MRI hasbeen a crucial modality for investigating rectalcancersince 1999 and isused to locateand stagerectal tumours, plan surgery and consider neoadjuvant therapy.1As under-staging may result in patients not being offered neoadjuvant therapy, accuracy of staging is important to prevent a worse outcome.Previous studies show that the accuracy ofMRstaging rangesbetween31%and100% due to varying protocols and inter-observer variability.2 Clinicians are aware of the limitations ofMRstaging, but limited studies have assessed patient outcomefromunder-staging.

MR rectal studies performed at Bankstown-Lidcombe Hospital between January 2015 and January 2021 were collected. All studies were performed using a Siemens 1.5T Avanto MRI machine. Of 125 studies: 59 had preoperative chemoradiotherapy, 41 went directly to surgery and 25 were excluded (no surgery, awaiting surgery etc.).MR staging results were compared to histopathology and analysed separately according to T (size) and N (nodal) stage for the 41 direct surgical candidates and the proportion of cases that were under-staged calculated. Of these, individual cases were then...

25 of 41 cases(61%) were accurately T staged.11 of41cases(27%) were under-staged,of whichfourmetthecriteria for neoadjuvant therapy. Two of those received adjuvant therapy and none demonstrated metastases on follow-up imaging. 18 of 35 cases (51%) were accurately N staged while 12 of 41 (29%) were under-staged. All under-staged cases were offered adjuvant therapy, however five had metastatic disease and four died. [Fig 4] [Fig 5]

Thisstudymeasured the accuracy ofrectal MRin staging as well astheimplications of under-staging. Our results show that while the proportion of T and Nunder-stagingwere similar,theclinical implications of N under-staging were more significant, with increased metastases and mortality. We are aware ofthelimitations in accurate N staging onMR,howeverhigher resolutionandthinner slices mayimprove accuracy.Thisstudy is also limited as patients considered suitable for neoadjuvant therapy may have gone directly to surgery due to advanced age, comorbidities or patient preference. This is a singlecentreproject and further multi-centrestudies may be beneficial. [Fig 6] [Fig...

Saklani A. Magnetic resonance imaging in rectal cancer: A surgeon’s perspective. World Journal of Gastroenterology. 2014 February 28; Volume 20(No 8): p2030. Keane C, Young M. Accuracy of magnetic resonance imaging for preoperative staging of rectal cancer. ANZ Journal of Surgery. 2013 October 8; Volume 84(No 10): p758-762. Glynne-Jones R, Wyrwicz L, Tiret E et al. Rectal cancer: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up. Annals of Oncology. 2017 July 1; Volume 28(No 4): p22-40.