Exploring the Pathogenesis of Atlanto-Occipital Instability in Chiari Malformation With Type II Basilar Invagination: A Systematic Morphological Study.

BACKGROUND: Our previous study suggested that atlanto-occipital instability (AOI) is common in patients with type II basilar invagination (II-BI). OBJECTIVE: To further understand the pathogenesis of AOI in Chiari malformations (CM) and CM + II-BI through systematic measurements of the bone structure surrounding the craniocervical junction. METHODS: Computed tomography data from 185 adults (80 controls, 63 CM, and 42 CM + II-BI) were collected, and geometric models were established for parameter measurement. Canonical correlation analysis was used to evaluate the morphological and positional relationships of the atlanto-occipital joint (AOJ). RESULTS: Among the 3 groups, the length and height of the condyle and superior portion of the lateral masses of the atlas (C1-LM) were smallest in CM + II-BI cases; the AOJ had the shallowest depth and the lowest curvature in the same group. AOJs were divided into 3 morphological types: type I, the typical ball-and-socket joint, mainly in the control group (100%); type II, the shallower joint, mainly in the CM group (92.9%); and type III, the abnormal flat-tilt joint, mainly in the CM + II-BI group (89.3%). Kinematic computed tomography revealed AOI in all III-AOJs (100%) and some II-AOJs (1.5%) but not in type I-AOJs (0%). Morphological parameters of the superior portion of C1-LM positively correlated with those of C0 and the clivus and significantly correlated with AOI. CONCLUSION: Dysplasia of the condyle and superior portion of C1-LM exists in both CM and II-BI cases yet is more obvious in type II-BI. Unstable movement caused by AOJ deformation is another pathogenic factor in patients with CM + II-BI.

Management of Symptomatic Sacral Perineural Cysts: A New Surgical Method.

BACKGROUND: Microsurgical techniques are increasingly being recommended for the treatment of symptomatic Tarlov cysts (TCs) due to improved long-term outcomes compared to those of other strategies. However, these techniques are associated with a high risk of cyst recurrence and cerebrospinal fluid (CSF) leakage, resulting in the surgical strategy of TCs remaining controversial. We hypothesize that incomplete closure of the ostium between the cyst and the subarachnoid space is the probable cause of surgical failure. Accordingly, we present a novel method of cyst separation and ostium closure that aims to block the ostium more firmly and reliably. METHODS: Thirty-five consecutive patients (21 females) underwent the modified ostium obstruction surgery due to symptomatic TCs. We collected and compared their outcomes at the final follow-up to evaluate the surgical effect. RESULTS: Thirty-five patients had 74 TCs (S2 level, 48.7%; mean diameter, 2.0 ± 1.0 cm); ostia nerve root fibers were found in all TCs. The mean follow-up duration was 37.8 (range, 13.5-76.8) months. At the final follow-up, 33 patients experienced complete or substantial resolution of the preoperative symptoms. The symptom with the highest improvement rate was radicular pain. Both the modified evaluation criteria for the efficacy of lumbar function criterion and Japanese Orthopedic Association score 29 showed an overall improvement rate of 94.3%. Two patients experienced surgery-related neurological dysfunction. No cyst recurrence or CSF leakage was observed. Magnetic resonance imaging showed that all cysts disappeared or significantly reduced postoperatively. CONCLUSIONS: The microscopic fenestration of cysts and modified ostium obstruction described herein is a safe and effective strategy for management of patients with symptomatic TCs and is associated with a low incidence of cyst recurrence and CSF leakage since it achieves complete closure of cyst ostium.

Evaluating Craniovertebral Stability in Chiari Malformation Coexisting with Type II Basilar Invagination: An Observational Study Based on Kinematic Computed Tomography and Its Clinical Application.

BACKGROUND: Treatment of Chiari malformation (CM) is controversial, especially when it coexists with "stable" or Type II basilar invagination (CM + II-BI). Precise evaluation of craniovertebral junction (CVJ) stability is crucial in such patients; however, this has never been validated. This study aimed to dynamically evaluate atlanto-condyle and atlantoaxial stability by kinematic computed tomography (CT) and report its surgical treatment. METHODS: The study recruited 101 patients (control, CM, and CM + II-BI groups: 48, 34, and 19 patients, respectively). During kinematic CT, the CVJ stability-related parameters were measured and compared between the 3 groups. The surgical strategy for treating CM + II-BI was based on these results. Preoperative and postoperative images were acquired, and functional scores were used to assess the outcome. RESULTS: Among the 3 groups, the length of the clivus and the height of the condyle were the shortest in the CM + II-BI group, which was accompanied by the greatest rotation of the atlas and atlanto-condyle facet movement on cervical flexion and extension. Moreover, in such patients, increased Chamberlain's baseline violation indicated the aggregate invagination of the odontoid in the flexed position, and asymmetric displacement of atlantoaxial facets was observed. Seventeen CM + II-BI patients underwent surgical treatment with atlantoaxial distraction and occipitocervical fusion. The syringomyelia width and tonsillar herniation decreased significantly, and functional scores indicated symptom relief and good outcomes. CONCLUSIONS: CVJ instability, especially the ultramovement of atlanto-condyle facets, commonly exists in II-BI as evaluated using kinematic CT. The surgical strategy of atlantoaxial distraction and occipitocervical fusion should be considered to treat such patients.