title: Retroperitoneal cyst: sonographic findings.
abstract: BACKGROUND
  Retroperitoneal cyst (RC) is a relatively rare disease, and its sonographic (US) findings have not been analyzed sufficiently.
  
  
  METHODS
  We studied US findings of five patients with RC, with special attention to location, size, shape, internal echoes, the presence or absence of lateral shadowing, and the mode of back echoes.
  
  
  RESULTS
  In all cases, the cyst was situated behind (four cases) or lateral to (one case) the pancreas: behind or lateral to the pancreatic head in two cases, behind the pancreatic body in one case, and behind the pancreatic tail in two cases. Four cases showed a round mass (three cases) or multiple round mass (one case). Internal echoes were present in those cases and showed a "pseudo-solid" pattern. In those cases, M-mode US confirmed the movement of those internal echoes. In the remaining case, the lesion was imaged as an irregularly shaped multilocular mass. No case showed posterior echo enhancement, and no case showed lateral shadowing. No blood flow signals from the lesion were seen.
  
  
  CONCLUSIONS
  Unlike ordinary cysts, RC usually is imaged as a round mass behind the pancreas, with dense internal echoes without lateral shadowing or posterior echo enhancement, which presents a "pseudo-solid" pattern. A diagnosis of RC should be considered when encountering a mass with such US findings.
authors.affiliation: First Department of Internal Medicine, Akita University School of Medicine, 1-1-1 Hondo, Akita-City, Akita 010-8543, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Konno
authors.forename: H
authors.initials: H
authors.lastname: Ishida
authors.forename: H
authors.initials: H
authors.lastname: Naganuma
authors.forename: T
authors.initials: T
authors.lastname: Komatsuda
authors.forename: M
authors.initials: M
authors.lastname: Sato
authors.forename: J
authors.initials: J
authors.lastname: Ishida
authors.forename: S
authors.initials: S
authors.lastname: Watanabe
mesh_terms: D002675:Child, Preschool; D003560:Cysts / Q000000981:diagnostic imaging* / Q000453:epidemiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012187:Retroperitoneal Space; D018615:Ultrasonography, Doppler, Color