title: The relative frequencies of causes of widespread ground-glass opacity: a retrospective cohort.
abstract: OBJECTIVE
  The purpose of our study was to determine the relative frequencies of causes of widespread ground-glass opacity (GGO) in an unselected, consecutive patient population and to identify any associated imaging findings that can narrow or reorganize the differential.
  
  
  METHODS
  The study was approved by the center's IRB and is HIPPA compliant. Cases with widespread GGO in the radiology report were identified by searching the Radiology Information System. Medical records and CT scan examinations were reviewed for the causes of widespread GGO. Associations between a less dominant imaging finding and a particular diagnosis were analyzed with the chi square test. Our study group consisted of 234 examinations with 124 women and 110 men and a mean age of 53.7 years.
  
  
  RESULTS
  A cause was established in 204 (87.2%) cases. Hydrostatic pulmonary edema was most common with 131 cases (56%). Interstitial lung diseases (ILD) were the next most common, most often hypersensitivity pneumonitis (HP) (n=12, 5%) and connective tissue disease related ILD (n=7, 3%). Infection accounted for 5% (12 cases). A few miscellaneous diseases accounted for 5 cases (2.1%). The combination of septal thickening and pleural effusions had a specificity of 0.91 for hydrostatic pulmonary edema (P<.001) while centrilobular nodules and air trapping had a specificity of 1.0 for HP. In 24 (10.2%) patients, increased opacification from expiration was incorrectly interpreted as representing widespread ground glass opacity. The relative frequency of disease dramatically changed according to the setting. In the inpatient setting, diffuse alveolar disease and diffuse infection accounted for all of the known diagnoses. Pulmonary edema accounted for 75% of the diagnoses and diffuse infection accounted for approximately 7%. In the outpatient setting, interstitial lung disease was the most common cause, accounting for 26 of 53 cases (49%). Regarding immunocompromised patients, hydrostatic pulmonary edema was still the most common cause (46%) with diffuse infection (24%) the next most likely diagnosis. For patients with bone marrow suppression, 80% of the cases were due to opportunistic viral infection.
  
  
  CONCLUSIONS
  Widespread GGO is most commonly a manifestation of hydrostatic pulmonary edema. Outpatients will most often have HP or connective tissue disease related ILD. Associated findings are helpful for the diagnosis of hydrostatic pulmonary edema and HP.
authors.affiliation: Hospital of the University of Pennsylvania, 3400 Spruce Street, Philadelphia, PA 19104, United States. Electronic address: Mike_hewitt@me.com.
authors.forename: Michael G
authors.initials: MG
authors.lastname: Hewitt
authors.affiliation: Hospital of the University of Pennsylvania, 3400 Spruce Street, Philadelphia, PA 19104, United States. Electronic address: Wallace.miller@uphs.upenn.edu.
authors.forename: Wallace T
authors.initials: WT
authors.lastname: Miller
authors.affiliation: Hospital of the University of Pennsylvania, 3400 Spruce Street, Philadelphia, PA 19104, United States. Electronic address: thomasjreilly@comcast.net.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Reilly
authors.affiliation: Hospital of the University of Pennsylvania, 3400 Spruce Street, Philadelphia, PA 19104, United States. Electronic address: Simpson80@gmail.com.
authors.forename: Scott
authors.initials: S
authors.lastname: Simpson
mesh_terms: D000368:Aged; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D008171:Lung Diseases / Q000000981:diagnostic imaging* / Q000209:etiology*; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*
keywords: CT; Chest; Ground-glass opacity