MR imaging for rectal cancer: the role in staging the primary and response to neoadjuvant therapy

Pre-operative staging is an essential aspect of modern rectal cancer management and radiological assessment is central to this process. An ideal radiological assessment should provide sufficient information to reliably guide pre-operative decision-making. Technical advances allow high-resolution imaging to not only provide prognostic information but to define the anatomy, helping the surgeon to anticipate potential pitfalls during the operation. The main imaging modality for local staging of rectal cancer is Magnetic Resonance Imaging (MRI), as it defines the tumour and relevant anatomy providing the most detail on the important prognostic factors that influence treatment choice. In addition, there is an emerging role for MRI in the assessment of the response to neoadjuvant therapy. This article is an evidence-based review of rectal cancer staging focusing on post-treatment assessment of response using MRI. The discussion extends into the implications for reliably assessing response and how this may influence future rectal cancer management.