Acute abdomen

Acute abdomen refers to severe abdominal pain lasting for ≤ 5 days. The underlying pathology may be intra-abdominal, thoracic, or systemic and may require urgent surgical intervention. The initial approach to acute abdomen should be to assess for immediately life-threatening causes (e.g., ruptured abdominal aortic aneurysm, bowel perforation) by checking vital signs, performing a quick physical examination, and immediately conducting the appropriate focused diagnostic tests (e.g., abdominal ultrasound, abdominal x-ray). Once emergency causes have been ruled out, a thorough history and physical examination should be performed to narrow the differential diagnoses and guide further diagnostic workup and therapy. Traumatic causes of abdominal pain, abdominal trauma, and chronic abdominal pain are not addressed here.

The diagnostic workup should be guided by the pretest probability of the diagnoses under consideration. The following list includes some commonly used diagnostic tools that can help to diagnose or rule out possible etiologies in a patient with acute abdominal pain.

Laboratory studies

• Blood gas analysis
• Lactate
• Troponin
• Serum glucose
• CBC
• Coagulation studies (e.g., INR, PT)
• BMP
• LFTs
• Lipase, amylase
• Blood type and screen
• ESR/CRP
• Urinalysis
• β-hCG urine test
• Cultures

A urine pregnancy test should be performed in every woman of reproductive age, regardless of current contraception use.
Patients with obvious signs of diffuse peritonitis do not require further diagnostic imaging and should proceed straight to surgical management.

Imaging ^{[2][3][4][5][6][7][8]}

Approach

• The initial imaging modality should be guided by the working diagnosis, as based on the patient history, vital signs, and examination.
• The following recommendations apply to nonpregnant adults.
• In pregnant women with acute abdominal pain, ultrasound and/or MRI of the abdomen and/or pelvis without contrast are the preferred initial imaging modalities.

By suspected diagnosis ^[5]

Suspected diagnosis	Recommended imaging modality
Acute coronary syndrome	ECG TTE
Hemorrhagic shock [6]	FAST
Bowel perforation [2]	CT abdomen and pelvis with IV contrast X-ray abdomen (upright and supine) with x-ray chest (upright)
Small bowel obstruction [3]
Intra-abdominal abscess	CT abdomen and pelvis with IV contrast
Acute diverticulitis [7]
Acute appendicitis [4]
Acute mesenteric ischemia [9]	CTA of the abdomen
Acute pancreatitis [10]	Ultrasound abdomen CT abdomen with IV contrast
Nephrolithiasis [11]	Ultrasound abdomen and pelvis CT abdomen and pelvis without contrast
Acute complicated pyelonephritis [6]	CT abdomen and pelvis with IV contrast
Suspected symptomatic AAA in a hemodynamically stable patient [12]	Ultrasound abdomen CT/MR angiography

By location of the pain

Site of pain
	Initial test of choice	Alternatives
RUQ pain [13]	Ultrasound abdomen	CT abdomen with IV contrast MRCP Acalculous cholecystitis suspected: HIDA scan
RLQ pain [4] or LLQ pain [7]	CT abdomen and pelvis with IV contrast	CT abdomen and pelvis without IV contrast MRI abdomen and pelvis with or without IV contrast Abdominal and/or pelvic ultrasound Suspected ovarian/testicular torsion: Duplex ultrasound of the pelvis (♀)/scrotum (♂)
LUQ pain [14]	CT abdomen with oral and IV contrast	Acute abdominal series
Suprapubic pain [14]	Ultrasound abdomen and pelvis	CT abdomen and pelvis with/without IV contrast MRI with/without IV contrast Transvaginal ultrasound
Pelvic pain [15]	Gynecological etiology suspected: Ultrasound pelvis (transabdominal and/or transvaginal) Nongynecological etiology suspected and β-HCG is negative: CT abdomen and pelvis with IV contrast	Suspected ovarian torsion: Duplex ultrasonography of pelvic adnexa MRI pelvis (+/- abdomen) with IV contrast
Nonlocalized pain [2]	CT abdomen and pelvis with IV contrast	CT abdomen and pelvis without IV contrast MRI abdomen and pelvis with/without IV contrast Ultrasound abdomen and/or pelvis Postoperative patients with acute abdomen: consider fluoroscopy (enema and/or upper abdominal series)

Consider diagnostic laparoscopy in hemodynamically stable patients in which the diagnosis is still unclear after complete physical examination and imaging. For patients with hemodynamic instability or severe abdominal distention, proceed to diagnostic laparotomy. ^[16]

In pregnant patients, regardless of the site of pain, ultrasound and MRI are the preferred initial imaging modalities.

	Clinical features	Diagnostic findings	Acute management
Acute coronary syndrome [17][18]	Heavy, dull, pressure/squeezing sensation Substernal or epigastric pain with radiation to left shoulder Nausea, vomiting Diaphoresis, anxiety Dizziness, lightheadedness, syncope Pain may improve with nitroglycerin.	ECG: nonspecific changes, ST-segment elevation/depression, T-wave inversions, Q waves Increased or normal troponin TTE: hypokinesis, regional wall motion abnormalities	See the acute management checklist for STEMI and acute management checklist for NSTEMI/UA.
Acute mesenteric ischemia [19][20][21][22]	Age > 60 years, embolic risk factors (e.g., atrial fibrillation, thrombophilia), cardiovascular disease Pain out of proportion to findings Severe, diffuse abdominal pain and distention Vomiting, diarrhea Melena, hematochezia	Labs: lactic acidosis, hyperkalemia, leukocytosis X-ray abdomen: normal (early stages), pneumatosis intestinalis (late stages) CT angiography: mesenteric arterial narrowing or occlusion, thickening of bowel wall, nonenhancing segments of solid organs or of the bowel wall, pneumatosis intestinalis	See the acute management checklist for acute mesenteric ischemia.
Rupture or impending rupture of AAA [23]	Age > 50 years Sudden, severe central abdominal, chest, and/or back pain Hypotension, shock Pulsatile mass in the midline of the abdomen Grey Turner sign and/or Cullen sign History of atherosclerosis, hypertension, and/or smoking	Imaging is only recommended in hemodynamically-stable patients with a low pretest probability of ruptured AAA. Abdominal ultrasound: aortic dilatation, periaortic fluid, intraperitoneal free fluid CT/MR angiography: retro- and intraperitoneal hemorrhage; localization of the ruptured/leaking site	See the acute management checklist for ruptured AAA.
Aortic dissection [24][25][26]	Sudden onset of severe, sharp tearing chest or abdominal pain that radiates to the back Hypotension, syncope, neurological symptoms Asymmetrical blood pressure, pulse deficit New diastolic murmur (due to aortic regurgitation) Symptoms of myocardial ischemia	Elevated D-dimer ECG: nonspecific ST-segment changes CXR: widening of the aorta CT angiography of chest/abdomen/pelvis : intimal flap with false lumen Transesophageal echocardiography (TEE): proximal aortic dissection, tamponade, aortic regurgitation	See the acute management checklist for aortic dissection.

	Clinical features	Diagnostic findings	Acute management
GI tract perforation [27][28][2]	Sudden onset of diffuse abdominal pain Nausea, vomiting Constipation/obstipation Diffuse abdominal guarding, rigidity, and rebound tenderness Absent bowel sounds Loss of liver dullness on RUQ percussion	Abdominal x-ray: pneumoperitoneum	See the acute management checklist for GI tract perforation and the acute management checklist for esophageal perforation.
Mechanical bowel obstruction [2][3][29][30]	Colicky abdominal pain Obstipation/bloating Progressive nausea and vomiting (late finding) Diffuse abdominal distention, tympanic abdomen, collapsed rectum on DRE Tinkling bowel sounds History of abdominal surgery	X-ray abdomen Dilated bowel loops proximal to the obstruction Rectal air shadow absent Multiple air-fluid levels CT abdomen with IV and oral contrast Similar findings as on x-ray Transition point at site of obstruction	See the acute management checklist for mechanical bowel obstruction.
Acute appendicitis [31][32][33][34]	RLQ, epigastric, and/or periumbilical pain (migrating abdominal pain) Fever Nausea, anorexia Guarding, tenderness, and rebound tenderness in the RLQ	Neutrophilic leukocytosis Abdominal CT scan with IV contrast : distended appendix with periappendiceal fat stranding Abdominal ultrasonography : noncompressible, aperistaltic, distended appendix, probe tenderness in the RLQ, Target sign	See the acute management checklist for acute appendicitis.
Peptic ulcer disease [35][36][37]	Epigastric pain Duodenal ulcer: pain relieved with food; weight gain Gastric ulcer: pain exacerbated by food; weight loss Signs of GI bleed History of NSAID intake	Anemia, positive FOBT (in cases of bleeding ulcer) Urea breath test for H. pylori: positive in most cases of PUD EGD: Mucosal erosions and/or ulcers are required for a definitive diagnosis.	See the acute management checklist for peptic ulcer disease.
Diverticulitis [38][39][40][41][42][43][44]	Fever LLQ pain Constipation Tender mass in LLQ	Labs: ↑ WBC CT with IV and oral contrast: colonic diverticula with pericolic mesenteric fat stranding	See the acute management checklist for diverticulitis.

	Clinical features	Diagnostic findings	Acute management
Acute pancreatitis [45][46][47]	Severe epigastric pain that radiates to the back (circumferential pain) Nausea, vomiting Epigastric tenderness, guarding, rigidity Hypoactive bowel sounds Possibly fever History of gallstones or alcohol use	↑ Lipase, amylase Hypocalcemia (poor prognostic indicator) Abdominal ultrasound: pancreatic edema, peripancreatic fluid, gallstones Abdominal CT with IV contrast : pancreatic edema, peripancreatic fat stranding, gallstones	See the acute management checklist for acute pancreatitis.
Symptomatic cholelithiasis [48][49][50]	Biliary colic: RUQ pain with radiation to the right shoulder Postprandial onset Nausea, vomiting Normal abdominal examination	Labs: normal Abdominal ultrasound: gallstones with posterior acoustic shadow	See the acute management checklist for biliary colic.
Choledocholithiasis [51][48]	RUQ pain Features of obstructive jaundice Nausea, vomiting Normal abdominal examination	Labs: ↑ ALP, AST, ALT, total bilirubin Abdominal ultrasound [52][53] Dilated common bile duct (CBD) Intrahepatic biliary dilatation Echogenic structure within the CBD with shadowing EUS: stone within the CBD MRCP or ERCP: filling defect in the contrast-enhanced duct	See the acute management checklist for choledocholithiasis.
Acute cholecystitis [48][49][54][55][56]	Severe RUQ pain Fever, chills Nausea, vomiting Right shoulder referred pain Murphy sign	Labs: ↑ WBC Abdominal ultrasound: sonographic Murphy sign , pericholecystic fluid collection, gallbladder wall thickening, and/or edema (double-wall sign) [57] HIDA scan : nonvisualization of the gallbladder	See the acute management checklist for acute cholecystitis.
Acute cholangitis [48][49][58][59] [54][60][61]	Charcot triad: RUQ pain, fever, and jaundice Reynold pentad	Labs ↑ WBC and CRP ↑ ALP, ↑ AST, ↑ ALT, ↑ GGT ↑ Total bilirubin Positive blood cultures RUQ ultrasound: biliary dilation and/or evidence of obstruction (e.g., choledocholithiasis), thickening of bile duct walls MRCP/ERCP : findings similar to those on ultrasound	See the acute management checklist for acute cholangitis.

	Clinical features	Diagnostic findings	Acute management
Ruptured ectopic pregnancy [62]	Sudden severe lower abdominal pain Vaginal bleeding or amenorrhea Lower abdominal guarding and tenderness Cervical motion tenderness, closed cervix Enlarged uterus Tachycardia, hypotension	↑ β-hCG Transabdominal/transvaginal ultrasound Free fluid within Morison pouch and/or pouch of Douglas Empty uterine cavity, thickened endometrial lining Adnexal mass Tubal ring sign	See the acute management checklist for ectopic pregnancy.
Ovarian torsion [63][64]	Sudden onset unilateral lower abdominal or pelvic pain Nausea, vomiting Unilateral iliac fossa tenderness	Pelvic (or transvaginal) ultrasound with Doppler velocimetry: enlarged, edematous ovaries with decreased blood flow Pelvic CT scan with IV contrast Unilateral thickened ovarian tube, enlarged ipsilateral ovary, and decreased enhancement of ipsilateral ovary Twisted vascular pedicle (whirlpool sign)	See the acute management checklist for ovarian torsion.
Testicular torsion [65]	Severe lower quadrant and testicular pain Nausea and vomiting Abnormally elevated position of the testis within the scrotum	Clinical diagnosis Doppler ultrasound: twisting of the spermatic cord; reduced perfusion of the affected testicle	See the acute management checklist for testicular torsion.
Acute pyelonephritis [6][66][67][68][69]	High fever, chills Flank pain with costovertebral angle tenderness (usually unilateral, may be bilateral) Dysuria, urinary frequency, urgency	Labs ↑ WBC, CRP, ESR Positive urinalysis Positive urine culture Renal ultrasound: edema and focal hypoechogenic areas CT pelvis with IV contrast: focal area(s) of hypoenhancement that extend to the cortical periphery	See the acute management checklist for acute pyelonephritis.

Approach

• Determine if the infection is community-acquired or healthcare-associated and how severe it is.
• Consider organisms commonly implicated in intra-abdominal infection (e.g., E. coli).
• Consider local resistance patterns.
• See also empiric antibiotic therapy for acute biliary infection.

Community-acquired infections ^[70][71][72]

• Coverage of the following organisms should be considered:
  • Enteric gram-positive streptococci
  • Enteric gram-negative aerobic and facultative bacilli
  • Fluoroquinolone-resistant E. coli
• Enterococcal coverage is not usually necessary for mild to moderate community-acquired infection but is recommended for severe infection.
• Fluoroquinolones are only recommended as a single-agent regimen if the hospital antibiogram indicates > 90% susceptibility of E. coli. ^[70]

Severity of infection	Suggested single-agent empiric regimen [70]	Suggested combination empiric regimen [70]
Mild or moderate infection	Cefoxitin Ertapenem Moxifloxacin Ticarcillin-clavulanate Tigecycline	Metronidazole PLUS one of the following Cefazolin Cefotaxime Ceftriaxone Cefuroxime Ciprofloxacin Levofloxacin
Severe infection and/or high-risk patient	Doripenem Imipenem-cilastatin Meropenem Piperacillin-tazobactam	Metronidazole PLUS one of the following Cefepime Ceftazidime Ciprofloxacin Levofloxacin

Metronidazole is contraindicated in the first trimester of pregnancy.

Healthcare-associated infections ^{[70][71][72][54]}

Healthcare-associated infections are more likely to be antibiotic-resistant and both institutional and individual patient antibiograms should be considered when choosing an empiric regimen!

• Coverage of the following organisms should be considered:
  • Enteric gram-positive streptococci
  • Enteric gram-negative aerobic and anaerobic bacilli (including Pseudomonas aeruginosa)
  • Enterococci
  • MRSA
• Agents to avoid as empiric therapy:
  • Cephalosporins as a single-agent regimen
  • Fluoroquinolones as a single-agent regimen
  • Ampicillin-sulbactam

Patient and/or institutional risk factors	Suggested empiric regimens [70]
Low risk (< 20%) of infection with resistant organism	1) Single-agent regimen Carbapenems Doripenem Imipenem-cilastatin Meropenem OR piperacillin-tazobactam
	2) Combination regimen Metronidazole PLUS one of the following: Ceftazidime Cefepime
High risk (> 20%) of infection with resistant organism	Single-agent or combination empiric regimen (see above) PLUS one of the following: Aminoglycoside Gentamicin Tobramycin Amikacin OR polymyxin [71] [73] OR a new combination beta-lactam Ceftolozane-tazobactam Ceftazidime-avibactam
High risk of MRSA	Combination empiric regimen (see above) PLUS vancomycin

Obtain cultures, if necessary, before the administration of empirical IV antibiotics.

For patients with a beta-lactam or carbapenem allergy, consider vancomycin with aztreonam and metronidazole.