🔬 Colonoscopy

An invasive endoscopic procedure used to visualise the entire large bowel and terminal ileum for diagnostic and therapeutic purposes.

Indications include the investigation of persistent change in bowel habit (particularly toward looseness), unexplained rectal bleeding, or iron deficiency anaemia without an upper gastrointestinal cause. It is used for the diagnosis and assessment of inflammatory bowel disease (IBD) activity. Additionally, it is indicated for colorectal cancer screening, surveillance of high-risk individuals (e.g., Lynch syndrome), and follow-up of previously identified polyps.

The procedure involves the insertion of a flexible fibre-optic camera through the anus into the colon, typically after a period of dietary restriction and oral laxative bowel preparation. Patients are usually offered conscious sedation (e.g., a benzodiazepine and opioid) or Entonox. The endoscopist navigates to the caecum—often evidenced by the ileocaecal valve and appendiceal orifice—and carefully inspects the mucosa upon withdrawal. Air or CO2 insufflation is used to distend the bowel for visualization.

A normal colonoscopy reveals a smooth, pink, glistening mucosal surface with a clearly visible submucosal vascular pattern. The endoscopist should identify the major landmarks: the rectum, sigmoid, descending colon, splenic flexure, transverse colon, hepatic flexure, ascending colon, and the caecum. The terminal ileum may also be intubated and should appear normally villous without ulceration.

Interpretation requires correlating visual findings with histological reports from biopsies or snared polyps. The Boston Bowel Preparation Scale is often used to ensure the quality of the view was sufficient to exclude pathology. A 'normal' colonoscopy suggests that symptoms may be functional (e.g., IBS) or located in the small bowel, whereas 'significant' findings are graded by the degree of dysplasia in polyps or the severity of mucosal inflammation in IBD.

Abnormal findings include the presence of polyps (adenomatous or serrated), diverticula, or ulceration and cobblestoning characteristic of Crohn’s disease. Neoplastic findings may present as fungating masses, circumferential narrowing, or friable malignant ulcers. In ulcerative colitis, findings range from loss of vascular markings and erythema to spontaneous bleeding and pseudopolyps, typically involving the rectum and extending proximally.

Colonoscopy is the gold standard for colorectal cancer (CRC) screening and the investigation of altered bowel habit or unexplained iron deficiency anaemia. It allows for definitive diagnosis via biopsy and therapeutic intervention through polypectomy, which significantly reduces the future incidence of CRC. Its role in surveillance for inflammatory bowel disease and post-polypectomy follow-up is central to long-term gastrointestinal management.

A common pitfall is the assumption that a normal colonoscopy excludes all causes of abdominal pain or diarrhoea; it does not assess small bowel pathology or functional disorders. Clinicians must also be wary of 'incomplete' procedures where the caecum was not reached, as right-sided lesions may be missed. Failure to stop certain anticoagulants appropriately prior to the procedure can lead to avoidable cancellations or bleeding complications.

The procedure is invasive and carries risks such as perforation or post-polypectomy haemorrhage. Its efficacy is highly dependent on the quality of bowel preparation; poor prep can lead to missed diminutive polyps or the need for early repeat. Difficult anatomy, such as severe diverticulosis or adhesions, may prevent the endoscopist from reaching the caecum, necessitating alternative imaging like CT Colonography.

Students must recognise the 'red flag' symptoms (NICE NG12) that necessitate urgent 2-week wait referral for colonoscopy. Understanding the complications (perforation risk ~1 in 1,000) and the importance of checking coagulation/antiplatelet status before the procedure is essential for finals.