Role of MRI in evaluation and staging of rectal carcinoma

Abstract

Colorectal cancer is the third most common cancer in malesand the second most common cancer in females; around 30-40% of colorectal cancers are located in the rectum. The advance in treatment of rectal cancer raised the need for proper preoperative staging to individualize treatment option according to patient condition without facing unnecessary treatment. MRI imaging proved to be the modality of choice for accurate staging of rectal cancer. It has high soft tissue contrast resolution providing excellent information regarding the site and size of tumor, the depth of mural and extramural tumor spread, involvement of the circumferential resection margin, the extent of any sphincteral involvement, extramural vascular invasion (EMVI) and lymph nodes. The main pitfalls that can be faced during an MRI is the difficulty in differentiation between T1, T2 and T2, T3 stages (moderate accuracy 67–86% for T-staging), however this can have little impact on the management of patients. Identification of malignant lymph node continues to be a problem for radiologists, but enlarged lymph node more than 8mm with presence of intranodal mixed signal intensity and irregular spiculated borders are the most reliable of lymph node metastasis. A new promising technique for detection of malignant lymph node using specific lymph node contrast like Ultrasmall superparamagnetic iron oxide (USPIO) shows promising results with additional benefit in evaluation of small nodes.