Can the Etiopathogenesis of Chiari Malformation Be Craniocervical Junction Stabilization Difference? Morphometric Analysis of Craniocervical Junction Ligaments

Geometric growth of the normal human craniocervical junction from 0 to 18 years old

The craniocervical junction (CCJ) forms the bridge between the skull and the spine, a highly mobile group of joints that allows the mobility of the head in every direction. The CCJ plays a major role in protecting the inferior brainstem (bulb) and spinal cord, therefore also requiring some stability. Children are subjected to multiple constitutive or acquired diseases involving the CCJ: primary bone diseases such as in FGFR-related craniosynostoses or acquired conditions such as congenital torticollis, cervical spine luxation, and neurological disorders. To design efficient treatment plans, it is crucial to understand the relationship between abnormalities of the craniofacial region and abnormalities of the CCJ. This can be approached by the study of control and abnormal growth patterns. Here we report a model of normal skull base growth by compiling a collection of geometric models in control children. Focused analyses highlighted specific developmental patterns for each CCJ bone, emphasizing rapid growth during infancy, followed by varying rates of growth and maturation during childhood and adolescence until reaching stability by 18 years of age. The focus was on the closure patterns of synchondroses and sutures in the occipital bone, revealing distinct closure trajectories for the anterior intra-occipital synchondroses and the occipitomastoid suture. The findings, although based on a limited dataset, showcased specific age-related changes in width and closure percentages, providing valuable insights into growth dynamics within the first 2 years of life. Integration analyses revealed intricate relationships between skull and neck structures, emphasizing coordinated growth at different stages. Specific bone covariation patterns, as found between the first and second cervical vertebrae (C1 and C2), indicated synchronized morphological changes. Our results provide initial data for designing inclusive CCJ geometric models to predict normal and abnormal growth dynamics.

A morphometric study of the atlanto-occipital joint in adult patients with Chiari malformation type I

BACKGROUND

There are many morphometric studies on Chiari malformation type I (CMI) patients, most of which focus on the posterior cranial fossa (PCF). Less attention has been paid to the atlanto-occipital joint. In this study, we aim to evaluate the morphological characteristics of the atlanto-occipital joint in CMI patients.

MATERIALS AND METHODS

The cervical CT imaging data of adult patients diagnosed with CMI but without any bony malformation in craniovertebral junction (CVJ) who were treated by the authors between January 2014 and December 2019 were retrospectively analyzed. The equal number of sex and age-matched healthy individuals were included as the control group. The morphometric analysis was performed by measuring the length and depth of the atlanto-occipital joint, and the depth/length ratio was calculated to evaluate the curvature of the joint.

RESULTS

A total of 47 patients (15 males and 32 females) were included. The mean age of patients was 47.49 ± 9.01 years (range 19-62 years). The mean depth/length ratio of the atlanto-occipital joint in CMI patients was 0.141 ± 0.065 (range 0.027 - 0.274), which was smaller than that of control individuals (0.228 ± 0.057, range 0.069 - 0.379). And the difference was statistically significant (p < .01).

CONCLUSIONS

The atlanto-occipital joints in CMI patients are significantly flatter compared with those in healthy controls. This morphological variation could lead to differences of the atlanto-occipital stability between CMI patients and normal population, which may be related to the pathogenesis of CMI.

An anatomical and radiological study of the tectorial membrane and its clinical implications

The radiological image of an intact tectorial membrane (TM) became an important favorable prognostic factor for craniovertebral instability. This study visualized the fascial layers of the TM and adjacent connective tissues with clinical significance by micro-CT and histological analysis. The TM firmly attached to the bony surface of the clivus, traversed the atlantoaxial joint posteriorly, and was inserted to the body of the axis showing wide distribution on the craniovertebral junction. The supradental space between the clivus, dens of the axis, anterior atlantooccipital membrane, and the TM contained profound venous networks within the adipose tissues. At the body of the axis, the compact TM layer is gradually divided into multiple layers and the deeper TM layers reached the axis while the superficial layer continued to the posterior longitudinal ligament of the lower vertebrae. The consistent presence of the fat pad and venous plexus in the supradental space and firm stabilization of the TM on the craniovertebral junction was demonstrated by high-resolution radiologic images and histological analysis. The evaluation of the TM integrity is a promising diagnostic factor for traumatic craniovertebral dislocation.

A new hypothesis for the pathophysiology of symptomatic adult Chiari malformation Type I

Chiari malformation Type I (CMI) is characterized by herniation of the cerebellar tonsils through the foramen magnum. The pathophysiology of CMI is not well elucidated; however, the prevailing theory focuses on the underdevelopment of the posterior cranial fossa which results in tonsillar herniation. Symptoms are believed to be due to the herniation causing resistance to the natural flow of cerebrospinal fluid (CSF) and exerting a mass effect on nearby neural tissue. However, asymptomatic cases vastly outnumber symptomatic ones and it is not known why some people become symptomatic. Recently, it has been proposed that CMI symptoms are primarily due to instability of either the atlanto-axial (AA) or the atlanto-occipital (AO) joint and the cerebellar tonsils herniate to prevent mechanical pinching. However, only a small percentage of patients exhibit clinical instability and these theories do not account for asymptomatic herniations. We propose that the pathophysiology of adult CMI involves a combination of craniocervical abnormalities which leads to tonsillar herniation and reduced compliance of the cervical spinal canal. Specifically, abnormal AO and/or AA joint morphology leads to chronic cervical instability, often subclinical, in a large portion of CMI patients. This in turn causes overwork of the suboccipital muscles as they try to compensate for the instability. Over time, the repeated, involuntary activation of these muscles leads to mechanical overload of the myodural bridge complex, altering the mechanical properties of the dura it merges with. As a result, the dura becomes stiffer, reducing the overall compliance of the cervical region. This lower compliance, combined with CSF resistance at the same level, leads to intracranial pressure peaks during the cardiac cycle (pulse pressure) that are amplified during activities such as coughing, sneezing, and physical exertion. This increase in pulse pressure reduces the compliance of the cervical subarachnoid space which increases the CSF wave speed in the spinal canal, and further increases pulse pressure in a feedback loop. Finally, the abnormal pressure environment induces greater neural tissue motion and strain, causing microstructural damage to the cerebellum, brainstem, and cervical spinal cord, and leading to symptoms. This hypothesis explains how the combination of craniocervical bony abnormalities, anatomic CSF restriction, and reduced compliance leads to symptoms in adult CMI.

Occipital condyle screw fixation after posterior decompression for Chiari malformation: Technical report and application

BACKGROUND

Surgical techniques for stabilization of the occipital cervical junction have traditionally consisted of screw-based techniques applied in conjunction with occipital plating and rods connected to subaxial instrumentation in the form of pars, pedicle, or lateral mass screws. In patients with type 1 Chiari malformation (CM-1) and evidence of occipital cervical junction instability who have undergone posterior decompression, the occipital condyle (OC) represents a potential alternative cranial fixation point. To date, this technique has only been described in pediatric case reports and morphometric cadaver studies.

METHODS

Patients underwent posterior fossa decompression for treatment of CM. Subsequently, patients received occipital cervical stabilization using OC screws.

RESULTS

Patients were successfully treated with no post-operative morbidity. Patient 2 was found to have pseudoarthrosis and underwent revision. Both patients continue to do well at 1-year follow-up.

CONCLUSION

Placement of the OC screw offers advantages over traditional plate-based occipital fixation in that bone removal for suboccipital decompression is not compromised by the need for hardware placement, screws are hidden underneath ample soft tissue in patients with thin skin which prevents erosion, and the OC consists of primarily cortical bone which provides for robust tricortical fixation. These cases demonstrate the novel application of the OC screw fixation technique to the treatment of occipital cervical junction instability in adult patients undergoing simultaneous posterior fossa decompression.

Is there a morphometric cause of Chiari malformation type I? Analysis of existing literature

Although many etiologies have been proposed for Chiari malformation type I (CM-I), there currently is no singular known cause of CM-I pathogenesis. Advances in imaging have greatly progressed the study of CM-I. This study reviews the literature to determine if an anatomical cause for CM-I could be proposed from morphometric studies in adult CM-I patients. After conducting a literature search using relevant search terms, two authors screened abstracts for relevance. Full-length articles of primary morphometric studies published in peer-reviewed journals were included. Detailed information regarding methodology and symptomatology, craniocervical instability, syringomyelia, operative effects, and genetics were extracted. Forty-six studies met inclusion criteria, averaging 93.2 CM-I patients and 41.4 healthy controls in size. To obtain measurements, 40 studies utilized MRI and 10 utilized CT imaging, whereas 41 analyzed parameters within the posterior fossa and 20 analyzed parameters of the craniovertebral junction. The most commonly measured parameters included clivus length (n = 30), tonsillar position or descent (n = 28), McRae line length (n = 26), and supraocciput length (n = 26). While certain structural anomalies including reduced clivus length have been implicated in CM-I, there is a lack of consensus on how several other morphometric parameters may or may not contribute to its development. Heterogeneity in presentation with respect to the extent of tonsillar descent suggests alternate methods utilizing morphometric measurements that may help to identify CM-I patients and may benefit future research to better understand underlying pathophysiology and sequelae such as syringomyelia.

Triangular-Shaped Odontoid Process With Chiari 1 Malformation Patient

Several anatomical variations of osseous structures around the craniovertebral junction (CVJ) have been observed in those presenting with Chiari 1 malformation (CM-1) due to the junction’s unique embryology and its pivotal role in neck stability. During a clinic visit, a 14-year-old female presented with the classic symptoms of CM-1. Upon follow-up imaging and confirmation of the inferiorly displaced cerebellar tonsils, a unique triangular-shaped odontoid process was identified. To our knowledge, this osseous malformation of the dens has not been reported in the current literature. This unique deviation may cause ligamentous instability and decreased motion capacity and predispose a patient to axial fractures. Thus, we aim to further discuss this case, cervical vertebrae axis (C2) embryology, and the resulting clinical significance of this observed odontoid process variant.

Cerebellar syndrome after occipital nerve block: A case report

BACKGROUND

Occipital nerve blocks are commonly used in the treatment of different types of refractory headaches. The procedure is considered safe, and serious complications have rarely been described.

CASE PRESENTATION

We report a serious complication of occipital nerve blockade secondary to the penetration of local anesthetic and non-steroidal anti-inflammatory drugs into the posterior fossa in a patient affected by type I Arnold Chiari malformation.

CONCLUSIONS

This case reminds that a proper injection technique is mandatory to avoid potentially severe complications when performing occipital nerve blocks.