, syrinx size.Preoperative upper limb numbness and upper limb weakness are unfavorable factors that influence the outcome of PFD in patients with CMI. However, the morphology of PCF cannot predict the response to PFD in patients with CMI.

Quality of Life After Combined Endonasal Endoscopic Odontoidectomy and Posterior Suboccipital Decompression and Fusion

BACKGROUND

Basilar invagination can result from systemic diseases that can weaken structural integrity of the craniocervical junction. Definitive treatment often requires ventral decompression and posterior decompression and fusion. Endonasal odontoidectomy is a relatively new minimal access procedure; quality of life (QOL) after this procedure has not been reported.

METHODS

We reviewed a consecutive database of endonasal odontoidectomy cases and identified patients having posterior decompression and fusion. Two QOL questionnaires were administered postoperatively: Sino-Nasal Outcome Test and 36-Item Short Form Survey. Comparisons with other endonasal or Chiari procedures were performed.

RESULTS

The study comprised 14 patients; 79% had Chiari malformation in addition to basilar invagination. Mean follow-up was 17.2 months. Symptomatic improvement occurred in 78.6% after surgery. Average postoperative Sino-Nasal Outcome Test scores were 39.2 ± 17.93, with worst scores in areas related to fatigue and sleep patterns but not nasal function. 36-Item Short Form Survey scores were lower in areas of physical function and general health but better for emotional health and pain. Compared with patients undergoing Chiari malformation surgery without endonasal odontoid resection or fusion, patients undergoing odontoidectomy had higher QOL in areas of role emotional, emotional well-being, and pain but worse QOL in general health and role physical.

CONCLUSIONS

Patients undergoing posterior decompression and fusion with endonasal odontoidectomy do well after surgery with respect to nasal function and emotional health. Patients who also have severe basilar invagination associated with systemic diseases demonstrate reduced QOL after surgery in areas of physical function and sleep leading to fatigue, irritability, and concentration difficulty, likely related to their systemic disease.

A Retrospective 2D Morphometric Analysis of Adult Female Chiari Type I Patients with Commonly Reported and Related Conditions

Purpose: Researchers have sought to better understand Chiari type I malformation (CMI) through morphometric measurements beyond tonsillar position (TP). Soft tissue and bone structures within the brain and craniocervical junction have been shown to be different for CMI patients compared to healthy controls. Yet, several morphological characteristics have not been consistently associated with CMI. CMI is also associated with different prevalent conditions (PCs) such as syringomyelia, pseudotumor, Ehlers-Danlos syndrome (EDS), scoliosis, and craniocervical instability. The goal of this study was two-fold: (1) to identify unique morphological characteristics of PCs, and (2) to better explain inconsistent results from case-control comparisons of CMI. Methods: Image, demographic, and PC information was obtained through the Chiari1000, a self-report web-accessed database. Twenty-eight morphometric measurements (MMs) were performed on the cranial MR images of 236 pre-surgery adult female CMI participants and 140 female healthy control participants. Custom software was used to measure 28 structures within the posterior cranial fossa (PCF) compartment, craniocervical junction, oral cavity, and intracranial area on midsagittal MR images for each participant. Results: Morphometric analysis of adult females indicated a smaller McRae line length in CMI participants with syringomyelia compared to those without syringomyelia. TP was reduced in CMI participants with EDS than those without EDS. Basion to posterior axial line was significantly longer in CMI participants with scoliosis compared to those without scoliosis. No additional MMs were found to differ between CMI participants with and without a specific PC. Four morphometric differences were found to be consistently different between CMI participants and healthy controls regardless of PC: larger TP and a smaller clivus length, fastigium, and corpus callosum height in CMI participants. Conclusion: Syringomyelia, EDS, and scoliosis were the only PCs that showed significant morphometric differences between CMI participants. Additionally, four midsagittal MR-based MMs were found to be significantly different between healthy controls and CMI participants regardless of the presence of one or more PCs. This study suggests that the prevalence of comorbid conditions are not strongly related to CMI morphology, and that inconsistent findings in the radiographic literature cannot be explained by varying prevalence of comorbid conditions in CMI study samples.

A points-based algorithm for prognosticating clinical outcome of Chiari malformation Type I with syringomyelia: results from a predictive model analysis of 82 surgically managed adult patients

OBJECTIVE Although various predictors of postoperative outcome have been previously identified in patients with Chiari malformation Type I (CMI) with syringomyelia, there is no known algorithm for predicting a multifactorial outcome measure in this widely studied disorder. Using one of the largest preoperative variable arrays used so far in CMI research, the authors attempted to generate a formula for predicting postoperative outcome. METHODS Data from the clinical records of 82 symptomatic adult patients with CMI and altered hindbrain CSF flow who were managed with foramen magnum decompression, C-1 laminectomy, and duraplasty over an 8-year period were collected and analyzed. Various preoperative clinical and radiological variables in the 57 patients who formed the study cohort were assessed in a bivariate analysis to determine their ability to predict clinical outcome (as measured on the Chicago Chiari Outcome Scale [CCOS]) and the resolution of syrinx at the last follow-up. The variables that were significant in the bivariate analysis were further analyzed in a multiple linear regression analysis. Different regression models were tested, and the model with the best prediction of CCOS was identified and internally validated in a subcohort of 25 patients. RESULTS There was no correlation between CCOS score and syrinx resolution (p = 0.24) at a mean ± SD follow-up of 40.29 ± 10.36 months. Multiple linear regression analysis revealed that the presence of gait instability, obex position, and the M-line-fourth ventricle vertex (FVV) distance correlated with CCOS score, while the presence of motor deficits was associated with poor syrinx resolution (p ≤ 0.05). The algorithm generated from the regression model demonstrated good diagnostic accuracy (area under curve 0.81), with a score of more than 128 points demonstrating 100% specificity for clinical improvement (CCOS score of 11 or greater). The model had excellent reliability (κ = 0.85) and was validated with fair accuracy in the validation cohort (area under the curve 0.75). CONCLUSIONS The presence of gait imbalance and motor deficits independently predict worse clinical and radiological outcomes, respectively, after decompressive surgery for CMI with altered hindbrain CSF flow. Caudal displacement of the obex and a shorter M-line-FVV distance correlated with good CCOS scores, indicating that patients with a greater degree of hindbrain pathology respond better to surgery. The proposed points-based algorithm has good predictive value for postoperative multifactorial outcome in these patients.

A morphometric assessment of type I Chiari malformation above the McRae line: A retrospective case-control study in 302 adult female subjects

PURPOSE

Type I Chiari malformation (CMI) is a radiologically-defined structural dysmorphism of the hindbrain and posterior cranial fossa (PCF). Traditional radiographic identification of CMI relies on the measurement of the cerebellar tonsils in relation to the foramen magnum with or without associated abnormalities of the neuraxis. The primary goal of this retrospective study was to comprehensively assess morphometric parameters above the McRea line in a group of female CMI patients and normal controls.

MATERIAL AND METHODS

Twenty-nine morphological measurements were taken on 302 mid-sagittal MR images of adult female CMI patients (n=162) and healthy controls (n=140). All MR images were voluntarily provided by CMI subjects through an online database and control participant images were obtained through the Human Connectome Project and a local hospital system.

RESULTS

Analyses were performed on the full dataset of adult female MR images and a restricted dataset of 229 participants that were equated for age, race, and body mass index. Eighteen group differences were identified in the PCF area that we grouped into three clusters; PCF structures heights, clivus angulation, and odontoid process irregularity. Fourteen group differences persisted after equating our CMI and control groups on demographic characteristics.

CONCLUSION

PCF structures reliably differ in adult female CMI patients relative to healthy controls. These differences reflect structural abnormalities in the osseous and soft tissue structures of the clivus, odontoid process, and cerebellum. Clinical and pathophysiological implications are discussed.

Syringohydromyelia in Patients with Chiari I Malformation: A Retrospective Analysis

BACKGROUND AND PURPOSE

The association of syringohydromyelia with Chiari I malformation has a wide range, between 23% and 80% of cases in the current literature. In our experience, this range might be overestimated compared with our observations in clinical practice. Because there is an impact of Chiari I malformation-associated syringohydromyelia on morbidity and surgical intervention, its diagnosis is critical in this patient population. Identifying related variables on the basis of imaging would also help identify those patients at risk of syrinx formation during their course of disease.

MATERIALS AND METHODS

We performed a retrospective analysis of the MR imaging studies of 108 consecutive cases of Chiari I malformation. A multitude of factors associated with syrinx formation were investigated, including demographic, morphometric, osseous, and dynamic CSF flow evaluation.

RESULTS

Thirty-nine of 108 (36.1%) patients with Chiari I malformation had syringohydromyelia. On the basis of receiver operating characteristic curve analysis, a skull base angle (nasion-sella-basion) of 135° was found to be a statistically significant classifier of patients with Chiari I malformation with or without syringohydromyelia. Craniocervical junction osseous anomalies (OR = 4.3, P = .001) and a skull base angle of >135° (OR = 4.8, P = .0006) were most predictive of syrinx formation. Pediatric patients (younger than 18 years of age) who developed syringohydromyelia were more likely to have associated skull base osseous anomalies than older individuals (P = .01).

CONCLUSIONS

Our findings support evidence of the role of foramen magnum blockage from osseous factors in the development of syringohydromyelia in patients with Chiari I malformation.