The small and large intestines

• The small and large intestines
• FUNCTIONAL ABNORMALITIES
• Megacolon and non-megacolon constipation
There is no single definition of constipation; however, a bowel frequency of less than one every 3 days would be considered. 1. Megacolon:
a. Hirschsprung’s disease;
b. non-Hirschsprung’s megarectum and megacolon;
2 non-megacolon:
a. slow transit;
b. normal transit.

Idiopathic megarectum and megacolon
This is a rare condition and the cause is not known, although in some it may result from poor toilet training during infancy and in others from a congenital abnormality of the intestinal myenteric plexus. It presents usually in the first 20 years with severe constipation.
Patients with idiopathic megarectum often present with faecal incontinence due to rectal faecal loading that requires manual evacuation. Patients with megacolon are more likely to present with abdominal distension and pain.
On clinical examination, there may be a hard faecal mass arising out of the pelvis and, on rectal examination, there is a large faecaloma in the lumen. The anus is usually patulous, perianal soiling is common, and sigmoidoscopy is usually impossible but may show melanosis coli if the patient has been taking laxatives over many years.
Investigation
Imaging
As there is an enlarged rectum, often with distension of the colon over a variable length, a radiograph should be taken without prior bowel preparation, using a small quantity of water-soluble contrast to prevent barium impaction. There is usually gross faecal loading of the enlarged rectum and colon and, when a contrast examination is carried out, the width of the colon measured at the pelvic brim is usually more than 6.5 cm.
Anorectal physiology tests demonstrate delayed first sensation and raised maximum tolerated volume.
Full-thickness rectal biopsy shows normal ganglion cells, a finding that definitively distinguishes this condition from Hirschsprung’s disease.


Medical treatment
This is directed at emptying the rectum and keeping it empty with enemas, washouts and sometimes manual evacuation under anaesthesia. Thereafter, the patient is encouraged to develop a regular daily bowel habit, with the use of osmotic laxatives to help the passage of semi formed stool. Rectal evacuation with suppositories and biofeedback therapy may be useful in resistant cases.
Surgical treatment
Surgical treatment is sometimes necessary if medical therapy fails.Options that are available include:
1. Resection of the dilated rectum and colon back to normal diameter colon with normal ganglion cells confirmed by frozen section at the time of surgery, which is followed by reconstruction with a coloanal anastomosis;
2. Colectomy with the formation of an ileorectal anastomosis;
3. Restorative proctocolectomy;
4. Vertical reduction rectoplasty, which is a new procedure designed to reduce the volume of the rectum by at least 50 (Williams);
5. Stoma formation, which may be used either as a salvage operation for failure of previous surgery or as a primary intervention.

Non-megacolon constipation
These are usually otherwise healthy individuals who seek help for constipation but eat a normal diet and have a normal colon on endoscopy and barium enema. Its cause is thought to involve slow whole-gut transit or a rectal evacuation problem.
Factors influencing bowel transit time include:
• Drugs: opiates, anti-cholinergics and ferrous sulphate;
• Diseases: neurological conditions (Parkinson’s disease, multiple sclerosis and diabetic nephropathy);
Hypothyroidism;
Hypercalcaemia.
Investigation
Whole-gut transit time can be measured by asking the patient to stop all laxatives and take a capsule containing radio-opaque markers. Retention of more than 80% of the shapes, 120 hours after ingestion, is abnormal.
Defaecating proctography may be helpful if the main complaint is difficulty in evacuating stools.
Treatment
This can be done in several ways:
1. Dietary fibre. This is the first-line treatment for people with mild constipation.
2. Laxatives. It is important that patients do not fall into a cycle of laxative abuse.
A number of types are available which include bulk, osmotic and stimulant agents.
3. Biofeedback. This involves conditioning and coordination of the abdominal and pelvic compartments.
Idiopathic slow-transit constipation
This disorder is usually seen in women and results from infrequent bowel actions, which may have been present since childhood or may suddenly follow abdominal or pelvic surgery.
This is a difficult condition to treat medically; dietary measures are usually unsuccessful, and surgical treatment is justified only after careful studies and when medical treatment has been exhausted.
Total colectomy and ileorectal anastomosis is the preferred procedure, but the results are unpredictable. Other types of surgery performed include stoma creation and segmental resection, but results are variable.

VASCULAR ANOMALIES (ANGIODYSPLASIA)
Capillary or cavernous haemangiomas are a cause of haemorrhage from the colon at any age.
In the middle-aged or elderly patient, haemangioma needs to be distinguished from other causes of sudden massive haemorrhage, such as diverticulitis, ulcerative colitis (UC) or ischaemic colitis. Angiodysplasia is a vascular malformation associated with ageing. It occurs particularly in the ascending colon and caecum of elderly patients.
The malformations consist of dilated tortuous submucosal veins and, in severe cases, the mucosa is replaced by massive dilated deformed vessels.
Clinical features
In the majority, the symptoms are subtle and patients can present with anaemia. About 10–15% can have brisk bleeds, which may present as melaena or significant per rectum bleeding that is often intermittent. There is an association with aortic stenosis. A mild form of von Willebrand’s disease has been thought to be involved. The coagulation abnormality resolves after aortic valve replacement.
Investigation
Provided that the bleeding is not too brisk, colonoscopy may show the characteristic lesion in the right colon. The lesions are only a few millimetres in size and appear as reddish, raised areas at endoscopy.
Selective superior and inferior mesenteric angiography shows the site and extent of the lesion by a blush.
If this fails, a radioactive test using technetium-99m (99mTc)-labelled red cells may confirm and localise the source of haemorrhage.
Treatment
The first principle is to stabilise an unstable circulation. Following this, the bleeding needs to be localised by colonoscopy. This allows simple therapeutic procedures such as cauterisation to be carried out.
In severe uncontrolled bleeding, surgery becomes necessary. On-table colonoscopy is carried out to confirm the site of bleeding. If it is still not clear exactly which segment of the colon is involved, then a total abdominal colectomy with ileorectal anastomosis may be necessary.

BLIND LOOP SYNDROME
If a blind loop of the small intestine is made, defects of absorption will appear.
If this occurs in the upper intestine, the defect is chiefly of fat absorption; if in the lower intestine, there is vitamin B12 deficiency.Essentially, the stasis produces an abnormal bacterial flora, which prevents proper breakdown of the food (especially fat) and mops up the vitamins that are present.
Temporary improvement will follow the use of antibiotics to destroy the bacteria causing the trouble, but the main treatment is surgical extirpation of the cause of the stasis where applicable.

DIVERTICULAR DISEASE
Diverticula can occur in a wide number of positions in the gut, from the oesophagus to the rectosigmoid. There are two varieties:
1- Congenital. All three coats of the bowel are present in the wall of the diverticulum, e.g. Meckel’s diverticulum.
2- Acquired. The wall of the diverticulum lacks a proper muscular coat. Most alimentary diverticula are thought to be acquired.
Small intestine
Most of these diverticula arise from the mesenteric side of the bowel, probably as the result of mucosal herniation through the point of entry of blood vessels.