title: The human foramen magnum--normal anatomy of the cisterna magna in adults.
abstract: BACKGROUND
  The goal of this study was to radiologically describe the anatomical characteristics of the cisterna magna (CM) with regard to presence, dimension, and configuration.
  
  
  METHODS
  In this retrospective study, 523 records were reviewed. We defined five CM types, the range of which covered all normal variants found in the study population. Characteristics of the CM were recorded and correlations between various posterior fossa dimensions and CM volume determined.
  
  
  RESULTS
  There were 268 female (mean age 50.9 ± 16.9 years) and 255 male (mean age 54.1 ± 15.8 years) patients. CM volume was smaller in females than in males and correlated with age (Pearson correlation, r = 0.1494, p = 0.0006) and gender (unpaired t test, r (2) = 0.0608, p < 0.0001). Clivus length correlated with CM volume (Pearson correlation, r = 0.211, p < 0.0001) and gender (unpaired t test, r (2) = 0.2428, p < 0.0001). Tentorial angle did not correlate with CM volume (Pearson correlation, r = -0.0609, p < 0.1642) but did correlate with gender (unpaired t test, r (2) = 0.0163, p < 0.0035). The anterior-posterior dimension of cerebrospinal fluid anterior to the brainstem correlated with CM volume (Pearson correlation, r = 0.181, p < 0.0001) and gender (unpaired t test, r (2) = 0.0205, p = 0.001).
  
  
  CONCLUSIONS
  The anatomical description and simple classification system we define allows for a more precise description of posterior fossa anatomy and could potentially contribute to the understanding of Chiari malformation anatomy and management.
authors.affiliation: Department of Neurological Surgery, Oregon Health & Science University, 3303 SW Bond Avenue, CH8N, Portland, OR, 97239, USA.
authors.forename: Nathaniel
authors.initials: N
authors.lastname: Whitney
authors.forename: Hai
authors.initials: H
authors.lastname: Sun
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Pollock
authors.forename: Donald A
authors.initials: DA
authors.lastname: Ross
mesh_terms: D000328:Adult; D002946:Cisterna Magna / Q000033:anatomy & histology*; D005260:Female; D005539:Foramen Magnum / Q000033:anatomy & histology*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D008953:Models, Anatomic; D009922:Oregon; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
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