The presentation of acute appendicitis includes abdominal pain, nausea, vomiting, and fever. As the appendix becomes more swollen and inflamed, it begins to irritate the adjoining abdominal wall. This leads to the localization of the pain to the right lower quadrant. This classic migration of pain may not be seen in children under three years. This pain can be elicited through signs and can be severe. Signs include localized findings in the right iliac fossa. The abdominal wall becomes very sensitive to gentle pressure (palpation). There is severe pain on sudden release of deep pressure in the lower abdomen (rebound tenderness). If the appendix is retrocecal (localized behind the cecum), even deep pressure in the right lower quadrant may fail to elicit tenderness (silent appendix). This is because the cecum, distended with gas, protects the inflamed appendix from pressure. Similarly, if the appendix lies entirely within the pelvis, there is usually complete absence of abdominal rigidity. In such cases, a digital rectal examination elicits tenderness in the rectovesical pouch. Coughing causes point tenderness in this area (McBurney's point), historically called Dunphy's sign.

Acute abdomen is occasionally used synonymously with peritonitis. While this is not entirely incorrect, peritonitis is the more specific term, referring to inflammation of the peritoneum. It manifests on physical examination as rebound tenderness, or pain upon "removal" of pressure more than on "application" of pressure to the abdomen. Peritonitis may result from several of the above diseases, notably appendicitis and pancreatitis. While rebound tenderness is commonly associated with peritonitis, the most specific finding is rigidity.

An acute abdomen refers to a sudden, severe abdominal pain. It is in many cases a medical emergency, requiring urgent and specific diagnosis. Several causes need surgical treatment.

The main manifestations of peritonitis are acute abdominal pain, abdominal tenderness and abdominal guarding, which are exacerbated by moving the peritoneum, e.g., coughing (forced cough may be used as a test), flexing one's hips, or eliciting the Blumberg sign (a.k.a. rebound tenderness, meaning that pressing a hand on the abdomen elicits less pain than releasing the hand abruptly, which will aggravate the pain, as the peritoneum snaps back into place). Rigidity (involuntary contraction of the abdominal muscles) is the most specific exam finding for diagnosing peritonitis (+ likelihood ratio: 3.9). The presence of these signs in a patient is sometimes referred to as peritonism. The localization of these manifestations depends on whether peritonitis is localized (e.g., appendicitis or diverticulitis before perforation), or generalized to the whole abdomen. In either case, pain typically starts as a generalized abdominal pain (with involvement of poorly localizing innervation of the visceral peritoneal layer), and may become localized later (with the involvement of the somatically innervated parietal peritoneal layer). Peritonitis is an example of an acute abdomen.

Peritonitis is inflammation of the peritoneum, the lining of the inner wall of the abdomen and cover of the abdominal organs. Symptoms may include severe pain, swelling of the abdomen, fever, or weight loss. One part or the entire abdomen may be tender. Complications may include shock and acute respiratory distress syndrome.

Causes include perforation of the intestinal tract, pancreatitis, pelvic inflammatory disease, stomach ulcer, cirrhosis, or a ruptured appendix. Risk factors include ascites and peritoneal dialysis. Diagnosis is generally based on examination, blood tests, and medical imaging.

Treatment often includes antibiotics, intravenous fluids, pain medication, and surgery. Other measures may include a nasogastric tube or blood transfusion. Without treatment death may occurs within a few days. Approximately 7.5% of people have appendicitis at some point in time. About 20% of people with cirrhosis who are in hospital have peritonitis.

Appendicitis is inflammation of the appendix. Symptoms commonly include right lower abdominal pain, nausea, vomiting, and decreased appetite. However, approximately 40% of people do not have these typical symptoms. Severe complications of a ruptured appendix include widespread, painful inflammation of the inner lining of the abdominal wall and sepsis.

Appendicitis is caused by a blockage of the hollow portion of the appendix. This is most commonly due to a calcified "stone" made of feces. Inflamed lymphoid tissue from a viral infection, parasites, gallstone, or tumors may also cause the blockage. This blockage leads to increased pressures in the appendix, decreased blood flow to the tissues of the appendix, and bacterial growth inside the appendix causing inflammation. The combination of inflammation, reduced blood flow to the appendix and distention of the appendix causes tissue injury and tissue death. If this process is left untreated, the appendix may burst, releasing bacteria into the abdominal cavity, leading to increased complications.

The diagnosis of appendicitis is largely based on the person's signs and symptoms. In cases where the diagnosis is unclear, close observation, medical imaging, and laboratory tests can be helpful. The two most common imaging tests used are an ultrasound and computed tomography (CT scan). CT scan has been shown to be more accurate than ultrasound in detecting acute appendicitis. However, ultrasound may be preferred as the first imaging test in children and pregnant women because of the risks associated with radiation exposure from CT scans.

The standard treatment for acute appendicitis is surgical removal of the appendix. This may be done by an open incision in the abdomen (laparotomy) or through a few smaller incisions with the help of cameras (laparoscopy). Surgery decreases the risk of side effects or death associated with rupture of the appendix. Antibiotics may be equally effective in certain cases of non-ruptured appendicitis. It is one of the most common and significant causes of severe abdominal pain that comes on quickly. In 2015 about 11.6 million cases of appendicitis occurred which resulted in about 50,100 deaths. In the United States, appendicitis is the most common cause of sudden abdominal pain requiring surgery. Each year in the United States, more than 300,000 people with appendicitis have their appendix surgically removed. Reginald Fitz is credited with being the first person to describe the condition in 1886.

Emergency action may be required if severe abdominal pain develops, particularly if it is accompanied by fever, rapid heart rate, tenderness when the abdomen is pressed, bloody diarrhea, frequent diarrhea, or painful bowel movements.

Colonoscopy is contraindicated, as it may rupture the dilated colon resulting in peritonitis and septic shock.

Diverticulitis typically presents with left lower quadrant abdominal pain of sudden onset. There may also be fever, nausea, diarrhea or constipation, and blood in the stool.

Patients with pancreatic abscesses may experience abdominal pain, chills and fever or the inability to eat. Whereas some patients present an abdominal mass, others do not. Nausea and vomiting may also occur.

There may be signs of septic shock. A physical examination reveals abdominal tenderness and possible loss of bowel sounds. An abdominal radiography shows colonic dilation. White blood cell count is usually elevated. Severe sepsis may present with hypothermia or leukopenia.

In complicated diverticulitis, an inflamed diverticulum can rupture, allowing bacteria to subsequently infect externally from the colon. If the infection spreads to the lining of the abdominal cavity (the peritoneum), peritonitis results. Sometimes, inflamed diverticula can cause narrowing of the bowel, leading to an obstruction. In some cases, the affected part of the colon adheres to the bladder or other organs in the pelvic cavity, causing a , or creating an abnormal connection between an organ and adjacent structure or other organ (in the case of diverticulitis, the colon and an adjacent organ).

Related pathologies may include:

- Bowel obstruction

- Peritonitis

- Abscess

- Bleeding

- Strictures

A number of complications may occur from cholecystitis if not detected early or properly treated. Signs of complications include high fever, shock and jaundice. Complications include the following:

- Gangrene

- Gallbladder rupture

- Empyema

- Fistula formation and gallstone ileus

- Rokitansky-Aschoff sinuses

Most people with gallstones do not have symptoms. When a gallstone lodges in the cystic duct, they experience biliary colic. Biliary colic is abdominal pain in the right upper quadrant or epigastric region. It is episodic, occurs after eating greasy or fatty foods, and leads to nausea and/or vomiting. People who suffer from cholecystitis most commonly have symptoms of biliary colic before developing cholecystitis. The pain becomes more severe and constant in cholecystitis. Nausea is common and vomiting occurs in 75% of people with cholecystitis. In addition to abdominal pain, right shoulder pain can be present.

On physical examination, fever is common. A gallbladder with cholecystitis is almost always tender to touch. Because of the inflammation, its size can be felt from the outside of the body in 25–50% of people with cholecystitis. Pain with deep inspiration leading to termination of the breath while pressing on the right upper quadrant of the abdomen usually causes pain (Murphy's sign). Murphy's sign is sensitive, but not specific for cholecystitis. Yellowing of the skin (jaundice) may occur but is often mild. Severe jaundice suggests another cause of symptoms such as choledocholithiasis. People who are old, have diabetes, chronic illness, or who are immunocompromised may have vague symptoms that may not include fever or localized tenderness.

An unremoved infected abscess may lead to sepsis. Also, multiple abscesses may occur. Other complications may include fistula formation and recurrent pancreatitis.

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).

The most common symptoms and signs include:

- severe epigastric pain (upper abdominal pain) radiating to the back in 50% of cases

- nausea

- vomiting

- loss of appetite

- fever

- chills (shivering)

- hemodynamic instability, including shock

- tachycardia (rapid heartbeat)

- respiratory distress

- peritonitis

- hiccup

Although these are common symptoms, they are not always present. Simple abdominal pain may be the sole symptom.

Signs that are less common, and indicate severe disease, include:

- Grey-Turner's sign (hemorrhagic discoloration of the flanks)

- Cullen's sign (hemorrhagic discoloration of the umbilicus)

- Pleural effusions (fluid in the bases of the pleural cavity)

- Grünwald sign (appearance of ecchymosis, large bruise, around the umbilicus due to local toxic lesion of the vessels)

- Körte's sign (pain or resistance in the zone where the head of pancreas is located (in epigastrium, 6–7 cm above the umbilicus))

- Kamenchik's sign (pain with pressure under the xiphoid process)

- Mayo-Robson's sign (pain while pressing at the top of the angle lateral to the Erector spinae muscles and below the left 12th rib (left costovertebral angle (CVA))

- Mayo-Robson's point – a point on border of inner 2/3 with the external 1/3 of the line that represents the bisection of the left upper abdominal quadrant, where tenderness on pressure exists in disease of the pancreas. At this point the tail of pancreas is projected on the abdominal wall.

- Pandiaraja's sign- ecchymosis of right axilla

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.

Colic in horses is defined as abdominal pain, but it is a clinical sign rather than a diagnosis. The term colic can encompass all forms of gastrointestinal conditions which cause pain as well as other causes of abdominal pain not involving the gastrointestinal tract. The most common forms of colic are gastrointestinal in nature and are most often related to colonic disturbance. There are a variety of different causes of colic, some of which can prove fatal without surgical intervention. Colic surgery is usually an expensive procedure as it is major abdominal surgery, often with intensive aftercare. Among domesticated horses, colic is the leading cause of premature death. The incidence of colic in the general horse population has been estimated between 4 and 10 percent over the course of their lifetime. Clinical signs of colic generally require treatment by a veterinarian.

Systemic complications include ARDS, multiple organ dysfunction syndrome, DIC, hypocalcemia (from fat saponification), hyperglycemia and insulin dependent diabetes mellitus (from pancreatic insulin-producing beta cell damage), malabsorption due to exocrine failure

- Metabolic

- Respiratory

- Renal

- Renal artery or vein thrombosis

- Renal failure

- Circulatory

- Arrhythmias

- Hypovolemia and shock

- myocardial infarct

- Pericardial effusion

- vascular thrombosis

- Gastrointestinal

- Gastrointestinal hemorrhage from stress ulceration;

- gastric varices (secondary to splenic vein thrombosis)

- Gastrointestinal obstruction

- Hepatobiliary

- Jaundice

- Portal vein thrombosis

- Neurologic

- Psychosis or encephalopathy (confusion, delusion and coma)

- Cerebral Embolism

- Blindness (angiopathic retinopathy with hemorrhage)

- Hematologic

- Anemia

- DIC

- Leucocytosis

- Dermatologic

- Painful subcutaneous fat necrosis

- Miscellaneous

- Subcutaneous fat necrosis

- Arthalgia

Pain is the most common presenting symptom. It is usually described as sharp right upper quadrant pain that radiates to the right shoulder, or less commonly, behind the breastbone. Nausea and vomiting can be associated with biliary colic. Individuals may also present with pain that is induced following a fatty meal and the symptom of indigestion. The pain often lasts longer than 30 minutes, up to a few hours.

Patients usually have normal vital signs with biliary colic, whereas patients with cholecystitis are usually febrile and more ill appearing. Lab studies that should be ordered include a complete blood count, liver function tests and lipase. In biliary colic, lab findings are usually within normal limits. Alanine aminotransferase and aspartate transaminase are usually suggestive of liver disease whereas elevation of bilirubin and alkaline phosphatase suggests common bile duct obstruction. Pancreatitis should be considered if the lipase value is elevated; gallstone disease is the major cause of pancreatitis.

Patients will present with a sudden onset of cramps/abdominal pain or a 'stitch'. The pain localises in the area of the umbilicus and can radiate to the lumbar and surrounding regions.

The major symptom and signs include an acute onset of right upper quadrant (RUQ) abdominal pain aggravated by breathing, coughing or laughing, which may be referred to the right shoulder. There is usually also tenderness on palpation of the right upper abdomen and tenderness to percussion of the lower ribs which protect the liver. Surprisingly there is often no or only minimal pelvic pain, vaginal discharge or cervical motion tenderness, which may lead to the diagnosis being missed. This may be due to infectious bacteria bypassing pelvic structures on the way to the liver capsule.

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.

Gastric volvulus or volvulus of stomach is a twisting of all or part of the stomach by more than 180 degrees with obstruction of the flow of material through the stomach, variable loss of blood supply and possible tissue death. The twisting can occur around the long axis of the stomach: this is called organoaxial or around the axis perpendicular to this, called mesenteroaxial. Obstruction is more likely in organoaxial twisting than with mesenteroaxial while the latter is more associated with ischemia. About one third of the cases are associated with a hiatus hernia. Treatment is surgical.

The classic triad (Borchardt's Triad) of gastric volvulus, described by Borchardt in 1904, consists of severe epigastric pain, retching (due to sour taste in mouth) without vomiting, inability to pass a nasogastric tube and reportedly occurs in 70% of cases. Sometimes severe pain at the top of left shoulder, this may be due to internal bleeding irritating the diaphragm upon respiration.

Abdominal compartment syndrome occurs when the abdomen becomes subject to increased pressure. Specific cause of abdominal compartment syndrome is not known, although some causes can be sepsis and severe abdominal trauma. Increasing pressure reduces blood flow to abdominal organs and impairs pulmonary, cardiovascular, renal, and gastro-intestinal (GI) function, causing multiple organ dysfunction syndrome and death.