Beyond Histologic Staging: Emerging Imaging Strategies in Colorectal Cancer with Special Focus on Magnetic Resonance Imaging

Abstract

).Colorectal cancer (CRC) is the third most common malignancy and second most common cause of cancer mortality in the United States, with over 132,000 new diagnoses and 49,000 deaths each year. 1 As these numbers indicate, CRC is curable in a substantial percentage of cases. Accurate staging is critical to the selection of a suitable treatment strategy and, consequently, to the achievement of optimal clinical outcomes. To this point, radiologic examinations are playing an increasingly important role in both the initial staging of CRC and the evaluation of response to neoadjuvant therapy. Moreover, imaging facilitates preoperative planning by delineating relationships between tumors and the adjacent anatomy, thereby defining the best surgical approach and minimizing risk of injury to surrounding structures.The imaging and treatment of CRC can be generally divided into two main components: (1) locoregional staging and management of primary tumors; and (2) the identification and management of distant metastases, which most commonly occur in the liver. The primary goal of locoregional treatment strategies is to achieve a margin-negative surgical resection, either primarily (for colon and rectal cancer) or after neoadjuvant chemotherapy and/or radiation (for rectal cancer only). Transrectal ultrasound (TRUS), computed tomography (CT), and magnetic resonance imaging (MRI) are the main imaging modalities for locoregional staging (►Table 1) and are focused on defining the local extent of the primary tumor (T-staging) as well as the status of local and regional lymph nodes (N-staging).While locoregional tumor management is important for preventing or minimizing invasion of adjacent structures and avoiding the associated morbidity, mortality in CRC is primarily determined by the hepatic disease burden. 2 Thus, the current treatment paradigm for liver metastases from both colon cancer and rectal cancer is surgical resection, which maximizes the chances for long-term survival. 3,4 For liver metastases deemed unresectable, neoadjuvant chemotherapy and percutaneous interventions can be employed to achieve hepatic tumor control and may eventually make resection feasible by reducing metastatic disease burden. 5-7 The imaging AbstractImaging plays an increasingly important role in the staging and management of colorectal cancer. In recent years, magnetic resonance imaging (MRI) has supplanted transrectal ultrasound as the preferred modality for the locoregional staging of rectal cancer. Furthermore, the advent of both diffusion-weighted imaging and hepatobiliary contrast agents has significantly enhanced the ability of MRI to detect colorectal liver metastases. In clinical practice, MRI routinely provides prognostic information, helps to guide surgical strategy, and determines the need for neoadjuvant therapies related to both the primary tumor and metastatic disease. Expanding on these roles for MRI, positron emission tomography (PET)/MRI is the newest clinical hybrid imaging modality and combines the metabolic information of P...

Treatment response of colorectal cancer liver metastases to neoadjuvant or conversion therapy: a prospective multicentre follow-up study using MRI, diffusion-weighted imaging and 1H-MR spectroscopy compared with histology (subgroup in the RAXO trial)

“…The high soft tissue contrast makes MRI a valuable tool in the characterisation and response evaluation of liver lesions, especially for lesions smaller than 10 mm and even more so in the presence of hepatic steatosis. 10 Modern MRI techniques combine anatomic and metabolic information of metastases and liver parenchyma. Diffusion-weighted imaging (DWI) describes the microscopic movement of water molecules, which is more limited in tissues with high cell density, intact cell membranes and viscous fluid.…”