title: Pulmonary nodules and the CT halo sign.
abstract: OBJECTIVE
  To determine whether the "halo sign" at computed tomography (CT) could be used to differentiate hemorrhagic from nonhemorrhagic pulmonary nodules.
  
  
  METHODS
  CT scans of 12 patients with hemorrhagic pulmonary nodules and of a control group of 10 patients with nonhemorrhagic pulmonary nodules were randomized and reviewed by two chest radiologists. Nodules were considered hemorrhagic if a surrounding halo of ground-glass attenuation was present.
  
  
  RESULTS
  Nodules were correctly identified as either hemorrhagic or nonhemorrhagic by both observers in 19 of the 22 cases (86%). Eight of the 12 patients with hemorrhagic nodules had an infectious process including invasive aspergillosis, candidiasis, cytomegalovirus, herpes simplex virus, or coccidioidomycosis. Four of 12 patients with hemorrhagic nodules had a noninfectious cause including Wegener granulomatosis, metastatic angiosarcoma, and Kaposi sarcoma.
  
  
  CONCLUSIONS
  Most hemorrhagic pulmonary nodules have a characteristic CT appearance consisting of a central area of soft-tissue attenuation with a surrounding halo of ground-glass attenuation that allows distinction from nonhemorrhagic nodules.
authors.affiliation: Department of Radiology, University of British Columbia, Vancouver, Canada.
authors.forename: S L
authors.initials: SL
authors.lastname: Primack
authors.forename: T E
authors.initials: TE
authors.lastname: Hartman
authors.forename: K S
authors.initials: KS
authors.lastname: Lee
authors.forename: N L
authors.initials: NL
authors.lastname: Müller
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006470:Hemorrhage / Q000000981:diagnostic imaging; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging; D008171:Lung Diseases / Q000000981:diagnostic imaging* / Q000473:pathology; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology; D008297:Male; D008875:Middle Aged; D003074:Solitary Pulmonary Nodule / Q000000981:diagnostic imaging* / Q000473:pathology; D014057:Tomography, X-Ray Computed