B42. Acute abdomen, differential diagnosis.
Acute abdomen is the name of the clinical presentation where a patient has acute onset abdominal pain. There’s a large number of conditions which can cause acute abdomen, from harmless to life-threatening, 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. These patients should be examined systematically to identify the underlying cause.
Life-threatening conditions
It’s important to recognise or exclude life-threatening conditions.
| 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 (ileus) | 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 (ileus) | Patient with recent abdominal surgery or known hernia | Abdominal distension, vomiting, absence of flatus |
| Constipation | Elderly patient, previous problems with constipation | Abdominal distension, palpable faecalith, no bowel movements for some time |
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 |
Physical examination of acute abdomen
Inspection
| Finding | Suspicious for |
|---|---|
| Inspect for any hernias | – |
| Patient lies completely still (any small movement causes pain) with knees bent | Peritonitis |
| Patients is curled up, writhes in agony, wants to keep moving | Biliary or renal colic |
Auscultation
| Finding | Suspicious for |
|---|---|
| Abnormally active, high-pitched bowel sounds | Early bowel obstruction |
| Absent bowel sounds | Late bowel obstruction |
| Bruit on auscultation | Abdominal aortic aneurysm |
Percussion
| Finding | Suspicious for |
|---|---|
| Even gentle percussion causes pain | Peritonitis |
| Shifting dullness on percussion | Ascites |
Palpation
| Finding | Suspicious for |
|---|---|
| Palpate the whole abdomen to locate the area of maximal pain, first superficially then deeper | – |
| Palpate for hepatomegaly or splenomegaly | – |
| Palpate for any masses | – |
| Muscular rigidity or “guarding” on palpation | Peritonitis |
| Rebound tenderness | Peritonitis |
| Markle sign/Heel-drop test | Peritonitis |
| Maximal pain at the McBurney’s point | Appendicitis |
| Palpation of contralateral McBurney’s point elicits pain at the McBurney’s point (Rovsing sign) | Appendicitis |
| Psoas sign | Appendicitis, especially retrocaecal appendicitis |
| Obturator sign | Appendicitis, especially pelvic appendicitis |
| Carnett sign | Abdominal wall pathology (rather than visceral pathology) |
| Murphy sign | Cholecystitis |
| Pain out of proportion to physical findings (severe pain but nontender, soft abdomen) | Mesenteric ischaemia |
Peritonitis may be local or generalised, and the physical findings will follow this. It’s important to know that, because the visceral organs aren’t innervated with somatic pain fibres, appendicitis isn’t painful in itself but causes pain because it causes localised peritonitis in the overlying peritoneum.
Markle sign is tested by asking the patient to stand on their toes and suddenly drop down on the heels with an audible thump, which causes localised pain. An alternative way to elicit this sign is to lift the patient’s legs slightly off the bed and striking the patient’s heels.
Carnett sign refers to increased tenderness when the abdominal wall muscles are voluntarily contracted.
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[1][2][3][4][5]. 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.
Imaging
If there is suspicion of serious pathology, including abdominal aortic aneurysm rupture, gastrointestinal perforation or ileus, an urgent CT with contrast is indicated. CT is also the preferred modality if diverticulitis or nephrolithiasis is suspected. In case of biliary disease like cholecystitis or gallstone, or pancreatitis or appendicitis is suspected, ultrasound is usually the first choice. For PID and ectopic pregnancy, transvaginal ultrasound is the first choice.
eFAST is a rapid (a few minutes) ultrasound protocol used in the context of trauma which can be used to identify free fluid in the peritoneum, which is presumably blood, as well as pneumothorax, haemothorax, or pleural effusion.
Ultrasound cannot visualise a retrocoecal appendix, and is therefore not completely sensitive for acute appendicitis. The presence of bowel gas also reduces visibility.