Meckel's diverticulum is a congenital diverticulum arising from failure of embryonic obliteration of the omphalomesenteric (vitelline) duct connecting the fetal gut to the yolk sac, that normally occurs during the fifth to seventh week of gestation. In contrast to other small-bowel diverticula, Meckel's diverticulum contains all intestinal layers and is antimesenteric. It is the most common congenital anomaly of the small intestine, found in 0.5 to 3.0 per cent of the population at postmortem examination. It is most often found within 1 metre of the ileocaecal valve and rarely up to 180 cm from the valve; the length of the diverticulum is usually less than 12 cm but can vary from 0.5 to 56 cm.

Meckel's diverticulum has a blood supply independent of that of the contiguous ileum, distinguishing it from ileal duplication; in addition, ileal duplication usually arises from the mesenteric border. The embryonic blood supply of the vitelline duct is by paired vitelline arteries, of which the right forms the superior mesenteric artery, while the left artery involutes. The blood supply to the diverticulum is derived from a remnant of one of these arteries. A mesodiverticular band may connect the diverticulum to the ileal mesentery; the contained vessel is often obliterated.

Simple Meckel's diverticulum represents the most common end-result among a set of omphalomesenteric duct anomalies, in which the entire duct is obliterated and is absorbed, with the exception of several centimetres attached to the small intestine (Fig. 1) 980. Other associated abnormalities of duct obliteration include the following:

(1)the entire vitelline duct persists, resulting in a fistula between the ileum and the umbilicus;

(2)the distal end of the duct persists as a sinus opening at the umbilicus or as an umbilical polyp;

(3)the duct lumen is obliterated but not absorbed, forming a fibrous band attached to the umbilicus, to other viscera, or with a free end;

(4)a segment of the duct remains patent, forming a cyst or ‘enterocystoma’ along its course;

(5)the mesodiverticular band described above;

(6)heterotopic tissue, usually consisting of gastric epithelium, is found in 30 to 50 per cent of cases, but may include pancreatic (5 per cent), colonic, jejunal, or duodenal elements;

(7)the diverticulum may be buried in an intramesenteric position or have a separate mesentery.

Meckel's diverticulum can be identified preoperatively by radionuclide scanning, barium contrast studies, arteriography, and occasionally by computerized tomographic scanning, with varying degrees of success. The pertechnetate anion (&sup9;&sup9;Tc&supm;) is selectively taken up and is secreted by gastric mucosal parietal cells in their normal and aberrant locations, as well as by thyroid and salivary glands and the choroid plexus. Thus, the demonstration of Meckel's diverticulum by abdominal scanning (Fig. 2) 981 as an extragastric localized area of uptake, which increases temporally in parallel with gastric mucosal uptake, depends on the presence of ectopic gastric mucosa. Scanning is most successful in cases of bleeding due to associated peptic ulceration in children. In the most experienced centres, the sensitivity of detection is 85 per cent and specificity is 95 per cent. However, &sup9;&sup9;Tc&supm; scanning may be less accurate than generally believed, particularly in adults, where the sensitivity is lower. A negative scan at any age does not exclude the diagnosis. Moreover, false-positive scans occur, ascribed to such unrelated conditions as small-bowel tumours, small-bowel obstruction, hydronephrosis, enteric duplication, and arteriovenous malformations.

The diagnosis of Meckel's diverticulum is occasionally suggested on plain abdominal films on the basis of an enterolith or radio-opaque foreign body in the right lower quadrant or a persistent right lower quadrant or subumbilical gas collection. On antegrade small-bowel barium studies, the diverticulum is sometimes directly visualized, or suspected by virtue of the mass effect on the adjacent ileum or frank obstruction. Because the diverticulum may only fill transiently, careful fluoroscopy is necessary. The diagnostic yield is increased by use of a small-bowel enema or enteroclysis, in which contrast is given following nasoduodenal or nasojejunal intubation. Barium enema examination may identify ileocolic or even ileo-ileal intussusception as the basis for obstruction. During episodes of major gastrointestinal bleeding due to Meckel's diverticulum, barium studies should not be done. Occasionally, extravasation of contrast dye is seen on mesenteric arteriography in actively bleeding patients, but the diagnostic yield is low.

The manifestations of Meckel's diverticulum are protean. The pathological complications of the diverticulum are related directly to the particular pattern of accompanying vitelline duct abnormalities. Thus they can mimic many intra-abdominal conditions. Meckel's diverticulum should be considered as a possible cause of any intra-abdominal disease in which the diagnosis is not evident. The complications of Meckel's diverticulum include bleeding, obstruction, diverticulitis, enterolith, and tumours, in addition to associated anomalies. The diagnosis is seldom made preoperatively (less than 4 per cent of cases), except in cases of lower gastrointestinal bleeding in the paediatric population. The pain or tenderness from inflammatory or obstructive complications of the diverticulum do not necessarily occur in the right lower quadrant, but may be located in other abdominal quadrants or vary in location due to small-bowel motility and the position of the diverticulum relative to the ileocaecal valve. Sixty per cent of Meckel's diverticula become symptomatic before the age of 10 years. The pattern of complications is also age-related, with bleeding most common in children (75 per cent of complications before 10 years of age) and rare after age 30. Small-bowel obstruction may occur at any age, but in children intussusception of the diverticulum is a more likely cause of obstruction. In children, obstruction and bleeding account for approximately equal proportions (30 to 35 per cent) of symptomatic cases. Diverticulitis accounts for 20 per cent of cases, with a peak incidence in older children. Persistent umbilical fistula is seen in neonates. Neoplasms and the hernia of Littré occur in older adults. The incidence of complications of the diverticulum is also related to gender. Although the anomaly is found equally among males and females, complications are observed 2 to 3 times more frequently in males.

Meckel's diverticulum is the most frequent cause of painless, major, lower gastrointestinal bleeding in a previously healthy infant. One-half of cases occur before 2 years of age. More than 95 per cent of bleeding Meckel's diverticula contain ectopic gastric mucosa, causing mucosal ulceration either in the diverticulum near the heterotopia or in the adjacent ileal mucosa. Bleeding may be intermittent or continuous, appearing as melaena or exsanguinating bleeding with frank blood and clots. The bleeding has sometimes been described as ‘brick red’. The bleeding is occasionally associated with pain, presumably due to the peptic ulceration. Spontaneous cessation of bleeding usually occurs. There may be chronic bleeding of lesser magnitude. The differential diagnosis includes juvenile polyps, arteriovenous malformation, intestinal haemangiomas, and blood dyscrasias. Diagnostic manoeuvres include haematological examination, sigmoidoscopy, and, when appropriate, contrast radiological studies, which are useful only to exclude other sources of bleeding. The sodium &sup9;&sup9;Tc&supm; pertechnetate scan, if positive, is usually diagnostic (Fig. 2) 981.

Treatment choices include surgical resection of the diverticulum or of the involved small bowel. Care must be taken not to miss a diverticulum adherent to the ileum. If diverticulectomy is elected, attention should be directed to removing any peptic ulcer in the adjacent ileum. At present the complication rates from small-bowel resection and diverticulectomy with closure are likely to be similar; in earlier reports diverticulectomy was assumed to be safer.

The diagnosis of peptic ulceration of Meckel's diverticulum in the absence of bleeding (‘dyspepsia Meckelii’) is uncommon. There may be episodes of abdominal pain in the right lower quadrant or in the region of the umbilicus with a temporal pattern similar to gastroduodenal peptic disease, but not directly relieved by alkali. Pain may be relieved by food intake in a delayed fashion.

The precise preoperative diagnosis of small-bowel obstruction due to Meckel's diverticulum is seldom made in the absence of a characteristic antecedent history of episodes of intermittent obstruction manifested by abdominal pain and vomiting and of peptic symptoms occurring in the absence of demonstrable upper gastrointestinal ulceration. Meckel's diverticulum may cause small-bowel obstruction through several different mechanisms:

1.Two per cent of cases of intussusception are due to Meckel's diverticulum. Intussusception occurs more frequently in children with heterotopic tissue acting as the leading point. The intussuscepting mass may also be due to diverticulitis or contained enterolith. Symptoms include abdominal pain, vomiting, and abdominal tenderness. In addition, rectal bleeding may occur and an abdominal mass may be appreciated. Obstruction may be intermittent, suggesting a reduction of the intussusception. In adults with intussusception due to the diverticulum, neoplasm in the diverticulum is a more likely cause; symptoms may be chronic and recurrent.

2.A persistent, obliterated vitelline duct attached to the umbilicus may serve as a fixed point for volvulus, or cause entrapment as an internal hernia.

3.The diverticulum may be attached by a band to another viscus, resulting in an internal hernia or serving as a fulcrum for volvulus.

4.Similarly, obstruction may occur due to herniation of the small bowel beneath a mesodiverticular band or volvulus.

5.The mesodiverticular band can cause obstruction by direct ileal compression.

6.Adhesive obstruction may arise secondary to prior inflammation of the diverticulum.

7.A diverticulum which becomes enlarged due to diverticulitis, or by obstruction of the mouth of the diverticulum, may cause obstruction by compression of the adjacent ileum.

8.The diverticulum may become inverted into the ileal lumen, causing an obturating obstruction.

9.The inguinal or femoral hernia described by Littré, mainly in the elderly, contains a strangulated diverticulum. Up to one-quarter of cases occur in umbilical hernias.

10.Rarely, an axial volvulus of the diverticulum occurs, resulting in infarction.

11.In one case of a very long diverticulum, obstruction was due to the formation of a true knot involving another viscus.

12.Obstruction may occur in neonates due to extrusion or prolapse of the ileum through the umbilicus via the patent vitelline duct.

Surgical treatment of obstruction found to be due to Meckel's diverticulum includes division of offending bands if present, and small-bowel resection or simple diverticulectomy, as well as resection of non-viable segments that may occur in volvulus or intussusception.

Acute diverticulitis may result from peptic ulceration associated with gastric heterotopia, contained enteroliths or foreign body, or obstruction or narrowing of the mouth of the diverticulum. The symptoms of abdominal pain, fever, and vomiting with signs of abdominal tenderness, sometimes in the right lower quadrant, are usually indistinguishable from the presentation seen in acute appendicitis. Abdominal tenderness may be located elsewhere than in the right lower quadrant. Meckel's diverticulitis is potentially more serious than appendicitis, because the process is not contained as often. Perforation and generalized peritonitis may ensue. When the inflammatory process involves an adjacent viscus, a fistula may form. Surgical resection and administration of antibiotics are dictated by the same considerations that apply to appendicitis.

Enteroliths are rare complications, forming in narrow-necked diverticula where there is stasis (see Section 16.10 114). True foreign bodies may lodge in the diverticulum. Both enteroliths and foreign bodies may be associated with diverticulitis, may result in bowel obstruction, or can cause haemorrhage from local pressure necrosis. Plain abdominal films that show calculi as well as small-bowel obstruction may cause diagnostic confusion with gallstone ileus.

Approximately 1 per cent of Meckel's diverticula developed neoplasms, which occur more often in men. These account for 1 per cent of the complications of Meckel's diverticulum and may be benign or malignant. In contrast to the small intestine per se, where adenocarcinoma is the most common histological type, carcinoid (34 per cent) and leiomyosarcoma (18–44 per cent) are most commonly identified in Meckel's diverticulum, while 12 to 20 per cent of tumours are adenocarcinomas. Among benign tumours, leiomyoma is the most frequent. Although the majority of carcinoids are incidental findings, 20 per cent are associated with metastases. Neoplasms of Meckel's diverticulum become apparent when they produce obstruction, sometimes as the leading point for intussusception, or when they cause haemorrhage (sometimes occult) or inflammation.

Whether or not to remove a Meckel's diverticulum when it is found incidentally at laparotomy is a source of controversy. Early series of cases, based on autopsy or pathological materials or on retrospective clinical studies that were often anecdotal, resulted in the conclusion that up to 34 per cent of patients with a diverticulum would suffer a complication. Surgery for complications of Meckel's diverticulum appeared to result in a higher incidence of mortality and morbidity than did incidental resection when an uncomplicated Meckel's was found at laparotomy, particularly in the elderly. Opinions regarding incidental diverticulectomy are based on:

(1)knowledge of the incidence of the anomaly in the population;

(2)the likelihood in that population of complications that may be related to age and gender or to the anomalous anatomic findings at laparotomy;

(3)The morbidity and mortality attributed to resection of a non-diseased diverticulum versus that for a complicated Meckel's diverticulum.

Whether the incidence in a population is 1 per cent or 2 per cent, and whether the complication rate is assumed to be 5 per cent or 10 per cent, would result in opposing recommendations.

A substantially larger percentage of Meckel's diverticula remain innocuous. From a study of a large population, Soltero and Bill concluded that at birth there is a 4.2 per cent risk of complications from Meckel's diverticulum over the lifetime of a patient, and that such risk was age-related, falling to 1 per cent at age 50 and to near zero in the elderly. Furthermore, the current mortality of surgery for complicated Meckel's diverticula is lower than in the past. On the other hand, the mortality for excision of incidental Meckel's diverticulum in youth is virtually nil, while the morbidity associated with small-bowel resection or enterotomy remains.

Nonetheless, certain guidelines may be offered. The most important factor is the age of the patient. The majority of surgeons would remove an incidental Meckel's diverticulum in children under 2 years of age, but most would not interfere with this lesion in patients over 30 to 40 years of age in the absence of complicating pathology. Relative indications for resection include diverticula in men and the nature of the pathological process that prompted the laparotomy, such as the presence or absence of appendicitis or peritonitis. Thus, in children or youths undergoing elective surgery, removal of an incidental Meckel's diverticulum is reasonable. Since ectopic tissue is found in 40 to 50 per cent or more of patients with complications of Meckel's diverticulum (compared with 6–10 per cent of patients with bland diverticula), the presence of palpable heterotopia may be an indication for resection. However, up to one-half of heterotopia may not be appreciated on palpation, although the larger ones usually are. There is insufficient evidence to argue that diverticula with a narrow orifice should be removed. Longer diverticula may be more likely to cause difficulties. Findings at surgery indicating prior diverticulitis, including scarring or adhesions, would dictate excision. The presence of a band to the umbilicus or other viscus would require, as a minimum, division of the band at any age.

In contrast to Meckel's diverticulum, small-bowel diverticula, like colonic diverticula, are acquired; they occur along the mesenteric border and usually lack muscular layers. The reported incidence of small-bowel diverticulosis varies between 0.2 and 4.6 per cent in autopsy series, no doubt dependent on the age of the population under study and the degree of enthusiasm of the prosector for their detection, using bowel insufflation. The mean age for detection is in the seventh decade. The diverticula may be single, but are usually multiple, and are confined to the jejunum in 80 to 90 per cent of cases, the remainder being in both jejunum and ileum or confined only to the ileum (Fig. 3) 982. Jejunal diverticulosis is associated (in 33–75 per cent of cases) with diverticula elsewhere in the gastrointestinal tract, particularly in the colon.

Small-bowel diverticulosis has been associated with disorders of intestinal motility in which there is ‘intestinal pseudo-obstruction’ due to myopathy or neuroenteric disorders; these pulsion diverticula, due to increased intraluminal pressure acting at weak points in the lumen, are proposed to represent the end-stage of a chronic intestinal motility disorder. At surgery the jejunal musculature may be thickened, with relative dilatation of the proximal bowel.

Because of an ageing population, the diagnoses of small-bowel diverticulosis and its complications are being made more frequently. Vague epigastric or periumbilical pain, bloating, and early satiety have been ascribed to small-bowel diverticulosis. However, these symptoms allow a specific diagnosis only by exclusion. The triad of anaemia, epigastric distress, and air–fluid levels on plain abdominal films may be a clue to the diagnosis. Small-bowel diverticulosis is most often discovered as a result of more dramatic complications. Except in the case of malabsorption, the cause is not often identified preoperatively.

Jejunal diverticula may be detected by barium studies of the small bowel, particularly on delayed films. Jejunal dyskinesia can be seen during fluoroscopy, where barium is not propelled normally, but moves in and out of the diverticula, associated with partial obstruction. The diagnostic yield is enhanced by small-bowel enteroclysis, in which the duodenum/jejunum is intubated and the bowel is insufflated and examined by the radiologist during compression.

Pathological consequences of small-bowel diverticulosis include diverticulitis, haemorrhage, obstruction, and malabsorption. The formation of enteroliths, fistulae to surrounding organs, asymptomatic pneumoperitoneum, and malignant tumours are less common complications.

The pathogenesis of small-bowel diverticulitis parallels that of colonic diverticulitis. The common presenting complaints are pain, nausea, vomiting, signs of sepsis, and abdominal tenderness. Occasionally a mass is palpable. The diagnosis is rarely made preoperatively, as the process may be localized in virtually any abdominal quadrant. Perforation may occur into the mesentery, can be walled off by adjacent organs, or may result in free perforation with generalized peritonitis. Older anecdotal reports of high mortality rates for perforated diverticulitis treated by surgical resection are no longer valid.

In addition to the ‘pseudo-obstruction’, or motility disorder, associated with small-bowel diverticulosis, frank mechanical obstruction may occur from diverticulitis, adhesions associated with the inflammatory process, enteroliths arising in a diverticulum, and volvulus about surrounding adhesions. Relief of the obstruction should include resection of the segment involved with diverticulitis. Enteroliths, usually composed of choleic acid, form in diverticula where there is stasis, and may lead to obstruction due to local diverticulitis or to obturation in more distal small bowel. Enterotomy to remove enteroliths is sufficient treatment, although resection of diverticula, if localized, may be advocated. When jejunal diverticulosis is found incidentally at laparotomy, resection should be carried out if there are signs of pseudo-obstruction of the involved segment (thickened bowel wall and proximal dilatation).

Haemorrhage from jejunal diverticulosis presents as massive rectal bleeding in more than two-thirds of instances, occasionally accompanied by haematemesis; bleeding is often recurrent. Initial endoscopy serves to exclude other sources. Arteriography is the procedure of choice thereafter for localization of the bleeding site, although sometimes the tagged red blood cell scan is useful. When preoperative localization of the bleeding site fails and laparotomy is still required, cross-clamping of the bowel above and below the bleeding site may be useful to define the segment which fills with blood, thus dictating resection. When bleeding cannot be localized in this way and the patient, usually elderly, has concurrent colonic diverticulosis, thought preoperatively to be a likely source, both colon resection and resection of the small-bowel segment involved with diverticulosis should be done.

Small-bowel diverticulosis is one possible cause of the ‘blind loop’ or ‘stagnant bowel syndrome’, in which there is stasis of intestinal contents, resulting in bacterial overgrowth. The metabolic consequences of bacterial overgrowth include megaloblastic anaemia, due to bacterial uptake of vitamin B&sub1;&sub2;, and to steatorrhoea, due to decreased bile salts as a result of bacterial hydrolysis of conjugated bile salts, with impaired micelle formation. In addition, there may be diarrhoea, weight loss, neuropathy, hypoproteinaemia, and mild abdominal pain associated with jejunal dyskinesia. In addition to laboratory evidence for malabsorption, stasis is also indicated by the presence of colonic bacteria in duodenal aspirates and by radiological detection of the diverticula. Initial treatment includes vitamin B&sub1;&sub2; parenteral supplementation and broad-spectrum antibiotics. Twenty-five per cent of patients do not respond to this treatment, and in these cases resection of the segment containing the diverticula is required. Because diverticula are usually in the jejunum, extended resections are relatively well tolerated.

Meckel's diverticulum

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