Lower Gastro Intestinal Endoscopy

COLONOSCOPY
Advances in bowel preparation have enhanced mucosal visualization during the examination. Targeted abdominal hand pressure to prevent loops in a mobile colon and regular patient position change to enhance mucosal views and remove residual bowel content are also important aids to
successful colonoscopy. It is essential that caecal intubation is confirmed to avoid missing pathology by incorrectly assuming that the caecal pole has been reached. Visualisation of the appendix orifice or preferably terminal ileal intubation is necessary to confirm a complete colonoscopy.
Mucosal biopsies may either be targeted to areas of abnormality or random to exclude microscopic colitis in a patient with chronic diarrhoea but a macroscopically normal mucosa. Despite the increasing sophistication of radiological techniques to assess the colon, such as CT colonography, the ability to biopsy areas
of abnormality and resect polyps will ensure that colonoscopy remains the most appropriate investigation for the majority of patients .Whichever modality is used, colonoscopy is essential to resect any polyps identified and biopsy unresectable lesions.
Therapeutic colonoscopy
The most common therapeutic procedure performed at colonoscopy is the resection of colonic polyps). Retrieved specimens can be assessed for risk factors for neoplastic progression and an appropriate surveillance strategy determined. Small polyps up to 5 mm should be removed by cheese-wiring with a ‘cold’ snare. Hot biopsy is a technique in which the tip of a small pedunculated polyp is grasped between
diathermy biopsy forceps and tented away from the bowel wall.
A brief burst of monopolar current is used to coagulate the stalk,allowing the polyp to be removed. This is rarely performed in current practice due to an increased risk of immediate and delayed thermal damage to the bowel wall, particularly in the right colon. Larger polyps with a defined stalk can be resected using snare polypectomy with coagulating current either en bloc or piecemeal depending on their size (Figure 14.14). Postpolypectomy bleeding can be prevented by the application of haemoclips or an endoloop to the polyp stalk. Sessile polyps extending over several centimetres can be removed by endoscopic mucosal resection, which involves lifting the polyp away from the muscularis propria with a submucosal injection of saline
to prevent iatrogenic perforation. Any residual polyp is obliterated with argon plasma coagulation. Care should be taken with all polypectomies in the right colon where the wall may only be 2–3 mm thick. Removal of large or extensive flat polyps should only be attempted by appropriately trained
endoscopists. Argon plasma coagulation (APC) and alternative thermal therapies such as heater probes are also used in the treatment of symptomatic angioectasias of the colon. Laser photocoagulation may be used to debulk colonic tumours not suitable for resection. As with benign oesophageal strictures,TTS balloons can be used to dilate short (less than 5 cm) colonic strictures. The dilatation of surgical anastomoses gives the most durable benefit as inflammatory strictures tend to recur even if intramucosal steroids are injected at the time of the dilatation Finally, the colonoscopic placement of self-expanding metal stents may provide excellent palliation of inoperable malignant strictures) and may also play an invaluable role in decompressing an obstructed colon to allow planned as opposed to emergency surgery.
Complications of colonoscopy
perforations as a result of excessive shaft tip pressure and with excessive air insufflation in severe diverticular disease.Total colonoscopy is contraindicated in the presence of severe colitis; a limited unprepped examination and careful mucosal biopsy only should be performed. Polypectomy is associated
with rate of perforation (approximately 1 per cent) and haemorrhage (1–2 per cent). Immediate haemorrhage should be managed by re-snaring the polyp stalk where possible and applying tamponade for several minutes followed by careful coagulation if this is unsuccessful. Submucosal adrenaline injection and the deployment of haemoclips are alternatives if this is not possible. Delayed haemorrhage may occur 1–14 days post-polypectomy and can normally be managed by conservative observation. Transfusion may occasionally be required, but repeat colonoscopy is rarely necessary. If recognised at the time of polypectomy, small perforations should be closed using clips and the patient admitted for observation. Symptoms of abdominal pain and cardiovascular compromise after a polypectomy should alert one to the risk of delayed perforation. Patients should be kept nil by mouth and receive intravenous resuscitation and antibiotics. Prompt assessment with plain radiography and a CT scan will often distinguish between a frank perforation and a transmural burn with associated localised peritonitis (the post-polypectomy syndrome). Assessment by an experienced colorectal surgeon is essential, as surgery is often the most appropriate course of action.
ENDOSCOPIC RETROGRADE CHOLANGIOPANCREATOGRAPHY
This procedure involves the use of a side-viewing duodenoscope, which is passed through the pylorus and into the second part ofthe duodenum to visualise the papilla. This is then cannulated,
either directly with a catheterr with the help of a guidewire. Occasionally, a small pre-cut is required to gain access. By altering the angle of approach one can selectively cannulate the pancreatic duct or biliary tree, which is then visualised under fluoroscopy after contrast injection. The significant range of complications associated with this procedure and improvements in radiological imaging usi ong magnetic resonance cholangiopancreatography (MRCP) have rendered much diagnostic ERCP obsolete, and thus most procedures are currently performed for therapeutic purposes. There is still a role for accessing cytology/biopsy specimens.
Therapeutic endoscopic retrogradecholangio pancreatography
It is essential to ensure that patients have appropriate assessment prior to therapeutic ERCP, which is associated with a significant morbidity and occasional mortality. All patients require routine
blood screening including a clotting screen. Assessment of respiratory and cardiovascular comorbidity is essential. Patients with an obstructed biliary system require antibiotic prophylaxis.
The use of supplementary oxygen and both cardiac and oxygen saturation monitoring during the procedure are essential because of the high levels of sedation that are often required. The most common indication for therapeutic ERCP is the relief of biliary obstruction due to gallstone disease and benign or malignant biliary strictures. The pre-procedural diagnosis can be confirmed by contrast injection, which will clearly differentiate the filling defects associated with gallstones and the luminal narrowing of astricture. If there is likely to be a delay in relieving an obstructed system, percutaneous drainage may be required.
The cornerstone of gallstone retrieval is an adequate biliary sphincterotomy, which is normally performed over a wellpositioned guidewire using a sphincterotome connected to an electrosurgical unit. Most gallstones less than 1 cm in diameter will pass spontaneously in the days and weeks following a sphincterotomy, but most endoscopists prefer to ensure duct clearance at the initial procedure to reduce the risk of impaction,
cholangitis or pancreatitis. This can be achieved by trawling the duct using a balloon catheter or by extraction using a wire basket. If standard techniques fail, large or awkwardly placed stones can be crushed using mechanical lithotripsy. If adequate stone extraction cannot be achieved at the initial ERCP it is
imperative to ensure biliary drainage with the placement of a removable plastic stent while alternative options are considered.
These include surgery, endoscopically directed shockwaves under direct choledochoscopic vision using a mother and baby scope, and extracorporeal shockwave lithotripsy with subsequent ERCP to remove stone fragments. Dilation of benign biliary strictures uses balloon catheters similar to those used in angioplasty inserted over a guidewire under fluoroscopic control. It is traditional to insert a temporary plastic stent to maintain drainage as several attempts at dilatation may be required. Self-expanding metal stents are most commonly used for the palliation of malignant biliary obstruction and are also normally inserted after a modest sphincterotomy. Correct stent placement can normally be confirmed by a flow of bile after release and by the presence of air in the biliary tree on follow-up plain abdominal radiographs. Stent malfunction, associated with recurrent or persistent biochemical cholestasis, may be due to poor initial stent position, stent migration, blockage with blood clot or debris, or tumour in-growth. A repeat procedure is required to assess the cause, which can usually be remedied by the insertion of a second stent through the original one.
ENDOSCOPIC ULTRASOUND
Endoscopic ultrasound which combines the traditional mucosal image with a separate ultrasound view that clearly depicts the intestinal layers and proximate extraintestinal structures. Its use has revolutionised
the staging and management of upper gastrointestinal and hepatobiliary malignancy, as the depth of invasion of a tumour can be accurately assessed at the same time that a biopsy is taken to confirm diagnosis . It allows sampling of paraoesophageal and coeliac lymph nodes and drainage of peripancreatic abscess or pseudocysts. The availability of linear and radial probes allows diagnosis and therapy to be appropriately
targeted. Its use requires dedicated training and in some centres EUS is performed by an endoscopist working alongside a radiologist. Due to the width and lack of flexibility of the endoultrasound scope, as well as the duration of complex therapeutic procedures, sedation is normally required, and some units perform tests using propofol-based anaesthesiaAll patients undergoing therapeutic endoscopic ultrasound require a normal coagulation screen. Complications include oversedation and oesophageal perforation during diagnostic procedures and haemorrhage/perforation during therapeutic procedures.
Indications for endoscopic ultrasound.
Diagnostic Staging of oesophageal/gastric malignancy Staging of hepatobiliary malignancy Diagnosis of choledoccal microlithiasis Therapeutic Biopsy of paraoesophageal lymph nodes Biopsy of submucosal upper gastrointestinal lesion Biopsy of pancreaticobiliary mass Biopsy of portal lymphadenopathy Transgastric drainage of pancreatic pseudocyst
FUTURE DIRECTIONS IN ENDOSCOPY
Chromoendoscopy, narrow band imaging and high resolution magnification endoscopy
Chromoendoscopy, which involves the topical application of stains or pigments to improve tissue localisation, characterisation or diagnosis. Several agents which can broadly be categorised as absorptive (vital) stains such as methylene blue, contrast (reactive) stains such as indigo carmine, and those used for tattooing such as India ink.Narrow band imaging (NBI) relies on an optical filter technology
that radically improves the visibility of capillaries, veins and other subtle tissue structures by optimising the absorbance and scattering characteristics of light. NBI uses two discrete bands of light: one blue at 415 nm and one green at 540 nm. Narrow band blue light displays superficial capillary networks whereas green light displays sub-epithelial vessels; when combined they offer an extremely high contrast image of the tissue surface.Autofluorescence images can also be used to increase a lesion’s discrimination. Finally, high-resolution magnifying endoscopy may be used alone or in combination with one of the above techniques to achieve near-cellular definition of the mucosa.