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Abstract #1550

Accuracy of MRI in Prediction of Transmural Invasion and Tumour-Free Resection Margin in Rectal Cancer

Peter Brotchie1, 2, Shalini Amukotuwa1

1MRI, Geelong Hospital, Geelong, Victoria, Australia; 2Radiology, University of Melbourne, Melbourne, Victoria, Australia

Local recurrence is a major obstacle in curative surgery for rectal carcinoma. The main factor affecting local recurrence is tumour involvement of the circumferential resection margin (CRM). If CRM is involved a long-course of chemoradiotherapy is given to reduce local recurrence rates. If not, a short-course of neoadjuvant radiotherapy decreases local recurrence in patients with transmural invasion of tumour. For these reasons, accurate pre-operative identification of transmural invasion and CRM involvement is needed. Rectal MRIs were performed on 101 consecutive patients with histologically proven rectal adenocarcinoma. Histopathologically, transmural invasion (T3 or T4) was present in 29 of 51 (T1 or T2) tumours and absent in 22 of 51. 25 of the 29 tumours with transmural invasion were correctly identified with 4 false negatives. 19 of the 22 tumours without transmural invasion were correctly identified with 3 false positives (Accuracy: 86%, Sens: 86%, Spec: 86 %, PPV: 89%, NPV: 83 %). Histopathologically CRM was involved in 7 of 48 tumours and not involved in 41 of 48 tumours. With MRI, CRM involvement was correctly identified in 7 of 7 cases and correctly identified as absent in 37 with 4 false positives (Sens 100%, Spec 90%, PPV 64%, NPV 100%).