Selected causes
Traumatic: blunt or perforating trauma to the stomach, bowel, spleen, liver, or kidney
Inflammatory:
Infections such as appendicitis, cholecystitis, pancreatitis, pyelonephritis, Peritonitis, pelvic inflammatory disease, hepatitis, mesenteric adenitis, or a subdiaphragmatic abscess
Perforation of a peptic ulcer, a diverticulum, or the caecum
Complications of inflammatory bowel disease such as Crohns disease or ulcerative colitis
Mechanical:
Small bowel obstruction secondary to adhesions caused by previous surgeries, intussusception, hernias, benign or malignant neoplasms
Large bowel obstruction caused by colorectal cancer, inflammatory bowel disease, volvulus, fecal impaction or hernia
Vascular: occlusive intestinal ischemia, usually caused by thromboembolism of the superior mesenteric artery

By system
A more extensive list includes the following:
Gastrointestinal
GI tract
Inflammatory: gastroenteritis, appendicitis, gastritis, esophagitis, diverticulitis, Crohns disease, ulcerative colitis, microscopic colitis
Obstruction: hernia, intussusception, volvulus, post-surgical adhesions, tumors, severe constipation, hemorrhoids
Vascular: embolism, thrombosis, hemorrhage, sickle cell disease, abdominal angina, blood vessel compression (such as celiac artery compression syndrome), superior mesenteric artery syndrome, postural orthostatic tachycardia syndrome
Digestive: peptic ulcer, lactose intolerance, celiac disease, food allergies, indigestion
Glands
Bile system
Inflammatory: cholecystitis, cholangitis
Obstruction: cholelithiasis, tumours
Liver
Inflammatory: hepatitis, liver abscess
Pancreatic
Inflammatory: pancreatitis
Renal and urological
Inflammation: pyelonephritis, bladder infection
Obstruction: kidney stones, urolithiasis, urinary retention, tumours
Vascular: left renal vein entrapment
Gynaecological or obstetric
Inflammatory: pelvic inflammatory disease
Mechanical: ovarian torsion
Endocrinological: menstruation, Mittelschmerz
Tumors: endometriosis, fibroids, ovarian cyst, ovarian cancer
Pregnancy: ruptured ectopic pregnancy, threatened abortion
Abdominal wall
muscle strain or trauma
muscular infection
neurogenic pain: herpes zoster, radiculitis in Lyme disease, abdominal cutaneous nerve entrapment syndrome (ACNES), tabes dorsalis
Referred pain
from the thorax: pneumonia, pulmonary embolism, ischemic heart disease, pericarditis
from the spine: radiculitis
from the genitals: testicular torsion
Metabolic disturbance
uremia, diabetic ketoacidosis, porphyria, C1-esterase inhibitor deficiency, adrenal insufficiency, lead poisoning, black widow spider bite, narcotic withdrawal
Blood vessels
aortic dissection, abdominal aortic aneurysm
Immune system
sarcoidosis
vasculitis
familial Mediterranean fever
Idiopathic
irritable bowel syndrome (IBS)(affecting up to 20% of the population, IBS is the most common cause of recurrent and intermittent abdominal pain)

By location
The location of abdominal pain can provide information about what may be causing the pain.
The foregut contains the pharynx, lower respiratory tract, portions of the esophagus, stomach, portions of the duodenum (proximal), liver, biliary tract (including the gallbladder and bile ducts), and the pancreas. The midgut contains portions of the duodenum (distal), cecum, appendix, ascending colon, and first half of the transverse colon. The hindgut contains the distal half of the transverse colon, descending colon, sigmoid colon, rectum, and superior anal canal.Each subsection of the gut has an associated visceral afferent nerve that transmits sensory information from the viscera to the spinal cord, traveling with the autonomic sympathetic nerves. The visceral sensory information from the gut traveling to the spinal cord, termed the visceral afferent, is non-specific and overlaps with the somatic afferent nerves, which are very specific. Therefore, visceral afferent information traveling to the spinal cord can present in the distribution of the somatic afferent nerve; this is why appendicitis initially presents with T10 periumbilical pain when it first begins and becomes T12 pain as the abdominal wall peritoneum (which is rich with somatic afferent nerves) is involved. Diagnosis
A thorough patient history and physical examination is used to better understand the underlying cause of abdominal pain. The process of gathering a history may include:
Identifying more information about the chief complaint by eliciting a history of present illness; i.e. a narrative of the current symptoms such as the onset, location, duration, character, aggravating or relieving factors, and temporal nature of the pain.