title: Evaluating mesorectal lymph nodes in rectal cancer before and after neoadjuvant chemoradiation using thin-section T2-weighted magnetic resonance imaging.
abstract: OBJECTIVE
  To apply thin-section T2-weighted magnetic resoance imaging (MRI) to evaluate the number, size, distribution, and morphology of benign and malignant mesorectal lymph nodes before and after chemoradiation treatment compared with histopathologic findings.
  
  
  METHODS
  Twenty-five patients with poor-risk adenocarcinoma of the rectum treated with neoadjuvant chemoradiation were evaluated prospectively. Thin-section T2-weighted MR images obtained before and after chemoradiation treatment were independently reviewed in consensus by 2 expert radiologists to determine the tumor stage, nodal size, nodal distribution, and nodal stage. Total mesorectal excision surgery after chemoradiation allowed MR nodal stage to be compared with histopathology using kappa statistics. Nodal downstaging was compared using the Chi-square test.
  
  
  RESULTS
  Before chemoradiation, 152 mesorectal nodes were visible (mean, 6.2 mm; 100 benign, 52 malignant) and 4 of 52 malignant nodes were in contact with the mesorectal fascia. The nodal staging was 7/25 N0, 10/25 N1, and 7/25 N2. After chemoradiation, only 29 nodes (mean, 4.1 mm; 24 benign, 5 malignant) were visible, and none were in contact with the mesorectal fascia. Nodal downstaging was observed: 20/25 N0 and 5/25 N1 (p < 0.01, Chi-square test). There was good agreement between MRI and pathologic T-staging (kappa = 0.64) and N-staging (kappa = 0.65) after chemoradiation.
  
  
  CONCLUSIONS
  Neoadjuvant chemoradiation treatment resulted in a decrease in size and number of malignant- and benign-appearing mesorectal nodes on MRI. Nodal downstaging and nodal regression from the mesorectal fascia were observed after treatment. MRI is a useful tool for assessing nodal response to neoadjuvant treatment.
authors.affiliation: Academic Department of Radiology, The Royal Marsden Hospital, Sutton, United Kingdom. dowmukoh@icr.ac.uk
authors.forename: Dow-Mu
authors.initials: DM
authors.lastname: Koh
authors.forename: Ian
authors.initials: I
authors.lastname: Chau
authors.forename: Diana
authors.initials: D
authors.lastname: Tait
authors.forename: Andrew
authors.initials: A
authors.lastname: Wotherspoon
authors.forename: David
authors.initials: D
authors.lastname: Cunningham
authors.forename: Gina
authors.initials: G
authors.lastname: Brown
mesh_terms: D000230:Adenocarcinoma / Q000188:drug therapy / Q000532:radiotherapy / Q000556:secondary*; D017024:Chemotherapy, Adjuvant; D006801:Humans; D008198:Lymph Nodes / Q000473:pathology*; D008207:Lymphatic Metastasis / Q000473:pathology; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009367:Neoplasm Staging; D011446:Prospective Studies; D018714:Radiotherapy, Adjuvant; D012004:Rectal Neoplasms / Q000188:drug therapy / Q000473:pathology* / Q000532:radiotherapy; D012007:Rectum; D012306:Risk