Despite advances in surgical and oncological treatment of rectal cancer, disease recurrence remains a significant clinical challenge. Accurate preoperative staging is crucial in risk stratifying patients and thereby determining the optimal treatment strategy and surveillance approach. Magnetic resonance imaging (MRI) has demonstrably revolutionised pre-operative staging in rectal cancer, offering detailed visualization of tumour characteristics and surrounding anatomy. However, despite this, modern staging systems fail to adequately recognise some key markers of poor prognosis which can be readily identified on imaging.

This thesis explores the prognostic significance of MRI-detected features of vascular invasion in rectal cancer in both the pre and post neo-adjuvant treatment phase. The data confirms that accurate MRI detection of tumour deposits can be readily taught with good interobserver agreement. Analysis of pelvic sidewall lesions demonstrates that tumour deposits and extramural venous invasion are clearly correlated with poor prognosis, where lymph nodes are not. In addition, I explore alternative methods for differentiating lesions in the mesorectum and present preliminary data on quantifying irregularity and how this might aid in diagnosis and prognostication. This work adds to the body of evidence in support of vascular pathways being the primary route for spread in rectal cancer.