Endoscopy 2004; 36 - 36
DOI: 10.1055/s-2004-834524

PN but not PT Determined by MRI May Accurately Stage Rectal Cancers after Neoadjuvant Radiochemotherapy

FM Smith 1, E Carton 1, RB Stephens 1, M Keoghan 1, C Brodie 1, C Stewart 1, E Gaffney 1, MJ Kennedy 1, JV Reynolds 1
  • 1Departments of Surgery, Pathology, Radiology, Medical and Molecular Oncology, St James's Hospital, Dublin 8. Database Manager, St James's Hospital, Dublin 8

Aims: To assess the accuracy of MRI staging in patients who underwent neoadjuvant radiochemotherapy (RCT) for locally advanced rectal cancer

Methods: Patients were identified using our colorectal database. A single consultant radiologist reviewed pre and post RCT MRI scans. Similarly, each resected tumour was assessed for pT and pN stage and assigned a tumour regression grade (TRG) by a pathologist.

Results: Pre and post RCT MRI scans were available for 14 patients. MRI did not detect change in T stage after RCT in any case. 6 patients demonstrated nodal downstaging by MRI which was reflected pathologically in 5 of 6 (83%) cases. In addition, the resected tumours from these patients showed large amounts of biological response to radiation having low TRGs and high amounts of shrinkage seen on MRI scans. In 6 of 7 (86%) patients whose nodal status did not change between scans, MRI correctly identified this.

Conclusions: MRI is unreliable for predicting T stage changes after RCT because it cannot differentiate between fibrosis and tumour. Nodal stage on the other hand may be assessed with reasonable accuracy. In addition, patients who undergo nodal downstaging seen on MRI would seem to have a high biological response to radiation.