Tumours of the large intestine

Benign

The term ‘polyp’ is a clinical description of any elevated tumour. It covers a variety of histologically different tumours shown in Table 57.2.

Polyps can occur either singly, synchronously in small numbers or as part of a polyposis syndrome. In familial adenomatous polyposis, more than 100 adenomas are present. It is important to be sure of the histological diagnosis because adenomas have significant malignant potential.

Adenomatous polyps

Adenomatous polyps vary from a tubular adenoma (Fig. 57.39), rather like a raspberry on a stalk, to the villous adenoma, a flat spreading lesion. Solitary adenomas are usually found during the investigation of colonic bleeding or sometimes fortuitously. Villous tumours more usually give symptoms of diarrhoea, mucus discharge and occasionally hypokalaemia. The risk of malignancy developing in an adenoma increases with increasing size of tumour, for example, in 1-cm diameter tubular adenomas there is a 10 per cent risk of cancer, whereas in villous adenomas over 2 cm in diameter there may be a 15 per cent chance of carcinoma. Adenomas larger than 5 mm in diameter are usually treated because of their malignant potential. Colonoscopic snare polypectomy or diathermy obliteration with hot biopsy forceps can be used. Huge villous adenomas of the rectum can be difficult to remove even with techniques per anus and occasionally proctectomy is required; the anal sphincter can usually be preserved.

Hamartomatous polyps

Peutz—Jeghers polyps may occur in the colon as either solitary or multiple lesions. Juvenile polyps may occur as multiple lesions in the colon often associated with a congenital defect such as a malrotation or Meckels’ diverticulum. They have minimal malignant potential and ate only removed if they are causing troublesome pain, bleeding or hypoproteinaemia.

Haemangioma

A localised submucous telangiectasis is often the cause of bleeding which may be profuse. If bleeding is continuing, both angiography and colonoscopy can help to localise the source. If found by colonoscopy the lesion can be removed endoscopically, whereas arteriographic detection can be followed by the use of vasopressin or microspheres to stop the haemorrhage. Often the only method of detecting it is to operate while the bleeding is in progress. The distribution of blood within the intestine is noted; scrutiny of the blood-containing portion of the colon may reveal the lesion but on-table colonoscopy could be necessary. The tumour is resected once located.

Lipoma

Lipoma is less frequently encountered in the large than in the small intestine. In the large intestine it is almost always confined to the caecum. The tumour is submucous and in more than half the cases it is the cause of an intussusception. On occasion a lipoma at the ileocaecal valve can be confused with a caecal cancer.

Familial adenomatous polyposis

Familial adenomatous polyposis (FAP) is a general neoplastic disorder of the intestine. Although the large bowel is mainly affected polyps can occur in the stomach, duodenum and small intestine. The main risk is large bowel cancer, but duodenal and ampullary tumours have been reported. It is inherited as a Mendelian dominant and the gene responsible (APC gene) has now been identified on the short arm of chromosome 5 (Bodmer). Males and females are equally affected. It can also occur sporadically without any previous sign or history, presumably by new mutations. There is often, in these cases, a history of large bowel cancer occurring in young adulthood or middle age suggesting pre­existing adenomatosis.

FAP can be associated with benign mesodermal tumours such as desmoid tumours and osteomas. Epidermoid cysts can also occur (Gardner’s syndrome); desmoid tumours in the abdomen invade locally to involve the intestinal mesentery and although nonmetastasising they can become unresectable.

Clinical features. Polyps are usually visible on sigmoidoscopy by the age of 15 years and will almost always be visible by the age of 30. Carcinoma of the large bowel occurs 10—20 years after the onset of the polyposis. One or more cancers will already be present in two-thirds of those patients presenting with symptoms.

Symptomatic patients. These are either new proposition or those from an affected family who have not been screened. They may have loose stools, lower abdominal pain, weight loss, diarrhoea and the passage of blood and mucus. Polyps are seen on sigmoidoscopy, and the number and distribution of polyps, and usually cancers if they ate symptomatic, are shown on a double-contrast barium enema. If in doubt colonoscopy is performed with biopsies to establish the number and histological type of polyps. If over 100 adenomas (Fig. 57.40) ate present the diagnosis can be made confidently but it is important not to confuse this with non­neoplastic forms of polyposis.

Asymptomatic patients. Usually members of affected families attend for screening. As yet there is no reliable means of knowing whether an individual is affected unless adenomas develop. If there are no adenomas by the age of 30, FAP is unlikely. Pigmented spots in the retina (CHIRPES) and deoxyribonucleic acid (DNA) tests for the FAP gene should make screening mote reliable in the future.

If the diagnosis is made during adolescence, operation is deferred usually to the age of 17 or 18.

Screening policy.

1.       All members of the family should be examined at the age of 10—12 years, repeated every 1—2 years.

2.       Most of those who are going to get polyps will have them at 20 and these requite operation.

3.       If there are no polyps at 20, continue with 5-yearly examination until age 50; if there are still no polyps there is probably no inherited gene. Carcinomatous change may exceptionally occur before the age of 20. Examination of blood relatives, including cousins, nephews and nieces, is essential and a family tree should be constructed and a register of affected families maintained.

Treatment. Colectomy with ileorectal anastomosis has in the past been the usual operation because it avoids an ileostomy in a young patient. The rectum is subsequently cleared of polyps by snaring or fulguration. The patients ate examined by flexible sigmoidoscopy at 6-monthly intervals thereafter. In spite of this, a proportion of patients develops carcinoma in the rectal stump. The risk of carcinoma in the St Mark’s series was 10 per cent over a period of 30 years.

The alternative and now more common operation is a restorative proctocolectomy with an ileoanal anastomosis. This has a higher complication rate than ileorectal anastomosis. It is indicated in patients with serious rectal involvement with polyps, those who are likely to be poor at attending for follow-up and those with an established cancer of the rectum or sigmoid. However, it is now used mote frequently for less severe cases.

Malignant

Adenocarcinoma of the colon

Pathology. Microscopically, the neoplasm is a columnar cell carcinoma originating in the colonic epithelium. Macro­scopically the tumour may take one of four forms (Fig. 57.41). Type 4 is the least malignant form. It is likely that all carcinomas start as a benign adenoma, the so-called ‘adenoma—carcinoma sequence’. The annular variety tends to give rise to obstructive symptoms whereas the others more commonly will present with bleeding. Site and distribution of cases of cancer are shown in Fig. 57.42. Tumours are more common in the left colon and rectum.

The spread of carcinoma of the colon. Generally this is a comparatively slow growing neoplasm.

Local spread

The tumour is limited to the bowel for a considerable time; it spreads round the intestinal wall and usually causes intestinal obstruction before it invades adjacent structures. The ulcerative type mote commonly invades locally and an internal fistula may result, for example, into the bladder. There may also be a local perforation with an abscess or even an external faecal fistula. The progression of invasion occurs across the submucosa into the musculatis propia and thence out into the serosa and fat, lymphatics and veins in the mesentery alongside the bowel wall.

Lymphatic spread

Lymph nodes draining the colon are grouped as follows:

  N1 — nodes in the immediate vicinity of the bowel wall;

N2 — nodes arranged along the ileo-colic, right colic, midcolic, left colic and sigmoid arteries;

N3 — the apical nodes around the superior and inferior mesenteric vessels where they arise from the abdominal aorta. Involvement of the lymph nodes by the tumour progresses in a gradual manner from those closest to the growth along the course of the lymphatic vessels to those placed centrally.

Bloodstream spread

This accounts for a large proportion (30—40 per cent) of late deaths. Metastases are carried to the liver via the portal system sometimes at an early stage before clinical or operative evidence is detected (occult hepatic metastases).

Staging colon cancer. Dukes’ classification was originally described for rectal tumours (see Chapter 60) but has been adopted for histopathological reporting of colon cancer as well. There have been numerous modifications of the original system leading to some confusion but in its most basic form Dukes’ classification for colon cancer is as follows.

Dukes’

A —   confined to bowel wall;

B —   through the bowel wall but not involving the free peritoneal serosal surface;

C — lymph nodes involved.

Dukes himself never described a D stage, but this is often used to describe either advanced local disease or metastases to the liver.

TNM classification. The TNM classification is more detailed and accurate but more demanding.

T — tumour stage:

  into submucosa;

T2 — into muscularis propria;

into pericolic fat but-not breaching serosa;

   breaches serosa or directly involving another organ.

N — nodal stage:

N0 no nodes involved;

N1 — 1—2 nodes involved;

N2 — 3 or more nodes.

M — metastases:

no metastases;

   metastases.

Ly — lymphatic invasion:

L0 — no lymphatic vessels involved;

   lymphatics involved.

V  — venous invasion:

V0 — no vessel invasion;

Vi — vessels invaded.

R — residual tumour:

R0 — no residual tumour;

   margins involved, residual tumour present.

Clinical features. Carcinoma of the colon usually occurs in patients over 50 years of age but it is not rare earlier in adult life. Twenty per cent of cases present as an emergency with intestinal obstruction or peritonitis. In any case of colonic bleeding in patients over the age of 40 a complete investigation of the colon is required. A careful family history should be taken. Those with first-degree relatives who have developed colorectal cancer at the age of 45 or below are at high risk and may be part of one of the colorectal cancer family syndromes.

Carcinoma of the left side of the colon

Most tumours occur in this location. They ate usually of the stenosing variety. The main symptoms are those of increasing intestinal obstruction.

Pain is referred to the suprapubic area. Patients will have episodes of colic; a constant ache may suggest an advanced tumour.

Alteration of bowel habit. An adult previously having a predictably regular bowel habit suddenly develops irregularity. There may be increasing difficulty in getting the bowels to move, requiring laxatives. The episodes of constipation may be followed by attacks of diarrhoea.

Palpable lump. The lump that is felt on abdominal, rectal or bimanual palpation is sometimes not the tumour itself, but impacted faeces above it. When the tumour is situated in a pendulous pelvic colon, a hard movable swelling may be felt in the rectovesical pouch on rectal examination.

Distension. Lower abdominal distension is not uncommon and, as with the pain, is relieved by passing flatus.

Carcinoma of the sigmoid

This follows the general pattern of the above, with these differences.

Pain is usually colicky from the outset.

Tenesmus. Low tumours may give rise to a feeling of the need for evacuation which may result in tenesmus accompanied by the passage of mucus and blood, especially in the early morning.

Bladder symptoms are not unusual and in some instances may herald a colovesical fistula.

Carcinoma of the transverse colon

This may be mistaken for a carcinoma of the stomach because of the position of the tumour together with anaemia and lassitude.

Carcinoma of the caecum and ascending colon

This may present with the following.

  Anaemia, severe and unyielding to treatment; there may be a palpable tumour present.

  The presence of a mass in the right iliac fossa. Colono­scopy may be needed to confirm the diagnosis.

  Caecal carcinoma is sometimes discovered unexpectedly at operation for acute appendicitis or for an appendix abscess failing to resolve. On rare occasions the appendix is inflamed, or even gangrenous, from the obstruction to its lumen by the tumour.

A carcinoma of the caecum can be the apex of an intussusception presenting with the symptoms of intermittent obstruction.

Metastatic disease

Patients may present for the first time with liver metastases and an enlarged liver, ascitis from carcinomatosis peritonei and, more rarely, rnetastases to the lung, skin, bone and brain.

Methods of investigation

Sigmoidoscopy. This is part of the routine investigation of patients passing blood and mucus that is really limited to the rectum.

Flexible sigmoidoscopy. The 60-cm, fibre-optic, flexible sigmoidoscope is being used increasingly in the out-patient clinic or in special rectal bleeding clinics. The patient is pre­pared with a disposable enema and sedation is not usually necessary.

Colonoscopy. This has the advantage of not only picking up a primary cancer but also having the ability to detect synchronous polyps or even multiple carcinomas which occur in 5 per cent of cases. It tends to be used in patients with bleeding as their main presenting symptom, those with known polyps and those in whom there is doubtful radiology. Ideally every case should be proven histologically before surgery. Full bowel preparation and sedation are necessary.

Radiology. Double-contrast barium enema is used routinely now. It shows a cancer of the colon as a constant irregular filling defect (Fig. 57.43). It is the investigation of choice in patients with predominant change in bowel habit as their presenting symptom. Ultrasonography is often used as a screening investigation for liver metastases, and CT is used in patients with large palpable abdominal masses to determine local invasion and is particularly used in the pelvis in the assessment of rectal cancer.

Treatment

Preoperative preparation. Full mechanical bowel preparation before colonic surgery is essential. The most commonly used method is dietary restriction to fluids only for 48 hours before surgery; on the day before operation two sachets of Picolax (sodium picosulphate) are taken to purge the colon.  In addition a rectal washout may be necessary. Alternatives include prograde lavage via a nasogastric tube using water or balanced electrolyte solutions. A stoma site is carefully discussed with the stoma care nursing specialist and antiembolus stockings are fitted; the patient is started on prophylactic sub­cutaneous heparin and intravenous prophylactic antibiotics are given at the start of surgery.

When intestinal obstruction is present, preparation in this way may precipitate abdominal pain and it may be safer to save preparation to the time of the operation using an on table lavage technique.

Operations

The test of operability. The abdomen is opened and the tumour assessed for resectability.

1.  The liver is palpated for secondary deposits, the presence of which is not necessarily a contraindication to resection because the best palliative treatment for carcinoma of the colon is removal of the tumour.

2. The peritoneum, particularly the pelvic peritoneum, is inspected for signs of small, white, seed-like, neoplastic implantations. Similar changes can occur in the omentum.

3. The various groups of lymph nodes that drain the involved segment are palpated. Their enlargement does not necessarily mean that they are invaded by metastases because the enlargement may be inflammatory.

4.       The neoplasm is examined with a view to mobility and operability. Local fixation, however, does not always imply local invasion because some tumours excite a brisk inflammatory response.

The operations to be described are designed to remove the primary tumour and its draining locoregional lymph nodes which may be involved by metastases. Lesser resections are indicated, however, should hepatic rnetastases render the condition curable nonsurgically. There is some evidence that early division of major blood vessels supplying the involved colon (no-touch technique — Turnbull) can slightly improve the number of curative operations.

Carcinoma of the caecum or ascending colon (Fig. 57.44) is treated when resectable by right hemicolectomy (Fig. 57.45).

The abdomen is opened, the peritoneum lateral to the ascending colon is incised and the incision carried around the hepatic flexure. The right colon is elevated, with the leaf of peritoneum containing its vessels and lymph nodes, from the posterior abdominal wall, taking care not to injure the ureter, spermatic vessels in the male or the duodenum. The peritoneum is separated medially neat the origin of the ileo-colic artery, which is divided together with the right colic artery when this has a separate origin from the superior mesenteric. The mesentery of the last 30 cm of ileum, and the leaf of raised peritoneum attached to the caecum, ascending colon and hepatic flexure, after ligation of the mesenteric blood vessels, is divided as far as the proximal third of the transverse colon. When it is cleat that there is an adequate blood supply at the resection margins, the right colon is resected and an end-to-end anastomosis fashioned between the ileum and transverse colon.

Carcinoma of the hepatic flexure. When the hepatic flexure is involved the resection must be extended correspondingly (Fig. 57.46).  

Carcinoma of the transverse colon. When there is no obstruction, excision of the transverse colon and the two flexures together with the transverse mesocolon and the greater omentum, followed by end-to-end anastomosis, can be used. An alternative is an extended right hemicolectomy (Fig. 57.46). Carcinoma of the splenic flexure or descending colon. The extent of the resection is from right colon to descending colon. Sometimes removal of the colon up to the ileum, with an ileorectal anastomosis, is preferable.

Carcinoma of the pelvic colon. The left half of the colon is mobilised completely (Fig. 57.47). So that the operation is radical, the inferior mesenteric artery below its left colic branch, together with the related paracolic lymph nodes, must be included in the resection. This entails carrying the dissection as far as the upper third of the rectum. Many surgeons advocate flush ligation of the inferior mesenteric artery on the aorta (high litigation). Provided that there is no obstruction primary anastomosis is the rule. Occasionally a protecting upstream stoma may be necessary. The methods of dealing with large bowel obstruction as a result of colon cancer are described in Chapter 58.

When a growth is found to be inoperable. In the upper part of the left colon, a transverse colostomy is performed. In the pelvic colon, a left iliac fossa colostomy is preferable. With an inoperable growth in the ascending colon a bypass using an ileo-colic anastomosis is the best procedure. Over 95 per cent of colonic carcinomas can, however, be resected.

Adjuvant therapy

See Chapter 60.

Hepatic metastases

It is important to biopsy hepatic metastases for histological diagnosis. Unless they are on the very surface and edge of the liver, they are not usually resected at the time of colonic surgery. Patients with up to two or three liver metastases confined to one lobe of the liver may be offered hepatic resection. Multiple painful hepatic metastases can be palliated by cytotoxic drugs, cryosurgery or laser therapy (Fig. 57.48).