Final answer:
Rectal cancer must be localized and accessible via colonoscopy to be resectable. Sigmoidoscopy can examine the lower third of the colon but may miss cancers beyond its reach. A full colonoscopy can remove precancerous polyps and cancerous lesions, whereas a virtual colonoscopy requires follow-up if abnormalities are found.
Step-by-step explanation:
To determine where rectal cancer must be to be resected, it's important to understand the diagnostic and therapeutic procedures involved. A colonoscopy is the gold standard and involves using a tiny camera at the end of a long tube to visualize the lining of the colon and rectum. This procedure not only detects precancerous polyps and cancerous lesions but also allows for their removal.
For a rectal cancer to be resected, it generally needs to be localized and accessible through the procedure. While sigmoidoscopy can inspect the rectum and lower third of the colon, a full colonoscopy is required for a complete examination and potential resection of cancerous lesions. Early-stage tumors that have not spread beyond the rectal wall or to distant sites are more likely to be resectable.
Other alternatives like a virtual colonoscopy using a CT scan can create detailed images to detect cancers or polyps, but if these tests yield positive results, a direct visual examination by colonoscopy is typically necessary.