Megacolon, also known as Hirschsprung's disease, is a congenital condition where part of the colon lacks nerve cells (ganglia), preventing normal contractions. This leads to dilation of the colon above the affected area. It is caused by failed migration of nerve cells during fetal development. The main symptoms are constipation and abdominal distension in infants. Diagnosis involves barium enema, rectal biopsy, and manometry to detect the absence of ganglia and abnormal contractions. The definitive treatment is surgical removal of the aganglionic segment and reconnection of the bowel.

1. MEGACOLON

2. Megacolon is of two types
(1) Congenital megacolon or primary
megacolon (Hirschsprung’s disease.
(2) Secondary or acquired megacolon.

3. PRIMARY MEGACOLON
(HIRSCHSPRUNG’S DISEASE)
Massive dilatation and hypertrophy of the colon
in children

5. Aetiology and Pathogenesis
• It is caused by absence of ganglionic cells of the
pelvic parasympathetic system in both
Auerbach’s plexus between the circular and
longitudinal muscle layers of the colon and
Meissner's plexus in the submucosa.
• It is believed to be the result of failure of
migration of neuroblasts into the gut from nerve
trunks.
• It usually occurs at the end of the first trimestar
of foetal life.

6. Aetiology and Pathogenesis
• Aganglionosis may result if there cessation of
migration of neuroblasts, which migrate from
the primitive node along the alimentary track
distalwise.
• The internal anal sphincter is aganglionic in
every case of Hirschsprung’s disease.
• This aganglionosis extends proximaliy to
variable distance according to the failure of
descent of the neuroblasts.

7. Aetiology and Pathogenesis
• Approximately 80% of cases involve the
rectosigmoid junction and 15% have aganglionic
segment extending as far proximaliy as the
hepatic flexure.
• The former condition is called ‘short segment
aganglionosis’ and the latter condition is called
‘long segment aganglionosis’.
• There are some cases where aganglionosis occurs
in skip areas, these are known as ‘segmental
aganglionosis’.

8. Aetiology and Pathogenesis
• There is absence of peristalsis in the
aganglionic segments thus producing
adynamic intestinal obstruction.
• Lack of peristalsis in the aganglionic segment
and failure of relaxation of the internal anal
sphincter produce varying degrees of
intestinal obstruction found in this disease.

9. PATHOLOGY
• The bowel proximal to the aganglionic
segment becomes gradually dilated and
hypertrophied for a variable length as the
peristaltic waves try to propel stools through
the obstructing aganglionic segment

10. PATHOLOGY
• There is a visible transition zone, usually 1 to 5
cm in length between the dilated bowel which
contains ganglionic cells on the proximal side
and normal sized aganglionic segment of
bowel on the distal side.
• All layers of the dilated intestine show gross
pathological changes.
• The mucous lining is chronically inflamed and
frequently ulcerated.

11. PATHOLOGY
• The pelvic mesocolon is elongated and
thickened and its blood vessels are large and
prominent.
• As in majority of cases the aganglionic
segment stops proximaliy at sigmoid colon,
the grossly dilated portion mostly involves the
upper sigmoid colon and lower descending
colon.

12. Clinical features
• This condition is more common in males and
it shows familial tendency.
• The symptoms appear within 3 days of birth
and the presenting features are as follows :
(i) Constipation
(ii) Abdominal distension

13. Clinical features
(i) Constipation
• The new born child fails to pass meconium
within first 2 or 3 days.
• If the little finger is introduced into the rectum
meconium is passed in inadequate amount
and toothpaste like.

14. Clinical features
(ii) Abdominal distension
This becomes obvious by the 3rd day.
Gradually the distension progressesand the colon
is involved in distension.
Visible peristalsis may be seen with loud
borborygmi.

15. Clinical features
• In some babies the symptoms may suggest
mild gastroenteritis or a feeding problem
associated with mild constipation.
• As the condition becomes more chronic the
baby fails to gain weight, becomes
hypoproteinaemic and suffers from
intermittent episodes of severe constipation
and diarrhoea.

16. Clinical features
• Eventually enterocolitis may develop, a lethal
complication of Hirschsprung’s disease.
• The clinical picture includes fever, vomiting,
watery or bloody diarrhoea, septic shock and
finally death.
• Enterocolitis develops due to invasion of
bacteria from the dilated colon through
erosion and ulceration in the mucosa into the
wall of the colon.
• Immediate vigorous management is indicated

17. Rectal examination
• Reveals that the rectum is empty and the anus
is free from any pathology.

18. Special Investigations
• 1. BARIUM ENEMA EXAMINATION
This should be done in unprepared bowel as
wash-outs may minimise the dilatation of the
gut above the obstruction.
Barium enema should be prepared with
normal saline and not with water, as
magacolon absorbs water much more rapidly
than normal bowel and may result in water
intoxication.

19. MEGA COLON

20. • This examination will demonstrate dilated colon
followed by narrow aganglionic segment.
• The diagnosis becomes difficult if the child has a
very short segment involved or if the entire colon
is aganglionic.
• In infants the proximal non-affected colon may
not become very much dilated, but in these cases
the retention of barium after 24 hours is quite
diagnostic.
• It is always essential that both anteroposterior
and lateral views should be taken as narrow short
segments may be overlapped by dilated proximal
colon in one of the views.

21. HIRSCHSPRUNG’S DISEASE

22. 2. RECTAL BIOPSY
• Will demonstrate absence of ganglionic cells in
the intramural and submucous plexuses.
• Biopsy should be taken at least 2 cm above
the dentate line.
• An attempt should be made to take full
thickness wall for biopsy, as superficial biopsy
cannot confirm presence or absence of
ganglion cells in the intramural plexus.

23. 3. MANOMETRIC STUDIES
• Can be done easily in the older children and
absence of relaxation of the internal anal
sphincter will confirm the diagnosis.

24. Treatment
The main curative treatment of this disease is
excision of the entire aganglionic segment
(the cause of functional obstruction) and
continuity is restored with normal sphincteric
control of the anus.
COLOSTOMY