Clinical features of intestinal pseudo-obstruction can include abdominal pain, nausea, severe distension, vomiting, dysphagia, diarrhea and constipation, depending upon the part of the gastrointestinal tract involved. In addition, in the moments in which abdominal colic occurs, an abdominal x-ray shows intestinal air fluid level. All of these features are also similar in true mechanical obstruction of the bowel.

Symptoms of ileus include, but are not limited to:

- moderate, diffuse abdominal discomfort

- constipation

- abdominal distension

- nausea/vomiting, especially after meals

- vomiting of bilious fluid

- lack of bowel movement and/or flatulence

- excessive belching

Decreased propulsive ability may be broadly classified as caused either by bowel obstruction or intestinal atony or paralysis. However, instances with symptoms and signs of a bowel obstruction occur, but with the absence of a mechanical obstruction, mainly in acute colonic pseudo-obstruction, Ogilvie's syndrome.

Intestinal pseudo-obstruction is a clinical syndrome caused by severe impairment in the ability of the intestines to push food through. It is characterized by the signs and symptoms of intestinal obstruction without any lesion in the intestinal lumen. Clinical features can include abdominal pain, nausea, severe distension, vomiting, dysphagia, diarrhea and constipation, depending upon the part of the gastrointestinal tract involved. The condition can begin at any age and it can be a primary condition (idiopathic or inherited) or caused by another disease (secondary).

It can be chronic or acute.

Depending on the level of obstruction, bowel obstruction can present with abdominal pain, swollen abdomen, abdominal distension, vomiting, fecal vomiting, and constipation.

Bowel obstruction may be complicated by dehydration and electrolyte abnormalities due to vomiting; respiratory compromise from pressure on the diaphragm by a distended abdomen, or aspiration of vomitus; bowel ischemia or perforation from prolonged distension or pressure from a foreign body.

In small bowel obstruction, the pain tends to be colicky (cramping and intermittent) in nature, with spasms lasting a few minutes. The pain tends to be central and mid-abdominal. Vomiting may occur before constipation.

In large bowel obstruction, the pain is felt lower in the abdomen and the spasms last longer. Constipation occurs earlier and vomiting may be less prominent. Proximal obstruction of the large bowel may present as small bowel obstruction.

The small intestine consists of the duodenum, jejunum and ileum. Inflammation of the small intestine is called enteritis, which if localised to just part is called duodenitis, jejunitis and ileitis, respectively. Peptic ulcers are also common in the duodenum.

Chronic diseases of malabsorption may affect the small intestine, including the autoimmune coeliac disease, infective Tropical sprue, and congenital or surgical short bowel syndrome. Other rarer diseases affecting the small intestine include Curling's ulcer, blind loop syndrome, Milroy disease and Whipple's disease. Tumours of the small intestine include gastrointestinal stromal tumours, lipomas, hamartomas and carcinoid syndromes.

Diseases of the small intestine may present with symptoms such as diarrhoea, malnutrition, fatigue and weight loss. Investigations pursued may include blood tests to monitor nutrition, such as iron levels, folate and calcium, endoscopy and biopsy of the duodenum, and barium swallow. Treatments may include renutrition, and antibiotics for infections.

Terms such as "functional colonic disease" (or "functional bowel disorder") refer in medicine to a group of bowel disorders which are characterised by chronic abdominal complaints without a structural or biochemical cause that could explain symptoms. Other "functional" disorders relate to other aspects of the process of digestion.

The consensus review process of meetings and publications organised by the Rome Foundation, known as the Rome process, has helped to define the functional gastrointestinal disorders. Successively, the Rome I, Rome II, Rome III and Rome IV proposed consensual classification system and terminology, as recommended by the Rome Coordinating Committee. These now include classifications appropriate for adults, children and neonates / toddlers.

The current Rome IV classification, published in 2016, is as follows:

A. Esophageal Disorders

- A1. Functional chest pain

- A2. Functional heartburn

- A3. Reflux hypersensitivity

- A4. Globus

- A5. Functional dysphagia

B. Gastroduodenal Disorders

- B1. Functional dyspepsia

- B1a. Postprandial distress syndrome (PDS)

- B1b. Epigastric pain syndrome (EPS)

- B2. Belching disorders

- B2a. Excessive supragastric belching

- B2b. Excessive gastric belching

- B3. Nausea and vomiting disorders

- B3a. Chronic nausea vomiting syndrome (CNVS}

- B3b. Cyclic vomiting syndrome (CVS)

- B3c. Cannabinoid hyperemesis syndrome (CHS)

- B4. Rumination syndrome

C. Bowel Disorders

- C1. Irritable bowel syndrome (IBS)

- IBS with predominant constipation (IBS-C)

- IBS with predominant diarrhea (IBS-D)

- IBS with mixed bowel habits (IBS-M)

- IBS unclassified (IBS-U)

- C2. Functional constipation

- C3. Functional diarrhea

- C4. Functional abdominal bloating/distension

- C5. Unspecified functional bowel disorder

- C6. Opioid-induced constipation

D. Centrally Mediated Disorders of Gastrointestinal Pain

- D1. Centrally mediated abdominal pain syndrome (CAPS)

- D2. Narcotic bowel syndrome (NBS)/ Opioid-induced GI hyperalgesia

E. Gallbladder and Sphincter of Oddi disorders

- E1. Biliary pain

- E1a. Functional gallbladder disorder

- E1b. Functional biliary sphincter of Oddi disorder

- E2. Functional pancreatic sphincter of Oddi disorder

F. Anorectal Disorders

- F1. Fecal incontinence

- F2. Functional anorectal pain

- F2a. Levator ani syndrome

- F2b. Unspecified functional anorectal pain

- F2c. Proctalgia fugax

- F3. Functional defecation disorders

- F3a. Inadequate defecatory propulsion

- F3b. Dyssynergic defecation

G. Childhood Functional GI Disorders: Neonate/Toddler

- G1. Infant regurgitation

- G2. Rumination syndrome

- G3. Cyclic vomiting syndrome (CVS)

- G4. Infant colic

- G5. Functional diarrhea

- G6. Infant dyschezia

- G7. Functional constipation

H. Childhood Functional GI Disorders: Child/Adolescent

- H1. Functional nausea and vomiting disorders

- H1a. Cyclic vomiting syndrome (CVS)

- H1b. Functional nausea and functional vomiting

- H1b1. Functional nausea

- H1b2. Functional vomiting

- H1c. Rumination syndrome

- H1d. Aerophagia

- H2. Functional abdominal pain disorders

- H2a. Functional dyspepsia

- H2a1. Postprandial distress syndrome

- H2a2. Epigastric pain syndrome

- H2b. Irritable bowel syndrome (IBS)

- H2c. Abdominal migraine

- H2d. Functional abdominal pain ‒ NOS

- H3. Functional defecation disorders

- H3a. Functional constipation

- H3b. Nonretentive fecal incontinence

External signs and symptoms are constipation 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 ulcers 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.

Diseases that affect the large intestine may affect it in whole or in part. Appendicitis is one such disease, caused by inflammation of the appendix. Generalised inflammation of the large intestine is referred to as colitis, which when caused be the bacteria "Clostridium difficile" is referred to as pseudomembranous colitis. Diverticulitis is a common cause of abdominal pain resulting from outpouchings that particularly affects the colon. Functional colonic diseases refer to disorders without a known cause, and include irritable bowel syndrome and intestinal pseudoobstruction. Constipation may result from lifestyle factors, impaction of a rigid stool in the rectum, or in neonates, Hirschprung's disease.

Diseases affecting the large intestine may cause blood to be passed with stool, may cause constipation, or may result in abdominal pain or a fever. Tests that specifically examine the function of the large intestine include barium swallows, abdominal x-rays, and colonoscopy.

Functional gastrointestinal disorders are very common. Globally, irritable bowel syndrome and functional dyspepsia alone may affect 16–26% of the population.

Signs and symptoms of DIOS include a sudden onset of crampy abdominal pain, vomiting, and a palpable mass (often in the right lower quadrant) in the abdomen. The characteristic abdominal pain is typically located in the center or right lower quadrant of the abdomen. X-rays of the abdomen may reveal stool in the colon and air-fluid levels in the small intestines.

Usually the patient has abdominal distention, pain and altered bowel movements. There may also be nausea and vomiting.

Causes of small bowel obstruction include:

- Adhesions from previous abdominal surgery (most common cause)

- Barbed sutures.

- Pseudoobstruction

- Hernias containing bowel

- Crohn's disease causing adhesions or inflammatory strictures

- Neoplasms, benign or malignant

- Intussusception

- Volvulus

- Superior mesenteric artery syndrome, a compression of the duodenum by the superior mesenteric artery and the abdominal aorta

- Ischemic strictures

- Foreign bodies (e.g. gallstones in gallstone ileus, swallowed objects)

- Intestinal atresia

After abdominal surgery, the incidence of small bowel obstruction from any cause is 9%. In those where the cause of the obstruction was clear, adhesions are the single most common cause (more than half).

Megacolon is an abnormal dilation of the colon (also called the large intestine). The dilation 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 fecalomas (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 usually 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 cause.

DIOS is sometimes classified by the degree of obstruction as incomplete or complete DIOS.

Early symptoms can include periodic abdominal pain, nausea, vomiting (sometimes green in color from bile), pulling legs to the chest area, and intermittent moderate to severe cramping abdominal pain. Pain is intermittent—not because the intussusception temporarily resolves, but because the intussuscepted bowel segment transiently stops contracting. Later signs include rectal bleeding, often with "red currant jelly" stool (stool mixed with blood and mucus), and lethargy. Physical examination may reveal a "sausage-shaped" mass, felt upon palpating the abdomen. Children, or those unable to communicate symptoms verbally, may cry, draw their knees up to their chest, or experience dyspnea (difficult or painful breathing) with paroxysms of pain.

Fever is not a symptom of intussusception. However, intussusception can cause a loop of bowel to become necrotic, secondary to ischemia due to compression to arterial blood supply. This leads to perforation and sepsis, which causes fever.

In rare cases, intussusception may be a complication of Henoch-Schönlein purpura (HSP), an immune-mediated vasculitis disease in children. Such patients who develop intussusception often present with severe abdominal pain in addition to the classic signs and symptoms of HSP.

Neonatal bowel obstruction (NBO) or neonatal intestinal obstruction is the most common surgical emergency in the neonatal period. It may occur due to a variety of conditions and has an excellent outcome based on timely diagnosis and appropriate intervention.

The diagnosis is suspected based on polyhydramnios in uteru, bilious vomiting, failure to pass meconium in the first day of life, and abdominal distension. The presentations of NBO may vary. It may be subtle and easily overlooked on physical examination or can involve massive abdominal distension, respiratory distress and cardiovascular collapse. Unlike older children, neonates with unrecognized intestinal obstruction deteriorate rapidly.

Regardless of cause, volvulus causes symptoms by two mechanisms:

- Bowel obstruction manifested as abdominal distension and bilious vomiting.

- Ischemia (loss of blood flow) to the affected portion of intestine.

Depending on the location of the volvulus, symptoms may vary. For example, in patients with a cecal volvulus, the predominant symptoms may be those of a small bowel obstruction (nausea, vomiting and lack of stool or flatus), because the obstructing point is close to the ileocecal valve and small intestine. In patients with a sigmoid volvulus, although abdominal pain may be present, symptoms of constipation may be more prominent.

Volvulus causes severe pain and progressive injury to the intestinal wall, with accumulation of gas and fluid in the portion of the bowel obstructed. Ultimately, this can result in necrosis of the affected intestinal wall, acidosis, and death. This is known as a closed loop obstruction because there exists an isolated ("closed") loop of bowel. Acute volvulus often requires immediate surgical intervention to untwist the affected segment of bowel and possibly resect any unsalvageable portion.

Volvulus occurs most frequently in middle-aged and elderly men. Volvulus can also arise as a rare complication in persons with redundant colon, a normal anatomic variation resulting in extra colonic loops.

Sigmoid volvulus is the most-common form of volvulus of the gastrointestinal tract. and is responsible for 8% of all intestinal obstructions. Sigmoid volvulus is particularly common in elderly persons and constipated patients. Patients experience abdominal pain, distension, and absolute constipation.

Cecal volvulus is slightly less common than sigmoid volvulus and is associated with symptoms of abdominal pain and small bowel obstruction.

Volvulus can also occur in patients with Duchenne muscular dystrophy due to the smooth muscle dysfunction.

Bowel infarction results from restricted blood supply to the bowel, most often due to bowel obstruction or occlusion of one of the mesenteric arteries.

Bowel obstruction is most often caused by intestinal adhesions, which frequently form after abdominal surgeries, or by chronic infections such as diverticulitis, hepatitis, and inflammatory bowel disease. The condition is difficult to diagnose properly, as the symptoms may resemble those of other bowel disorders.

Patients who have undergone extensive resection of the small bowel may develop malabsorption, indicating the need for dietary supplements.

Volvulus is a rare but life-threatening cause of bowel infarction which requires immediate medical attention. Central abdominal pain which is resistant to narcotic analgesia may be an indication of bowel infarction.

Most of the symptoms of BLS are non specific but nevertheless warrant the utmost attention. These include:

- Loss of appetite

- Nausea

- Flatulence

- Diarrhea

- Fullness after a meal

- Fatty stools (steatorrhea)

- Unintentional weight loss

- Generalised weakness

As a result of the concomitant vitamin and mineral deficiencies that occur as a result of the malabsorption associated with BLS patients with advanced cases should be investigated for:

- Vitamin B12 deficiency

- Folate deficiency

- Iron deficiency

- Vitamin E deficiency

Fecal vomiting, also called feculent vomiting and stercoraceous vomiting is a kind of vomiting wherein the material vomited is of fecal origin. It is a common symptom of gastrojejunocolic fistula and intestinal obstruction in the ileum. Fecal vomiting is often accompanied by an odor of feces on the breath and other gastrointestinal symptoms, including abdominal pain, abdominal distension, dehydration, and diarrhea. In severe cases of bowel obstruction or constipation (such as those related to Clozapine-treatment) fecal vomiting has been identified as a cause of death.

Fecal vomiting occurs when the bowel is obstructed for some reason, and intestinal contents cannot move normally. Peristaltic waves occur in an attempt to decompress the intestine, and the strong contractions of the intestinal muscles push the contents backwards through the pyloric sphincter into the stomach, where they are then vomited.

Fecal vomiting can also occur in cats.

Fecal vomiting does not include vomiting of the proximal small intestine contents, which commonly occurs during vomiting.

Ogilvie syndrome is the acute dilation of the colon in the absence of any mechanical obstruction in severely ill patients.

Colonic pseudo-obstruction is characterized by massive dilatation of the cecum (diameter > 10 cm) and right colon on abdominal X-ray. It is a type of megacolon, sometimes referred to as "acute megacolon", to distinguish it from toxic megacolon.

The condition carries the name of the British surgeon Sir (1887–1971), who first reported it in 1948.

Colic can be divided broadly into several categories:

1. excessive gas accumulation in the intestine (gas colic)

2. simple obstruction

3. strangulating obstruction

4. non-strangulating infarction

5. inflammation of the gastrointestinal tract (enteritis, colitis) or the peritoneum (peritonitis)

6. ulceration of the gastrointestinal mucosa

These categories can be further differentiated based on location of the lesion and underlying cause (See Types of colic).

Intussusception is a medical condition in which a part of the intestine folds into the section next to it. It typically involves the small bowel and less commonly the large bowel. Symptoms include abdominal pain which may come and go, vomiting, abdominal bloating, and bloody stool. It often results in a small bowel obstruction. Other complications may include peritonitis or bowel perforation.

The cause in children is typically unknown while in adults a lead point is often present. Risk factors in children include certain infections, diseases like cystic fibrosis, and intestinal polyps. Risk factors in adults include endometriosis, bowel adhesions, and intestinal tumors. Diagnosis is often supported by medical imaging. In children, ultrasound is preferred while in adults a CT scan is preferred.

Intussusception is an emergency requiring rapid treatment. Treatment in children is typically by an enema with surgery used if this is not successful. Dexamethasone may decrease the risk of another episode. In adults, surgical removal of part of the bowel is more often required. Intussusception occurs more commonly in children than adults. In children, males are more often affected than females. The usual age of occurrence is six to eighteen months old.