title: The circumventricular organs of the brain: conspicuity on clinical 3T MRI and a review of functional anatomy.
abstract: OBJECTIVE
  The circumventricular organs (CVOs) occupy seven midline locations around the ventricles. They contain specialized ependymal cells called tanycytes and have an incomplete blood-brain barrier (BBB). We hypothesized that appearances of the lesser known CVOs on contrast-enhanced MRI might lead to confusion in image interpretation whereby they might be mistaken for pathology-related abnormal contrast enhancement. We therefore assessed the normal appearances and prevalence of contrast enhancement of the CVOs on routine clinical brain MRI and reviewed the functional anatomy of the CVOs.
  
  
  METHODS
  We retrospectively reviewed sagittal and coronal pre- and post-contrast T1-weighted brain 3T MR images in 100 adult patients with normal findings. We assessed the presence of the median eminence (ME), neurohypophysis (NH), pineal gland (PG), subforniceal organ (SFO), organum vasculosum of the lamina terminalis (OVLT), subcommissural organ (SCO), and the area postrema (AP).
  
  
  RESULTS
  The frequency of contrast enhancement of the seven CVOs was as follows: ME in 100 %, NH in 96 %, PG in 84 %, SFO in 1 %, OVLT in 34 %, SCO in 0 %, and AP in 2 %.
  
  
  CONCLUSIONS
  The main CVOs (ME, NH, and PG) are well known and appreciated on brain imaging. However, there is a little awareness of the minor CVOs among neuroimagers. This is the first study of contrast enhancement prevalence of the SF, OV, SC, and AP on brain MRI. All the latter are small, faint, rarely visualized, and therefore not likely to cause misinterpretation with significant sources of pathology that cause breakdown of the BBB, such as tumor or inflammation.
authors.affiliation: Department of Radiology, Addenbrooke's Hospital, 218 Hills Road, CB2 2QQ Cambridge, UK.
authors.forename: Avril
authors.initials: A
authors.lastname: Horsburgh
authors.forename: Tarik F
authors.initials: TF
authors.lastname: Massoud
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001812:Blood-Brain Barrier; D001921:Brain / Q000033:anatomy & histology*; D002648:Child; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D055815:Young Adult