What is Endoscopy?
Endoscopy allows direct visual examination, biopsy sampling and therapeutic treatment of the gastro-intestinal tract. Small caliber nasendoscopes allow visualisation of the nasopharynx, oropharynx and throat (pharynx and larynx). Upper GI endoscopy views the oesophagus, stomach and duodenum (OGD). Endoscopic retrograde cholangiography and pancreatography (ERCP) is performed via duodenoscopy, which allows cannulation of the duodenal papilla. Technological advances are allowing clinicians to view the small bowel via capsular endoscopy. The whole of the colon can be examined using colonoscopy.
What is a Nasendoscopy?
This allows visualization of the nose, mouth and pharynx
Describe the oesophagus
Muscular tube approximately 25cm long originating in the neck at the level of the lower border of the cricoid cartilage to the cardiac orifice of the stomach at the level of the seventh costal cartilage.
At endoscopy the cricopharyngeal sphincter marks the commencement of the oesophagus.
Landmarks occasionally visible during endoscopy include the indentation from the left main bronchus (T5) or the pulsation of the left atrium (T6-7).
The main landmark visible within the oesophagus is the oesophagogastric mucosal junction where the pale pink squamous oesophageal mucosa abuts the dark red gastric mucosa.
This point can be measured using the endoscope and is usually 38-40cm from the incisor teeth in the adult patient.
Chronic acid exposure leading to reflux oesophagitis may cause metaplasia of the lower oesophageal squamous epithelium to gastric columnar epithelium (Barrett’s oesophagus).
Describe the blood supply of the oesophagus
- The upper 2/3 of the oesophagus receives its blood supply from the inferior thyroid artery and the aortic branches and drains directly into the systemic circulation by the inferior thyroid vein and azygos branches.
- The lower 1/3 of the oesophagus receives its blood supply from the left gastric branch of the celiac trunk and the left inferior phrenic artery. Thus the oesophagus has a mixed venous drainage into the portal system via the left gastric vein and into the systemic circulation via the azygous vein creating a porto-systemic anastamosis.
- Oesophageal varicies may occur in patients with portal hypertension
What are the mechanisms preventing reflux?
The stomach is entered as the endoscope passes through the lower oesophageal sphincter, which is a physiological sphincter which helps keep chyme within the stomach and reducing reflux. The other mechanisms aiding this process are:
- Acute angle of entry of the oesophagus into the stomach produces a valve like effect
- The mucosal folds at the oesophagogastric junction act as a valve
- The right crus of the diaphragm acts as a ‘pinch cock’
- The positive intra-abdominal pressure compresses the walls of the intra-abdominal oesophagus
Describe the stomach
- It is divided into a cardia, fundus, body and pyloric antrum. It has a greater and lesser curve and the incisura angularis lies in the lesser curve and marks the division between the body and pyloric antrum.
- The pyloric antrum narrows to produce the pyloric canal. At the end of the canal lies the pyloric sphincter (muscular thickening of the distal pylorus), which controls passage of stomach contents into the duodenum.
- The lining of the stomach has longitudinal ridges known as rugae. These gastric folds have vary in size.
- Gastric ulceration is most commonly benign and often found on the lesser curve at the angulus. Malignancy should be suspected if an ulcer has irregular margins, but many early cancers may appear like small benign ulcers, thus a biopsy is mandatory at endoscopy.
Explain about the duodenum
- The duodenum is the 1st part of the small intestine. From its origin at the pyloric sphincter it passes in a C-shape around the head of the pancreas to form the jejunum at the duodenojejunal flexure (DJ flexure), which is supported by the ligament of Treitz.
- It commences at the L1 to the right of the midline curving around to the right of the midline at L2/3 and the duodenojejunal flexure. It starts intraperitoneally but becomes a retroperitoneal organ along its course.
- Macroscopically the endothelium differs from stomach endothelium, this can be seen on passing through the pylorus
Describe about the 1st division of the duodenum
1st or superior part is 5cm long
It is overlapped by the liver and gallbladder. Occasionally gallstones may cause erosion from the gallbladder to the 1st part of the duodenum leading to a choledocoduodenal fistula, which can subsequently give rise to gallstone ileus as the gallstones travel through the small bowel and eventually obstructs the lumen.
Duodenal ulcers are commonly located in the 1st part of the duodenum. An anterior ulcer may perforate causing peritonitis where as a posterior ulcer may erode into the gastroduodenal artery (which is closely related to the posterior wall) resulting in massive haemorrhage or into the pancreas causing severe pain radiating to the lumbar region.
Describe the 2nd division of the duodenum
2nd or descending part is retroperitoneal, 7.5cm long and descends in a curve around the head of the pancreas
- The major duodenal papilla lays half way along the posteromedial aspect of the 2nd part of the duodenum. It signifies the opening of the main pancreatic duct (of Wirsung). The opening at the duodenal papilla is guarded by the sphincter of Oddi. The accessory pancreatic duct of Santorini open a little above the duodenal papilla (see bilary tree section for more details).
- The transition from the embryonic forgut to the midgut occurs at the duodenal papilla. As such the duodenum as a blood supply originating from both the celiac access (foregut) and the superior mesenteric artery (midgut).
- Ulceration in the 2nd part of the duodenum is less common than the 1st and suggests either pancreatic disease or Zollinger-Ellison syndrome (characterized by gastrin-secreting tumours, which cause multiple, refractory and recurrent peptic ulcers in the distal duodenum and proximal jejunum)
Describe the 3rd division of the duodenum
- 3rd or horizontal part is 10cm long and runs transversely at the level of L2/3 crossing the aorta below the origin of the superior mesenteric artery.
- The close relation of the duodenum to the abdominal aorta may lead to the development of a aorto-duodenal fistula in patients with disease of the duodenum or aorta. This usually presents as upper GI haemorrhage (this is rare).
- The duodenum is located between the superior mesenteric artery (anterior) and aorta (posterior). When patient have dramatic weight loss they may develop SMA syndrome where duodenal obstruction (partial or complete) is caused by external compression of the duodenum by the aorta and SMA.
Describe the 4th division of the duodenum
4th or ascending portion is 2.5cm in length, is retroperitoneal and ascends to the left of the midline to L1 where it turns left to form the duodenojejunal flexure, also known as the DJ flexure. At this point the jejunum has a mesentery and becomes intraperitoneal.
A well-marked duodenal fold, the suspensory ligament of Treitz that, descends from the right crus of the diaphragm marks the duodenojejunal flexure.
It is thought that contraction of the ligament of Treitz aids the peristaltic movement of its contents by widening the angle of the flexure.
The ligament of Treitz is fibrous and anchors the start of the jejunum and in a deceleration injury may lead to a traction injury in the jejunum and subsequent perforation.
The ligament of Treitz loops around the duodenum at the duodenal-jejunal junction - divides the upper and lower intestines - pulls the duodenum up. Hooks the duodenum up in a c-shape.
What is Endoscopic Retrograde Cholangio Pancreatography?
ERCP allows endoscopic and radiological examination of the biliary tree and pancreatic duct, biopsy sampling and therapeutic procedures to relieve obstructive jaundice.
Describe the biliary tree
- The biliary tree is examined in a retrograde fashion by cannulating the duodenal papilla, through the sphincter of Oddi into the small widening at the distal end of the common bile duct (Ampulla of Vater).
- The biliary tree commences within the liver from the intrahepatic ducts, which form the left and right hepatic ducts.
- The common hepatic duct is formed by the convergence of the left and right hepatic ducts at the porta hepatis. It is approximately 4cm in length.
- The cystic duct arising from the gallbladder joins the common hepatic duct to form the common bile duct.
Describe the common bile duct
The common bile duct is approximately 10cm in length and up to 7mm in diameter. The CBD passes behind the duodenum to run in a groove in the posterior aspect of the head of pancreas or within the pancreas substance. It then opens into the duodenum midway along the 2nd part.
- Blockage of the common bile duct will lead to obstruction of the bile flow and subsequent jaundice and disruption to the enterohepatic circulation of bile salts.
- Patients will present with yellow discolouration, dark urine and pale stool.
- Painless obstructive jaundice is commonly secondary to a tumour. The most common tumour to cause obstructive jaundice is a carcinoma of the head of the pancreas, which obstructs the CBD as it passes either through or in close relation to the head of pancreas. Other tumours, which cause obstructive jaundice, include cholangiocarcinoma (bile duct cancer), adenocarcinoma of the duodenum or extrinsic compression of the bile duct from a tumour in the liver.
- Painful obstructive jaundice is more likely to suggest gallstone disease (remember that nothing is ever 100 %).
- On ultrasound scanning the sonographer will measure the diameter of the CBD to ascertain whether there is any sign of obstruction jaundice, thus it is important to remember that the maximum diameter of the bile duct is 7mm. Care had to be taken when evaluating patients who have had a previous ERCP as it is likely they will have had a sphincterotomy and subsequent dilatation of the CBD.
More detail about the common bile duct….
Superior to the duodenum the common bile duct runs in the free edge of the lesser omentum along with the portal vein and hepatic artery. This free edge of omentum is the anterior border of the epiploic foramen of Winslow, the entrance to the lesser sac
Control of hepatic haemorrhage may be gained by applying pressure to the free edge of the lesser sac and occluding the portal vein and hepatic artery. This is known as the Pringle manouver and is utilised in hepatobiliary surgery
Describe small bowel endoscopy
- The small intestine varies from 3 to 10 meters in length. It is divided into the jejunum (~2/5) and ileum (~3/5). There is no sharp demarcation between the 2. It has a mesentery approximately 15cm in length which attaches the entire small bowel to the posterior abdominal wall from the DJ flexure to the left of L2 passing obliquely to the right sacro-iliac joint.
- It is relative difficult to examine endoscopically. The traditional methods are push enteroscopy, sonde enteroscopy or intraoperative enteroscopy. Recently technological advances have allowed the development of capsule endoscopy.
- Jejunum has a thicker wall due to an increased number, larger and taller pilcae circulares (circular folds of mucosa) than in the ileum.
- The jejunum also appears a deeper red in colouration due to its greater blood supply from a small number (1 or 2) of large vascular arcades.
- The juejunal wall has tall villi with deep crypts. In celiac disease these villi and crypts atrophy
- A Meckel’s diverticulum may be found in the distal ileum. It is a remnant of the embryonic vitellointestinal duct. It is said to be found 2 feet from the ileocaecal valve, occur in 2 % of the population and be 2 inches long (rule of 2’s). It may contain gastric mucosa, which secretes acid. This may cause bleeding or inflammation and should be considered as a differential diagnosis with unexplained GI blood loss or acute abdominal pain.
- The small bowel has aggregates of lymphoid tissue within its wall known as Peyer’s patches. The ileum in particular has a large number of Peyer’s patches. These can enlarge particularly in lymphoma and cause intestinal luminal obstruction.
Describe colonoscopy and the large intestine
- The large intestine is examined in a retrograde fashion from the anus to the caecum using a colonoscope. The left side of the colon can be examined in isolation using a sigmoidoscope.
- The entire colon is between 100-180cm and is classically said to be longer in females despite their smaller stature.
- The colon is distinguished by 3 longitudinal bands of muscle along its length, which form taenia coli and converge at the base of the appendix. The taenia coli often cause the internal lumen of the colon to appear triangular. This is especially apparent in the transverse colon.
- The lengths of muscle are shorter than the colon itself and so bunch the colonic wall to form haustrations (sacculations). On a plain radiograph of distended colon the sacculations appear as incomplete lines occurs the lumen of the colonic wall. In contrast distended small bowel has mucosal folds (valvulae conniventes) project across the entire width of the bowel wall
- The large intestine can be further subdivided into the caecum and appendix, ascending colon, transverse colon, descending colon, sigmoid colon, rectum and anal canal.
Describe the caecum and appendix
- The ileocaecal junction is marked by a valve, which signifies the start of the large intestine. This valve is formed by oblique entrance and partial invagination of the ileum into the caecum forming folds. The valve prevents back flow of colonic contents during peristalsis. In large bowel obstruction the caecum may dilate to the point of necrosis or perforation if the ileocaecal valve is competent as it prevents back flow of excess air and colonic contents which may not pass distally
- The caecum is the first part of the large intestine. It lies in the right iliac fossa.
20% of colonic tumours occur in the caecum and right side of the colon and often present with a mass, change in bowel habit, iron deficiency anaemia or pain.
- The appendix is a blind ending structure which arises from the postero-medial aspect of the caecum approximately 3cm below the ileocaecal valve. Its position is highly variable due to its embryonic origin as a direct out-pouching on the lateral side of the caecum. The differential overgrowth of the caecal wall causes its medial and often inferior displacement. The appendix orifice can be located endoscopically by visualizing the convergence of the three taeniae coli at the pole of the caecum
Describe the ascending colon
Ascending colon is 12-20cm long, it passes superiorly from the caecum to the hepatic flexure where the transverse colon commences.
Describe the transverse colon
- Transverse colon is approximately 45cm in length and is highly mobile. It commences at the hepatic flexure and traverses the abdomen to the splenic flexure.
- The transverse colon is highly mobile and often difficult to navigate endoscopically.
- It is classically said to lie at the level of the umbilicus but may hang down into the pelvis. This is more common in females and a possible reason why ~70% of difficult colonoscopies appear to be in the female population.
Describe the descending colon
Descending colon is approximately 22-30cm in length
Describe the sigmoid colon
- Sigmoid (sigmoid shape) colon has an average length of 37cm but may be as long as 70cm.
- The sigmoid colon has the largest number of appendices epiploicae on its outer surface. These are fat-filled peritoneal tags found on the colon (except for the caecum or rectum).
- Due to the length of the sigmoid colon and its loose mesenteric attachment the sigmoid may twist on its self, forming a sigmoid volvulous. This will present clinically with symptoms of large bowel obstruction and has a classical radiological appearance. It is commonly treated using flexible sigmoidoscopy.
- 25% of colon cancers occur in the sigmoid colon.
- In the western world the sigmoid colon is the most common location of colonic diverticulum. These are out-pouchings of the bowel wall. They commonly occur at the point where the artery pierces the muscular wall causing a weakness. 10% of the population aged 40 have diverticulosis compared to 60% of 80 year olds. They may cause diverticular disease, diverticulosis or diverticulitis.
- True diverticula involve all layers of the structure including muscularis propria and adventitia. False diverticula do not involve muscular layers or adventitia.
Describe the rectum including Inflammatory Bowel Disease
- Rectum (from the Latin straight) is approximately 12cm and commences anterior to the sacrum at S3 and leads to the anal canal. Unlike other mammals the human rectum is not straight. It curves anteriorly following the sacrum and then turns at approximately 90degrees through the pelvic diaphragm. It also as 3 lateral curves corresponding with mucosal folds or the valves of Houston.
- The rectum appears circular on endoscopic examination despite it having the 3 taeniae coli due to its thick circular muscle layer needed to cope with formed stool. The tubular appearance is broken by haustral folds.
- 50% of colon cancers are found within the rectum.
- If the mucosa is found to be friable and erythematous it inflammation. Often macroscopic appearances may appear normal to the naked eye with patients who have inflammatory bowel symptoms. If the colon is biopsied the pathology report often suggests significant disease. Inflammation of the colon maybe caused by infection, autoimmune conditions which includes Ulcerative Colitis and Crohn’s and iatrogenic causes such as radiotherapy
- We commonly see inflammatory bowel disease caused by Crohn’s or Ulcerative Colitis.
- Ulcerative colitis tends to occur in the rectum and spread proximally throughout the colon. The areas of inflammation are continuous and the mucosa is highly friable.
- Crohn’s tends to give patchy or focal areas of inflammation known as skip lesions. The associated ulcers are often deep and fissuring and produce a cobblestoned appearance
Describe the anal canal
- Anal canal is 4cm in length and ends as the anal orifice.
- The upper part of the anal canal is part of the hindgut and is lined by columnar epithelium (mucosa).
- The mid anal canal represents the transition between the endoderm of the hindgut and the ectoderm of the proctodaeum invagination from the skin. This area is marked by the valves of Ball, which arise from the vertical columns of Morgagni, which extend from the upper rectum. The apparent line formed by the valves is known as the dentate or pectineal line
- Below the dentate line the anal canal is covered by stratified squamous epithelium.
