title: Rectal gas volume: Defining cut-offs for screening for evacuation disorders in patients with constipation.
abstract: BACKGROUND
  Diagnosis of rectal evacuation disorders (RED) is currently based on anorectal manometry (ARM) and evacuation tests in specialized laboratories; we recently showed higher rectal gas volume (RGV) and maximum rectal gas transaxial area (MRGTA) measured on abdominal and pelvic computed tomography (CT) in patients with documented RED.The aim of this study was to obtain cut-off values of RGV, MRGTA, and rectal area on scout film (RASF) to differentiate constipated patients with RED from those without RED, based on ARM, balloon expulsion test (BET), and colon transit test.
  
  
  METHODS
  We identified 118 constipated patients (65 with RED) with prior record of CT. Using standard CT software, we used a variable region of interest (ROI) program to measure RGV, MRTGA, and RASF, as previously described. We constructed receiver operating characteristics curves based on different values, and we estimated AUC, specificity, and positive predictive value (PPV) to detect RED in patients with constipation.
  
  
  RESULTS
  Receiver operating characteristics of the models to predict RED showed AUC 0.751 for RGV and 0.737 for MRGTA (both P<.001), and 0.623 for RASF (P=.029). At specificity of 90%, RGV of 30 mL had a PPV 77.3%, MRGTA of 10 cm2had a PPV 75.0%, and RFAS of 9 cm2had a PPV of 68.8% for identifying constipated patients with RED.
  
  
  CONCLUSIONS
  Rectal gas measurements on abdominal imaging may indicate RED in patients with constipation. At ~90% specificity for RED, RGV of 20 or 30 mL or MRGTA of 10 cm2on CT has PPV ~75%, and RASF of >9 cm2has PPV of ~69%.
authors.affiliation: Clinical Enteric Neuroscience Translational and Epidemiological Research (C.E.N.T.E.R.), Mayo Clinic, Rochester, MN, USA.
authors.forename: S-Y
authors.initials: SY
authors.lastname: Park
authors.affiliation: Clinical Enteric Neuroscience Translational and Epidemiological Research (C.E.N.T.E.R.), Mayo Clinic, Rochester, MN, USA.
authors.forename: D
authors.initials: D
authors.lastname: Khemani
authors.affiliation: Clinical Enteric Neuroscience Translational and Epidemiological Research (C.E.N.T.E.R.), Mayo Clinic, Rochester, MN, USA.
authors.forename: A
authors.initials: A
authors.lastname: Acosta
authors.affiliation: Clinical Enteric Neuroscience Translational and Epidemiological Research (C.E.N.T.E.R.), Mayo Clinic, Rochester, MN, USA.
authors.forename: D
authors.initials: D
authors.lastname: Eckert
authors.affiliation: Clinical Enteric Neuroscience Translational and Epidemiological Research (C.E.N.T.E.R.), Mayo Clinic, Rochester, MN, USA.
authors.forename: M
authors.identifier: http://orcid.org/0000-0001-6472-7514
authors.initials: M
authors.lastname: Camilleri
mesh_terms: D000328:Adult; D003248:Constipation / Q000000981:diagnostic imaging* / Q000453:epidemiology / Q000503:physiopathology*; D005260:Female; D005740:Gases; D006801:Humans; D008297:Male; D008875:Middle Aged; D012002:Rectal Diseases / Q000000981:diagnostic imaging* / Q000453:epidemiology / Q000503:physiopathology*; D012007:Rectum / Q000000981:diagnostic imaging / Q000503:physiopathology; D014057:Tomography, X-Ray Computed / Q000379:methods
chemical_list: D005740:Gases
keywords: area; colonic transit; radiograph; specificity