ENDOSCOPY. A CLINICAL TECHNIQUE: Principle, components of the instrument, guideline to use the instrument, types & clinical application.

Direct visualization of the interior of the hollow gastrointestinal organs is one of the most powerful diagnostic and therapeutic modalities in modern medicine. The earliest endoscopes were rigid instruments, allowing visualization along a straight line. Fibreoptic instruments, which transmit light around curves, extended the range of endoscopy.
Modern video endoscopes use a charge-coupled device, or an electronic camera, to capture and transmit images electronically, so there is no optical limit to their movement. Most instruments have channels for insufﬂation and suction and to introduce instruments, such as forceps, for taking biopsies.

Rigid instruments

These are stainless steel or plastic tubes with a light source and a single channel for observation and instrumentation. The rigid sigmoidoscope can be inserted up to 20·cm into the rectum and proximal sigmoid colon, and is routinely used to diagnose proctitis and rectal tumours. The shorter and wider proctoscope allows examination of the anal canal and rectum. Haemorrhoids can be treated by sclerotherapy or elastic band ligation through a proctoscope. Rigid oesophagogastroscopes are now mainly used to treat oesophageal obstruction caused by foreign bodies, such as food boluses, because the wide channel allows rapid removal or displacement of the obstruction.
Flexible upper gastrointestinal endoscopy The oesophagus, stomach and proximal duodenum are routinely visualized and the distal duodenum and jejunum may occasionally be seen.
Diagnostic uses Investigation of heartburn, dyspepsia and occult blood loss are the commonest indications. Biopsies can be taken to diagnose Helicobacter pylori infection, inﬂammation or neoplasia. Plastic brushes can be rubbed along lesions, capturing superﬁcial cells or pathogens to diagnose cancer and infection. Jejunal ﬂuid can be aspiratedand examined for pathogens such as Giardia lamblia.

Therapeutic uses

The commonest lesions treated endoscopically are bleeding peptic ulcers, which can be injected with epinephrine (adrenaline) to cause vasospasm, and ruptured oesophageal varices, which can be injected with sclerosant or ligated with rubber bands to halt bleeding and cause ﬁbrosis and subsequent obliteration. Other bleeding lesions may be treated using lasers or electrocautery. Obstruction caused either by gastro-oesophageal tumours or by benign strictures can be relieved by dilatation using balloon or rigid dilators, and plastic or metal stents can then be introduced to maintain patency of the lumen. Pneumatic dilatation or endoscopic injection of botulinum toxin into the lower oesophageal sphincter may relieve obstruction caused by achalasia.

Complications

Upper endoscopy itself is relatively safe and can be performed with or without light sedation of the patient. Therapy such as dilatation may cause rupture of the oesophagus.

Enteroscopy

Long, thin instruments with a rigid outer casing that straightens the shaft proximally can be introduced into the jejunum and ileum. The tip of a Sonde enteroscope is propelled by peristalsis and can reach the distal small intestine. Unfortunately, the distance either instrument has progressed cannot be reliably ascertained and biopsies cannot be taken with Sondeenteroscopes.

Colonoscopy and ﬂexible sigmoidoscopy

Fibreoptic and video colonoscopes allow examination of the entire large intestine and the terminal ileum. The patient must be adequately prepared beforehand with powerful laxativesto remove solid material from the colon. During the examination, light sedationand analgesiaare usually necessary. In ﬂexible sigmoidoscopy the instrument is only inserted into the left side of the colon.

Diagnostic uses

The commonest indications include investigation of altered bowel habit, rectal bleeding, suspected colorectal cancerand inﬂammatory bowel disease. Colonoscopic screening for colon cancer is advocated for patients at high risk, for example, those with a strong family history of the disease, and there is a debate about introducing population-wide screening. The normal colonic mucosa is smooth and shiny with a regular vascular pattern. Pouches or diverticulae can be easily detected, as can inﬂamed, ulcerated or bleeding areas, polyps and malignant tumours. Biopsiesfor histology can safely be taken and polyps and small tumours removed by snaringand electrocautery. Ileoscopy: the tip of the colonoscope can be manoeuvred through the ileocaecal valve into the terminal ileum.
Therapeutic uses Bleeding lesions can be treated by electrocautery or heat coagulation and small polyps removed (polypectomy). Large tumours causing bleeding or obstruction can be treated with lasers, and stentsintroduced to maintain a patent lumen.

Complications

There is a small risk of colonic perforation, and of bleedingfollowing polypectomy. Sedation and analgesia may also cause respiratory depression.

Endoscopic retrograde cholangiopancreatography and biliary endoscopy

A duodenoscope with a sideways-facing tip allows visualization and cannulation of the ampulla of Vater. Contrast material can then be injected into the pancreatic and biliary ducts and X-ray images taken. Close-up ultrasound images can be obtained by inserting compact ultrasound probes into the duct. Cannulae and instruments can be introduced to obtain brushings or biopsies, remove gallstones, and dilate strictures. The sphincter of Oddi may be cut (sphincterotomy), allowing gallstones to pass spontaneously. Endoscopic retrograde cholangiopancreatography (ERCP) is usually performed to investigate and treat obstructive jaundice. Larger bile ducts can also be viewed with very ﬁne ﬂexible endoscopes inserted percutaneously into the liver. Injecting contrast material into the pancreatic duct can provoke pancreatitis.

Future directions

Advanced instruments are making endoscopy safer and more versatile. Ingeniously designed instruments that can be inserted alongside the endoscope or through the biopsy channel are expanding the range of therapeutic interventions to include cutting and suturing, enabling endoscopic surgery. Wireless capsule endoscopy: tiny encapsulated electronic cameras can be swallowed, allowing visual data be collected remotely, by radio transmission. Images are thus obtained from areas that cannot be reached by conventional endoscopic instruments, although biopsies cannot yet be taken.