Virtual colonoscopies are a valuable cancer screening tool
Posted on 18 Aug 2021
Colorectal cancer is among the most commonly diagnosed cancers in South Africa: one in every 83 men and one in every 131 women will be diagnosed with it in their lifetime.
Those are sobering statistics, but as radiologist Dr Tharbit Hartley points out, colorectal cancer is also “highly treatable” if detected early through screening. Dr Hartley, of Cape Radiology at Mediclinic Constantiaberg in Cape Town, explains: “The Radiological Society of South Africa (RSSA) position statement on screening says screening is appropriate and recommended for most people from age 50. A follow up should take place every five years.”
For some, though, the idea of undergoing a colonoscopy is unsettling – it’s an unavoidably invasive and potentially uncomfortable procedure many would prefer to avoid. However, as with so many other areas of modern medicine, advances in technology mean that even colonoscopies have gone virtual. No, that doesn’t mean consulting your radiologist via Zoom: a virtual colonoscopy is, Dr Hartley explains, “a minimally invasive exam to screen for cancer of the large intestine [colon cancer]”.
The procedure is also known as screening CT (computed tomography) colonography. “Unlike traditional colonoscopy, which requires a scope to be inserted into your rectum and advanced through your colon, virtual colonoscopy uses a CT scan to produce hundreds of cross-sectional images of your abdominal organs. The images are combined and digitally manipulated to provide a detailed view of the inside of the colon and rectum.”
Radiologists can then look for abnormal collections of cells, called polyps, which attach to and grow on the inner lining of the colon or rectum.
“Polyps are non-cancerous, but colorectal cancer often develops from one particular type of polyp, called adenomas. The goal of a colorectal cancer screening is to detect and remove adenomas and other polyps as early as possible, before they become cancerous,” Dr Hartley explains.
For a traditional colonoscopy, a doctor inserts a flexible metal tube with a camera on the end into the colon through the rectum. This tube is manoeuvred through the entire length of the colon – usually between 152cm to 184cm. If a doctor finds a polyp during the colonoscopy, it can be removed without the need for another procedure. Given the invasive nature of the procedure, Dr Hartley says, “there is a slight risk of colon perforation or bleeding”.
The CT colonography differs. A small tube is inserted a few centimetres into the rectum to gently inflate the colon with gas or air. Dr Hartley explains that this “helps make the images of the colon clearer”. A low-dose radiation CT scanner then produces images of the entire colon. An additional colonoscopy is required if any polyps are found during the scan.
Patients benefit from virtual colonoscopy in several ways. Perhaps the most obvious is that it’s less invasive, seldom requires any pain medicine or anaesthetic, and takes less time than traditional colonoscopy. In addition, it’s an effective detection tool. “Studies have shown that virtual colonoscopy has detection rates similar to those of traditional colonoscopy for cancer and most polyps of biological importance,” Dr Hartley says.
The virtual procedure may pick up other issues: “Because virtual colonoscopy involves imaging the entire abdominal and pelvic area, problems unrelated to colon cancer — such as an abnormality in the kidneys, liver or pancreas that may or may not be important — could potentially be detected.”
And, amid a pandemic, virtual colonoscopy is a pragmatic approach to lowering the spread of COVID-19. The process requires only one healthcare worker to get close to the patient while inserting the catheter into the rectum, rather than the three or four required to monitor the patient before, during and after the traditional procedure.