title: MR imaging of normal perivascular space expansion at midbrain.
abstract: OBJECTIVE
  A previous investigation of the MR imaging findings in the midbrain reported expanded perivascular (PV) spaces in only the ponto-mesencepalic junction (PMJ) in 20% of healthy subjects, whereas pathologically expanding PV spaces have been reported at the mesencephalo-diencephalic junction (MDJ) as multi-lobulated, cystic lesions with signal intensity compatible with that of CSF that cause aqueductal stenosis. To clarify the anatomical distinctions between normally expanded and pathologically expanding PV spaces, we defined their distribution in the normal midbrain by using high-spatial-resolution MR imaging.
  
  
  METHODS
  Heavily T2-weighted MR imaging was performed in 115 adult subjects with neurologic complaints without cerebral disease. Histologic studies were performed from two normal midbrain blocks.
  
  
  RESULTS
  Expanded PV spaces were visible at the PMJ in 87% of subjects and at the MDJ in 63% of subjects. On axial images, ovoid or linear lesions with signal intensity compatible to CSF were present behind the cerebral peduncle at both the PMJ and MDJ. These areas varied from less than 1 mm to 5 mm (maximum diameter on coronal sections). Histologic studies confirmed the distribution of expanded PV spaces, as noted on MR images.
  
  
  CONCLUSIONS
  This study, by using high-spatial-resolution MR imaging, revealed that expanded PV spaces were visible at the PMJ and MDJ. Our finding of expanded PV spaces normally present at the MDJ may be related to pathologically expanding PV spaces, which should be kept in mind as a differential diagnosis for intraparenchymal cystic lesions in the midbrain with signal intensity compatible to CSF.
authors.affiliation: Department of Neurological Surgery and Pathology, Chiba University Graduate School of Medicine, Chiba, Japan.
authors.forename: Naokatsu
authors.initials: N
authors.lastname: Saeki
authors.forename: Motoki
authors.initials: M
authors.lastname: Sato
authors.forename: Motoo
authors.initials: M
authors.lastname: Kubota
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Uchino
authors.forename: Hisayuki
authors.initials: H
authors.lastname: Murai
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Nagai
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ishikura
authors.forename: Seitaro
authors.initials: S
authors.lastname: Nomura
authors.forename: Iichiro
authors.initials: I
authors.lastname: Matsuura
authors.forename: Akira
authors.initials: A
authors.lastname: Yamaura
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D004027:Diencephalon; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008636:Mesencephalon / Q000033:anatomy & histology*; D008875:Middle Aged; D011149:Pons; D012016:Reference Values