Operative findings and surgical outcomes in patients undergoing Chiari 1 malformation decompression: relationship to the extent of tonsillar ectopia



The diagnosis of Chiari 1 malformation is based on the extent of tonsillar ectopia.


To examine the relationship between the extent of tonsillar ectopia and the intra-operative findings and clinical outcome following Chiari decompression surgery.


Patients were divided into four groups depending on the position of the cerebellar tonsil (T): group 1: 0 < T < 3; group 2: 3 ≤ T ≤ 5; group 3: 5 < T ≤ 10; and group 4: T > 10. Intra-operative observations were recorded with regard to compression of the brain stem by posterior inferior cerebellar artery (pica), neuroma formation along the first cervical (C1), and accessory spinal nerves (XI), and pallor of the cerebellar tonsils. Brain stem auditory evoked potentials, (BAEP), were monitored in each case. One hundred sixty-eight patients accrued between 2009 and 2013 agreed to participate in an outcome study to determine the effectiveness of foramen magnum decompression. Findings across the four groups were compared using one-way ANOVA. Observed differences were further subjected to paired analysis. Intra-group comparisons were made using the paired t test. A P value less than 0.05 was considered statistically significant.


There were 98 patients in group 1, 147 patients in group 2, 180 patients in group 3, and 63 patients in group 4. The mean extent of tonsillar ectopia was 0.4, 4.0, 7.1, and 14.3 mm in the four groups respectively. The prevalence of tonsillar pallor was greatest in group 4. Otherwise, there was no difference observed in the operative findings. A reduction of > 0.1 msec in the wave III–wave V latency of the BAEP was noted in all four groups with equal frequency. One hundred ten patients complied with at least 6 months follow-up. There was no difference in the prevalence of symptoms between the four groups at the time of initial evaluation and at 6 weeks and 6 months following surgery. There was a statistically significant reduction in the intensity of individual symptoms 6 months following surgery regardless of the extent of tonsil ectopia.


Other than the finding of tonsillar pallor, there was no relationship between the extent of tonsillar ectopia and the intraoperative anatomical and physiological observations, nor was there any relationship to the likelihood of symptomatic improvement following surgery. These observations call into question the focus on the extent of tonsillar of ectopia in assessing the patient who presents with symptoms of the Chiari malformation.

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We are indebted to the efforts of Stephan Dullweber for database construction and management and to Betty Kaimans for tireless data monitoring and entry.

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Correspondence to Dan S Heffez.

Ethics declarations

The study that was approved by The New England Institutional Review Board.

Conflict of interest

Dr. Heffez developed the Chiari plate and has received royalties from KLS Martin. The authors declare that they have no conflict of interest.

Informed consent

For this type of study formal consent is not required. Some patients undergoing surgery after December 2008 participated in a prospective treatment outcome study approved by the New England Institutional Review Board. Consent was obtained for study participation.

This article does not contain any studies with human participants performed by any of the authors. Human participation is limited to standard medical care.

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Heffez, D.S., Golchini, R., Ghorai, J. et al. Operative findings and surgical outcomes in patients undergoing Chiari 1 malformation decompression: relationship to the extent of tonsillar ectopia. Acta Neurochir 162, 1539–1547 (2020). https://doi.org/10.1007/s00701-019-04172-0

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  • Chiari 1 malformation
  • Operative findings
  • Tonsillar ectopia
  • Outcomes