title: Evolution of cerebellar tonsillar ischemia to cerebellar tonsillar cysts in the Chiari I malformation: radiological, surgical, and histological evidence.
abstract: BACKGROUND
  Rare reports in the literature have documented the presence of a cyst at the tip of the cerebellar tonsil in patients with Chiari I malformation. The current study aimed to better elucidate these cysts and identify their etiology via a histological and radiologically analysis.
  
  
  METHODS
  We prospectively reviewed all new Chiari I malformation (CM-I) patients who presented to our clinic during a 2-year period. This was a pediatric cohort made up of 340 children aged 3 to 18 years. Specifically, all patients were screened for ischemic or cystic lesions of the herniated cerebellar tonsils on MRI.
  
  
  RESULTS
  Out of 340 patients, 2.9 % were found to have signal changes on MRI consistent with ischemia or cysts in the cerebellar tonsils. Of the 340 patients, 20 % underwent posterior fossa decompression. Of the 67 patients, cerebellar tonsillar ischemia was observed in 10.4 % and cerebellar tonsillar cysts were seen in 6 %. Four of the seven operative patients with cerebellar tonsillar ischemia and concomitant syringomyelia and three of these patients with tonsillar cysts concomitant syringomyelia and cerebellar tonsillar cysts underwent subpial dissection of some cerebellar tonsil to ensure that CSF egress from the fourth ventricle to the cervical subarachnoid space, and this transected tissue was also sent for histological analysis. Three of the four patients found to have intraoperative tonsillar cysts were noted to have tonsillar ischemic changes on preoperative imaging in this same region. For both ischemic and cystic cerebellar tonsils, histologically, the tissue demonstrated loss of Purkinje cells with concomitant Bergmann gliosis. The ischemic and cystic tissues were virtually the same, histologically.
  
  
  CONCLUSIONS
  Based on our findings, cerebellar tonsillar ischemia and cysts in patients with CM-I can often be seen radiologically. Histologically, these ischemic and cystic tissues are the same. Moreover, we document patients where ischemic lesions progressed to cysts, radiologically. Taken together, cerebellar tonsillar ischemia and cysts are on a continuum and represent chronic compression of this herniated part of the cerebellum.
authors.affiliation: Seattle Science Foundation, Seattle, WA, USA. shane.tubbs@childrensal.org.|Pediatric Neurosurgery, Children's of Alabama, 1600 7th Ave South, Lowder 400, Birmingham, AL, 35233, USA. shane.tubbs@childrensal.org.
authors.forename: R Shane
authors.initials: RS
authors.lastname: Tubbs
authors.affiliation: Pediatric Neurosurgery, Children's of Alabama, 1600 7th Ave South, Lowder 400, Birmingham, AL, 35233, USA.
authors.forename: Amin
authors.initials: A
authors.lastname: Demerdash
authors.affiliation: Swedish Neuroscience Institute, Seattle, WA, USA.
authors.forename: Rod J
authors.initials: RJ
authors.lastname: Oskouian
authors.affiliation: Pediatric Neurosurgery Associates, Children's Healthcare of Atlanta, Atlanta, GA, USA.
authors.forename: Joshua J
authors.initials: JJ
authors.lastname: Chern
authors.affiliation: Pediatric Neurosurgery, Children's of Alabama, 1600 7th Ave South, Lowder 400, Birmingham, AL, 35233, USA.
authors.forename: W Jerry
authors.initials: WJ
authors.lastname: Oakes
mesh_terms: D000293:Adolescent; D001139:Arnold-Chiari Malformation / Q000150:complications / Q000000981:diagnostic imaging / Q000601:surgery; D002545:Brain Ischemia / Q000209:etiology*; D020863:Central Nervous System Cysts / Q000209:etiology*; D002531:Cerebellum / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery*; D002648:Child; D002675:Child, Preschool; D018450:Disease Progression; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D011446:Prospective Studies; D012189:Retrospective Studies
keywords: Brain; Cerebellum; Chiari; Neurosurgery; Pediatrics