title: Is "black geode" sign a characteristic MRI finding for extracranial schwannomas?
abstract: OBJECTIVE
  To evaluate whether the "black geode" sign is a characteristic magnetic resonance imaging (MRI) finding for extracranial schwannomas.
  
  
  METHODS
  Forty-three patients with pathologically confirmed extracranial schwannomas underwent preoperative gadolinium-enhanced MRI. The black geode sign was defined as the appearance of enhanced outer and inner rings. MR images were retrospectively reviewed for size, configuration, and signal intensity of the lesions in addition to the presence of the black geode sign.
  
  
  RESULTS
  Gadolinium-enhanced T1-weighted images revealed the black geode sign in seven of 43 patients (16%). The thickness of inner rings (mean 0.6 cm, range 0.3-0.8 cm) was significantly greater than that of outer rings (mean 0.2 cm, range 0.1-0.3 cm) (P < 0.01). While outer rings were circular or elliptical in shape with smooth contours, inner rings had a lobular configuration with irregular thickness and contours. The degrees of enhancement were significantly stronger with inner rings than with outer rings (P < 0.01). In histopathological correlation of five patients who underwent total excision, inner and outer rings corresponded to peridegenerative areas and fibrous capsules, respectively.
  
  
  CONCLUSIONS
  The black geode sign may be fairly specific to extracranial schwannomas on gadolinium-enhanced MR images.
authors.affiliation: Department of Radiology, Gifu University School of Medicine, Gifu, Japan. hkato@gifu-u.ac.jp
authors.forename: Hiroki
authors.initials: H
authors.lastname: Kato
authors.forename: Masayuki
authors.initials: M
authors.lastname: Kanematsu
authors.forename: Takatoshi
authors.initials: T
authors.lastname: Ohno
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Nishimoto
authors.forename: Koji
authors.initials: K
authors.lastname: Oshima
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Hirose
authors.forename: Hironori
authors.initials: H
authors.lastname: Nishibori
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003287:Contrast Media / Q000008:administration & dosage; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D018317:Nerve Sheath Neoplasms / Q000175:diagnosis* / Q000473:pathology / Q000601:surgery; D009442:Neurilemmoma / Q000175:diagnosis* / Q000473:pathology / Q000601:surgery; D010525:Peripheral Nerves / Q000473:pathology / Q000601:surgery; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D055815:Young Adult
chemical_list: D003287:Contrast Media