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
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.