Megacolon and nonmegacolon constipation

There is no single definition of constipation that can be described according to the character of the stools, the frequency of evacuation and the ease of evacuation. Generally speaking a bowel frequency of less than one every 3 days would be considered abnormal. This group of conditions can be divided into:

1.  megacolon:

(a)   Hirschsprung’s disease,

(b)  non-Hirschsprung’s megarectum and megacolon; 2. nonmegacolon:

(a)   slow transit,

(b)   normal transit.

Hirschsprung’s disease

Pathology

The major feature of Hirschsprung’s disease is an absence of ganglion cells in the neural plexus of the intestinal wall, together with hyper­trophy of the nerve trunks. This is believed to result from a failure of migration of neuroblasts into the gut from vagal nerve trunks at the end of the first trimester of foetal life.

The loss of ganglion cells extends for a variable distance above the anorectal junction. In about two-thirds of patients the rectum and lower sigmoid colon are involved, but involvement of extremely short segments of the lower rectum or the whole intestinal tract have been described.

The severity of symptoms is not always consistent with the length of the intestinal segment involved and may be related to the number of acetylcholinesterase-positive nerve fibres.

The absence of ganglion cells gives rise to a contracted nonperistaltic segment with a dilated hypertrophied segment of normal colon above it (Fig. 57.2).

Clinical features

Hirschsprung’s disease occurs in approximately one in 4500 live births. It shows a familial tendency and is more common in males than in females. The clinical picture varies from acute intestinal obstruction in neonates to chronic constipation in later life.

1. In neonates the delayed passage of meconium together with mild abdominal distension should alert the paediatrician to the diagnosis of Hirschsprung’s disease. It is often complicated by enterocolitis which may result in perforation and septicaemia, and there is still a high mortality from Hirschsprung’s disease at this age.

2.  Chronic constipation starting in the first few weeks of life. The classic picture of gross abdominal distension, chronic constipation and failure to thrive should be rare with a greater awareness of the diagnosis.

3. Severe constipation without soiling in otherwise healthy children and adults can he caused by a short segment of Hirschsprung’s disease. Faecal soiling is not usually a feature of the condition.

Diagnosis

Rectal biopsy. Confirmation of the diagnosis depends on histological demonstration of aganglionosis and hypertrophic nerve fibres in the nerve plexus. The pathologist has to be able to see a representative area of at least one nerve plexus in the biopsy. In children this can be obtained by a suction rectal biopsy or, in adults, by a formal strip, full-thickness, rectal biopsy. Specimens are usually taken from just above the anorectal junction. One is sent for biochemistry and one for histochemistry and histopathology (Fig. 57.3).

Anorectal manometry. This is a useful screening test in the constipated young child or adult who is otherwise fit. The rectosphincteric inhibitory reflex is absent. It should not be carried out in ill neonates because of poor anal tone.

Radiology. Erect and supine abdominal radiographs are useful. If the large intestine is obstructed, they will show distended loops of small and large intestine with fluid levels consistent with a low intestinal obstruction. Intramural gas will indicate enterocolitis, and free peritoneal gas, a perforation.

An enema using a water-soluble contrast medium will often confirm the diagnosis and indicate the length and site of involved intestine. A rectal examination should not be performed before radiology because it may dilate the abnormal segment and modify the radiological features. The contrast is instilled through a fine 5 Fr catheter under screening control with the patient in the lateral position. The coning down of the transition zone, irregularity in the mucosa and abnormal contractions of the intestine are important positive findings.

Treatment

This depends on the age of the patient, the length of the involved segment, the severity of symptoms and the presence of enterocolitis.

In the neonate presenting with obstruction or any child or adult presenting with enterocolitis, an initial colostomy is performed. The site of the colostomy should be as low as possible in the ganglionated segment. A peroperative frozen section biopsy is taken to establish the presence of ganglia. This is important as the transition zone may be difficult to locate precisely.

In the child or adult with constipation alone, the dilated intestine can be evacuated with repeat rectal saline washouts and enemas as a first step. The choice of surgical procedure to follow will depend on the length of the involved segment.

Short segment disease with minimal symptoms may respond to an extended myectomy removing a strip of rectal wall up to the area where normal ganglion cells start.

Long segment disease may be helped by one of the four operations shown below. The definitive operation is preceded by a temporary colostomy for a few months which allows the proximal distended colon to return to its normal calibre. If a neonate requires a colostomy the definitive operation is delayed until the child weighs approximately 10 kg when the pelvis is still shallow but wide enough to give good access. The child will be between 10 months and 1 year of age and toilet training can usually start soon after the operation.

In some older children it may be possible to clear the retained faeces with enemas and laxatives; if so it may be possible to perform a one-stage operation.

Duhamel operation

The aganglionic segment is removed down to the level of the peritoneal reflection over the rectum. The rectum is divided and dosed. The sacral hollow is opened and the normal colon brought down to the posterior aspect of the rectal stump. With an anal retractor in place a transverse incision is made from the level in the posterior wall just above the anal sphincter. The normal colon is then grasped and sewn to the transverse incision in the rectum. The spur between the rectum and normal colon is then divided with a stapler.

Swenson’s procedure

The rectum is mobilised from above taking care to dissect immediately outside the fascia propia, preserving autonomic nerves to the bladder and seminal vesicles. The intestine is transected proximally through normal colon, the presence of ganglion cells having first been checked for by frozen section biopsy. The mobilised aganglionic segment is then everted out through the anus, the everted rectal mucosa is cleaned, and the anterior half of the junction between the top of the anal canal and the rectum is opened transversely. The proximal normal colon is then pulled through this opening and an end-to-end anastomosis made between the colon and anal canal as the aganglionic segment is excised. Once the anastomosis is complete it is reduced hack into the anal canal.

Colo-anal anastomosis

This is usually reserved for older children, teenagers and adults. The rectum is mobilised as before and transected just above the level of the pelvic floor. The normal colon is then joined to the top of the anal canal either directly with a stapling tecnhique or by a sleeve technique following a mucosectomy of the upper anal canal and rectum, a procedure described by both Soave and Parks.

Restorative proctocolectomy

In cases of Hirichsprung’s disease involving the entire colon, it is possible to reconstruct with an ileoanal pouch procedure (see Chapter 60).

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 by a congenital abnormality of the intestinal myenteric plexus.

Investigation

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.

Radiology. As there is an enlarged rectum often with distention of the colon over a variable length, a radiograph should he 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 (Fig. 57.4).

Anorectal physiology tests show abnormally large volumes inflated in the rectum to induce a feeling of rectal fullness, and inhibition of the internal and external anal sphincters is present but at much larger volumes than normal. Full-thickness rectal biopsy shows normal ganglion cells which 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 laxatives and repeated enemas as necessary.

Surgical treatment

Surgical treatment is necessary sometimes if medical therapy fails. Resection of the dilated rectum and colon (Fig. 57.5) back to normal diameter colon with normal ganglion cells confirmed by frozen section at the time of surgery is followed by reconstruction with a colo-anal anastomosis.

Nonmegacolon constipation

Although constipation is often regarded as a trivial symptom some patients are greatly disabled by abdominal pain, distension, reliance on laxatives and difficulty with defecation. 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.

Investigation

Whole gut transit time can be measured by asking the patient to stop all laxatives and take a capsule containing radio opaque markers (Fig. 57.6). Retention of more than 80 per cent of the shapes, 120 hours after ingestion, is abnormal.

Defecating proctography may be helpful if the main complaint is difficulty in passing stools.

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. They have delayed transit using marker studies and may or may not be able to empty the rectum normally (Fig. 57.6).

This is a difficult condition to treat medically; dietary measures are usually unsuccessful and surgical treatment is only justified after careful studies and when medical treatment has been exhausted. Total colectomy and ileorectal anastomosis is the preferred procedure but the results are unpredictable. One-third of patients continues to have diarrhoea or constipa­tion and two-thirds persisting abdominal pain. It is essential to exclude underlying psychiatric or psychological problems.

Obstructed defecation

Some patients complain of extreme difficulty in expelling stool. They may have repeated attempts at rectal evacuation and their transit is often normal. The common feature in these patients is weakness of the pelvic floor which descends on straining. Patients may resort to digital evacuation or pressure on the perineum or within the vagina to assist defecation. The cause is not known. It may arise from damage to pelvic nerves caused by prolonged straining at stool or childbirth.

Defecation proctography will show abnormal evacuation. There may be an intussusception with the upper rectum folding in to the lower rectum or an anterior rectocele where the rectum bulges forward into the posterior wall of the vagina (Fig. 57.7).

Biofeedback training may be helpful in some patients; dietary therapy and laxatives are usually unsuccessful. Sur­gery is a last resort, and either a defunctioning ileostomy or a colostomy with colostomy irrigation is used in intractable cases.