The role of imaging in the pre-operative staging and post-operative follow-up of rectal cancer.

Developments in rectal cancer imaging have revolutionised the management of this condition. It has become increasingly important for oncologists and surgeons to have a working insight into radiological assessment in order to make informed clinical decisions. In this context, we discuss the role that imaging plays in the pre-operative staging, post-operative follow-up and therapy of this disease including some novel advances in the field. Rectal cancer outcomes have improved due to modern surgical techniques, namely total mesorectal excision. Meticulous pre-operative assessment remains key. Conventional TNM staging now appears less crucial compared to assessing tumour distance from the potential plane of surgical resection (particularly the circumferential margin bounded by the mesorectal fascia), and this is reliant on high-quality imaging. Those with margin threatening disease can be offered downstaging chemoradiotherapy to facilitate successful resection. Endorectal ultrasound is useful for T staging and CT for detecting metastases. Malignant lymph node identification remains a problem and the use of size and morphological criteria may lead to misdiagnosis. In the post-operative setting, intensive follow-up is associated with improved outcomes but there are many variations in protocols. Most modalities struggle to differentiate tumour from reactive or fibrotic tissue and functional imaging is being investigated as the solution. PET scanning, particularly PET/CT, has been a major recent development. It has superior utility in detecting recurrent disease, including when conventional imaging is negative, detects occult metastases and may significantly enhance our ability to deliver accurate radiotherapy. Imaging has also opened up avenues for guided therapies aimed at ablating liver metastases. Radiofrequency ablation, in particular, is being used successfully and can improve survival of stage four patients.