Etiology

Acute abdomen refers to the rapid onset of severe symptoms of abdominal pathology. Acute abdomen may indicate a potentially life-threatening condition that requires urgent surgical intervention.

The commonest causes of acute abdomen are:[13]

  • nonspecific abdominal pain

  • renal colic

  • biliary colic

  • cholecystitis

  • appendicitis

  • diverticulitis.

Likely etiology varies according to age. Renal colic and appendicitis are more common in patients <60 years, while gallbladder disease and diverticulitis are more common in older patients.[13][14]

Gastrointestinal causes

  • Acute abdomen may result from inflammation causing peritonitis (e.g., appendicitis, diverticulitis, Meckel diverticulitis), bowel obstruction, perforated viscus, or infection.

  • Bowel obstruction occurs when there is a mechanical interruption to the flow of intestinal contents. The commonest causes of small bowel obstruction are intra-abdominal adhesions from previous surgery and incarcerated hernia.[15] Large bowel obstruction is usually caused by a colorectal tumor.[16] Large bowel volvulus or stricture are other possible causes.

  • A gastric or duodenal ulcer may erode the wall of the stomach or duodenum leading to perforation. Esophageal perforation (Boerhaave syndrome) and Mallory-Weiss tear result in esophageal laceration and gastrointestinal hemorrhage. Perforation can also occur as a consequence of untreated inflammation or obstruction.

  • Ulcerative colitis and Crohn disease may present with abdominal pain secondary to the inflammatory process or due to the complication of obstruction.

  • Infective processes include gastroenteritis, infectious colitis, and typhlitis (neutropenic enterocolitis).

Genitourinary causes

  • Renal and ureteric stones, and pyelonephritis, are urologic causes of abdominal pain.

  • Obstructed renal and ureteric stones can cause renal colic: severe, acute flank pain that may radiate to the ipsilateral groin, commonly associated with nausea and vomiting. Rarely, this is accompanied by macroscopic hematuria. As stones pass and get lodged in the distal ureter or intramural tunnel, this can lead to bladder irritation manifested as urinary frequency or urgency. Ipsilateral testicular and groin pain may occur rarely in men with obstructive stones.

  • Common signs and symptoms of pyelonephritis include acute-onset fever, chills, severe back or flank pain, nausea and vomiting, and costovertebral angle tenderness.

  • In men, testicular torsion should be considered.

  • Gynecologic causes of acute abdomen include ectopic pregnancy, ruptured ovarian cyst, ovarian torsion, pelvic inflammatory disease, and endometriosis.

Hepatobiliary and pancreatic causes

  • Biliary colic is characterized by steady, severe pain in the right upper quadrant (RUQ). Symptoms last between 15 minutes and 5 hours.

  • Cholecystitis is biliary pain lasting more than 5 hours and is accompanied by features of inflammation, e.g., fever, marked RUQ tenderness, and leukocytosis.

  • Pancreatitis typically presents with sudden onset epigastric or left upper quadrant (LUQ) pain, which may radiate to the back. The majority of patients also have nausea and vomiting. The most common causes are gallstones and excessive alcohol consumption.

  • Infectious causes include hepatitis and hepatic abscess. Fitz-Hugh Curtis syndrome, a complication of pelvic inflammatory disease, comprises RUQ abdominal pain associated with perihepatitis.

Vascular causes

  • Vascular pathologies may result in intra-abdominal hemorrhage, including abdominal aortic dissection, ruptured aortic aneurysm, and ruptured splenic artery aneurysm.

  • Ischemic causes include acute mesenteric ischemia and infarction, ischemic colitis, and splenic infarct.

  • Vaso-occlusive episodes in sickle cell crises can present with abdominal pain.

  • Budd-Chiari syndrome involves hepatic venous outflow obstruction and the abdominal pain may present with hepatomegaly and ascites.

  • Splenic infarct can cause LUQ pain.

Metabolic and toxic causes

  • Metabolic causes of acute abdomen include uremia, diabetic ketoacidosis, Addisonian crisis, and hypercalcemia.

  • Inherited metabolic disorders include acute intermittent porphyria and hereditary Mediterranean fever.

  • Heavy metal poisoning may be caused by medical/environmental/occupational exposure (e.g., mercury, lead, arsenic).

  • Withdrawal from opioids may result in abdominal cramping pain.

Musculoskeletal causes

  • Psoas abscess is most commonly due to a tuberculous abscess, which has extended from the lumbar vertebra into the psoas muscle.

  • Abdominal wall hematoma may occur spontaneously or secondary to trauma, exercise, coughing, or a procedure.

Other

  • Radiation enteritis and spider bites are other less common causes of an acute abdomen.

Nonspecific abdominal pain (NSAP)

  • Describes abdominal pain of <7 days' duration, when history, examination, and investigation have not revealed a cause of abdominal pain. It is a diagnosis of exclusion.

  • A large retrospective study conducted in Finland found that NSAP was the most common diagnosis in patients who attended the emergency department with acute abdominal pain.[17] NSAP remained the most diagnosed condition throughout the 26 years of the study, despite presumed improvement in radiographic techniques over the course of data collection.

  • NSAP seems more common in children than adults. One prospective study of children admitted under surgery with NSAP found that 2.3% were readmitted with abdominal pain during the subsequent 30 days, 0.5% had an operation or invasive procedure within 3 months of their original admission, and 0.2% had missed appendicitis.[18]

  • A cohort study conducted in Sweden reported that 2.2% of patients who were discharged from the emergency department with a diagnosis of NSAP were diagnosed with cancer within 12 months.[19] The majority of patients who were diagnosed with cancer were ≥60 years.

  • A retrospective study conducted in Denmark reported that 16% of patients discharged with NSAP were readmitted with abdominal pain within 3 months; 39% received a confirmed diagnosis of a somatic condition at the return visit.[20] 40% of those readmitted with a specific diagnosis were for biliary tract pathology. Comorbidity, nausea, vomiting, and leukocytosis at the primary admission were significantly associated with a missed significant diagnosis.[20]

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