25. 1 Acute pancreatitis
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NORMAL STRUCTURE
The small intestine consists of the duodenum, jejunum and ileum. The jejunum and ileum together extend from the duodenojejunal junction to the ileocaecal valve. The jejunum accounts for the proximal 40 per cent and the ileum for the distal 60 per cent.
The wall of the small bowel consists of the mucosa, submucosa, the muscle coat (muscularis propria) and the serosa. The mucosa is composed of an epithelial layer, a. lamina propria and a muscularis mucosa.
The small gut is suspended by its mesentery which extends from the left side of the second lumbar vertebra to the right iliac fossa. The number of arterial arcades in the mesentery increase in number from 1 to 2 in the proximal jejunum to 4 to 5 in the distal ileum, a finding that helps to distinguish the two at operation. The luminal surface of the Jejunum shows more prominent valvulae connlventes and in the lower part of the ileum they almost disappear. The mucosa has a basal layer; villi project upwards from this layer and crypts of Lieberkuhn descend downwards from it. The villous folds increase the absorptive surface. The villi can be narrow and finger-like or broad and leaf-like. Each consists of , a core of lamina propria and a covering of epithelial cells which are either absorptive-type cells (entero-cytes) or goblet cells which secrete mucus. The crypt linings contain Paneth cells and endocrine cells in addition to the enterocytes and goblet cells. The endocrine cells contain cytoplasmic granules that contain 5 hydroxytryptamine and various peptides. Other cells containing cholecystokinin and motllin are also present. The mucosal surface is thrown up into folds (valvulae conniventes) which are visible macroscoplcally and on plain abdominal X-ray when the small bowl is distended with gas as in intestinal obstruction.
The whole of the jejunum and ileum Is supplied by the superior mesenteric artery and venous drainage is to the portal vein. The lymphatics drain to the superior mesenteric nodes.
The large bowel consists of the caecum, ascending colon, hepatic flexure, transverse colon, splenic flexure, descending colon, sigmoid colon and rectum. The caecum is the part below the Ileocaecal valve. The sigmoid colon extends from the brim of the pelvis to the rectum and the rectum starts opposite the sacral promontory.
The large bowel wall, like the small bowel wall, consists of a mucosa, a submucosa, a muscularis propria and a serosa. The epithelium of the mucosa forms tubules which are nonbranching and parallel to each other and extend down to the muscularis mucosa. There are no villl. The surface cells are mainly absorptive in type while the crypts are lined mainly by goblet cells and occasional endocrine cells.
Very few lymphatics pass through the submucosa into the lamina propria and this is of Importance In the pathology of malignant disease. The muscularis propria has an inner circular and outer longitudinal layer. The longitudinal coat of muscle is condensed into three bands termed taenlae coll and the large bowel Is characterised by sacculations or haustra which appear on X-ray as Incomplete septa projecting into the gas shadow when the colon Is distended.
The colon from the caecum to the splenic flexure is supplied by the superior mesenteric artery. The rest of the colon is supplied by the inferior mesenteric artery. The rectum is supplied by the superior rectal artery (a branch of the inferior mesenteric), the middle rectal artery (a branch of the internal iliac), and the inferior rectal arteries (from the internal pudendal). Lymphatic drainage is to the epicolic, paracolic and the Intermediate nodes and then follows the course of the arteries.
Meckel's Diverticulum
The vitellointestinal duct connects the midgut to the yolk sac in embryonic life. If the proximal portion persists it forms a Meckel's diverticulum
This is present in about 2 per cent of the population and it lies on the antimesenteric border of the ileum, approximately 2 feet from the ileocaecal valve. It measures up to 2 inches in length. The tip may be connected to the umbilicus by a fibrous cord although it is usually free. A terminal branch of the superior mesenteric artery crosses the ileum to supply the diverticulum.
The muscle coat of the divertilculum Is continuous with that of the ileum. The lining mucosa is small bowel in type but may contain ectopic mucosa. The ectopic mucosa is gastric in 80 per cent of the cases, the remainder being pancreatic or colonic. Gastric epithelium may give rise to peptic ulceration either in the diverticulum or in the adjacent ileum.
Meckel's divertlculum makes itself known only by its complications. A patient with Meckel's diverticulum has about 4 per cent chance of developing a complication in a lifetime. In order of frequency, these complications are as follows.
1. Haemorrhage per rectum This Is due to peptic ulceration in the heterotopic gastric epithelium in the Meckel's diverticulum. It presents with painless, periodic, brisk and severe bleeding in childhood.
2. Intestinal obstruction Intestinal obstruction is caused by a fibrous cord or by the diverticulum inverting and causing an Intussusception or becoming incarcerated In a femoral or inguinal hernia (Littre's hernia).
3. Meckel's diverticulitis The symptoms are akin to acute appendicitis. Acute inflammation is usually associated with obstruction of the mouth of the diverticulum by oedema, food residue or foreign body. A diverticulum may perforate into the general peritoneal cavity and the clinical picture resembles a perforated duodenal ulcer. Urgent surgery is required whether or not perforation has taken place.
Investigations
A firm preoperative diagnosis of Meckel's diverticulum is unusual except in children with rectal bleeding or in the case of an umbilical fistula. In rectal bleeding, radioisotope scanning has been found useful. Tc99m pertechnetate is Injected intravenously. The isotope is taken up by the gastric mucoid cells and will show as a hot spot, usually in the lower abdomen to the right of the umbilicus. It is difficult to identify a diverticulum on routine barium examination because of the overlying loops of bowel and because the diverticulum is self emptying.
Management
The suggested management of Meckel's diverticulum is outlined in Chart 45.1.
1. Diverticulum is excised together with a wedge resection of the adjacent ileum.
2. It should not be amputated at its base and invaginated in the same way as a vermiform appendix because of the risk of stricture and it may act as an apex of intussusception.
3. Moreover, it does not remove the heterotopic epithelium completely if such be present. It Is better to resect a small segment of ileum containing the diverticulum because it is here that the ectopic gastric mucosa and ulceration is often situated, rather than in the diverticulum Itself. After resection, the bowel continuity Is restored by end-to-end anastomosis.
Hirschsprung's Disease (Congenital Megacolon)
During normal embryonic development, pre-ganglionic parasympathettc nerve fibres from both the vagal and sacral outflow grow into the bowel. Ganglion cells later migrate from the neural crest and pass along these fibres to take up their place in the submucosal and intermuscular plexus. In Hirschsprung's disease, there is a partial failure of ganglion cell migration and the ganglion cells in a segment of large bowel are absent.
Hirschsprung's disease shows a familial tendency and occurs in about one in 20,000 births. Males are affected five times more than females. Most cases of agangllonosis involve the rectum and rectosigmoid but longer segments of absent ganglion cells may also occur, and total colonic aganglionosis, although rare, is also seen.
Aganglionic colon does not allow normal peristalsis to occur and functional obstruction supervenes.
Clinical Features
The patient usually comes in Infancy, sometimes In early childhood and occasionally in adult life.
Infants The infant fails to pass meconium during the first 2 or 3 days of life. By the third day. the abdominal distension is obvious and complete obstruction may occur. As a rule, the relief is given by a small enema or by passing a greased examining finger (with expulsion of stool and flatus).
At times, there is chronic obstruction characterised by chronic constipation alternated by episodes of diarrhoea associated with passage of large amounts of foul smelling gas.
Children The Infants who survive may present during childhood as (1) constipation dating from birth. The stools are hard and likened to "goat pellet" (2) malnutrition, and (3) abdominal distension. The abdomen has a characteristic appearance. Abdominal muscles become thin from stretching and there are prominent veins on it. Impacted stools in the greatly dilated sigmoid colon can be palpated across the lower abdomen.
Rectal examination reveals a normal or contracted anus and a rectum without faeces.
Adults Very occasionally, the symptoms become severe as late as in the adult life when the patient seeks advice.
Diognosis
Plain abdominal X-rays in infants show dilated loops of bowel, but it is difficult to distinguish between small and large bowels in infancy. A barium (in saline) enema X-ray should be performed. It is done in an unprepared bowel (as the preliminary washout often minimises the dilatation of the gut above the obstruction). The barium enema should be prepared with normal saline (not with water) because the megacolon absorbs water much more rapidly than normal colon and this may result in water intoxication. In infants, the barium is retained for 24 hours or more and delayed films after 24 hours are necessary.
In children, the characteristic radiological finding is a narrow agangllonic segment, the funnel shaped transitional zone, and the increasingly dilated proximal colon.
Rectal biopsy Definitive diagnosis is made on either a full thickness rectal biopsy or a partial thickness suction biopsy. Partial thickness "mucosal" biopsy may be taken from the posterior rectal wall with a suction biopsy capsule, without anaesthesia. If the histology findings are equivocal, it Is necessary to take a 1x2 cm full thickness rectal biopsy from the posterior rectum proximal to the dentate line, .under anaesthesia. The two cardinal features are a complete absence of ganglion cells and an increase in nonmyelinated nerve fibres in the submucosa and In the Inter -muscular plane. Since these nerves are chollnergic, an increase in acetylcholine activity in specially stained sections is helpful In diagnosis and even superficial biopsies in expert hands may be diagnosed. The site of biopsy must be about 2 cm above the dentate line.
Differential Diagnosis
The main differential diagnosis is with idlopathic megacolon (functional constipation). It occurs in older children or in adults. The dilatation extends up to the anus which means that the rectum is also dilated. This may be a result of habitual constipation. Rectal examination reveals a loaded rectum. Treatment consists of regularisation of bowel habits.
Complications
1. Death rate of untreated agangllonic megacolon In infancy may be very high. A serious complication is the development of enterocolitls.
2. Ischaemic necrosis and perforation of the bowel above the agangllonic segment may develop and cause a presentation similar to neonatal necrotlsing enterocolitls.
Treatment
The aim of surgery Is to excise the whole length of the agangllonic segment (which Is the cause of the functional obstruction) and to restore continuity. In other words, the upper limit of resection must include the transitional zone and a little of healthy dilated colon above it while the lower limit should be so designed as to preserve the anal canal with Its sphincters.
The majority of patients are neonates or infants and in these an emergency colostomy Is required to save life and the definitive operation of resection has to be postponed to a later date. One stage surgery is only done for those who are In moderately fair health and over the age of 2 years.
Colostomy may be either left iliac or transverse colostomy. During the operation of colostomy, it is always advisable to put a marker with black silk at the lowermost limit of the dilated ganglionic segment and it helps during the operation of resection.
Definitive operation Three type of operation are practised.
1. Swenson's operation
2. Duhamel's operation
3. Soave's operation
1. Swenson's operation It is a combined abdominal and anal approach. The inferior mesenteric artery Is divided and the sigmold colon and rectum are mobilised to as far down as possible. During mobilisation, dissection is done as close to the wall of the gut as possible, in order to avoid injury to the pelvic nerves, etc. A line of junction between the ganglionic and the aganglionic segments is made out and the gut is divided a little proximal to this junction. The distal cut end is closed in the form of a stump. A long artery forceps is now introduced per anus and the stump is held with the tip of the forceps. As the artery forceps is withdrawn, the distal loop of gut containing agangllonic segment and the normally Innervated anal canal, are everted. A transverse Incision is made on the anterior wall of this everted loop, 2 cm from the anus. Through this opening, the long forceps Is reintroduced and the proximal divided end of the colon is pulled through It. The anal canal is completely divided along the same line in which it was Incised on Its anterior wall. Thus, the whole length of the agangllonic segment is resected. To the cut end of the anal canal. Is anastomosed the cut end of the "pulled through" colon. The suture line together with the anal canal Is Inverted through the anus.
The above is the historical description of the original Swenson procedure. With the use of the stapling device, there Is no need to evert the anal and end-to-end anastomosis is possible within the pelvis.
2.. Duhamel's Operation In Swenson's, the normal rectal sensation Is lost In the absence of the rectum. In Duhamel's, only the aganglionic segment of the colon is excised per abdomen and the rectum is preserved. The cut end of the rectum is closed. The upper cut end of the colon is brought down behind the rectum. It is then made to traverse through the posterior wall of the anal canal between the fibres of the internal sphincter, so that it finally emerges at the anus posteriorly, but in the submucous plane (i.e. not in the anal lumen). After an interval of 3 weeks an enterotribe is used to crush the partition between the two lumens.
The end of the proximal colon is anastomosed to an incision made in the posterior wall of the rectum, 1 cm above the dentate line. The intervening spur of rectum and bowel is divided and a side-to-anastomosis is made with a stapler to form a common rectal reservoir.
3. Soave's operation It also retains the rectum, excising only the aganglionic part of the colon. The rectum is denuded of its mucous membrane. Thereafter, the proximal colon is pulled ' through the lumen of the rectum and the anal canal, and is sutured to the anus .
DIVERTICULAR DISEASE OF THE COLON
They are the acquired herniations of mucosa protruding through the circular muscle at the points where the blood vessels penetrate the colonic wall. They are devoid of any muscle in the wall. Diverticula vary from a few millimetres to several centimeters in diameter, the necks may be narrow or wide, and some contain inspissated faecal matter. The condition may be localised to one part of the colon, usually the sigmoid colon.
While diverticulosis of the colon is so common in the West, it is rare in the Indian subcontinent. This rarity is partly due to the high residue diet of Indians, as compared to the refined low residue diet of Europeans. High intraluminal pressure and weakness of the colonic wall may be two factors important in the pathogenesis of diverticula.
Diverticulosis remains asymptomatic in most people and is detected incidently on barium enema X-rays. In addition to diverticula, barium enema films may show segmental spasm and muscular thickening that narrow the lumen and give it a "saw tooth" appearance .
In some, the disordered colonic function may cause symptoms of distension, flatulence and a sensation of heaviness in the lower abdomen. Excessive colonic segmentation can cause severe colic pain in the left iliac fossa. This pain waxes and wanes rapidly and is in fact due to spastic obstruction of the colon.
Diverticulosis should be treated with a high residue diet. It is. however, not certain that complications of diverticulosis can be so avoided. Breakfast cereals are the most convenient agents to use. Pain may require antispasmodics. Habitual purgation should be avoided.
Colonoscopy may become necessary for massive haemorrhage to rule out carcinoma.
COLONIC DIVERTICULITIS
It either occurs with perforation due to raised intraluminal pressure or begins as an infection in a diverticulum. Only one diverticulum is involved at a time, usually in the sigmoid colon. Episodes of diverticulltis may be followed by years free of symptoms, but the condition is essentially progressive — the longer the duration, the worse are the symptoms and the greater the risk of complications.
Clinical Features
The acute attack consists of localised abdominal pain that is mild to severe. It resembles acute appendicitis except that it is situated In the left lower quadrant. The patient may pass loose stools or may be constipated. Abdominal distension may be relieved by passage of flatus. Inflammation adjacent to the urinary bladder may produce dysuria. Nausea and vomiting depend on the location and severity of the inflammation. Physical findings Include low grade fever, mild abdominal distension, left lower quadrant tenderness, and a left lower quadrant or pelvic mass.
Complications
These Include the following.
1. Perforation Small-sized perforation may lead to localised inflammation In the colonic wall or paracollc tissues. Macroperforation results in more extensive bacterial contamination and more serious infection such as an abscess or generalised peritonitis.
2. Fistula formation An abscess may be confined by adjacent structures or may enlarge and spread; it may reabsorb with antibiotic treatment or drain spontaneously into the lumen of the bowel or into an adjacent viscus to form a fistula. Coloveslcal fistula is the commonest type which typically presents as pncumaturia. Patients rarely pass urine per rectum as the colonic pressure is higher than the bladder pressure.
3. Intestinal obstruction Small bowel may adhere to an inflamed area and cause small bowel obstruction.
4. Haemorrhage Haemorrhage usually occurs in diverticulosis rather than divertlculitis. Since the divertlcula protrude through the colonic wall where blood vessels enter, it is perhaps not surprising that erosion or ulceratlon of the wall of the divertlculum will lead to massive haemorrhage.
Investigations
Plain X-ray abdomen may show free abdominal air if a divertlculum has perforated into the general peritoneal cavity. If inflammation is localised, there is a picture of ileus, multiple fluid levels, etc.
CT-scan is proving to be more useful than water soluble contrast enema. Contrast enhanced CT may show perlcolic abscess or fistula. The location of an abscess accessible for percutaneous drainage provides a major therapeutic advantage.
Barium enema is contralndicated during the initial stages of an acute attack lest barium leaks into the peritoneal cavity. Water soluble contrast media used under low pressure is, however, safe. It is preferable to defer the barium enema until the episode of acute diverticulitis has settled.
Flexible sigmoidoscopy and colonoscopy should also be avoided during an attack. It is, however, useful in the later stages to evaluate other abnormalities. Cystoscopy may reveal oedematous change in the bladder area adjacent to diverticulitis.
Differential Diagnosis
Free perforation of a diverticulum with generalised peritonitis may be dificult to differentiate from the other causes of perforation.
Acute localised diverticulitis may simulate appendicitis except that the pain is on the left side. Amoebic colitis may present as pain and tenderness in the left iliac fossa.
A difficult differentiation lies between diverticulitis and carcinoma of the colon. Persistent bleeding should not be attributed to diverticular disease until malignancy has been excluded.
Management
Generally, nothing is given by mouth, nasogastric suction is instituted, intravenous fluids are given and, parenteral antibiotics administered. Analgesics are prescribed. As acute manifestations subside, oral feeding is resumed gradually. The diagnosis must be confirmed by an Investigative work-out.
Surgical Treatment
Immediate operation is required if generalised peritonitis is present. Abdominal pain. mass, fever or leucocytosis that fells to improve after 3-4 days of medical therapy also Indicates surgical intervention.
At laparotomy, the peritoneal fluid varies from turbid to purulent to grossly faecal. The extent of colonic inflammation, the amount of peritonitis, the patient's general condition, and the surgeon's experience and preferences determine the type of operation to be performed.
1. Primary resection with anastomosis It is not safe, if the bowel is oedematous or there is gross infection in the surgical field because of the risk of anastomotic leakage.
Resection for sigmold diverticulitis should include the rectosigmoid distally to the point where the taenlae become confluent; anastomosis being performed to the proximal rectum, which is always free of diverticula. The distal descending colon is removed but there Is no need to resect too much proximally even if involved with diverticula; they do not become symptomatic in the absence of the high pressure zone of the sigmoid.
2. Primary resection without anastomosis (2 stage procedure) The diseased bowel is removed, the proximal end is brought out as a temporary colostomy, and the distal colonic stump is closed (Hartmann procedure). Intestinal continuity being restored In a second operation after the inflammation subsides.
3. Three-stage procedure A preliminary transverse colostomy can be done as a first stage and the paracollc abscess is drained; in the second stage operation the left colon is resected; and after further two weeks the colostomy is closed. Colovesical fistula may cause surprisingly little disturbance to the patient. Pneumaturia may be recollected only in response to direct questioning. A fistula requires surgical treatment only if it persists and there is never a need for emergency operation. Diverticulitis is managed by bluntly dissecting the colon from the bladder, resecting the colon, and performing a primary anastomosis.