title: Circumferential resection margins of rectal tumours post-radiotherapy: how can MRI aid surgical planning?
abstract: BACKGROUND
  Magnetic resonance imaging (MRI) is known to have high predictive accuracy for circumferential resection margin (CRM) involvement of pre-treatment rectal tumours. This study aims to assess predictive accuracy of MRI for CRM involvement in rectal cancers post-long-course chemoradiotherapy (CRT) and in particular to understand how this information can influence surgical planning.
  
  
  METHODS
  Forty-seven rectal cancers treated with CRT followed by bowel resection in one hospital since 2005 were reviewed for clinical, radiological and pathological characteristics. Using a validated pro forma, a radiologist blinded to final histology and original MRI report predicted CRM status from post-CRT MRI images. Results were compared to histological CRM status of final specimen, and differential analysis by type of surgical operation was performed.
  
  
  RESULTS
  Overall accuracy of MRI for CRM involvement post-CRT was 72 % with a negative predictive value of 92 %. Abdominoperineal excision (APE) post-CRT was associated with non-significantly higher rates of histologically involved CRM than anterior resection (AR; 41 vs. 21 %) as were mucinous adenocarcinomas when compared to non-mucinous (56 vs. 21 %). Overall accuracy and positive predictive value were non-significantly higher for cancer treated with a standard APE than AR, and negative predictive value was high for both groups.
  
  
  CONCLUSIONS
  MRI post-CRT has high negative predictive value for CRM status. Such information is of particular clinical relevance in low rectal cancers treated with APE as it can indicate when a standard surgical approach is likely to be sufficient.
authors.affiliation: Department of Surgery, St George's Healthcare NHS Trust, London, UK, ermcglone@gmail.com.
authors.forename: E R
authors.initials: ER
authors.lastname: McGlone
authors.forename: V
authors.initials: V
authors.lastname: Shah
authors.forename: C
authors.initials: C
authors.lastname: Lowdell
authors.forename: D
authors.initials: D
authors.lastname: Blunt
authors.forename: P
authors.initials: P
authors.lastname: Cohen
authors.forename: P M
authors.initials: PM
authors.lastname: Dawson
mesh_terms: D002288:Adenocarcinoma, Mucinous / Q000473:pathology; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D059248:Chemoradiotherapy; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local; D009367:Neoplasm Staging; D011237:Predictive Value of Tests; D012004:Rectal Neoplasms / Q000473:pathology / Q000601:surgery* / Q000628:therapy; D012189:Retrospective Studies