The correct interpretation of acute abdominal pain is one of the most challenging demands made of any physician. A detailed history and physical examination is of utmost importance in case of an abdominal pain.

Abdominal pain is the pain that is felt in the abdomen. Abdominal pain can arise from the tissue of the abdominal wall that surrounds the abdominal cavity. The organs of the abdomen comprise stomach, intestines, colon, liver, gall bladder and pancreas.

Sometimes, pain is felt in the abdomen even though it is related to the pathology of some other organs. Vice versa, the pain can be felt in the other parts of the body even though it is originated from the abdomen.

Sometimes, the abdominal pain is referred as stomach pain.

Causes of abdominal pain

Abdominal pain can be caused by inflammation such as:

• Appendicitis (inflammation of the appendix)

• Diverticulitis

• Colitis

• Cholecystitis (inflammation of the gall bladder with or without gall stones) or (blockage of bile duct by gall stone)

• Hepatitis (inflammation of the liver)

• Parietal peritoneal inflammation

- bacterial contamination – e.g. perforated appendix, pelvic inflammatory disease

- chemical irritation – e.g. perforated ulcer, pancreatitis

Apart from inflammation, the possible causes are:

• Chronic constipation

• Excessive gas

• Food allergy

• Food poisoning

• Heart burn and indigestion

• Parasitic infections

• Sickle cell crisis

• Hernia

The abdominal pain due to any mechanical obstruction of the organ:

• Obstruction of the small or large intestine

• Obstruction of the biliary tree

• Obstruction of the ureters

The abdominal pain due to vascular disturbances:

• Embolism or thrombosis

• Vascular rupture

• Pressure or torsional occlusion

• Sickle cell anemia

Pain due to the pathology of the abdominal wall:

• Distortion or traction of mesentery

• Trauma or infection of muscles

Distension of visceral surfaces:

• Hepatic or renal capsule

Mechanisms of pain originating in the abdomen:

The pain of peritoneal inflammation is steady and aching in character and is located directly over the inflamed area, its exact reference being possible because it is transmitted by somatic nerves supplying the parietal peritoneum.

The intensity of the pain is dependant on the type and amount of foreign substance to which the peritoneal surfaces are exposed in a given period of time.

For example, the sudden release into the peritoneal cavity of a small quantity of sterile acid gastric juice causes much more pain than the same amount of grossly contaminated neutral fecal material.

Enzymatically, active pancreatic juice incites more pain and inflammation than does the same amount of sterile bile containing no potent enzymes. Blood and urine are often so bland as to go undetected if exposure of the peritoneum has not been sudden and massive. In the case of bacterial contamination, such as in pelvic inflammatory disease, the pain is frequently of low intensity early in the illness until bacterial multiplication has caused the elaboration of irritating substances.

The pain of peritoneal inflammation is invariably accentuated by pressure or changes in tension of the peritoneum, whether produced by palpation or by movement as in coughing or sneezing. Consequently, the patient of peritonitis lies quietly in bed, preferring to avoid motion, in contrast to the patient with colic, who may writhe incessantly.

Another characteristic feature of peritoneal irritation is tonic reflex spasm of the abdominal muscle and this spasm depends on the location of the inflammatory process, the rate at which it develops and the integrity of the nervous system.

Spasm over a perforated retrocecal appendix or perforated ulcer into the lesser peritoneal sac may be minimal or absent because of the protective effect of overlying viscera.

As in pain of peritoneal inflammation, a slowly developing process often greatly attenuates the degree of muscle spasm. Catastrophic abdominal emergencies such as perforated ulcer have been repeatedly associated with minimal or occasionally no detectable pain or muscle spasm in obtunded, seriously ill, debilitated elderly patients or in psychotic patients.

Obstruction of hollow viscera

The pain of obstruction of hollow abdominal viscera is classically described as intermittent or colicky.

Yet the lack of a truly cramping character should not be misleading, because distension of a hollow viscus may produce steady pain with only occasional exacerbations.

Although not early as well localized as the pain of peritoneal inflammation, some useful generalities can be made concerning its distribution.

Obstruction of small intestine

The colicky pain of obstruction of the small intestine is usually periumbilical or supraumbilical and is poorly localized. As the intestine becomes progressively dilated with loss of muscular tone, the colicky nature of the pain may become less apparent.

With superimposed strangulating obstruction, pain may spread to the lower lumbar region if there is traction of the root of mesentery. The colicky pain of colonic obstruction is of lesser intensity than that of the small intestine and is often located in the infraumbilical area. Lumbar radiation of pain is common in colonic obstruction.

Distension of biliary tree

Sudden distension of the biliary tree produces a steady rather than colicky type of pain; hence the term biliary colic is misleading. Acute distension of the gall bladder usually causes pain in the right upper quadrant with radiation to the right posterior region of the thorax or to the tip of the right scapula and distension of the common bile duct is often associated with pain in the epigastrium radiating to the upper part of the lumbar region.

The pain of distension of the pancreatic ducts is similar to that described for distension of the common bile duct, but in addition is very frequently accentuated by recumbency and relieved by the upright position.

Obstruction of urinary bladder

Obstruction of the urinary bladder results in dull suprapubic pain, usually low in intensity. Restlessness without specific complaint of pain may be the only sign of a distended bladder in an obtunded patient.

In contrast, acute obstruction of the intravesicular portion of the ureters is characterized by severe suprapubic and flank pain which radiates to the penis, scrotum or inner aspect of the upper region of the thigh.

Obstruction of the ureteropelvic junction is felt as pain in the costovertebral angle, whereas obstruction of the remainder of the ureters is associated with flank pain which often extends into the corresponding side of the abdomen.

Vascular disturbances

A frequent misconception, despite abundant experience to the contrary, is that pain associated with intra – abdominal vascular disturbances is sudden and catastrophic in nature.

The pain of embolism or thrombosis of the superior mesenteric artery or that of impending rupture of an abdominal aortic aneurysm certainly may be severe and diffuse. Yet, just as frequently, the patient with occlusion of superior mesenteric artery has only mild continuous diffuse pain for 2 or 3 days before vascular collapse or findings of peritoneal inflammation appear.

The early, seemingly insignificant discomfort is caused by hyperperistalsis rather than peritoneal inflammation. Absence of tenderness and rigidity in the presence of continuous diffuse pain in a patient likely to have vascular disease is quite characteristic of occlusion of the superior mesenteric artery.

Abdominal pain with radiation to the sacral region, flank or genitalia should always signal the possible presence of a rupturing abdominal aortic aneurysm. This pain may persist over a period of several days before rupture and collapse occur.

Abdominal wall

Pain arising from the abdominal wall is usually constant and aching. Movement, prolonged standing and pressure accentuate the discomfort and muscle spasm. In the case of hematoma of the rectus sheath, now most frequently encountered in association with anti-coagulant therapy, a mass may be present in the lower quadrants of the abdomen. Simultaneous involvement of muscles in other parts of the body usually serves to differentiate myositis of the abdominal wall from an intraabdominal process which might cause pain in the same region.

Referred pain in abdominal diseases

Pain referred to the abdomen from the thorax, spine or genitalia may prove a vexing diagnostic problem, because diseases of the upper abdominal cavity such as acute cholecystitis or perforated ulcer are frequently associated with intrathoracic complications.

Intra thoracic diseases

A very rare but a possible symptom of the upper thoracic disease must be considered in every patient with abdominal pain, especially if the pain is in the upper part of the abdomen.

Systemic questioning and examination directed towards detecting the presence or absence of myocardial or pulmonary infarction, pneumonia, pericarditis, or esophageal disease (the intrathoracic disease which often requires abdominal emergencies) will often provide sufficient clues to establish the proper diagnosis.

Diaphragmatic pleuritis resulting from pneumonia or pulmonary infarction may cause pain in the right upper quadrant and pain in the supraclavicular area, the latter radiation to be sharply distinguished from the referred sub scapular pain caused by acute distension of extrahepatic biliary tree.

The ultimate decision as to the origin of abdominal pain may require deliberate and planned observation over a period of several hours, during which time required questioning and examination will provide the proper explanation.

Referred pain of thoracic origin is often accompanied by splinting of the involved hemi thorax with respiratory lag and decrease in excursion more marked than that seen in the presence of intraabdominal disease.

Palpation over the area of the referred pain in the abdomen also does not usually accentuate the pain and in many instances actually seems to relieve it.

Referred pain from spine region

Referred pain from the spine, which usually involves compression or irritation of nerve roots, is characteristically intensified by certain motions such as cough, sneeze or strain and is associated with hyperesthesia over the involved dermatomes. Pain referred to the abdomen from the testicles or seminal vesicles is generally accentuated by the slightest pressure on either of these organs. The abdominal discomfort is of dull aching character and is poorly localized.

Neurogenic causes

Causalgic pain may occur in diseases that injures nerves of sensory type. It has a burning character and is usually limited to the distribution of a given peripheral nerve. Normal stimuli such as touch or change in temperature may be transformed into this type of pain, which is also frequently present in a patient at rest.

Even though the pain may be precipitated by gentle palpation, rigidity of the abdominal muscles is absent, and the respirations are not disturbed. Distension of the abdomen is uncommon and the pain has no relationship to the intake of food.

Psychogenic pain varies enormously in type and location but usually has no relation to meals. It is often at its onset markedly accentuated during the night. Nausea and vomiting are rarely observed, and the patient occasionally complaints of such symptoms. Spasm is seldom induced in the abdominal musculature and if present, does not persist, especially if the attention of the patient can be distracted. Persistent localized tenderness is rare, and if found, the muscle spasm in the area is inconsistent and often absent.

Restriction of the depth of respiration is the most common respiratory abnormality, but this is in the nature of a smothering or choking sensation and is part of an anxiety state. It occurs in the absence of thoracic splinting or change in the respiratory rate.