Colorectal cancer
Medical imaging

A colorectal cancer is sometimes initially discovered on CT scan.

Presence of metastases is determined by a CT scan of the chest, abdomen and pelvis. Other potential imaging tests such as PET and MRI may be used in certain cases. MRI is particularly useful to determine local stage of the tumor and to plan the optimal surgical approach.

MRI is also performed after completion of neoadjuvant chemoradiotherapy to identify patients who achieve complete response. Patients with complete response on both MRI and endoscopy may not require surgical resection and can avoid unnecessary surgical morbidity and complications. Patients selected for non-surgical treatment of rectal cancer should have periodic MRI scans, receive physical examinations, and undergo endoscopy procedures to detect any tumor re-growth which can occur in a minority of these patients. When local recurrence occurs, periodic follow up can detect it when it is still small and curable with salvage surgery. In addition, MRI tumor regression grades can be assigned after chemoradiotherapy which correlate with patients' long-term survival outcomes.
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