megacolon

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megacolon

 [meg″ah-ko´lon]
dilatation and hypertrophy of the colon.
Megacolon. From McKinney et al., 2000
acquired megacolon colonic enlargement associated with chronic constipation, but with normal ganglion cell innervation.
acute megacolon toxic megacolon.
aganglionic megacolon (congenital megacolon) Hirschsprung's disease.
toxic megacolon acute dilatation of the colon associated with amebic dysentery or ulcerative colitis; called also acute megacolon.

meg·a·co·lon

(meg'ă-kō'lon),
A condition of extreme dilation of the colon.
Synonym(s): giant colon

megacolon

/mega·co·lon/ (meg´ah-ko″lon) dilatation and hypertrophy of the colon.
acquired megacolon  colonic enlargement associated with chronic constipation, but with normal ganglion cell innervation.
aganglionic megacolon , congenital megacolon Hirschsprung's disease; that due to congenital lack of myenteric ganglion cells in a segment of the large bowel, with loss of motor function in that segment and massive dilatation of the colon proximally.
idiopathic megacolon  acquired m.
toxic megacolon  that associated with amebic or ulcerative colitis.

megacolon

(mĕg′ə-kō′lən)
n.
Extreme dilation and hypertrophy of the colon.

megacolon

[meg′əkōlən]
Etymology: Gk, megas + kolon, colon
abnormal massive dilation of the colon that may be congenital, toxic, or acquired. Congenital megacolon (Hirschsprung's disease) is caused by the absence of autonomic ganglia in the smooth muscle wall of the colon. Toxic megacolon is a grave complication of ulcerative colitis and may cause perforation of the colon, septicemia, and death. Colonoscopy and surgery are the usual treatments for toxic and congenital megacolon. Acquired megacolon is the result of a chronic refusal to defecate, which usually occurs in children who are psychotic or mentally retarded. The colon becomes dilated by an accumulation of impacted feces. Laxatives, enemas, and psychiatric treatment are often necessary.

megacolon

A massively distended colon with decreased peristaltic activity, due to defective innervation (congenital), intraluminal overgrowth of microorganisms or of psychogenic origin.

Clinical findings
Intestinal obstruction, constipation, vomiting, abdominal distension, poor weight gain, retarded growth.

Management
Temporary colostomy for bowel rest, followed by resection of affected bowel segment.
 
Prognosis
Symptoms eliminated in ± 90% of patients with surgery; outcomes better with early intervention.

Megacolon—Congenital and Acquired
Congenital (Congenital aganglionosis, Hirschsprung’s disease)
A disease affecting 1:5000 live births, with a sibling risk of 1% for girls and 5% for boys; Hirschsprung’s disease (HD) is ten-fold more common in Down syndrome; other anomalies in HD include hydrocephalus, VSD, cryptorchism, diverticulosis of the urinary bladder, renal cysts and agenesis, polyposis coli and Laurence-Moon-Biedl syndrome.
 
Pathology
In affected regions the colon is narrowed and the intramural ganglion cells are absent in both the submucosal (Meissner’s) and myenteric (Auerbach’s plexi).
 
Molecular genetics
Megacolon is associated with mutations in the RET gene.
 
Management
Resection of aganglionic colon.
 
Acquired
A condition related to narcotics or disruption of ganglionic innervation (e.g., idiopathic hypomotility, neuropathies (parkinsonism), multiple sclerosis, myotonic dystrophy, diabetic neuropathy, Chagas’ disease, smooth muscle disorders (amyloidosis and progressive systemic sclerosis) and metabolic disease (hypokalemia)), lead poisoning, porphyria, pheochromocytoma, hypothyroidism. It may be due to intraluminal overgrowth of microorganisms in Crohn’s disease and ulcerative colitis (toxic megacolon), characterised by mucosal necrosis, transmural inflammation and systemic toxicity with high fever, tachycardia, leukocytosis and diarrhoea.

In psychogenic megacolon, no radiologic or pathologic defects are present; it  may be related to a “fixation” in Freud’s anal retentive stage of psychosexual development, with constipation of later onset than in HD, possibly 2º to abuse of anthracine laxatives.

megacolon

A massively distended colon with ↓ activity, due to defective innervation–congenital, intraluminal overgrowth of microorganisms or of psychogenic origin Clinical Intestinal obstruction, constipation, vomiting, abdominal distension, poor weight gain, retarded growth Management Temporary colostomy for bowel rest, followed by resection of affected bowel segment Prognosis Sx eliminated in ± 90% of Pts with surgery; outcomes better with early intervention
Megacolon
Congenital megacolon Congenital aganglionosis, Hirschsprung's disease A disease affecting 1:5000 live births, with a sibling risk of 1% for girls and 5% for boys; Hirschsprung's disease–HD is ten-fold more common in Down syndrome; other anomalies in HD include hydrocephalus, VSD, cryptorchism, diverticulosis of the urinary bladder, renal cysts and agenesis, polyposis coli, Laurence-Moon-Biedl syndrome Treatment Resection of aganglionic colon
Acquired megacolon A condition related to narcotics or disruption of ganglionic innervation–eg idiopathic hypomotility, neuropathies–parkinsonism, multiple sclerosis, myotonic dystrophy, diabetic neuropathy, Chagas' disease, smooth muscle disorders–amyloidosis and progressive systemic sclerosis and metabolic disease–hypokalemia, lead poisoning, porphyria, pheochromocytoma, hypothyroidism and may be due to intraluminal overgrowth of microorganisms in Crohn's disease and ulcerative colitis–toxic megacolon–characterized by mucosal necrosis, transmural inflammation and systemic 'toxicity' associated with high fever, tachycardia, leukocytosis and diarrhea; in psychogenic megacolon, no radiologic or pathologic defects are present–the condition may be related to a 'fixation' in Freud's anal retentive stage of psychosexual development, with constipation of later onset than in HD, possibly 2º to abuse of anthracine laxatives  

meg·a·co·lon

(meg'ă-kō-lŏn)
A condition of extreme dilation and hypertrophy of the colon.

megacolon

Enlargement (hypertrophy) and widening (dilation) of part or all of the COLON associated with severe and intractable CONSTIPATION. Megacolon may be CONGENITAL or acquired. Congenital megacolon is an AUTOSOMAL RECESSIVE condition caused by the local absence of the nerves responsible for PERISTALSIS.

Megacolon

Dilation of the colon.

meg·a·co·lon

(meg'ă-kō-lŏn)
Condition involving extreme dilation of the colon.

megacolon

(meg´əkō´lən),
n an abnormal dilation of the colon that may be congenital, toxic, or acquired.
megacolon, acquired,
n a result of a chronic refusal to defecate, usually occurring in children who are psychotic or mentally retarded.
megacolon, congenital,
n caused by the absence of autonomic ganglia in the smooth muscle wall of the colon.
megacolon, toxic,
n a serious complication of ulcerative colitis that may result in perforation of the colon, septicemia, and death.

megacolon

dilatation and hypertrophy of the colon.

acquired megacolon
colonic enlargement associated with chronic constipation, but with normal ganglion cell innervation. Most common in dogs and cats, the usual causes are dietary factors, lack of exercise, prostatic enlargement, anal disease and neurological deficits.
aganglionic megacolon
due to congenital absence of myenteric ganglion cells and abnormal motor activity in a distal segment of the large bowel. There is continuous spasm in the aganglionic segment that causes a stenosis, and a massive distention of the normal proximal colon develops secondarily. The disease in humans is called Hirschsprung's disease and a similar, but not identical, condition occurs in piebald mice and Overo horses. Congenital megacolon may occur in dogs and cats, but acquired disease is much more common. Called also congenital megacolon.
congenital megacolon
see aganglionic megacolon (above).
idiopathic megacolon
recurrent episodes of constipation in aging cats over a long period of time is believed to lead to the progressive development of a dilated colon.
Enlarge picture
Barium enema in an aged cat with idiopathic megacolon. By permission from Ettinger SJ, Feldman E, Textbook of Veterinary Internal Medicine, Saunders, 2004
inherited megacolon
is presumed in fattening pigs in which there is abdominal distention and wasting without rectal stricture.
psychogenic megacolon
seen in cats and dogs that will not defecate indoors. Prolonged fecal retention causes loss of the defecation reflex, especially in aged patients.