Small Intestine Surgery Notes

Small Intestine

Small Intestine Introduction:

Truly speaking small intestines extends from pylorus to ileocecal junction. However, for all practical purposes, it is discussed as starting from duodenojejunal flexure till caecum. Small intestines play an important role not only in the transfer of food contents distally but in the digestion, absorption and secretion of the contents. Being the central portion of the GI tract with long length, many diseases affect the intestine. Surgically important topics such as intestinal tuberculosis, inflammatory bowel diseases and few tumors are discussed in this chapter.

Read And Learn More: Gastrointestinal Surgery Notes

Embrtology And Development

• The small intestine develops from the midgut.
• This midgut loop has cranial and caudal limbs.
• As the elongation starts from 5th week of foetal life, cranial limb develops into distal duodenum, jejunum and proximal ileum.
• Distal ileum and proximal two-thirds of transverse colon are developed from caudal limb.
• Midgut also rotates 270°. Thus, proximal jejunum will go to left side and ileum will go to right side.
• Anomalies can occur during rotation resulting in malrotation.
• Vitellointestinal (VI) duct joins the junction of cranial and caudal intestines which is about 2 feet away from ileocaecal junction.
• When VI duct is not obliterated, various anomalies occur. One of them is Meckel’s diverticulum.
• Caecum which is present in the right hypochondrium descends into the right iliac fossa region.

Small Intestine Anatomy

• Small intestine consists of proximal 2/5 jejunum and distal 3/5 ileum. It is about 6 metres in length.
• Small intestine starts at duodenojejunal flexure just to the left of the inferior mesenteric vein. Surgical importance: To identify the first (short) loop of jejunum for gastrojejunostomy.
• Small intestine ends at ileocaecal junction. In cases of intestinal obstruction, trace up to ileocaecal junction. If caecum is distended, it is a case of large bowel obstruction. If caecum is collapsed, it is a case of small bowel obstruction.
• Jejunum resides in the left side of the peritoneal cavity and ileum on the right side.
• Differences between jejunum and ileum.

Small Intestine Blood Supply:

• Superior mesenteric artery is the artery of the midgut which supplies the entire midgut (entire small intestine). Jejunal arteries are end-arteries.
• Mesenteric border of the intestine gets more blood supply when compared to anti-mesenteric border. Hence, in cases of diminished blood supply, antimesenteric border becomes ischaemic first.
• Venous drainage is through superior mesenteric vein.

Small Intestine Mesentery:

• It is a fan-shaped fold of peritoneum which attaches jejunum and ileum to posterior abdominal wall.
• Blood vessels and lymphatics course in between the folds of peritoneum.
• It extends from the left of duodenojejunal flexure (left of L2) vertebra to the right sacroiliac joint, thus fixing the ileocaecal junction there.

• The importance of the direction of the mesentery is appreciated in the following examples:
  • The mesenteric cyst moves at right angles to the direction of the mesentery.
  • Mesenteric lymph nodes can be clinically palpable as a nodular or a smooth mass.
  • Horizontal tear in the mesentery causes more gangrene of the bowel than vertical tear.
• Structures crossed by mesentery: Duodenum, aorta, inferior vena cava, right ureter, right psoas major and right gonadal vein.

Small Intestine Innervation

• Parasympathetic: These are derived from vagus. It is secretomotor, thus helping in secretion and motility of small intestines. Nerve fibres traverse through coeliac ganglion. Afferent fibres do not carry pain impulses.
• Sympathetic: These fibres arise from three sets of splanchnic nerves. Their ganglion cells are located in a plexus around base of superior mesenteric artery. Pain is mediated through sympathetic system.

Small Intestine Lymphatics

• From mucosa, lymphatics pass through the wall of the bowel to regional lymph nodes, then into lymph nodes at base of superior mesenteric artery.
• Then it flows into cisterna chyli and then into thoracic duct and empty into venous system at confluence of left internal jugular and subclavian veins.
• Extravasation of few tumour emboli outside this confluence results in enlargement of supraclavicular lymph nodes. They are about 4 to 6 in number and are called Virchow’s nodes. This clinical sign is described as Troisier’s sign1.
• Peyer’s patches are major deposits of lymphatic tissue in the distal bowel. Tuberculosis and typhoid fever affect the Peyer’s patches.

Microscopic Anatomy:

• Basic unit of small bowel mucosa is the villus, which is a finger-like projection. Each villus is covered with tall columnar epithelium.
• Goblet cells, Paneth cells and endocrine cells are seen in the crypts. Goblet cells are mature mucous cells. Endocrine cells (enterochromaffin cells) have cytoplasmic granules which secrete 5-hydroxytryptamine, neurotensin, glucagon and motilin. Importantly, mucosal cell-mediated immunity is brought by mucosal T lymphocytes.

Physiological Functions

• Motility: Two types of muscle contractions occur— one which does not propagate—it exposes the food contents to the absorptive surface for a longer time by causing segmentation allowing better absorption of the fooAnother type is peristaltic which propagates the food contents. Control of peristalsis is done by myenteric plexus. Time taken by the solid food contents to reach from mouth to colon is about 4 hours.
• Absorption and digestion: Except calcium and iron, almost everything is absorbed in the small intestines.

To give a few examples: Out of 6–10 litres of water, almost 80% water is absorbed in the small intestine and only 10–20% is discharged into colon. Thus in cases of terminal ileal obstruction, about 8–10 litres of fluid accumulate resulting in gross distension of the abdomen and dehydration. Carbohydrates and fat are mainly absorbed in duodenum and proximal jejunum. Proteins require pancreatic enzymes. Hence, they are broken down in the jejunum into amino acids and peptides. Conjugated bile acids are absorbed in the terminal ileum wherein enterohepatic circulation takes place and again they are secreted in the bile.

Thus in ileal resections or diseases like Crohn’s disease, more amount of bile acids enter colon resulting in diarrhoea due to increased secretion of water and electrolytes.

Absorption and digestion:

Ileostomy

• Ileostomy is a surgical procedure wherein a loop of the ileum or end of the ileum is brought to the exterior (surface of the body).
• Two types are usually done: End ileostomy and loop ileostomy.
• End ileostomy is done following total proctocolectomy. It is a permanent ileostomy. The ileum is brought out through the lateral edge of rectus abdominis. It should project at least 5 cm outside
• Loop ileostomy is done to divert gastrointestinal contents to protect ileo-pouch anastomosis. It is a temporary ileostomy which is closed after 6–8 weeks.
• Permanent ileostomy is also required following total colectomy for carcinoma colon. It is an end ileostomy.
• Ileostomy care includes maintenance of fluid and electrolyte balance, use of disposable ileostomy bag and skin protection.
• Complications of an ileostomy are similar to that of colostomy—retraction, prolapse, bleeding, stenosis.
• Precautions—living with an ileostomy.

1. Ileostomy bag has to be fitted well to the body surface. It needs to be adjusted often.

2. Ileostomy has to be emptied 4–6 times depending upon the requirement.

3. Chewed and masticated food is better.

4. Avoid gas forming diet. Patients will learn slowly what to take and what not to take.

5. Long-term complications include—gallstones, kidney stones, adhesions and intestinal obstruction.

Radiation Enteropathy

Radiation damages rapidly growing cells of intestine also when they are exposed to it. It typically happens when radiation is given to the pelvis after rectal resections or radiation given to treat carcinoma cervix. Incidence is 5% after 4500 cGy units to 30% after 6000 cGy units. The chief factor is radiation-induced damage to the blood vessel supplying the bowel wall.

Surgical Complications Of Enteric Fever Risk Factors:

• Radiation dose more than 5000 cGy
• Previous laparotomy (if bowel loops are fixed due to adhesions)
• Pre-existing vascular disease
• Diabetes
• Hypertension

Surgical Complications Of Enteric Fever Clinical Types:

• Acute: It manifests as colicky abdominal pain, bloating, loss of appetite, diarrhoea, etIt happens during 2nd week of treatment, because inflammatory changes are maximum during that period.
• Chronic: This occurs after 18 months and 6 years after radiotherapy.
• Chronic intestinal ischaemia occurs resulting in stricture and intestinal obstruction. Some cases are due to fibrosis, dense pelvic adhesions, bowel entrapment into the fibrosis, fistula formation and pelvic abscess.
• When there is no obstruction, conservative line of treatment is followed.
• If there is obstruction, laparotomy with resection, bypass or any other treatment depending upon the findings.
• Surgery can be difficult because of dense adhesions.

Surgical Complications Of Enteric Fever Prevention:

• Modern imaging and radiotherapy units.
• Radio-opaque markers such as titanium clips at the time of initial surgery.
• Decreasing the size of the radiation field.
• Reperitonisation of the bowel, using absorbable mesh cover over intestines, omental transposition also have been used.

Surgical Complications Of Enteric Fever Treatment:

• Sucralfate, mucosal protective agent, can be used in case of bleeding due to radiation proctitis.
• Antioxidants, probiotics, statins and angiotensin converting enzyme inhibitors are used when radiotherapy treatment is on.

Small Bowel Tumours

• Benign tumours such as lipoma, hamartoma, polyps can occur.
• Malignant tumours such as adenocarcinoma, gastrointestinal stromal tumours (GIST), carcinoid and lymphoma can occur in the small intestine.

Peutz-Jeghers Syndrome

(Familial Hamartomatous Polyposis):

This syndrome is characterised by:

1. Familial tendency

2. Melanosis of mucosa of lip, cheek, interdigital space and even perianal skin.

Comparison of two hamartomatous polyposis syndromes:

3. Multiple polyps in the small bowel and large bowel mainly in the jejunum. They are hamartomatous polyps.

• It is an autosomal dominant disease.

Surgical Complications Of Enteric Fever Clinical Presentation:

• Runs in families.
• As a cause of bleeding per rectum, results in chronic anaemi
• Can cause adult intussusception.
• Rarely, it can turn into malignancy.
• Female patients have increased chances of breast and cervical cancer (see clinical notes).

Surgical Complications Of Enteric Fever Treatment:

• Blood transfusion to correct anaemia
• Resection of that portion of bowel containing polyp, in cases of bleeding or intussusception.

We had 3 interesting cases of Peutz-Jegher syndrome.

• The first case was of a boy of 14 years, who presented with acute intestinal obstruction. At laparotomy, there were 3 intussusceptions in the jejunum due to polyps.
• About 15 large polyps were removed after doing an enterotomy.
• The second case was a 50-year-old lady, who presented with duodenal carcinomEndoscopy revealed polyps in the stomach and duodenum. Specimen of pancreaticoduodenectomy revealed it as a case of Peutz-Jegher syndrome. This lady did not have pigmentation of the oral mucosa.
• The third case was of a 35-year-old male who has been coming to our hospital with intermittent bleeding and anaemiEndoscopy revealed multiple polyps in the stomach and duodenum. Small bowel enema demonstrated multiple polyps in the small bowel. Even proctoscopy showed multiple polyps in the rectum. He is being managed conservatively.

Adenocarcinoma

• Incidence is 40% of small bowel tumours. Overall, small bowel tumours are rare.
• Duodenum is the commonest site of adenocarcinom If it arises from first part and second part, it may require Whipple’s pancreaticoduodenectomy. From the third part, early cases of adenocarcinoma can be resected without removal of pancreas.
• Some familial diseases predispose to adenocarcinom They are familial polyposis coli, adenomas, Crohn’s disease, etc.
• Clinical features include vague features like nausea, poor appetite, crampy abdominal pain, bleeding and intestinal obstruction.
• Diagnosis is by CT scan.
• Push enteroscopy has the advantage of visualization of the growth and to take biopsy.
• Other option is capsule endoscopy. It is time consuming and biopsy is not possible.
• Resection with at least 7 cm margin with lymphadenectomy is the treatment of choice.
• There is no role for radiotherapy and chemotherapy.