title: Ventral compression in adult patients with Chiari 1 malformation sans basilar invagination: cause and management.
abstract: BACKGROUND
  A small subset of patients with adult Chiari I malformation without basilar invagination (BI) and instability show ventral cervicomedullary distortion/compression and have symptoms pertaining to that. The cause of this ventral compression remains speculative. Additionally, it is unclear if these patients would require ventral decompression with posterior fusion or only posterior decompression would suffice.
  
  
  METHODS
  Sixteen adult patients with Chiari I malformation with significant ventral cervicomedullary compression, in the absence of BI, were included in the study. Atlantoaxial dislocation (AAD) was excluded in these patients by flexion-extension craniovertebral junction X-rays and computed tomography (CT). Their clinical profile, especially symptoms pertaining to cervicomedullary compression, i.e. dysphagia, dysarthria and spasticity, were graded. The ventral cervicomedullary compression (VCMC) was quantified using pBC2 (maximum perpendicular distance to the basion-infero posterior point of the C2 body) on sagittal magnetic resonance imaging (MRI) and only those patients with pBC2 ≥9 mm were included. Furthermore, retroversion of dens and retro odonotid tissue thickness was calculated in each patient. Fifteen patients underwent posterior decompression alone and one refused surgery. Follow-up was done every 3 months. Repeat MRI was done at 1 year following surgery to look for pBC2.
  
  
  RESULTS
  The mean pBC2 was 11 ± 0.2 mm. Retroversion of dens was responsible for VCMC in three patients and periodontoid crown in 13. There was no correlation between the tonsillar descent, age and the pBC2. All patients improved in symptoms of cervicomedullary compression following surgery. One patient worsened 6 months after initial improvement. The pBC2 did not change, as seen on follow-up MRI done in five patients.
  
  
  CONCLUSIONS
  VCMC in adult patients with Chiari I malformation in the absence of BI and/or AAD is due to periodontoid tissue (crown) or retroverted dens. Though a long-term study is required, it appears that all patients with Chiari I malformation, irrespective of the VCMC, can be given a chance with posterior decompression alone. Transoral decompression with posterior fusion may be required in a small subset of patients who fail to improve or worsen following posterior decompression only.
authors.affiliation: Department of Neurosurgery, Postgraduate Institute of Medical Education and Research, Chandigarh, India. drpravin_salunke@yahoo.co.uk
authors.forename: Pravin
authors.initials: P
authors.lastname: Salunke
authors.forename: Sukumar
authors.initials: S
authors.lastname: Sura
authors.forename: Sameer
authors.initials: S
authors.lastname: Futane
authors.forename: Ashish
authors.initials: A
authors.lastname: Aggarwal
authors.forename: N K
authors.initials: NK
authors.lastname: Khandelwal
authors.forename: Rajesh
authors.initials: R
authors.lastname: Chhabra
authors.forename: Kanchan K
authors.initials: KK
authors.lastname: Mukherjee
authors.forename: Sunil K
authors.initials: SK
authors.lastname: Gupta
mesh_terms: D000293:Adolescent; D000328:Adult; D001139:Arnold-Chiari Malformation / Q000150:complications / Q000175:diagnosis / Q000601:surgery; D003388:Cranial Fossa, Posterior / Q000002:abnormalities* / Q000000981:diagnostic imaging / Q000601:surgery; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009777:Occipital Bone / Q000002:abnormalities* / Q000000981:diagnostic imaging / Q000601:surgery; D009809:Odontoid Process / Q000002:abnormalities* / Q000000981:diagnostic imaging / Q000601:surgery; D011859:Radiography; D012189:Retrospective Studies; D013117:Spinal Cord Compression / Q000209:etiology / Q000473:pathology / Q000601:surgery; D055815:Young Adult