The small bowel, which comprises the duodenum, jejunum, and ileum, represents approximately 75 per cent of the length of the gastrointestinal tract. The duodenum is about 25 cm long, the jejunum 200 cm, and the ileum 300 cm. This varies widely, and the length of the normal adult small bowel ranges from 300 cm to 850 cm. Since the small bowel provides 80 to 90 per cent of the surface area of the gastrointestinal tract, it might be expected to harbour most of the neoplasms. In fact, more lesions occur in the oesophagus, stomach, colon, and rectum, although the disparity is less for benign tumours than for malignant tumours. Hamartomas are randomly scattered through the gut.

To set the incidence of tumours in perspective, only 1.5 to 6 per cent of all gastrointestinal tumours arise in the small intestine and 20 to 25 per cent of these are found in the short duodenal segment. The population incidence of benign tumours is approximately 0.1 to 0.8 per cent.

Several hypotheses have been advanced to explain the relative scarcity of small bowel neoplasia, including the fluid nature of the contents and their rapid transit, decreasing exposure to ingested carcinogens; a low concentration of bacteria and alkaline pH, which might reduce the endogenous formation of carcinogens; detoxification of carcinogens by enzymes such as benzopyrene hydroxylase which are present in the mucosa; and the presence of protective immune factors, notably IgA, which is secreted especially in the ileum.

At least half of all benign enteric lesions are asymptomatic and are found incidentally at laparotomy or autopsy. Innocent lesions may also be observed during investigation of the gastrointestinal tract. Symptoms caused by the remainder vary from non-specific complaints, such as nausea, dyspepsia, discomfort in the epigastrium or right upper quadrant, fatigue, bloating, and weight loss, to haemorrhage or obstruction.

Obstruction is the presenting feature in 40 to 70 per cent of cases. Although often partial and recurrent, it can be sudden and complete. Intussusception is a frequent type of obstruction, with the tumour acting as the apex of the intussusceptum. In other instances obstruction may be due to a mass effect of the lesion or to volvulus. Rarely, stenosis of the bowel occurs, due to the local effects of vasoactive peptides secreted by a carcinoid tumour.

Haemorrhage, which is the presenting feature in 20 to 50 per cent of cases, is frequently occult and causes anaemia, but major bleeding can lead to both haematemesis and melaena. More than 90 per cent of gastrointestinal haemorrhagic events stem from the oesophagus, stomach, proximal duodenum, and colorectum. It is important to consider small bowel lesions once these more accessible sources have been excluded. Occasionally mucocutaneous pigmentation (in Peutz–Jeghers syndrome), café-au-lait spots (neurofibromatosis) or telangiectasia (Osler–Rendu–Weber syndrome) will alert the clinician to the presence of small bowel lesions.

Periampullary lesions can cause jaundice or pancreatitis, or a large tumour may be palpable. Serosal lesions may perforate, bleed, or fistulate, and gastrinoma presents with intractable ulceration.

Duodenal lesions are more amenable to accurate diagnosis than are jejunoileal lesions. Upper gastrointestinal endoscopy is the mainstay for detecting lesions in the first and second parts of the duodenum, and has the added advantage of allowing biopsies to be taken. Among contrast studies hypotonic duodenography is preferable to simple barium meals for detecting small lesions.

The jejunum and the ileum are the least accessible parts of the gut to evaluate without recourse to laparotomy. Radiographic options are a barium meal and follow-through examination, or an intubated small bowel meal (small bowel enema), which gives superior pictures; contrast is instilled rapidly through a transpyloric tube. The terminal ileum can frequently be seen on a barium enema and is visible in 20 to 30 per cent of colonoscopies. Many vascular lesions lie within the wall of the small bowel and will escape detection unless superior mesenteric angiography is performed.

In patients with active haemorrhage isotope scanning should also be considered, using Tc-99m-labelled sulphur colloid or Tc-99m-labelled red blood cells. Such techniques allow bleeding rates as low as 0.1 ml/min to be detected, while 0.5 to 1 ml/min is usually necessary to enable a lesion to be localized angiographically. A careful search should be made on the arteriogram for the vitelline artery of a Meckel's diverticulum and for the early filling vein of an angiodysplasia. Laparotomy is an important investigation in small bowel disease and should not be overly delayed. Most actively bleeding lesions are readily seen or felt. In obscure cases, cross-clamping the bowel at various levels may localize the source. Lastly, operative enteroscopy can be undertaken by passing a colonoscope either by mouth or through a small enterostomy or, in a retrograde direction, from a caecostomy. Transillumination of the bowel wall from within may be more productive than endoscopic inspection of the mucosa (Fig. 1) 991.

Small bowel endoscopy (enteroscopy) in the conscious patient has recently been described. A 5-mm diameter endoscope is introduced into the gastrointestinal tract transnasally and passes down the small intestine, with the help of peristalsis. In one study the endoscope reached the distal ileum or colon in 36 of 60 patients examined in this way. Average intubation time was 6 h, and a possible site of bleeding was identified in 20 patients.

Another technique currently undergoing assessment is percutaneous endoscopy. Access is achieved through the abdominal wall into the stomach or caecum, using the same technique as that for endoscopic insertion of feeding gastrostomies. Examination of the bowel can be achieved by introducing an endoscope through the created fistula. Further evaluation is needed.

Ultrasound, computerized tomography (CT), and magnetic resonance imaging have all been used in assessing small bowel lesions: at present CT is the most productive, especially for lesions in the duodenum. Lipomas can be differentiated from other tissues throughout the gastrointestinal tract when CT is combined with intraluminal contrast; this information may prevent unnecessary laparotomy. The efficacy of ultrasound is limited by the presence of bowel gas, while the accuracy of magnetic resonance imaging is reduced by poor resolution due to respiratory movements and peristalsis.

The intestinal wall is composed of mucosa, submucosa, muscularis and serosa; the autonomic nerve supply is found chiefly in the submucosal and muscular layers. The proximal duodenum is distinguished by the presence of Brunner's glands while the ileum has a relative abundance of lymphoid follicles. The mucosa contains villi and crypts. Villi are lined by columnar cells, which are absorptive in nature, and mucus-secreting goblet cells. Each villus has a central stroma containing blood and lymphatic vessels. Crypts are lined by undifferentiated cells, which develop as they grow on to the villus, by enteroendocrine cells, which secrete a variety of biologically active peptides, and by occasional Paneth cells.

Classification of small bowel tumours is not straightforward. The distinction between hamartomas and true neoplasms is often unclear, and the malignant nature of some lesions is controversial. For our purposes, lesions will be discussed under three main headings: benign neoplasms, intermediate neoplasms, and hamartomatous lesions (Table 1) 320. Frankly malignant tumours are discussed elsewhere. Intermediate neoplasms are lesions that have a definite malignant potential but can be difficult to classify histopathologically. The clearest example is an endocrine tumour (jejunoileal carcinoid or duodenal gastrinoma). Villous adenoma and smooth muscle tumours may also be difficult to classify as clearly benign or malignant, but are considered to be ‘benign’ in this classification. For completeness, heterotopic tissues and duplications within the small bowel will be briefly considered (Table 1) 320.

The low prevalence of these lesions has already been stressed. Among benign tumours, leiomyomas, lipomas, adenomas, and haemangiomas are relatively common, while others are rare.

These lesions are generally polypoid, whereas most villous (papillary) adenomas are sessile. Tubular adenomas are relatively common in the duodenum and much less so in the distal small bowel. They are usually single but may be multiple. The symptoms that they cause include abdominal pain and varying degrees of obstruction or haemorrhage, depending on the position and size of the polyp. A lesion near the major pancreatic papilla may cause obstructive jaundice.

There are numerous reports of malignant change occurring in these neoplasms, a situation that is thought to reflect the adenoma–carcinoma sequence in the colon. The incidence of malignant change increases with the size, site, and number of lesions as well as with histological type. In one series the mean diameter of benign polyps was 2.65 cm, compared with 3.7 cm for those containing both benign and malignant elements. The average diameter of jejunal carcinomas was 4.3 cm and of ileal carcinomas 4.7 cm. Malignant change is more likely to occur in periampullary lesions than elsewhere in the duodenum or jejunoileum. Villous adenomas are more likely to undergo malignant change than are tubular adenomas, and multicentricity increases this risk.

Adenomas should be removed, in view of their premalignant potential. Histological examination of the whole specimen will then allow an accurate assessment of actual or potential malignancy. The best treatment for jejunal and ileal polyps is unclear: some clinicians believe that local enterotomy with excision of the lesion is adequate, but others favour segmental resection. Duodenal polyps less than 2 cm in diameter may be removed endoscopically in one piece (Fig. 2) 992. Formal laparotomy and duodenotomy are required for adequate excision of larger lesions. The adenomas of familial polyposis are considered below.

Although these interesting lesions are rare, they have been identified in the duodenum with increasing frequency during recent years. The distinction between tubular and villous adenomas is not always clear cut: some adenomas have both tubular and villous elements (‘tubulovillous adenoma’), as occurs in the large bowel. The mean age at presentation of a villous adenoma is 60 years, and there is no sex preponderance. Common symptoms include obstructive jaundice, obstruction, and occult bleeding. Most lesions arise within the second part of the duodenum, and the mean diameter is approximately 4 cm.

The crucial feature of these tumours is their strong propensity for malignant change, which mimics their behaviour in the colon and rectum (Fig. 3) 993,994. Carcinoma has been reported in 35 to 63 per cent of lesions, and size is a poor predictor of malignant transformation. Tumours in the proximal duodenum can be identified by endoscopy, but hypotonic duodenography or other contrast studies are usually necessary to demonstrate distal lesions.

Proper management of these tumours requires accurate detection and assessment of any malignant change; unfortunately, this is often not possible before excision. Distant metastases obviously indicate malignancy, but endoscopic biopsy can give false negative results in 25 to 56 per cent of patients with localized lesions, probably because of the large size of the lesion and hence the sampling error. Computerized tomography may indicate invasion into surrounding tissues. In many instances, however, definitive diagnosis can only be obtained after removal of the whole lesion and histological examination.

At laparotomy, distant metastases must be excluded, and the duodenum should then be assessed; if there is obvious infiltration or induration a diagnosis of malignancy is likely. Frozen section biopsy at this stage may indicate malignant change, in which case radical resection should be entertained in the form of a pancreatoduodenectomy. If the diagnosis is still unclear a duodenotomy can be performed and submucous resection undertaken. If the lesion lies close to the ampulla, local excision of the ampulla with reimplantation of the ducts or sphincteroplasty has been described. If peroperative (or subsequent) histological analysis demonstrates malignant change, a more extensive resection can be considered. There is a local recurrence rate of 28 per cent after submucous resection; as a consequence it has been argued that radical resection of all villous tumours should be undertaken in fit subjects.

Snare endoscopic removal can be undertaken in patients unfit for major surgery. However, this technically difficult procedure often leads to piecemeal resection and incomplete retrieval of the tumour. Endoscopic laser ablation has also been used successfully. Damage to the ampulla from either of these therapies can be avoided with an endoscopic stent. Lesions distal to the ampulla can be removed by segmental resection of bowel.

The follow-up of these patients should be determined by the final histology and the extent of resection. For locally excised lesions regular endoscopy is mandatory.

Familial polyposis coli is an autosomal dominant disease characterized by the presence of multiple adenomatous polyps in the colon and rectum. Patients with Gardner's syndrome have additional extracolonic manifestations; these are currently considered to be different expressions of the same disease due to variable penetration of the abnormal genes.

It is now clear that polyposis coli is not confined to the colon: in the last 20 years gastroduodenal polyps have been described, and the term familial adenomatous polyposis is often preferred. Most gastric polyps are hyperplastic and will not be considered further, except to state that we have recently encountered one patient with this condition who developed metachronous carcinomas of the stomach and duodenum.

Adenomatous polyps have been reported in the duodenum of 24 to 93 per cent of patients with familial adenomatous polyposis. These lesions, which are usually multiple and occur mainly in the second part of the duodenum, share the affinity of sporadic solitary adenomas for the periampullary region. The consensus of opinion is that these polyps are premalignant: there have been many reports of periampullary carcinoma developing. Indeed, this malignancy is the most common extracolonic carcinoma in familial adenomatous polyposis, occurring in 2 to 12 per cent of patients. In those with abdominal colectomy it may actually be more common than carcinoma of the rectum.

The natural history of these polyps is unclear. A recent report indicated no progression of duodenal lesions in 14 of 17 patients over an average observation period of 7.1 years. It is interesting that in one further patient a 1.7-cm polyp in the duodenal cap was overlooked and 22 months later a carcinoma was present.

All patients with familial adenomatous polyposis require upper gastrointestinal endoscopy at some stage. Hypotonic duodenography and an intubated small bowel meal may be needed for further delineation of duodenal or jejunoileal disease. Biopsy specimens should be taken from the periampullary region to detect microscopic lesions in ‘normal’ mucosa. Tumours less than 0.5 cm in diameter may either be observed or destroyed endoscopically, but larger lesions should be removed. Regular surveillance is indicated.

Jejunoileal polyps have also been reported. Although there are few data regarding their natural history, the risk of carcinoma appears low. Excision must still be considered, especially when the chance of malignant change is increased, as it is in the tubulovillous or villous types of adenoma.

These rare lesions are confined to the duodenum and three forms have been described: polypoid and isolated or diffuse nodular hyperplasia. Adenomas usually arise proximal to the papilla and are less than 1 cm in diameter (although there is one report of a lesion 12 cm in diameter). Many small lesions will be asymptomatic, but larger ones can present with non-specific upper abdominal gastrointestinal symptoms, occult or major haemorrhage, or obstruction. There is one report of duodenal malignancy originating from Brunner's glands. Treatment is removal, either by endoscopy (for small lesions) or surgery (for larger lesions). Concomitant microcarcinoids were recently reported in one resection specimen.

Circumscribed nodular hyperplasia is characterized by sessile projections in the duodenal cap, whilst in the diffuse form the lesions are found throughout the duodenum. Although the underlying reasons are unclear, the incidence seems to be higher in patients with chronic renal failure. Presentation is often incidental, as the condition is usually asymptomatic; vague discomfort, haemorrhage, or obstruction can occur. Diagnosis requires endoscopy or a barium meal, which demonstrates a cobblestone mucosal appearance. Provided a confident diagnosis can be made, no treatment is usually necessary.

These lesions become apparent in the sixth and seventh decade and are usually pedunculated, intraluminal lesions, although some are submucosal. They vary from 0.5 to 8 cm in diameter. Some reports indicate that lipomas are more common in the ileum than in the duodenum or jejunum.

Most lipomas are small and asymptomatic, but once they exceed 4 cm in diameter symptoms such as intussusception or (rarely) bleeding from surface ulceration can develop. Even lipomas less than 1 cm in diameter can cause serious haemorrhage.

Lipomas almost certainly have no malignant potential, although a solitary case of liposarcoma of the ileum has been described. Symptomatic lesions should be removed either endoscopically or surgically, and there is also a case for removing asymptomatic duodenal lipomas because of their potential for causing obstruction, obstructive jaundice, and haemorrhage.

Leiomyomas are common small bowel neoplasms which usually present in the fifth or sixth decade and probably have an equal sex distribution. Macroscopically they appear either as extraluminal, intramural, dumb-bell lesions or as intraluminal lesions; most are extraluminal (Fig. 4) 995. They occur throughout the small bowel, but predominantly in the jejunum and ileum.

Intraluminal lesions usually present with haemorrhage secondary to mucosal ulceration (Fig. 5) 996, but obstruction can arise from intussusception or due to a mass effect. Extraluminal lesions can become enormous and undergo central necrosis with a risk of haemorrhage; these tumours may be palpable. Unusual presentations include volvulus, perforation, and fistula formation.

Leiomyomas are vascular and may be demonstrated by angiography. Extramural lesions can also be detected by CT scan, whereas intraluminal forms are more likely to be visible on contrast studies, when they appear as lesions with a central crater. Leiomyomas have a definite malignant potential, and histological distinction between benign and malignant forms can be difficult: although the frequency of mitoses can be a distinguishing feature it is not pathognomonic. For this reason, leiomyomas should be resected with a clear margin of tissue (Fig. 6) 997.

Neurofibromas, schwannomas, gangliocytic paragangliomas, paragangliomas, and ganglioneuromas are included in this category. All are derived from nervous tissue, either the nerve sheath, paraganglia, or ganglia.

Neurofibromas are the most common subtype. Most of them are not associated with other diseases, but 11 to 25 per cent of patients with von Recklinghausen's disease develop lesions in the gastrointestinal tract. Isolated neurofibromas tend to occur in the ileum, whereas in neurofibromatosis the jejunum and stomach are preferentially involved, followed by the ileum and duodenum. Lesions are usually subserosal, but they can be intramural or intraluminal. Ulceration leading to bleeding is the usual presentation, but bowel obstruction can occur. Schwannomas may present in a similar manner. Some 15 to 20 per cent of neurofibromas are reported to be malignant, and treatment is by excision of the affected bowel.

Gangliocytic paragangliomas are rare. Lesions are polypoid, appearing predominantly in the second part of the duodenum but sometimes in the distal duodenum or jejunum (Fig. 7) 998,999. In a review of 39 cases the mean age of presentation was 52 years; symptoms included haemorrhage (62 per cent) and abdominal pain (21 per cent), but a few tumours were asymptomatic (13 per cent). Paragangliomas and ganglioneuromas are rare.

These rare lesions develop within the wall of the small bowel and are usually asymptomatic, although they may present with intussusception and obstruction. The histological diagnosis can be confused with inflammatory lesions or with smooth muscle tumours or neurogenic tumours.

Three forms are recognized: capillary haemangiomas, cavernous haemangiomas, and multiple telangiectasia. Simple capillary lesions can be single or multiple (Fig. 8) 1000,1001, while cavernous haemangiomas are usually single. Most appear as a polypoid mass (Fig. 9) 1002, but a diffuse infiltrating form has also been described. Symptoms include haemorrhage or, more rarely, obstruction. In patients with multiple telangiectasia numerous lesions 1 to 5 mm in diameter are evident in the bowel: a hereditary form of this condition is Osler–Weber–Rendu disease. Occasionally these lesions are part of a generalized haemangiomatosis. Malignant change is extremely rare in haemangiomas, and it is important not to confuse multiple lesions with metastases.

Investigation includes radiological contrast studies, which may demonstrate either polypoid or stenosing lesions. Selective mesenteric angiography can identify abnormalities, but the technique is more likely to be productive when bleeding is active. If operation is required, transillumination of the bowel may demonstrate small lesions, but the technique can be difficult when there is blood in the lumen. Intraoperative endoscopy may also be helpful. Symptomatic neoplasms should be treated by simple excision. If multiple abnormalities are present, only bowel associated with the lesion should be excised so as to conserve intestine.

There are also vascular abnormalities of the small bowel which, although not true neoplasms, should be considered in the differential diagnosis of gastrointestinal bleeding. Differences of opinion exist regarding their nomenclature: arteriovenous malformation, angiodysplasia, vascular malformation, and ectasia have all been used to describe these vascular abnormalities. Intestinal lesions have been classified into three groups: Group 1 comprises solitary lesions in the right colon, usually occurring in patients over 55; Group 2 contains lesions in the small bowel in younger patients, thought to be congenital; and Group 3 comprises patients in whom multifocal lesions exist, as in hereditary haemorrhagic telangiectasia. An alternative classification includes congenital arteriovenous malformations, which can present at any age, or idiopathic angiodysplasia, which is acquired in later years.

Although the overall prevalence of these lesions is low, they are a common cause of obscure gastrointestinal bleeding. They arise within the submucosa, and erosion through the mucosa is required to produce detectable haemorrhage. They occur predominantly in the right colon, but can also be found in the jejunum and ileum, stomach, and duodenum in decreasing frequency.

The preoperative investigation of choice is selective mesenteric angiography, which may even demonstrate lesions that are not bleeding at the time. Radiological features include localized vascular tufts and opacification of early draining veins. In patients with active bleeding, an indication of the part of the bowel that is responsible can be obtained by isotope scanning with labelled red blood cells. Identification of these lesions at laparotomy may require endoscopy or peroperative radiographic localization.

A resection specimen of bowel thought to include the lesion may not contain any histological abnormality. If at all possible localization should be attempted by injecting the specimen with a barium gelatin mixture or latex material.

These occasional lesions include lymphangiomas, lymphatic cysts, and lymphangiectasia. Lymphangiomas are composed of multiple lymphatic channels and appear as smooth round lesions protruding into the lumen of the bowel. Lymphatic cysts can be recognized as small yellow nodules on the mucosal or serosal surface (Fig. 10) 1003. Both lymphangiomas and lymphatic cysts are benign and rarely cause symptoms. Treatment is by simple excision.

Primary lymphangiectasia is probably a congenital disease in which the lymph vessels of the bowel are abnormally dilated. Patients present with hypoproteinaemia and protein-losing enteropathy, and a low serum albumin. Secondary lymphangiectasia is thought to be an acquired form of the condition and is associated with diseases such as lymphoma, carcinoma, and sarcoidosis.

Knowledge of these lesions is developing at a rapid pace and a full discussion of endocrine tumours is beyond the scope of this text: relevant features only have been summarized.

Carcinoid tumours develop from neural crest cell lines and are included in the APUDoma group of lesions (APUD = amine precursor uptake and decarboxylation). In the bowel they may be classified in accordance with their derivation from the foregut (including the duodenum), midgut (including the jejunoileum), and hindgut. The foregut and midgut lesions can be identified microscopically by staining with ammoniacal silver nitrate (argentaffin). Midgut carcinoids are argentaffin positive: high levels of 5-hydroxytryptamine (serotonin) are secreted. By contrast, foregut carcinoids are argentaffin negative and secrete low levels of serotonin. These lesions may also secrete a variety of peptides including gastrin, somatostatin, and glucagon.

The appendix is the most common site of carcinoid tumour, followed by the ileum, jejunum, rectum, and duodenum. Most ileal lesions are found distally, while the more unusual duodenal carcinoids are concentrated proximally in the first and second part of the duodenum. Rare associations between duodenal carcinoid tumours (often somatostatinomas) and neurofibromatosis, alone or in combination with phaeochromocytoma, have been reported. Twenty to 30 per cent of carcinoids are multicentric.

Lesions typically appear as submucosal nodules which grow slowly towards either the mucosa or the serosa; they may become polypoid in appearance, and ulceration can occur. Serosal lesions in the jejunum and ileum are associated with fibrosis and subsequent stenosis, owing to local vasoconstrictor peptides secreted by the tumour (Fig. 11) 1004. This phenomenon may cause obstruction.

Clinical presentation is usually during the fifth decade and both sexes are affected equally. Some 70 to 80 per cent of jejunal and ileal tumours are asymptomatic, and symptoms that do occur are often non-specific. However, episodes of obstruction can result from intussusception or kinking of the bowel due to local fibrosis, and bleeding is a rare presenting feature.

Carcinoid syndrome is not a feature of local, non-metastasizing lesions in the gastrointestinal tract, since 5-hydroxytryptamine is metabolized in the liver. The syndrome may be evident if carcinoids drain directly into the systemic circulation, for example if the primary lesions are in the bronchus or ovary, or if liver metastases are present.

Eighty per cent of duodenal lesions cause symptoms due to ulceration, obstruction, and jaundice; their presence may also be heralded by the effects of vasoactive secretions, including gastrin, somatostatin, and glucagon.

Some authorities believe that carcinoid tumours are benign with a malignant potential, while others consider that they are all malignant. Once the primary tumour exceeds 2 cm in diameter, there is an 80 to 90 per cent chance of metastases developing; thus size is the dominant factor determining malignant change.

Although wide excision is preferable for carcinoids in view of the malignant potential, treatment depends on the site of the lesion. A full laparotomy is always necessary to exclude the presence of multicentric lesions. Lesions in the jejunum and ileum can be managed by wide local excision, including the draining mesenteric lymph nodes. Treatment of terminal ileal tumours may require a right hemicolectomy. An intense vasospastic reaction can be provoked by handling larger carcinoids during surgery. Small duodenal neoplasms may be dealt with by local excision, but pancreatoduodenectomy is indicated for large tumours. Small duodenal lesions have been treated conservatively in patients with a high operative risk.

Duodenal gastrinomas are present in 13 to 38 per cent of patients in whom the tumour is located. These tumours may be small (2 mm diameter) and only detectable by duodenotomy and eversion of the mucosa to allow adequate visualization and palpation. Forty to 60 per cent are not associated with lymph node metastases and consequently have a good prognosis.

A hamartoma is best defined as ‘an excessive focal overgrowth of mature normal cells and tissues in an organ composed of identical cellular elements’. As previously indicated, histopathologists disagree over the classification of many enteric lesions. Among those already discussed in the preceding sections, Brunner's gland adenoma, neurofibroma, gangliocytic paraganglioma, haemangioma, and lymphangioma have all been described as hamartomas. Several lesions are generally accepted as hamartomas and these will now be described.

This is the most common syndrome affecting the small intestine and is inherited in an autosomal dominant fashion. Multiple polyps, either pedunculated or sessile, can occur throughout the intestinal tract, but the small bowel is mainly affected: usually the jejunum, but sometimes the ileum or duodenum. Polyps are usually 0.5 to 1 cm in diameter but may be larger. Groups of polyps can appear in different areas sequentially. The disease is associated with mucocutaneous pigmentation, notably on the face, lips, buccal mucosa, palms, and soles.

Most patients present within the first three decades of life. The two main features are obstruction and haemorrhage: recurrent episodes of colic are commonly due to intussusception, and haemorrhage can lead to anaemia. Malignancy may occur in 2 to 3 per cent of patients and is most common in the duodenum. In the colon malignant change may be due wholly, or in part, to carcinoma developing in coexistent adenomatous polyps, but this has not been reported in the small bowel.

Treatment should generally be conservative. If surgery is required for complications, local resection is sensible as repeated procedures may be needed in the future.

These are rare conditions. Juvenile polyposis syndromes have been reported to affect both the small and the large bowel. Malignant change has not been reported in juvenile polyps of the small bowel in these conditions.

The Cronkhite–Canada syndrome is characterized by polyposis throughout the gastrointestinal tract, causing diarrhoea and steatorrhoea. Associated ectodermal changes include alopecia, nail dystrophy, and skin hyperpigmentation.

Tissue identified in a site at which it is not usually present is referred to as heterotopic. In the small bowel this abnormality may be either localized or disseminated.

Gastric mucosa can appear in the duodenum or in developmental abnormalities of the small bowel, such as Meckel's diverticulum or duplications. Gastric heterotopia in the duodenum seems to be of little clinical significance: it is detected endoscopically only if the lesion appears as a polyp (which can occasionally cause symptoms) or a prominent fold, but both these are rare. Gastric (oxyntic) mucosa in a Meckel's diverticulum may be associated with a peptic ulcer which can bleed or perforate. Treatment is by Meckelian diverticulectomy. Since technetium is taken up by oxyntic mucosa, scintigraphy may localize the source of haemorrhage.

Heterotopic pancreatic tissue can occur in the duodenum and upper jejunum or in a Meckel's diverticulum (Fig. 12) 1005,1006. The appearances are usually of a nodule within the submucosa or muscularis, although polypoid forms have been reported. Most of these ectopic masses are asymptomatic. Small lesions at the ampulla can cause biliary obstruction, mimicking periampullary cancer, and large lesions can produce obstruction or haemorrhage from mucosal ulceration. Symptomatic lesions should be locally removed, as should incidental lesions discovered at laparotomy if the surgeon is in diagnostic doubt. Combinations of heterotopic tissues are rare, but gastric mucosa and pancreatic tissue have been observed both in the duodenum as a submucosal mass and in Meckel's diverticulum.

Endometriosis can affect the small bowel, albeit rarely. In a review of over 7000 cases, only 12 per cent involved the gastrointestinal tract, of which 72 per cent affected the sigmoid colon and rectum; small bowel was affected in only 7 per cent. In the small bowel the ileum is most often affected.

Diagnosis is difficult. It may be suggested by symptoms indicating varying degrees of obstruction, including nausea, vomiting, colic, and diarrhoea, which are more prominent on a cyclical basis, in line with menstruation. It must be remembered however that patients with endometriosis may develop obstructive symptoms due to adhesions secondary to the disease itself. Most cases of small bowel endometriosis will be diagnosed at laparoscopy or laparotomy as an incidental finding, rather than as a cause of small bowel symptoms.

If symptomatic, the affected segment of bowel should be resected. If asymptomatic lesions are present and malignancy can be excluded, current developments in the management of the endometriosis, including endocrine therapy or laser ablation, may preclude the necessity for bowel resection.

Half of these rare intestinal lesions affect the jejunum or ileum. They appear within the mesentery of the bowel in two main forms: cystic with no communication with the lumen of the bowel, or tubular, connected with the bowel lumen either proximally or distally. The lumen of the duplication is lined with intestinal epithelium plus part or all of the normal muscle components. Gastric heterotopia occurs in 15 to 36 per cent of cases.

Up to 85 per cent of patients present in infancy (before 2 years), but symptoms can occur in later years. The presentation is usually with an abdominal mass or obstruction, and rarely by ulceration of heterotopic gastric mucosa or adjacent small bowel mucosa, causing bleeding or perforation.

Treatment is by excision of the affected segment of bowel. The lesion cannot usually be removed from adjacent bowel, owing to the common blood supply. If the duplication is extensive, surgical options include opening both ends of the lesion into the bowel, coring out mucosa through multiple incisions or attempts at local removal, which may be facilitated in the rare event of a separate mesentery.

Ashley SW, Wells SA, Jr. Tumors of the small intestine. Semin Oncol 1988; 15: 116–28.

Chappuis CW, Divincenti FC, Cohn I Jr. Villous tumors of the duodenum. Ann Surg 1989; 209: 593–9.

Dial P, Cohn I Jr. Tumors of the jejunum and ileum. In: Scott HW Jr, Sawyers JL, eds. Surgery of the stomach, duodenum and small intestine. Boston: Blackwell Scientific Publications, 1987: 937–51.

Feldman JM. Carcinoid tumors and syndrome. Semin Oncol 1987; 14: 237–46.

Frimberger E, Hagenmuller F, Classen M. Endostomy: a new approach to small-bowel endoscopy. Endoscopy 1989; 21: 86–8.

Herbsman H, et al. Tumors of the small intestine. Curr Probl Surg 1980; 17: 127–82.

Kaplan EL, et al. Gastrinomas: a 42-year experience. World J Surg1990; 14: 365–76.

Lewis BS, Waye JD. Chronic gastrointestinal bleeding of obscure origin: role of small bowel enteroscopy. Gastroenterology 1988; 94: 1117–20.

Monk JE, Smith BA, O'Leary JP. Arteriovenous malformations of the small intestine. South Med J 1989; 82: 18–22.

Morson BC, Dawson IMP, Day DW, Jass JR, Price AB, Williams GT. Benign epithelial tumours and polyps. In L Morson BC, Dawson IMP, eds., Morson and Dawson's gastrointestinal pathology. 3rd edn. Oxford: Blackwell Scientific Publications 1990: 351–9.

Morson BC, Dawson IMP, Day DW, Jass JR, Price AB, Williams GT. Malignant epithelial tumours. In: Morson BC, Dawson IMP, eds. Morson and Dawson's gastrointestinal pathology. 3rd edn. Oxford: Blackwell Scientific Publications 1990: 360–71.

Morson BC, Dawson IMP, Day DW, Jass JR, Price AB, Williams GT. Non-epithelial tumours. In: Morson BC, Dawson IMP, eds. Morson and Dawson's gastrointestinal pathology. 3rd edn. Oxford: Blackwell Scientific Publications, 1990: 372–87.

Perey BJ. Neoplasms of the duodenum. In: Scott HW, Jr., Sawyers JL, eds. Surgery of the stomach, duodenum and small intestine. Boston: Blackwell Scientific Publications, 1987: 571–84.

Perzin KH, Bridge MF. Adenomas of the small intestine: a clinicopathologic review of 51 cases and a study of their relationship to carcinoma. Cancer 1981; 48: 799–819.

Sarre RG, Frost AG, Jagelman DG, Petras RE, Sivak MV, McGannon E. Gastric and duodenal polyps in familial adenomatous polyposis: a prospective study of the nature and prevalence of upper gastrointestinal polyps. Gut 1987; 28: 306–14.

Stahl C, Grimes E. M. Endometriosis of the small bowel. Case reports and review of the literature. Obstet Gynecol Surv 1987; 42: 131–5.

Wander JV, Das Gupta TK, Neurofibromatosis. Curr Probl Surg 1977; 14: 1–81.