Tag: Atlanto-occipital instability

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Exploring the Pathogenesis of Atlanto-Occipital Instability in ChiariMalformationWith Type II Basilar Invagination: A Systematic Morphological Study

Neurosurgery 92:837–853, 2023

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.

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Transcondylar approach for resection of lateral medullary cavernous malformation

Acta Neurochir (2018) 160:291–294

Resection of a medullary cavernous malformation requires aggressive exposure, but there is controversy on how much occipital condyle can be safely removed during the transcondylar approach.

Method We describe and demonstrate the use of the transcondylar approach to a medullary cavernous malformation, with emphasis on adequate surgical exposure while preserving the atlanto-occipital joint.

Conclusions Despite conservative handling of the occipital condyle, craniocervical stability may vary in patients after transcondylar surgery. A “dynamic” computer tomography, with views of the atlanto-occipital joint at each end-rotational extreme, may be the best postoperative assessment tool to evaluate the stability of the craniocervical junction.

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Atlanto-occipital Instability Following Endoscopic Endonasal Approach for Lower Clival Lesions

Atlanto-occipital Instability Following Endoscopic Endonasal Approach for Lower Clival Lesions

Neurosurgery 77:888–897, 2015

The endoscopic endonasal approach (EEA) for craniocervical lesions involving the lower clivus and occipital condyles carries an unclear risk of atlantooccipital (AO) instability requiring arthrodesis.

OBJECTIVE: Elucidate risk factors for AO instability following EEA for clival lesions.

METHODS: We reviewed patients with clival tumors who underwent EEA at our institution between 2002 and 2012. Resection of the lower clivus, foramen magnum, AO joint, and occipital condyles were evaluated on fine-cut postoperative computed tomography.

RESULTS: Two hundred twelve patients (mean age 47.9 years, 57.1% male) underwent transclival EEA for lower clival lesions. In addition to the lower clivus, resection involved the condyle in 14.2% of patients, the foramen magnum in 16.5%, and the AO joint in 1.4%. Quantification of condyle resection revealed complete resection in 3 cases, 75% resection in 8 cases, 50% resection in 6 cases, and 25% resection in 13 cases. Seven of these patients had EEA combined with an open, far-lateral approach. In total, 7 patients required arthrodesis following EEA (3.3%), 4 of them after a combined approach. All patients who underwent arthrodesis had primary bone tumors such as chordoma, chondrosarcoma, or osteosarcoma (P = .022). Degree of condyle resection was a significant factor predisposing to occipitocervical instability (P = .001 and P < .001 for 75% and 100% condyle resection, respectively). Use of a combined approach was significantly associated with arthrodesis (P < .001).

CONCLUSION: EEA resection of the occipital condyles that results in greater than 75% condyle resection or EEA in combination with an open approach significantly increases the risk of AO instability and likely necessitates AO fixation.

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