Acute abdomen

Acute abdomen refers to acute onset abdominal pain. There’s a large number of conditions which can cause acute abdomen, and so knowing the differential diagnosis and investigations to distinguish them is important. The presence of typical risk factors, gender, and age for a specific cause can also help the diagnosis, and so knowing these is important as well. It’s important to remember that atypical presentations exist, of course.

Life-threatening conditions

It’s important to recognise or exclude life-threatening conditions, including AAA rupture, mesenteric ischaemia, GI perforation, ectopic pregnancy, etc.

Disorder	Typical patient	Typical findings
Abdominal aortic aneurysm rupture	Elderly male patient with cardiovascular risk factors, especially hypertension or known AAA	Triad of severe acute abdominal pain, pulsatile abdominal mass, haemodynamic instability
Mesenteric ischaemia	Elderly patient with cardiovascular risk factors or atrial fibrillation	“Pain out of proportion to the physical examination” (severe pain but normal physical examination), often peritonitic
Gastrointestinal perforation	Elderly patient with known ulcer or GI disease, recent abdominal surgery	Severe, diffuse abdominal pain, often peritonitic
Acute bowel obstruction	Patient with recent abdominal surgery or known hernia	Abdominal distension, vomiting, absence of flatus
Ruptured ectopic pregnancy	Any female of childbearing age	Amenorrhoea, abdominal pain, vaginal bleeding, positive hCG
(Inferior) Myocardial infarction	Older patient with diabetes	Epigastric pain
Aortic dissection	Elderly male patient with cardiovascular risk factors, especially hypertension	Tearing/ripping pain, associated symptoms of downstream ischaemia

Differential diagnosis by location

Different causes of acute abdomen cause pain in certain typical areas.

Right upper quadrant (RUQ)

The right upper quadrant is home to the liver and biliary system, and therefore also home to most cases of pain caused by hepatic and biliary disorders.

Disorder	Typical patient	Typical findings
Cholecystitis	Patient with the 6 Fs	Steady, severe RUQ or epigastric pain, positive Murphy sign
Cholelithiasis		Intense, dull, constant RUQ or epigastric discomfort, sweating, nausea, vomiting
Cholangitis		Charcot’s triad of fever, RUQ abdominal pain, jaundice
Acute pancreatitis	Patient with alcoholism, 6Fs, known hypertriglyceridaemia	RUQ or epigastric pain, band-like radiation to the back, nausea, vomiting
Hepatitis	IV drug user, paracetamol intoxication, recent travel abroad	RUQ pain, liver tenderness, elevated liver enzymes
Lower lobe pneumonia	–	Basal crepitations, coughing, dyspnoea

Epigastrium

Disorder	Typical patient	Typical findings
Peptic ulcer disease/gastritis	Smoking, NSAID use, known H. pylori	Epigastric/LUQ pain, indigestion, reflux symptoms
Acute pancreatitis	Patient with alcoholism, gallstone risk factors, or known hypertriglyceridaemia	RUQ or epigastric pain, band-like radiation to the back, nausea, vomiting
Abdominal aortic aneurysm rupture	Elderly male patient with cardiovascular risk factors, especially hypertension or known AAA	Triad of severe acute abdominal pain, pulsatile abdominal mass, haemodynamic instability
Lower lobe pneumonia	–	Basal crepitations, coughing, dyspnoea

Left upper quadrant (LUQ)

The left upper quadrant is home to the spleen, pancreas, and stomach.

Disorder	Typical patient	Typical findings
Peptic ulcer disease/gastritis	Smoking, NSAID use, known H. pylori	Epigastric/LUQ pain, indigestion, reflux symptoms
Splenic infarct/rupture	Recent abdominal trauma	Tender/enlarged spleen
Lower lobe pneumonia	–	Basal crepitations, coughing, dyspnoea

Right lower quadrant (RLQ)

The right lower quadrant is home to the appendix, terminal ileum, as well as the ovary, fallopian tube, and referred pain from the testis.

Disorder	Typical patient	Typical findings
Acute appendicitis	Young adult, previously healthy	Pain originating periumbilically, later migrating to the McBurney point. Tenderness. Positive Rovsing, psoas, or obturator sign.
Inflammatory bowel disease	Young adult, known history of GI complaints	Local peritonitis, mildly elevated inflammatory parametres
Ruptured ectopic pregnancy	Any female of childbearing age	Amenorrhoea, abdominal pain, vaginal bleeding, positive hCG
Ovarian torsion	Known ovarian cyst or tumour	Unilateral lower abdominal or pelvic pain, nausea/vomiting, palpable adnexal mass
Testicular torsion	Young male (teenager)	Testicular and lower abdominal pain, swollen and tender testis, horisontal testicle

Left lower quadrant (LLQ)

The left lower quadrant is home to the part of the colon most frequently affected by diverticulitis, as well as the ovary, fallopian tube, and referred pain from the testis.

Disorder	Typical patient	Typical findings
Diverticulitis	Elderly patient	Low-grade fever, nausea/vomiting, recent change in bowel habits
Ruptured ectopic pregnancy	Any female of childbearing age	Amenorrhoea, abdominal pain, vaginal bleeding, positive hCG
Ovarian torsion	Known ovarian cyst or tumour	Unilateral lower abdominal or pelvic pain, nausea/vomiting, palpable adnexal mass
Testicular torsion	Young male (teenager)	Testicular and lower abdominal pain, swollen and tender testis

Diffuse abdominal pain

Disorder	Typical patient	Typical findings
Diabetic ketoacidosis	Young patient without known T1D, or patient with known T1D and poor compliance, recent stress/infection	Polyuria, neurological symptoms, dehydration, fruity odour, Kussmaul breathing
Porphyria attack	Known porphyria, recent drug change or infection	Brown or reddish urine
Mesenteric ischaemia	Elderly patient with cardiovascular risk factors or atrial fibrillation	“Pain out of proportion to the physical examination” (severe pain but normal physical examination), often peritonitic
Acute bowel obstruction	Patient with recent abdominal surgery or known hernia	Abdominal distension, vomiting, absence of flatus

Any quadrant

Disorder	Typical patient	Typical findings
Ureteric colic/nephrolithiasis	History of stone disease	Colicky pain, flank pain, haematuria
Pyelonephritis	Women, pregnancy, known urinary tract obstruction	Tender costovertebral angle on percussion, fever, chills, UVI symptoms

Initial management

Routine investigations

Initial management involves performing routine investigations, including blood test (WBCs, CRP, Hb, amylase/lipase, liver function tests, electrolytes), obtaining IV access and providing fluids if necessary, and analgesia.

To exclude ectopic pregnancy and atypical presentation of myocardial infarction, serum hCG should be measured in all females of childbearing age and an ECG should be obtained in all patients, or at least the elderly ones.

Analgesia

Many are afraid of giving strong analgesics which may mask physical examination findings and interfere with the diagnosis, but multiple high-quality studies (RCTs) have disproved this. Therefore, there’s no good reason patients shouldn’t be relieved of their pain, usually with strong analgesics like morphine or oxycodone.

History and physical examination

The patient’s history and physical examination should be taken. Characterisation of the timing and features of the pain is especially important. It’s important to recognise features suggestive of severe disease, like severe, opioid-refractory pain, haemodynamic instability, sudden onset pain, and signs of peritonitis. Care should be made in elderly, where typical signs of the specific diseases may be absent, and severe disease may present without findings of severe disease.