Basilar invagination and Chiari malformation associated with cerebellar atrophy: report of two treated cases

Basilar Impression: A Systematic Review and Meta-Analysis of Clinical Features, Operative Strategies, and Outcomes

OBJECTIVE

Basilar impression (BI) is a rare yet debilitating abnormality of the craniovertebral junction, known to cause life-threatening medullary brainstem compression. Our study analyzes surgical approaches for BI and related outcomes.

METHODS

A systematic review was conducted using PubMed, Google Scholar, and Web of Science electronic databases according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines to critically assess primary articles examining BI.

RESULTS

We analyzed 87 patients from 65 articles, mostly female (55.17%) with a mean age of 46.31 ± 17.94 years, commonly presenting with motor (59.77%) and sensory deficits (55.17%). Commonly employed procedures included posterior occipitocervical fusion (24.14%), anterior decompression (20.69%), and combined anterior decompression with posterior fusion (21.84%). Patients who underwent anterior approaches were found to be older (55.38 ± 17.67 vs. 45.49 ± 18.78 years, P < 0.05) and had a longer duration from symptom onset to surgery (57.39 ± 64.33 vs. 26.02 ± 29.60 months, P < 0.05) compared to posterior approaches. Our analysis revealed a significant association between a longer duration from symptom onset to surgery and an increased likelihood of undergoing odontoidectomy and decompression (odds ratio: 1.02, 95% confidence interval: 1.00-1.03, P < 0.05). Furthermore, after adjusting for all other covariates, a history of rheumatoid arthritis and the use of a posterior approach were significantly associated with an elevated risk of postoperative complications (P < 0.05).

CONCLUSIONS

The treatment approach to complex craniovertebral junction disease should be tailored to the surgeon's experience and the nature of the compressive pathology.

Severe Cerebellar Degeneration and Chiari I Malformation - Speculative pathophysiology based on a systematic review

BACKGROUND

Symptomatic Chiari Type I Malformation (CM) is treated with posterior fossa decompression with or without duroplasty. We have noticed some cases with concomitant severe cerebellar ataxia due to cerebellar atrophy. The aim of this study is to review the literature of CM associated with severe cerebellar atrophy and discuss its potential physiopathology.

METHODS

A systematic literature review in the Pubmed Database was performed using the following key-terms: "cerebellar atrophy Chiari", and "cerebellar degeneration Chiari". Articles reporting the presence of cerebellar degeneration/atrophy associated with CM were included.

RESULTS

We found only six studies directly discussing the association of cerebellar atrophy with CM, with a total of seven cases. We added one case of our own practice for additional discussion. Only speculative causes were described to justify cerebellar atrophy. The potential causes of cerebellar atrophy were diffuse cerebellar ischemia from chronic compression of small vessels (the most mentioned speculative cause), chronic raised intracranial pressure due to CSF block, chronic venous hypertension, and association with platybasia with ventral compression of the brainstem resulting in injury of the inferior olivary nuclei leading to mutual trophic effects in the cerebellum. Additionally, it is not impossible to rule out a degenerative cause for cerebellar atrophy without a causative reason.

CONCLUSIONS

Severe cerebellar atrophy is found in some patients with CM. Although chronic ischemia due to compression is the most presumed cause, other etiologies were proposed. The real reasons for cerebellar degeneration are not known. Further studies are necessary.

Cervicomedullary angle as an independent radiological predictor of postoperative neurological outcome in type A basilar invagination

To propose an independent radiological index to evaluate surgical outcomes of A type basilar invagination, a retrospective study was conducted to compare the clinical outcome between procedures 1 and 2 by applying intraoperative consistent traction and manual reduction. Moreover, the atlantodental interval (ADI), cervicomedullary angle (CMA), bilateral sagittal inclination of atlantoaxial joint (SIAA) were measured and compared to pre-operation. Postoperatively, only these patients undergoing procedure 2 achieved significant neurological improvement. The ADIs and the SIAAs decreased in both groups, these differences are statistically significant between pre- and post- operation. For postoperative CMAs, only these patients undergoing modified surgery gained significant improvement of angle with mean 141°. We concluded that the CMA or SIAA could be a radiological predictor to evaluate surgical outcome in BI, among which the CMA is a more independent and easily measurable predictor that is closely correlated with satisfactory neurological improvements. Moreover, procedure 2 with intraoperative resistant cranial traction and manual reduction can help us achieve a good CMA.

Cerebellar atrophy with Chiari malformation: An example of trans-synaptic degeneration?

A 23-year old man was found to have a Chiari Type 1 malformation and cerebellar atrophy. While this association has previously been described, the remote cerebellar atrophy is difficult to explain. We believe the answer lies with our finding of signal hyperintensity on MR imaging at the level of the inferior olives. This suggest hypertrophic olivary degeneration, caused by trans-synaptic degeneration following disruption to the Guillain-Mollaret triangle. Propagation of this process to the cerebellar Purkinje cells occurs in some cases. We describe a case in support of this hypothesis and review previously published evidence.

Basilar Invagination and Atlantoaxial Dislocation: Reduction, Deformity Correction and Realignment Using the DCER (Distraction, Compression, Extension, and Reduction) Technique With Customized Instrumentation and Implants

Objective

The technique of distraction, compression, extension, and reduction (DCER) is effective to reduce, realign, and relieve cranio-spinal compression through posterior only approach.

Methods

Study included all patients with atlantoaxial dislocation and basilar invagination (BI) with occipitalized C1 arch. Study techniques included Nurick grading, computed tomography scan to study atlanto-dental interval, BI, hyper-lordosis, and neck tilt. Sagittal inclination (SI), coronal inclination (CI), cranio-cervical tilt, presence of pseudo-joints, and anomalous vertebral artery were also noted. Patients underwent DCER with/without joint remodeling or extra-articular distraction (EAD) based on the SI being <100°, 100°–160°, or >160° respectively. In cases with pseudo-joints, joint remodeling was performed in type I and EAD in type II. Customized ‘bullet shaped’ PSC spacers (n=124) and prototype of the universal craniovertebral junction reducer (UCVJR, n=36) were useful.

Results

A total of 148 patients with average age 27.25±17.43 years, ranging from 3 to 71 years (87 males) were operated. Nurick’s grading improved from 3.14±1.872 to 1.22±1.17 (p<0.0001). Fifty-two percent of total joints (n=154/296 joints) were either type I (19%)/type II (33%) pseudo-j oints. All traditional indices such as Chamberlein line, McRae line, atlanto-dental interval, and Ranawat line improved (p<at least 0.001). BI, SI, and CI values correlated with type of pseudo-joints (p<0.0001). Side of neck tilt correlated with the type of pseudo-joint (p<0.0001). Cervical hyperlordosis improved significantly (p<0.0001).

Conclusion

Occipito-C2 pseudo-joints are important in determining the severity of BI. Asymmetrical pseudo-joint causes coronal/neck tilt. Type of pseudo-joint can strategize by DCER. Customized instruments and implants make technique safe, effective and easier.

Distraction, Compression, Extension, and Reduction Combined With Joint Remodeling and Extra-articular Distraction: Description of 2 New Modifications for Its Application in Basilar Invagination and Atlantoaxial Dislocation: Prospective Study in 79 Cases

BACKGROUND

Recent strategies for treatment of basilar invagination (BI) and atlantoaxial dislocation (AAD) are based on simultaneous posterior reduction and fixation.

OBJECTIVE

To describe new modifications of the procedure distraction, compression, extension, and reduction (DCER), ie, joint remodeling (JRM) and extra-articular distraction (EAD) in patients with "vertical" joints, and to quantify the improvement in joint indices, ie, sagittal inclination (SI), craniocervical tilt (CCT), and coronal inclination.

METHODS

Prospective study (May 2010 to September 2014). Joint indices measured included (normal values): SI (87.15 ± 5.65°), CCT (60.2 ± 9.2°), and coronal inclination (110.3 ± 4.23°). Surgical procedures included DCER alone (performed in SI <100°, group I) or JRM with DCER (in SI: 100-160°, group II), or EAD with DCER in severe BI with almost vertical joints (SI >160°, group III).

RESULTS

Seventy-nine patients were selected (mean, 22.5 years of age). All conventional indices improved significantly (P < .001). CCT improved in all groups (P < .01); group I (n = 32): 54 ± 8.7° (preoperative 80.71 ± 12.72°); group II (n = 40): 58 ± 7.0° (preoperative 86.5 ± 14°); group III (n = 7): 62 ± 10.0° (preoperative 104 ± 11.2°). SI improved in both group I and II, P < .01 (cannot be measured in group III). At long-term follow-up (n = 64, 29 ± 8 months, range 12-39 months), the Nurick grade improved to 1.5 ± 0.52 (preoperative: 3.4 ± 0.65; P < .001).

CONCLUSION

DCER seems to be an effective technique in reducing both BI and AAD. JRM and EAD with DCER are useful in moderate to severe BI and AAD (with SI >100°). Joint indices provide useful information for surgical strategy and planning.

Clinical Presentation of Chiari I Malformation and Syringomyelia in Children

Chiari I malformation and syringomyelia may be associated with a wide spectrum of symptoms and signs in children. Clinical presentations vary based on patient age and relative frequency; some diagnoses represent incidental radiographic findings. Occipitocervical pain, propagated or intensified by Valsalva maneuvers (or generalized irritability in younger patients unable to communicate verbally), and syringomyelia with or without scoliosis are the most common clinical presentations. Cranial nerve or brainstem dysfunction also may be observed in younger patients, and is associated with more complex deformity that includes ventral compression secondary to basilar invagination, retroflexion of the dens, and/or craniocervical instability.

The severity of basilar invagination and atlantoaxial dislocation correlates with sagittal joint inclination, coronal joint inclination, and craniocervical tilt: a description of new indexes for the craniovertebral junction

BACKGROUND

Joint-distraction and intra-operative manipulation surgeries to correct basilar invagination (BI) and atlantoaxial dislocation (AAD) are becoming standard procedures. However, current data are unable to aid in the understanding of normal and abnormal morphology of the C1/C2 joints.

OBJECTIVE

To study various aspects of C1/C2 joint morphology to create normative and patient data on joint abnormalities that could provide the surgeon with objective data for surgical planning and approach.

METHODS

Seventy patients (age, 15-45 years) were compared with an equal number of age- and sex-matched control subjects (age, 21.9±8.2 years) with irreducible BI and AAD from a developmental origin (May 2010-July 2013). Joint anatomy was studied with the use of thin-slice computed tomography scans. The joint parameters studied included sagittal joint inclination, craniocervical tilt, coronal joint inclination, surface area, joint overlap index, and joint reciprocity. The severity of BI and the severity of AAD were compared.

RESULTS

Sagittal joint inclination and craniocervical tilt significantly correlated with both BI and AAD (P<.01). Coronal joint inclination correlated with BI (P=.2). The mean sagittal joint inclination value in control subjects was 87.15±5.65° and in patients with BI and AAD was 127.1±22.05°. The mean craniocervical tilt value in controls was 60.2±9.2° and in patients with BI and AAD was 84.0±15.1°. The mean coronal joint inclination value in control subjects was 110.3±4.23° and in patients with BI and AAD was 121.15±14.6°.

CONCLUSION

This study has demonstrated for the first time the important role of joint orientation and its correlation with the severity of BI and AAD and has described new joint indexes.

Is atlantoaxial instability the cause of Chiari malformation? Outcome analysis of 65 patients treated by atlantoaxial fixation

OBJECT

Understanding that atlantoaxial instability is the cause of Chiari malformation (CM), the author treated 65 patients using atlantoaxial stabilization. The results are analyzed.

METHODS

Cases of CM treated using atlantoaxial fixation during the period from January 2010 to November 2013 were reviewed and analyzed. Surgery was aimed at segmental arthrodesis.

RESULTS

The author treated 65 patients with CM in the defined study period. Fifty-five patients had associated syringomyelia. Forty-six patients had associated basilar invagination. Thirty-seven patients had both basilar invagination and syringomyelia. Three patients had been treated earlier using foramen magnum decompression and duraplasty. According to the extent of their functional capabilities, patients were divided into 5 clinical grades. On the basis of the type of facetal alignment and atlantoaxial instability, the patients were divided into 3 groups. Type I dislocation (17 patients) was anterior atlantoaxial instability wherein the facet of the atlas was dislocated anterior to the facet of the axis. Type II dislocation (31 patients) was posterior atlantoaxial instability wherein the facet of the atlas was dislocated posterior to the facet of the axis. Type III dislocation (17 patients) was the absence of demonstrable facetal malalignment and was labeled as "central" atlantoaxial dislocation. In 18 patients, dynamic images showed vertical, mobile and at-least partially reducible atlantoaxial dislocation. All patients were treated with atlantoaxial plate and screw fixation using techniques described in 1994 and 2004. Foramen magnum decompression or syrinx manipulation was not performed in any patient. Occipital bone and subaxial spinal elements were not included in the fixation construct. One patient died, and death occurred in the immediate postoperative phase and was related to a vertebral artery injury incurred during the operation. One patient had persistent symptoms. In the rest of the patients there was gratifying clinical improvement. More remarkably, in 7 patients, the symptoms of lower cranial nerve paresis improved. No patient worsened in their neurological function after surgery. Reductions in the size of the syrinx and regression of the CM were observed in 6 of 11 cases in which postoperative MRI was possible. During the follow-up period, there was no delayed worsening of neurological function or symptoms in any patient. Sixty-three patients improved after surgery, and the improvement was sustained during the average follow-up period of 18 months.

CONCLUSIONS

On the basis of outcomes in this study, it appears that the pathogenesis of CM with or without associated basilar invagination and/or syringomyelia is primarily related to atlantoaxial instability. The data suggest that the surgical treatment in these cases should be directed toward atlantoaxial stabilization and segmental arthrodesis. Except in cases in which there is assimilation of the atlas, inclusion of the occipital bone is neither indicated nor provides optimum stability. Foramen magnum decompression is not necessary and may be counter-effective in the long run.

Complex Chiari malformations in children: an analysis of preoperative risk factors for occipitocervical fusion

OBJECT

Chiari malformation Type I (CM-I) is a congenital anomaly often treated by decompressive surgery. Patients who fail to respond to standard surgical management often have complex anomalies of the craniovertebral junction and brainstem compression, requiring reduction and occipitocervical fusion. The authors hypothesized that a subgroup of "complex" patients defined by specific radiographic risk factors may have a higher rate of requiring occipitocervical fusion.

METHODS

A retrospective review was conducted of clinical and radiographic data in pediatric patients undergoing surgery for CM-I between 1995 and 2010. The following radiographic criteria were identified: scoliosis, syringomyelia, CM Type 1.5, medullary kinking, basilar invagination, tonsillar descent, craniocervical angulation (clivoaxial angle [CXA] < 125°), and ventral brainstem compression (pB-C2 ≥ 9 mm). A multivariate Cox regression analysis was used to determine the independent association between occipitocervical fusion and each variable.

RESULTS

Of the 206 patients who underwent CM decompression with or without occipitocervical fusion during the study period, 101 had preoperative imaging available for review and formed the study population. Mean age at surgery was 9.1 years, and mean follow-up was 2.3 years. Eighty-two patients underwent suboccipital decompression alone (mean age 8.7 years). Nineteen patients underwent occipitocervical fusion (mean age 11.1 years), either as part of the initial surgical procedure or in a delayed fashion. Factors demonstrating a significantly increased risk of requiring fusion were basilar invagination (HR 9.8, 95% CI 2.2-44.2), CM 1.5 (HR 14.7, 95% CI 1.8-122.5), and CXA < 125° (HR 3.9, 95% CI 1.2-12.6).

CONCLUSIONS

Patients presenting with basilar invagination, CM 1.5, and CXA < 125° are at increased risk of requiring an occipitocervical fusion procedure either as an adjunct to initial surgical decompression or in a delayed fashion. Patients and their families should be counseled in regard to these findings as part of a preoperative CM evaluation.