title: Staging rectal cancer: MRI compared to MDCT.
abstract: OBJECTIVE
  To audit the accuracy with which pre-operative MRI and multi-detector row CT determine the relationship between rectal tumour and the circumferential resection margin (CRM).
  
  
  METHODS
  The MR and CT scans of 72 patients with rectal adenocarcinoma were retrieved. The relationship between tumour and the mesorectal fascia was determined by two observers, who classified appearances into three categories: no tumour within 5 mm of the mesorectal fascia; tumour within 5 mm of the mesorectal fascia ('threatened' margin); tumour at the mesorectal fascia ('involved' margin). Agreement with post-operative histopathology was assessed by Kappa statistics.
  
  
  RESULTS
  There was poor agreement between both MRI and CT, and post-operative histology, both in all 72 patients and in the 42 who had received no pre-operative therapy or short-course radiotherapy only. Both imaging modalities had a tendency to overstage patients whose CRM was uninvolved subsequently. However, the negative predictive value for an uninvolved margin was 81.8% by MRI and 84.6% by CT. There was no patient with an involved margin by histopathology whose imaging had suggested the margin was uninvolved.
  
  
  CONCLUSIONS
  Both pre-operative MRI and multi-detector row CT have high negative predictive values for a subsequently uninvolved resection margin.
authors.affiliation: Department of Radiology, Royal Lancaster Infirmary, Morcambe Bay, Lancaster, United Kingdom.
authors.forename: Alasdair
authors.initials: A
authors.lastname: Taylor
authors.forename: Andrew
authors.initials: A
authors.lastname: Slater
authors.forename: Nicholas
authors.initials: N
authors.lastname: Mapstone
authors.forename: Stuart
authors.initials: S
authors.lastname: Taylor
authors.forename: Steve
authors.initials: S
authors.lastname: Halligan
mesh_terms: D000230:Adenocarcinoma / Q000175:diagnosis / Q000473:pathology*; D000368:Aged; D000369:Aged, 80 and over; D006801:Humans; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D009367:Neoplasm Staging; D012004:Rectal Neoplasms / Q000175:diagnosis / Q000473:pathology*; D012007:Rectum / Q000473:pathology; D014057:Tomography, X-Ray Computed