AUTHOR AND EDITOR INFORMATION

Section 1 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

INTRODUCTION

Section 2 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Background

Megacolon, as well as megarectum, is a descriptive term. It denotes dilatation of the colon that is not caused by mechanical obstruction. While the definition of megacolon has varied in the literature, most researchers use the measurement of greater than 12 cm for the cecum as the standard. Because the diameter of the large intestine varies, the following definitions would also be considered: greater than 6.5 cm in the rectosigmoid region and greater than 8 cm for the ascending colon. 

Megacolon can be divided into the following 3 categories:

• Acute megacolon (pseudo-obstruction)
• Chronic megacolon, which includes congenital, acquired, and idiopathic causes
• Toxic megacolon

This article is devoted to chronic (noncongenital) megacolon.

Pathophysiology

The pathophysiology of chronic megacolon is incompletely understood. It likely represents an amalgam of primary disorders involving muscular and nervous systems of the intestine. Much basic science work has been performed in this area.

For example, with respect to the large bowel reacting to its luminal contents, fatty acids appear to reduce the volume of the proximal large bowel. Opiate narcotics, on the other hand, reduce the propensity of the colon to constrict.

Control of colonic contractility is through a complex interaction of intrinsic colonic nerves, splanchnic nervous control, and central nervous system input. The final common pathway of intrinsic nervous control of colonic motility is via postganglionic nerves: stimulatory cholinergic nerves and inhibitory nitric oxide-releasing nerves. Evidence suggests that excessive production of nitric oxide may be the mechanism for toxic megacolon in ulcerative colitis; as yet, there is no evidence for a possible role of nitric oxide in chronic megacolon unrelated to inflammatory bowel disease.

Studies in mouse models and in children with chronic colonic pseudo-obstruction show abnormalities involving the number and function of the interstitial cells of Cajal (intestinal pacemaker cells).  Inherited disorders likely involve abnormal maturation and function of these cells, whereas acquired disorders demonstrate decreased numbers of them.

Animal studies show that the splanchnic nerves can dramatically affect colonic motility, both to contract and relax the colon. Extrinsic adrenergic nerves seem mainly to act by reducing acetylcholine release from intrinsic postganglionic nerves, although a direct action on smooth muscle cells cannot be excluded. At this time, the respective roles of the intrinsic and splanchnic nerves in inducing megacolon have yet to be clarified.

Some experts believe it is common practice to separate the disorders associated with chronic megacolon into the following: (1) colonic inertia (eg, generalized delayed transit), and (2) rectosphincteric dyssynergy (eg, functional outlet obstruction).

Frequency

United States

No large-scale studies have been conducted to determine prevalence/incidence of acquired megacolon.

International

The most common cause of megacolon worldwide is infection with Trypanosoma cruzi (Chagas disease).

Mortality/Morbidity

No large-scale studies have been conducted to determine prevalence/incidence of acquired megacolon. However, once present, the approximate risk of a spontaneous perforation from nontoxic megacolon is 3%.

Race

Race has not been documented to play a role in megacolon.

Sex

• The frequency of acquired megacolon is equally distributed between the sexes.
• The congenital megacolon, Hirschsprung disease, predominantly occurs in males.

Age

Although clinically chronic megacolon can occur in any age group, inherited types usually present in young patients, and acquired types usually present in older patients.

CLINICAL

Section 3 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

History

• Historically, chronic megacolon has been categorized into 2 groups, according to when symptoms begin.
• • The congenital group experiences onset of constipation before age 1 year.
  • The acquired group develops symptoms after age 10 years until adulthood.

Physical

• Physical examination generally reveals a distended abdomen, which may or may not be tense.
• Tympany is invariably present.
• Digital rectal examination may demonstrate a hard mass of stool just above the anorectal ring.  Digital rectal examination in a patient with Hirschsprung disease may bring about a large gush of retained fecal material.
• Megarectum with a rectum distended with stool, if chronic, tends to cause the anus to gape open secondary to the dysfunction of the internal sphincter mechanism. These patients may present with factitious diarrhea secondary to overflow incontinence.

Causes

• Causes of acquired megacolon
• • Neurologic diseases
  • • Chagas disease
    • Parkinson disease
    • Myotonic dystrophy
    • Diabetic neuropathy
    • Spinal cord injury
    • Paraneoplastic neuropathy
    • Amyloidosis
  • Systemic diseases
  • • Scleroderma
    • Dermatomyositis/polymyositis
    • Systemic lupus erythematosus
    • Mixed connective tissue disease
  • Metabolic diseases
  • • Hypothyroidism
    • Hypokalemia
    • Porphyria
    • Pheochromocytoma
  • Medication-induced conditions
  • Idiopathic
  • • Nonfamilial visceral neuropathy (sporadic hollow visceral neuropathy or chronic idiopathic intestinal pseudo-obstruction)
    • Results from damage to the myenteric plexus from drugs or viral infections
  • The most common nonmechanical cause of acquired megacolon is infection with T cruzi (Chagas disease).
  • • This infection results in the destruction of the enteric nervous system.
    • While this disease was originally confined to South America, recent estimates indicate that 350,000 people in the United States are seropositive, a third of whom are thought to have chronic Chagas disease.
• Causes of congenital megacolon
• • Enteric neuropathies
  • • Hirschsprung disease (congenital aganglionosis)
    • • It is caused by a single gene mutation of the RET proto-oncogene on band 10q11.2.
      • The defect occurs in 1 in 5000 live births.
      • Some cases are familial, with an overall incidence of 3.6% among siblings of index cases.
    • Waardenburg-Shah syndrome (piebaldism, neural deafness, megacolon)
    • Multiple endocrine neoplasia type 2A (MEN 2A) or 2B (MEN 2B)
  • Visceral myopathies
  • • Mitochondrial neurogastrointestinal encephalopathy (MNGIE) - Only type III involves marked dilatation of the colon
    • Oculogastrointestinal neuropathy (OGIN)
    • Idiopathic
  • In the newborn period, an unrecognized imperforate anus may be the cause of megacolon.

DIFFERENTIALS

Section 4 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Other Problems to Be Considered

Intestinal/colonic obstruction (eg, malignancy, imperforate anus, fecal impaction, rectal prolapse)

WORKUP

Section 5 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Lab Studies

• Laboratory studies are important to exclude other etiologies, including electrolyte abnormalities (eg, calcium, magnesium, phosphorus).
• Thyroid function tests should also be performed.

Imaging Studies

• Abdominal plain films are useful for initial screening and assessment of severity.
• After plain films reveal the megacolon, water-soluble contrast enema may be helpful for a number of reasons.
  
  
  • Accurately assesses the size of the colon
  • Helps to differentiate the presence of megacolon, megarectum, or both
  • Helps to define the anatomy
  • Can be used therapeutically to evacuate the colon
• Distinguishing a colonic inertia etiology from that of a functional outlet obstruction is probably best accomplished by colonic marker transit studies. Numerous ways to perform this test are available.
  
  
  • One method is to instruct the patient to consume 30 g of dietary fiber daily and to stop using laxatives, enemas, and all other nonessential medications for at least 2 days prior to (as well as during) the test.
  • The patient swallows the markers, and abdominal plain films are obtained on days 1, 3, and 5.
  • Patients with colonic inertia tend to have markers distributed throughout the large bowel from cecum to rectum, while patients with outlet obstruction exhibit markers proceeding normally through the colon but accumulating in the rectum.

Other Tests

• Anorectal manometry may help to distinguish congenital from acquired megacolon.
  
  
  • The presence of a rectoanal inhibitory response means that there are intact ganglia, and the patient does not have Hirschsprung disease.
  • If the inhibitory response is absent, a rectal biopsy is still needed to confirm the diagnosis of Hirschsprung disease. 
• Pudendal nerve latency testing may elucidate problems related to peristaltic movement, anatomical and/or mechanical problems with evacuation, and nerve-associated problems with defecation.

Procedures

• Colonoscopy should be used to rule out an obstructive/mechanical cause of colonic dilatation.

Histologic Findings

Histology is helpful for determining the etiology of the condition. Although full-thickness biopsy is the criterion standard to establish a diagnosis of Hirschsprung disease, mucosal suction biopsy is adequate in most instances. The absence of ganglion cells is characteristic of Hirschsprung disease, and specific stains for acetylcholinesterase are used to highlight abnormal morphology. Other than Hirschsprung disease, however, the presence of ganglion cells does not specify one cause over another. For most cases, there is no indication for histology because Hirschsprung disease is not considered or excluded by normal manometric findings.

TREATMENT

Section 6 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Medical Care

• In the absence of perforation, initial management is conservative. Some experts believe a role exists for as-needed fecal disimpaction and for evacuation by enemas and suppositories.
• Pay close attention to exclusion of any underlying cause. If identified, correct electrolyte/metabolite abnormalities, and remove medications that may influence colonic motility (eg, narcotics, anticholinergic agents, calcium channel antagonists).
• The use of biofeedback for a colonic inertia etiology for chronic megacolon is probably not effective, although successful treatment of functional outlet obstruction with biofeedback has been reported.
• In patients requiring hospitalization, decompression using nasogastric tubes and rectal tubes may assist in treatment. When such tubes are used, anecdotal experience has demonstrated that frequent position changes for the patient may help to improve decompression.
• If the dilatation persists or worsens, colonoscopic decompression can be attempted, with consideration of placement of a decompression tube, per rectum, to the right side of the colon.
  
  
  • Unfortunately, following decompression, the dilatation usually recurs; therefore, decompression with colonoscopy must be carefully considered, as it is not without risk in an unprepared, dilated colon.
  • Many gastroenterologists no longer consider placement of a drainage tube at the time of colonoscopy, as it nearly always becomes clogged with stool and rapidly ceases to function. 
• Beyond these options for the treatment of acute megacolon, the recommended regimen for chronic megacolon in a stable patient is as follows:
  
  
  • Empty the bowel (eg, osmotic laxatives, enemas, suppositories, cathartics, digital disimpaction).
  • Practice a bowel habit retraining program (eg, scheduled times for defecation, increased physical activity if possible).
  • Consume bulking agents/bowel agents.
  • Slowly alter/individualize the regimen.

Surgical Care

• Surgical care is generally recommended if the dilatation is persisting or worsening after the above medical measures have been exhausted.
  
  
  • Megacolon operative options include total abdominal colectomy with ileorectal anastomosis, total proctocolectomy with ileostomy, and total proctocolectomy with ileoanal anastomosis, depending on the site of the colon affected.
  • Total abdominal colectomy with ileorectal anastomosis is the operation of choice of megacolon with normal-sized rectum.

Consultations

These problems require a multidisciplinary approach, including the primary care provider, a gastroenterologist, a nutritionist/dietitian, and possibly a surgeon.

Diet

Patients with acquired, nonacute megacolon should follow a high-fiber, high-fluid intake diet, which usually helps to decrease constipation. Some patients with severe constipation state that a high-fiber diet produces greater difficulty with bloating and constipation.

MEDICATION

Section 7 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

A high water intake is an essential measure. A minimum of 6-8 8-oz glasses a day is recommended.

Bulking agents, through the increase of fiber, are also important. Many agents are on the market for this purpose and typically contain psyllium husk or cellulose; each patient may respond differently to each agent. No single agent is superior to another.

Laxatives may be considered and continued if found to be helpful. The best laxatives for this purpose are osmotic agents, such as magnesium salts, sorbitol, or lactulose (the latter two may increase flatulence). Patients need encouragement to take sufficient amounts to produce a result. Stimulant laxatives are best left as a last resort because they may possibly induce deterioration in the ability of the colon to evacuate. Typical stimulant laxatives are senna and bisacodyl-containing medications. Many patients take natural herbal laxatives; these typically contain cascara.

Tegaserod, a 5HT4 agonist, was approved for use in chronic constipation and in women with constipation-predominant irritable bowel syndrome. Its role in chronic pseudo-obstruction had not been determined.

Drug Category: Laxatives

Increase peristalsis of the intestine, reducing the time toxic substances remain in the lower GI tract.

FOLLOW-UP

Section 8 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Further Outpatient Care

• Maintenance of a strict bowel habit retraining program, as described in Medical Care, is important.

Complications

• The most dangerous complication is perforation, which rarely occurs. Perforation is generally due to overdistension of the bowel or to stercoral ulcer. If the etiology is overdistension, perforation typically occurs in the cecum. Stercoral ulcers typically occur in the sigmoid/rectosigmoid region.

Prognosis

• Prognosis is related to the severity of the megacolon and the severity of the patient's comorbid diseases.
• While some patients cannot be managed on any type of bowel program and quickly require surgery, other patients may be maintained on a strict bowel program. No detailed longitudinal studies, however, have been performed to assess strict prognostic associations or indicators.

Patient Education

• Education of the patient with regard to the strict bowel program is essential to management. Maintaining effective management requires extensive effort and discipline from both the health care provider and the patient. To this end, educating the patient about the entire process is crucial.

MISCELLANEOUS

Section 9 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Medical/Legal Pitfalls

• Medicolegal pitfalls might include failure to diagnose certain etiologies of megacolon, including Hirschsprung disease, imperforate anus, and colorectal cancer.

REFERENCES

Section 10 of 10

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

• Barnes PR, Lennard-Jones JE, Hawley PR, Todd IP. Hirschsprung's disease and idiopathic megacolon in adults and adolescents. Gut. May 1986;27(5):534-41. [Medline].
• Camilleri M. Acute and chronic pseudo-obstruction. In: Felman M, Friedman LS, Sleisenger MH, eds. Sleisenger & Fordtran's Gastrointestinal and Liver Disease. 8^th ed. Philadelphia: Saunders; 2007:2679-2702.
• Camilleri M. Dysmotility of the small intestine and colon. In: Yamada T, ed. Textbook of Gastroenterology. Vol 1. 4^th ed. Philadelphia: Lippincott Williams & Wilkins; 2003:1486-1529.
• Harari D, Minaker KL. Megacolon in patients with chronic spinal cord injury. Spinal Cord. Jun 2000;38(6):331-9. [Medline].
• Krishnamurthy S, Heng Y, Schuffler MD. Chronic intestinal pseudo-obstruction in infants and children caused by diverse abnormalities of the myenteric plexus. Gastroenterology. May 1993;104(5):1398-408. [Medline].
• Lane RH, Todd IP. Idiopathic megacolon: a review of 42 cases. Br J Surg. May 1977;64(5):307-10. [Medline].
• Metcalf AM, Phillips SF, Zinsmeister AR, MacCarty RL, Beart RW, Wolff BG. Simplified assessment of segmental colonic transit. Gastroenterology. Jan 1987;92(1):40-7. [Medline].
• Miyamoto M, Egami K, Maeda S, Ohkawa K, Tanaka N, Uchida E, et al. Hirschsprung's disease in adults: report of a case and review of the literature. J Nippon Med Sch. Apr 2005;72(2):113-20. [Medline].
• Nicholls RJ, Kamm MA. Proctocolectomy with restorative ileoanal reservoir for severe idiopathic constipation. Report of two cases. Dis Colon Rectum. Dec 1988;31(12):968-9. [Medline].
• Porter NH. Megacolon: A physiological study. Proc R Soc Med. 1961;54:1043.
• Preston DM, Lennard-Jones JE, Thomas BM. Towards a radiologic definition of idiopathic megacolon. Gastrointest Radiol. 1985;10(2):167-9. [Medline].
• Stabile G, Kamm MA, Hawley PR, Lennard-Jones JE. Colectomy for idiopathic megarectum and megacolon. Gut. Dec 1991;32(12):1538-40. [Medline].
• Stryker SJ, Pemberton JH, Zinsmeister AR. Long-term results of ileostomy in older patients. Dis Colon Rectum. Nov 1985;28(11):844-6. [Medline].

Article Last Updated: Aug 3, 2007