title: Magnetic resonance imaging prediction of an involved surgical resection margin in low rectal cancer.
abstract: OBJECTIVE
  Low rectal cancers (<5 cm from the anal verge), compared with all others, have greater positive resection margin rates, attributed to mesorectal tapering and higher perforation risk. The aim of this study was to assess positive resection margin prediction by using magnetic resonance imaging staging.
  
  
  METHODS
  The following features were analyzed by using preoperative magnetic resonance imaging from 101 consecutive patients with low rectal tumors: tumor location (posterior/anterior) and magnetic resonance stage (Stage 1-2, tumor within the intersphincteric plane; Stage 3-4 tumor extending into the intersphincteric plane). Magnetic resonance imaging tumor regression grade was measured where posttreatment magnetic resonance imaging was available and compared with histopathologic findings.
  
  
  RESULTS
  Seventy of 101 patients had abdominoperineal excisions, and 31 of 101 had low anterior resections. Using logistic regression, positive resection margin odds were higher for magnetic resonance Stages 3 to 4 than Stages 1 to 2 by a factor of 17.7 (P < 0.001), and positive resection margin odds were higher by a factor of 2.8 for anterior vs. posterior tumors (P = 0.026). Magnetic resonance imaging tumor regression grade strongly predicted for positive resection margins; 11 of 15 patients with little treatment response had positive resection margins, compared with 2 of 15 with >50 percent complete treatment response on magnetic resonance imaging (P < 0.001).
  
  
  CONCLUSIONS
  Significant magnetic resonance imaging positive resection margin predictors are tumor into or beyond the intersphincteric plane and magnetic resonance imaging tumor regression grade.
authors.affiliation: Pelican Cancer Foundation, North Hampshire Hospital, Basingstoke, Hampshire, United Kingdom.
authors.forename: Gisella V
authors.initials: GV
authors.lastname: Salerno
authors.forename: Ian R
authors.initials: IR
authors.lastname: Daniels
authors.forename: Brendan J
authors.initials: BJ
authors.lastname: Moran
authors.forename: R J
authors.initials: RJ
authors.lastname: Heald
authors.forename: Karen
authors.initials: K
authors.lastname: Thomas
authors.forename: Gina
authors.initials: G
authors.lastname: Brown
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001003:Anal Canal / Q000473:pathology* / Q000601:surgery; D017024:Chemotherapy, Adjuvant; D005260:Female; D006801:Humans; D016015:Logistic Models; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D020360:Neoadjuvant Therapy; D009367:Neoplasm Staging / Q000379:methods; D018714:Radiotherapy, Adjuvant; D012004:Rectal Neoplasms / Q000473:pathology* / Q000601:surgery* / Q000628:therapy