title: Exploitation of Simple Classification and Space Created by the Tumor for the Treatment of Foramen Magnum Meningiomas.
abstract: OBJECTIVE
  The resection of foramen magnum meningiomas (FMMs) presents neurosurgical challenges. We propose a simple classification of the tumor location and the operating space created by the tumor to help treatment planning.
  
  
  METHODS
  We retrospectively analyzed 16 FMMs and divided them into 3 groups based on the tumor location--clival, foraminal, and atlantal tumors. The distance between the condyle and the neuraxis at the level of the foramen magnum was measured and defined as the available operative space (AOS). We also reviewed intraoperative video recordings to assess the surgical exposure of the tumor by the space created by the FMM and compared it with the AOS.
  
  
  RESULTS
  There were 4 clival, 8 foraminal, and 4 atlantal tumors. The AOS of the clival tumors was 10 mm ± 1.7, the AOS of the foraminal tumors was 18 mm ± 3.7, and the AOS of the atlantal tumors was 12 mm ± 2.1. All foraminal and atlantal tumors could be detached without a brain retractor. Because a major portion of the clival tumors was covered by the spinomedullary junction, a brain spatula was needed to obtain the required surgical space. The difference in AOS between clival and foraminal/atlantal tumors was statistically significant (P = 0.044). Although 4 patients experienced postoperative complications, the average postoperative Karnofsky performance scale score improved. The surgical complication rate was significantly lower in foraminal and atlantal FMMs than in clival FMMs (P = 0.027).
  
  
  CONCLUSIONS
  The simple classification of the tumor location helped to assess surgical difficulties. Knowledge of the space created by the FMMs between the condyle and the neuraxis is useful for planning the approach strategy, especially for estimating the available working space without resection of the occipital condyle.
authors.affiliation: Department of Neurosurgery, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan. Electronic address: yamahatad3@gmail.com.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Yamahata
authors.affiliation: Department of Neurosurgery, Hiroshima University Graduate School of Biomedical Sciences, Hiroshima, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Yamaguchi
authors.affiliation: Department of Neurosurgery, Aichi Medical University, Nagakucte, Aichi, Japan.
authors.forename: Masakazu
authors.initials: M
authors.lastname: Takayasu
authors.affiliation: Department of Neurosurgery, Atsuchi Neurosurgical Hospital, Kagoshima, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Takasaki
authors.affiliation: Department of Neurosurgery, Aichi Medical University, Nagakucte, Aichi, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Osuka
authors.affiliation: Department of Neurosurgery, Aichi Medical University, Nagakucte, Aichi, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Aoyama
authors.affiliation: Department of Neurosurgery, Aichi Medical University, Nagakucte, Aichi, Japan.
authors.forename: Muneyoshi
authors.initials: M
authors.lastname: Yasuda
authors.affiliation: Department of Neurosurgery, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Tokimura
authors.affiliation: Department of Neurosurgery, Hiroshima University Graduate School of Biomedical Sciences, Hiroshima, Japan.
authors.forename: Kaoru
authors.initials: K
authors.lastname: Kurisu
authors.affiliation: Department of Neurosurgery, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan.
authors.forename: Kazunori
authors.initials: K
authors.lastname: Arita
mesh_terms: D000328:Adult; D000368:Aged; D001270:Cervical Atlas / Q000473:pathology / Q000601:surgery; D003388:Cranial Fossa, Posterior / Q000473:pathology / Q000601:surgery; D003389:Cranial Nerve Diseases / Q000209:etiology; D020209:Cranial Nerve Injuries; D005260:Female; D005539:Foramen Magnum / Q000473:pathology / Q000601:surgery; D006801:Humans; D008297:Male; D008577:Meningeal Neoplasms / Q000145:classification / Q000473:pathology* / Q000601:surgery*; D008579:Meningioma / Q000145:classification / Q000473:pathology* / Q000601:surgery*; D008875:Middle Aged; D019635:Neurosurgical Procedures / Q000009:adverse effects / Q000295:instrumentation / Q000379:methods*; D012189:Retrospective Studies; D012307:Risk Factors; D019292:Skull Base Neoplasms / Q000145:classification / Q000473:pathology* / Q000601:surgery*
keywords: Craniovertebral junction; Foramen magnum; Meningioma; Posterolateral approach; Transcondylar fossa