Megacolon
Encyclopedia
Megacolon is an abnormal dilation of the colon
(a part of the large intestine
s). The dilatation is often accompanied by a paralysis
of the peristaltic
movements of the bowel. In more extreme cases, the feces consolidate into hard masses inside the colon, called fecaloma
s (literally, fecal tumor), which can require surgery
to be removed.
A human colon is considered abnormally enlarged if it has a diameter greater than 12 cm in the cecum
(it is normally less than 9 cm), greater than 6.5 cm in the rectosigmoid
region and greater than 8 cm for the ascending colon. The transverse colon is usually less than 6 cm in diameter.
A megacolon can be either acute or chronic
. It can also be classified according to etiology
.
of very long duration, abdominal bloating
, abdominal tenderness and tympany, abdominal pain
, palpation
of hard fecal masses and, in toxic megacolon, fever
, low blood potassium
, tachycardia
and shock. Stercoral ulcer
s are sometimes observed in chronic megacolon, which may lead to perforation of the intestinal wall in approximately 3% of the cases, leading to sepsis
and risk of death.
, it is a congenital disorder of the colon in which nerve cells of the myenteric or Auerbach's plexus
in its walls, also known as ganglion cells, are absent. It is a rare disorder (1:5 000), with prevalence among males being four times that of females. Hirschsprung’s disease develops in the fetus
during the early stages of pregnancy
. The exact genetic
cause remains unsolved, although in familial cases (in which families have multiple affected patients), it seems to exhibit autosomal dominant transmission, with a gene
called RET, in chromosome
10, being dominant. Seven other genes seem to be implicated, however. If untreated, the patient can develop enterocolitis
.
and pseudomembranous colitis
, two chronic inflammation
s of the colon. Its mechanism is incompletely understood. It is probably due to an excessive production of nitric oxide
, at least in ulcerative colitis. The prevalence is about the same for both sexes.
In Central
and South America
, the most common incidence of chronic megacolon is that observed in ca. 20% of patients affected with Chagas disease
. Chagas is caused by Trypanosoma cruzi
, a flagellate protozoan transmitted by the feces of a hematophagous
insect
, the assassin bug, when it feeds. Chagas can also be acquired congenitally, through blood transfusion
or organ transplant, and rarely through contaminated food (for example garapa
). There are several theories on how megacolon (and also megaesophagus
) develops in Chagas disease. The Austrian
-Brazilian physician
and pathologist Fritz Köberle
was the first to propose a coherent hypothesis based on the documented destruction of the Auerbach's plexus in the walls of the intestinal tracts of Chagas patients, the so-called neurogenic hypothesis. In this, the destruction of the autonomic nervous system
innervation of the colon leads to a loss of the normal smooth muscle
tone of the wall and subsequent gradual dilation. His research proved that, by extensively quantifying the number of neurons of the autonomic nervous system in the Auerbach's plexus, that: 1) they were strongly reduced all over the digestive tract; 2) that megacolon appeared only when there was a reduction of over 80% of the number of neurons 3) these pathologies appeared as a result of the disruption of the neurally integrated control of peristalsis
(muscular annular contraction) in those parts where a strong force is necessary to impel the luminal bolus
of feces
; and 4) Idiopathic megacolon and Chagas megacolon appear to have the same etiology, namely the degeneration of the Auerbach's myoenteric plexus.
Why T. cruzi causes the destruction, however, remains to be elucidated: there are evidences for the presence of specific neurotoxin
s as well as a disordely immune system
reaction.
is achieved mainly by plain and contrasted radiographical
and ultrasound
imaging. Colonic marker transit studies are useful to distinguish colonic inertia from functional outlet obstruction etiologies. In this test, the patient swallows a water soluble bolus of radio-opaque contrast and films are obtained 1, 3 and 5 days later. Patients with colonic inertia show the marker spread throughout the large intestines, while patients with outlet obstruction exhibit slow accumulations of markers in some places. A colonoscopy
can also be used to rule out mechanical obstructive causes. Anorectal manometry
may help to differentiate acquired from congenital forms. Rectal biopsy is recommended to make a final diagnosis of Hirschsprung disease.
There are several surgical approaches to treat megacolon, such as a colectomy
(removal of the entire colon) with ileorectal anastomosis
(ligation of the remaining ileus and rectum segments), or a total proctocolectomy
(removal of colon, sigmoid and rectum) followed by ileostomy
or followed by ileoanal anastomosis.
Colon (anatomy)
The colon is the last part of the digestive system in most vertebrates; it extracts water and salt from solid wastes before they are eliminated from the body, and is the site in which flora-aided fermentation of unabsorbed material occurs. Unlike the small intestine, the colon does not play a...
(a part of the large intestine
Intestine
In human anatomy, the intestine is the segment of the alimentary canal extending from the pyloric sphincter of the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine...
s). The dilatation is often accompanied by a paralysis
Paralysis
Paralysis is loss of muscle function for one or more muscles. Paralysis can be accompanied by a loss of feeling in the affected area if there is sensory damage as well as motor. A study conducted by the Christopher & Dana Reeve Foundation, suggests that about 1 in 50 people have been diagnosed...
of the peristaltic
Peristalsis
Peristalsis is a radially symmetrical contraction and relaxation of muscles which propagates in a wave down the muscular tube, in an anterograde fashion. In humans, peristalsis is found in the contraction of smooth muscles to propel contents through the digestive tract. Earthworms use a similar...
movements of the bowel. In more extreme cases, the feces consolidate into hard masses inside the colon, called fecaloma
Fecaloma
A fecaloma, also called fecalith, fecolith and coprolith, i.e., a "stone" made of feces, is a hardening of feces into lumps of varying size inside the colon, which may appear whenever chronic obstruction of transit occurs, such as in megacolon and chronic constipation...
s (literally, fecal tumor), which can require surgery
Surgery
Surgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, or to help improve bodily function or appearance.An act of performing surgery may be called a surgical...
to be removed.
A human colon is considered abnormally enlarged if it has a diameter greater than 12 cm in the cecum
Cecum
The cecum or caecum is a pouch, connecting the ileum with the ascending colon of the large intestine. It is separated from the ileum by the ileocecal valve or Bauhin's valve, and is considered to be the beginning of the large intestine. It is also separated from the colon by the cecocolic...
(it is normally less than 9 cm), greater than 6.5 cm in the rectosigmoid
Rectum
The rectum is the final straight portion of the large intestine in some mammals, and the gut in others, terminating in the anus. The human rectum is about 12 cm long...
region and greater than 8 cm for the ascending colon. The transverse colon is usually less than 6 cm in diameter.
A megacolon can be either acute or chronic
Chronic (medicine)
A chronic disease is a disease or other human health condition that is persistent or long-lasting in nature. The term chronic is usually applied when the course of the disease lasts for more than three months. Common chronic diseases include asthma, cancer, diabetes and HIV/AIDS.In medicine, the...
. It can also be classified according to etiology
Etiology
Etiology is the study of causation, or origination. The word is derived from the Greek , aitiologia, "giving a reason for" ....
.
Signs and symptoms
External signs and symptoms are constipationConstipation
Constipation refers to bowel movements that are infrequent or hard to pass. Constipation is a common cause of painful defecation...
of very long duration, abdominal bloating
Bloating
Bloating is any abnormal general swelling, or increase in diameter of the abdominal area. As a symptom, the patient feels a full and tight abdomen, which may cause abdominal pain sometimes accompanied by increased borborygmus or more seriously the total lack of borborygmus.-Symptoms:The most common...
, abdominal tenderness and tympany, abdominal pain
Abdominal pain
Abdominal pain can be one of the symptoms associated with transient disorders or serious disease. Making a definitive diagnosis of the cause of abdominal pain can be difficult, because many diseases can result in this symptom. Abdominal pain is a common problem...
, palpation
Palpation
Palpation is used as part of a physical examination in which an object is felt to determine its size, shape, firmness, or location...
of hard fecal masses and, in toxic megacolon, fever
Fever
Fever is a common medical sign characterized by an elevation of temperature above the normal range of due to an increase in the body temperature regulatory set-point. This increase in set-point triggers increased muscle tone and shivering.As a person's temperature increases, there is, in...
, low blood potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
, tachycardia
Tachycardia
Tachycardia comes from the Greek words tachys and kardia . Tachycardia typically refers to a heart rate that exceeds the normal range for a resting heart rate...
and shock. Stercoral ulcer
Stercoral ulcer
Stercoral ulcer is an ulcer of the colon due to pressure and irritation resulting from severe, prolonged constipation. It is most commonly located in the rectum. Individuals with this condition are at risk for stercoral perforation....
s are sometimes observed in chronic megacolon, which may lead to perforation of the intestinal wall in approximately 3% of the cases, leading to sepsis
Sepsis
Sepsis is a potentially deadly medical condition that is characterized by a whole-body inflammatory state and the presence of a known or suspected infection. The body may develop this inflammatory response by the immune system to microbes in the blood, urine, lungs, skin, or other tissues...
and risk of death.
Cause
- Congenital or aganglionic megacolon
- Medication
- Acquired megacolon, of which there are several possible etiologies:
- IdiopathicIdiopathicIdiopathic is an adjective used primarily in medicine meaning arising spontaneously or from an obscure or unknown cause. From Greek ἴδιος, idios + πάθος, pathos , it means approximately "a disease of its own kind". It is technically a term from nosology, the classification of disease...
megacolon - Toxic megacolonToxic megacolonToxic megacolon is an acute form of colonic distension. It is characterized by a very dilated colon , accompanied by abdominal distension , and sometimes fever, abdominal pain, or shock....
- Megacolon secondary to infectionInfectionAn infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
- Other neurologic, systemic and metabolic diseases
- Idiopathic
Aganglionic megacolon
Also called Hirschsprung's diseaseHirschsprung's disease
Hirschsprung's disease , or congenital aganglionic megacolon is a serious medical problem where the enteric nervous system is missing from the end of the bowel. The enteric nervous system is a complex network of neurons and glia that controls most aspects of intestinal function...
, it is a congenital disorder of the colon in which nerve cells of the myenteric or Auerbach's plexus
Auerbach's plexus
A part of the enteric nervous system, Auerbach's plexus , exists between the longitudinal and circular layers of muscularis externa in the gastrointestinal tract and provides motor innervation to both layers of the mucosa, having both parasympathetic and sympathetic input, whereas Meissner's plexus...
in its walls, also known as ganglion cells, are absent. It is a rare disorder (1:5 000), with prevalence among males being four times that of females. Hirschsprung’s disease develops in the fetus
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
during the early stages of pregnancy
Pregnancy
Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...
. The exact genetic
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
cause remains unsolved, although in familial cases (in which families have multiple affected patients), it seems to exhibit autosomal dominant transmission, with a gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
called RET, in chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
10, being dominant. Seven other genes seem to be implicated, however. If untreated, the patient can develop enterocolitis
Enterocolitis
Enterocolitis is an inflammation of the colon and small intestine. However, most conditions are categorized as one or the other of the following:* Enteritis is the inflammation of the small intestine...
.
Toxic megacolon
Toxic megacolon is mainly seen in ulcerative colitisUlcerative colitis
Ulcerative colitis is a form of inflammatory bowel disease . Ulcerative colitis is a form of colitis, a disease of the colon , that includes characteristic ulcers, or open sores. The main symptom of active disease is usually constant diarrhea mixed with blood, of gradual onset...
and pseudomembranous colitis
Pseudomembranous colitis
Pseudomembranous colitis, a cause of antibiotic-associated diarrhea , is an infection of the colon. It is often, but not always, caused by the bacterium Clostridium difficile. Because of this, the informal name C. difficile colitis is also commonly used. The illness is characterized by...
, two chronic inflammation
Inflammation
Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...
s of the colon. Its mechanism is incompletely understood. It is probably due to an excessive production of nitric oxide
Nitric oxide
Nitric oxide, also known as nitrogen monoxide, is a diatomic molecule with chemical formula NO. It is a free radical and is an important intermediate in the chemical industry...
, at least in ulcerative colitis. The prevalence is about the same for both sexes.
Chagas disease
Megacolon can be associated with Chagas disease.In Central
Central America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...
and South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
, the most common incidence of chronic megacolon is that observed in ca. 20% of patients affected with Chagas disease
Chagas disease
Chagas disease is a tropical parasitic disease caused by the flagellate protozoan Trypanosoma cruzi. T. cruzi is commonly transmitted to humans and other mammals by an insect vector, the blood-sucking insects of the subfamily Triatominae most commonly species belonging to the Triatoma, Rhodnius,...
. Chagas is caused by Trypanosoma cruzi
Trypanosoma cruzi
Trypanosoma cruzi is a species of parasitic euglenoid trypanosomes. This species causes the trypanosomiasis diseases in humans and animals in America...
, a flagellate protozoan transmitted by the feces of a hematophagous
Hematophagy
Hematophagy is the practice of certain animals of feeding on blood...
insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
, the assassin bug, when it feeds. Chagas can also be acquired congenitally, through blood transfusion
Blood transfusion
Blood transfusion is the process of receiving blood products into one's circulation intravenously. Transfusions are used in a variety of medical conditions to replace lost components of the blood...
or organ transplant, and rarely through contaminated food (for example garapa
Garapa
Garapa or Caldo de cana is the Brazilian Portuguese term for the juice of raw sugar cane. Sugar cane juice is consumed as a beverage worldwide, and especially in regions where sugarcane is commercially grown such as Southeast Asia, South Asia, and Latin America...
). There are several theories on how megacolon (and also megaesophagus
Megaesophagus
Megaesophagus is a condition in humans, cats and dogs where peristalsis fails to occur properly and the esophagus is enlarged. Normally, when the dog's esophagus is functioning properly, it acts as a muscle and pushes the food down the esophagus into the stomach. However, when a dog has...
) develops in Chagas disease. The Austrian
Austrians
Austrians are a nation and ethnic group, consisting of the population of the Republic of Austria and its historical predecessor states who share a common Austrian culture and Austrian descent....
-Brazilian physician
Physician
A physician is a health care provider who practices the profession of medicine, which is concerned with promoting, maintaining or restoring human health through the study, diagnosis, and treatment of disease, injury and other physical and mental impairments...
and pathologist Fritz Köberle
Fritz Köberle
Fritz Köberle was an Austrian-Brazilian physician, pathologist and scientist, discoverer of the neurogenic mechanism of the chronic phase of Chagas disease, a human parasitic disease caused by Trypanosoma cruzi, a protozoan.-Life:Fritz Köberle was born in Eichgraben, Austria, and studied medicine...
was the first to propose a coherent hypothesis based on the documented destruction of the Auerbach's plexus in the walls of the intestinal tracts of Chagas patients, the so-called neurogenic hypothesis. In this, the destruction of the autonomic nervous system
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...
innervation of the colon leads to a loss of the normal smooth muscle
Smooth muscle
Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...
tone of the wall and subsequent gradual dilation. His research proved that, by extensively quantifying the number of neurons of the autonomic nervous system in the Auerbach's plexus, that: 1) they were strongly reduced all over the digestive tract; 2) that megacolon appeared only when there was a reduction of over 80% of the number of neurons 3) these pathologies appeared as a result of the disruption of the neurally integrated control of peristalsis
Peristalsis
Peristalsis is a radially symmetrical contraction and relaxation of muscles which propagates in a wave down the muscular tube, in an anterograde fashion. In humans, peristalsis is found in the contraction of smooth muscles to propel contents through the digestive tract. Earthworms use a similar...
(muscular annular contraction) in those parts where a strong force is necessary to impel the luminal bolus
Bolus (digestion)
In digestion, a bolus is a mass of food that has been chewed at the point of swallowing. Once a bolus reaches the stomach, digestion begins....
of feces
Feces
Feces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus or cloaca during defecation.-Etymology:...
; and 4) Idiopathic megacolon and Chagas megacolon appear to have the same etiology, namely the degeneration of the Auerbach's myoenteric plexus.
Why T. cruzi causes the destruction, however, remains to be elucidated: there are evidences for the presence of specific neurotoxin
Neurotoxin
A neurotoxin is a toxin that acts specifically on nerve cells , usually by interacting with membrane proteins such as ion channels. Some sources are more general, and define the effect of neurotoxins as occurring at nerve tissue...
s as well as a disordely immune system
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
reaction.
Diagnosis
DiagnosisDiagnosis
Diagnosis is the identification of the nature and cause of anything. Diagnosis is used in many different disciplines with variations in the use of logics, analytics, and experience to determine the cause and effect relationships...
is achieved mainly by plain and contrasted radiographical
Radiography
Radiography is the use of X-rays to view a non-uniformly composed material such as the human body. By using the physical properties of the ray an image can be developed which displays areas of different density and composition....
and ultrasound
Ultrasound
Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Ultrasound is thus not separated from "normal" sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is...
imaging. Colonic marker transit studies are useful to distinguish colonic inertia from functional outlet obstruction etiologies. In this test, the patient swallows a water soluble bolus of radio-opaque contrast and films are obtained 1, 3 and 5 days later. Patients with colonic inertia show the marker spread throughout the large intestines, while patients with outlet obstruction exhibit slow accumulations of markers in some places. A colonoscopy
Colonoscopy
Colonoscopy is the endoscopic examination of the large bowel and the distal part of the small bowel with a CCD camera or a fiber optic camera on a flexible tube passed through the anus. It may provide a visual diagnosis and grants the opportunity for biopsy or removal of suspected...
can also be used to rule out mechanical obstructive causes. Anorectal manometry
Anorectal manometry
Anorectal manometry is a technique used to measure contractility in the anus and rectum.It may be used to assist in the diagnosis of Hirschprung disease....
may help to differentiate acquired from congenital forms. Rectal biopsy is recommended to make a final diagnosis of Hirschsprung disease.
Treatment
Possible treatments include:- In stable cases, use of laxativeLaxativeLaxatives are foods, compounds, or drugs taken to induce bowel movements or to loosen the stool, most often taken to treat constipation. Certain stimulant, lubricant, and saline laxatives are used to evacuate the colon for rectal and/or bowel examinations, and may be supplemented by enemas under...
s and bulking agents, as well as modifications in dietDiet (nutrition)In nutrition, diet is the sum of food consumed by a person or other organism. Dietary habits are the habitual decisions an individual or culture makes when choosing what foods to eat. With the word diet, it is often implied the use of specific intake of nutrition for health or weight-management...
and stool habits are effective. - CorticosteroidCorticosteroidCorticosteroids are a class of steroid hormones that are produced in the adrenal cortex. Corticosteroids are involved in a wide range of physiologic systems such as stress response, immune response and regulation of inflammation, carbohydrate metabolism, protein catabolism, blood electrolyte...
s and other anti-inflammatory medication is used in toxic megacolon. - Disimpaction of feces and decompression using anorectal and nasogastric tubes.
- When megacolon worsens and the conservative measures fail to restore transit, surgerySurgerySurgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, or to help improve bodily function or appearance.An act of performing surgery may be called a surgical...
may be necessary.
There are several surgical approaches to treat megacolon, such as a colectomy
Colectomy
Colectomy consists of the surgical resection of any extent of the large intestine .-History:Sir William Arbuthnot-Lane was one of the early proponents of the usefulness of total colectomies, although his overuse of the procedure called the wisdom of the surgery into question.-Indications:Some of...
(removal of the entire colon) with ileorectal anastomosis
Anastomosis
An anastomosis is the reconnection of two streams that previously branched out, such as blood vessels or leaf veins. The term is used in medicine, biology, mycology and geology....
(ligation of the remaining ileus and rectum segments), or a total proctocolectomy
Proctocolectomy
Proctocolectomy is the surgical removal of the rectum and all or part of the colon. It is a most widely accepted surgical method for ulcerative colitis and Familial adenomatous polyposis .- References :...
(removal of colon, sigmoid and rectum) followed by ileostomy
Ileostomy
An ileostomy is a surgical opening constructed by bringing the end or loop of small intestine out onto the surface of the skin. Intestinal waste passes out of the ileostomy and is collected in an external pouching system stuck to the skin...
or followed by ileoanal anastomosis.