Acute Abdomen

Acute abdomen, which is in many cases a surgical emergency, is the sudden onset of abdominal pain that may be caused by inflammation, infection, perforation, ischemia, or obstruction. The location of the pain, its characteristics, and associated symptoms (e.g., jaundice) are important tools that help narrow the differential diagnosis. Patients will typically have severe tenderness with associated rigidity and rebound tenderness. Laboratory evaluation will demonstrate leukocytosis, acidosis, and in some cases, abnormal hepatic function tests. Imaging helps narrow the differential diagnosis; first-line imaging is always an upright chest X-ray to evaluate for pneumoperitoneum. The treatment and prognosis of acute abdomen strongly depend on the underlying cause, but the vast majority of these cases constitute a surgical emergency with associated morbidity and mortality.

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Overview

Definition

Acute abdomen is the constellation of signs and symptoms associated with severe abdominal pain and peritonitis that frequently requires emergency surgical intervention.

Epidemiology

  • Abdominal pain, in general, comprises 5%–10% of ED visits.
  • About ⅓ of patients > 65 years old with abdominal pain will require surgical intervention.
  • Acute abdomen:
    • Young individuals: Appendicitis is the most common cause.
    • Older individuals with acute abdomen most commonly have:
      • Biliary disease
      • Bowel obstruction
      • Intestinal ischemia
      • Diverticulitis

Etiology

Nonsurgical causes of acute abdomen:

  • Endocrine/metabolic causes:
    • Acute intermittent porphyria
    • Hereditary Mediterranean fever
    • Uremia
    • Diabetic ketoacidosis
  • Hematologic causes:
    • Sickle cell crisis
    • Acute leukemia
  • Toxins and drugs:
    • Lead poisoning
    • Narcotic withdrawal
    • Black widow spider poisoning

Surgical causes of acute abdomen:

  • Hemorrhage:
    • Trauma
    • Ruptured aneurysm
    • Hemorrhagic pancreatitis (usually does not require surgical intervention initially)
    • Mallory–Weiss tear
    • Ruptured ectopic pregnancy
  • Infection:
    • Appendicitis
    • Diverticulitis
    • Hepatic abscess
    • Meckel diverticulitis
  • Perforation:
    • Perforated gastric ulcer
    • Perforated diverticulum
    • Perforated tumor
    • Boerhaave syndrome
  • Obstruction:
    • Small- or large-bowel obstruction due to adhesions or malignancy
    • Volvulus
    • Incarcerated hernia
    • Intussusception
  • Ischemia:
    • Mesenteric thrombosis or embolism
    • Ovarian torsion
    • Ischemic colitis
    • Testicular torsion
    • Strangulated hernia

Anatomy

Boundaries of the abdominal cavity

  • Superiorly: diaphragm
  • Inferiorly: pelvic inlet
  • Anteriorly: abdominal wall muscles and lower ribs
  • Posteriorly: ribs, spine, and paraspinal muscles

External anatomy

For descriptive purposes, the abdomen can be divided into 4 quadrants or 9 regions.

Quadrants:

Divided into 4 quadrants by 2 perpendicular lines crossing at the umbilicus):

Right upper quadrant (RUQ):
  • Right lobe of the liver
  • Gallbladder
  • Pylorus of the stomach
  • First 3 parts of the duodenum
  • Head of the pancreas
  • Right kidney
  • Right adrenal gland
  • Distal ascending colon
  • Hepatic flexure of the colon
  • Right half of the transverse colon
Left upper quadrant (LUQ):
  • Left lobe of the liver
  • Spleen
  • Stomach
  • Jejunum
  • Proximal ileum
  • Body and the tail of the pancreas
  • Left kidney
  • Left adrenal gland
  • Left half of the transverse colon
  • Splenic flexure of the colon
  • Superior part of the descending colon
Right lower quadrant (RLQ):
  • Majority of the ileum
  • Cecum and appendix
  • Proximal ascending colon
  • Proximal right ureter
  • Right ovary
  • Right uterine tube
  • Right half of the uterus
  • Right half of the urinary bladder
Left lower quadrant (LLQ):
  • Distal descending colon
  • Sigmoid colon
  • Left ureter
  • Left ovary
  • Left uterine tube
  • Left half of the uterus
  • Left half of the urinary bladder

Regions:

The abdomen can be divided into regions with 4 lines:

  • 2 transverse lines:
    • Subcostal line: through the 10th costal cartilage
    • Intertubercular line: connects the tubercles of the iliac crests
  • 2 vertical lines: right and left midclavicular lines
Right hypochondriac regionEpigastric regionLeft hypochondriac region
Right lumbar regionUmbilical regionLeft lumbar region
Right iliac regionHypogastric regionLeft iliac region
Abdominal quadrant regions

Abdominal quadrant regions:
There are (a) 9 abdominal regions and (b) 4 abdominal quadrants in the peritoneal cavity.

Image: “Abdominal quadrant regions” by OpenStax. Download for free at http://cnx.org/contents/17e4eea8-a005-45af-b835-f756a014cd48@3. License: CC BY 3.0

Internal anatomy

Relationship of intra-abdominal organs to peritoneal cavity:

  • Intraperitoneal:
    • Stomach and small intestine
    • Liver
    • Spleen
    • Transverse colon
    • Duodenal bulb and pancreatic tail
  • Extraperitoneal: bladder
  • Retroperitoneal organs can be grouped in the SAD PUCKER mnemonic:
    • Suprarenal glands 
    • Aorta and inferior vena cava
    • Duodenum (except the 1st part)
    • Pancreas (except the tail)
    • Ureters
    • Colon (descending and ascending)
    • Kidneys
    • Esophagus
    • Rectum

Pain and innervation patterns

  • Visceral innervation: 
    • Innervation of internal organs
    • Senses the distention of a hollow viscus (e.g., stomach, intestines)
    • Pain:
      • Vague and poorly localized 
      • Epigastric, periumbilical, or hypogastric in location
  • Parietal innervation:
    • Segmental nerves that innervate the peritoneum
    • Transmit the pain from peritoneal irritation usually secondary to inflammation or internal bleeding
    • Sharper and more localized pain
  • Referred pain:
    • Pain perceived at a site different from the source of pain
    • Secondary to innervation of different sites by the same nerve roots
    • Classic example: diaphragmatic irritation perceived as shoulder pain due to both structures being innervated by C3–C5 roots

Clinical Presentation

The hallmark of acute abdomen is acute onset of severe abdominal pain that may or may not be associated with other symptoms. A detailed history and physical exam should be performed to determine the correct course of action.

History

  • Description of pain:
    • Onset
    • Location
    • Duration
    • Description
    • Radiation
    • Severity
    • Aggravating or alleviating factors: Peritonitis is classically exacerbated by movement.
  • Associated symptoms:
    • Nausea
    • Vomiting
    • Diarrhea
    • Melena or hematochezia
    • Fever
  • Past history:
    • Previous similar episodes
    • Underlying medical conditions
    • Preceding trauma (car accident, assault)
    • Prior abdominal surgeries
    • Recent travel, toxic exposures, food poisoning

Physical examination

  • Exam should always start with visual inspection to note things such as: 
    • Jaundice
    • Pallor
    • Work of breathing
    • Patient’s behavior:
      • Trying to lie still
      • Grimacing 
  • A full set of vital signs should be obtained and constitutional signs noted:
    • Fever
    • Tachycardia
    • Hypotension
    • Tachypnea
    • Altered mental status
  • A thorough abdominal exam should be completed:
    • Inspection:
      • Distention
      • Bruising (Cullen or Grey–Turner sign: hemorrhagic pancreatitis)
      • Bulging, skin discoloration (would suggest strangulated hernia)
    • Percussion: 
      • Tympanic (bowel distention or pneumoperitoneum)
      •  Dull (ascites or blood)
    • Auscultation: 
      • Typically, acute abdomen will be associated with hypoactive or absent bowel sounds.
      • Can have hyperactive bowel sounds in cases of high-grade bowel obstruction
    • Palpation: 
      • Typically, diffuse tenderness in all quadrants
      • Can have more pronounced tenderness in one site, which could help narrow the diagnosis
    • Peritoneal signs:
      • Rebound tenderness: Pain is suddenly worse when manual pressure is removed.
      • Guarding: involuntary or voluntary contraction of the abdominal wall
      • Rigidity: constant involuntary abdominal muscle contraction

Diagnosis

Laboratory studies

  • CBC:
    • ↑ WBCs
    • ↓ or  ↑ hemoglobin (bleeding versus hemoconcentration due to dehydration)
  • Basic metabolic panel: ↑ BUN and creatinine 
  • Amylase and lipase: ↑ in cases of pancreatitis
  • Hepatic function panel:
    •  ↑ or normal total and direct bilirubin
    •  ↑ or normal liver enzymes
  • Lactate: high levels indicative of sepsis/hypoperfusion
  • Urinalysis: to rule out urinary tract infection
  • Infectious stool panel
  • Blood cultures

Imaging studies

  • X-ray:
    • Upright chest X-ray:
      • First-line imaging in evaluating a patient with abdominal pain to rule out perforated viscus
      • Can identify as little as 1 mL of intra-abdominal free air
      • Can also reveal significant gastric dilation
    • Lateral decubitus abdominal film:
      • Can detect 5–10 mL of intra-abdominal free air
      • Identifies dilated loops of bowel, air fluid levels, and volvulus
  • Abdominal ultrasonography:
    • Right upper quadrant:
      • Gallbladder pathology
      • Hepatic pathology
      • Evaluate for free fluid
    • Right lower quadrant:
      • Appendiceal pathology
      • Ovarian and adnexal pathology
  • CT scan:
    • Second-line test after plain films
    • IV contrast and oral contrast (if tolerating oral intake)
    • Very specific for intra-abdominal pathology:
      • Perforation: free air
      • Bowel obstruction with dilated loops of bowel and air fluid levels
      • Bowel ischemia with pneumatosis, enhancing intestinal walls and portal venous gas
      • Intra-abdominal hematoma: with IV contrast can identify a vascular source
A chest radiograph demonstrating pneumoperitoneum

Upright chest X-ray showing pneumoperitoneum (arrows)

Image: “A chest radiograph demonstrating pneumoperitoneum” by Manabu Kaneko et al. License: CC BY 4.0

Management

Acute abdomen is a surgical emergency or urgency in the vast majority of cases. The initial evaluation should determine the cases that do not require surgical treatment.

Initial management

Resuscitation:

  • The first step should always be resuscitation of the patient.
  • Obtain reliable large-bore IV access.
  • Fluid bolus of 30 mL/kg for hypotension and tachycardia
  • Electrolyte correction
  • Airway protection/mechanical ventilation for impaired mental status or respiratory distress
  • Broad-spectrum IV antibiotics can be administered empirically.
  • Pain management

Evaluation:

  • Thorough history and physical exam 
  • Obtain labs, including CBC, basic metabolic panel, lactate, hepatic function panel.
  • Early blood cultures
  • Imaging:
    • In the majority of cases, there is at least time to obtain an upright chest X-ray to evaluate for free air.
    • Free air on imaging is an indication for immediate surgical intervention.
    • Without evidence of free air in a stable patient, there is time to obtain a CT scan.

Operative management

Surgical treatment is usually needed unless a nonsurgical cause has been established. If surgical intervention is warranted, there are two approaches:

  • Diagnostic laparoscopy:
    • Minimally invasive approach using a laparoscope to explore the abdomen
    • Most helpful in triaging the abdomen and deciding whether an open approach is needed
    • Sometimes, a definitive intervention can be performed laparoscopically.
    • Technically limited in difficult-to-access areas and complex surgical repairs
    • Should be avoided in cases of significantly dilated bowel owing to risk of perforation with port insertion and laparoscopic instruments
    • Should not be performed in cases in which diagnosis is clear and open intervention will definitely be required
  • Exploratory laparotomy:
    • Open surgical approach, typically through a midline incision
    • Allows for visual and tactile examination of all the abdominal quadrants and their contents
    • Approach of choice in cases of gross abdominal contamination with bile or enteric contents
    • Allows for repair of the source of contamination as well as irrigation of the abdominal cavity

References

  1. Squires, R. A., Postier, R. G. (2012). In Mattox, K. L., Evers, B. M., Beauchamp, R. D., Townsend, C. M. (Eds.), Sabiston Textbook of Surgery: The Biological Basis of Modern Surgical Practice, 19th ed. pp. 1141–1159.
  2. Penner, R. M., Fishman, M. B. (2020). Evaluation of the adult with abdominal pain. In Kunins L. (Ed.), UpToDate. Retrieved April 4, 2021, from https://www.uptodate.com/contents/evaluation-of-the-adult-with-abdominal-pain
  3. Cahalane, M. J. (2019). Overview of gastrointestinal tract perforation. In Chen, W. (Ed.), UpToDate. Retrieved April 4, 2021, from https://www.uptodate.com/contents/overview-of-gastrointestinal-tract-perforation
  4. Bordejanou, L., Yeh, D. D. (2020). Management of small bowel obstruction in adults. In Chen, W. (Ed.), UpToDate. Retrieved April 4, 2021, from https://www.uptodate.com/contents/management-of-small-bowel-obstruction-in-adults
  5. Daley, B. J. (2019). Peritonitis and abdominal sepsis. In Roy, P. K. (Ed.), Medscape. Retrieved April 6, 2021, from https://emedicine.medscape.com/article/180234-overview#a2

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