title: Reversed halo sign on high-resolution CT of cryptogenic organizing pneumonia: diagnostic implications.
abstract: OBJECTIVE
  The aim of our study was to evaluate the usefulness of the reversed halo sign on high-resolution CT in the diagnosis of cryptogenic organizing pneumonia.
  
  
  METHODS
  Between 1996 and 2001, we saw 31 patients with biopsy-proven cryptogenic organizing pneumonia. During the same period, we also saw 30 patients with non-cryptogenic organizing pneumonia diseases, from which cryptogenic organizing pneumonia should be differentiated: Wegener's granulomatosis (n = 14), diffuse bronchioloalveolar carcinoma (n = 10), chronic eosinophilic pneumonia (n = 5), and Churg-Strauss syndrome (n = 1). Two independent observers analyzed CT findings and recorded how frequently the so-called reversed halo sign (central ground-glass opacity and surrounding air-space consolidation of crescentic and ring shape) was seen on high-resolution CT.
  
  
  RESULTS
  The most common patterns of parenchymal abnormalities of cryptogenic organizing pneumonia were ground-glass opacity (28/31 patients, 90%) and consolidation (27/31, 87%). The ground-glass opacity pattern showed random distribution, and the consolidation pattern showed subpleural or peribronchovascular (20/27 patients, 74%) distribution with predominance in the middle or lower lung zone. The reversed CT halo sign was seen in six (19%) of 31 patients with cryptogenic organizing pneumonia and in none of the patients with the diseases that needed to be differentiated from cryptogenic organizing pneumonia on CT.
  
  
  CONCLUSIONS
  The reversed halo sign, although seen only in one fifth of patients with the disease, appears relatively specific to make a diagnosis of cryptogenic organizing pneumonia on CT.
authors.affiliation: Department of Diagnostic Radiology, Yonsei University College of Medicine, YongDong Severance Hospital, Seoul 135-270, Korea.
authors.forename: Sang Jin
authors.initials: SJ
authors.lastname: Kim
authors.forename: Kyung Soo
authors.initials: KS
authors.lastname: Lee
authors.forename: Young Hoon
authors.initials: YH
authors.lastname: Ryu
authors.forename: Young Cheol
authors.initials: YC
authors.lastname: Yoon
authors.forename: Kyu Ok
authors.initials: KO
authors.lastname: Choe
authors.forename: Tae Sung
authors.initials: TS
authors.lastname: Kim
authors.forename: Ki Jun
authors.initials: KJ
authors.lastname: Sung
mesh_terms: D000328:Adult; D000368:Aged; D018549:Cryptogenic Organizing Pneumonia / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D014057:Tomography, X-Ray Computed