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

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.

eFAST

eFAST (extended focused assessment with sonography in trauma) is a rapid (a few minutes) ultrasound protocol used in the context of blunt or penetrating trauma which can be used to identify free fluid in the peritoneum, which is presumably blood, as well as pneumothorax, haemothorax, or pleural effusion. It involves examining a certain set of abdominal and thoracic regions for free fluid.

Order of examination:

Hepatorenal region -> Pericardium -> Perisplenic -> Suprapubic -> Right and left chest

However, it should be kept in mind that a negative eFAST doesn’t rule out intraabdominal injury, as eFAST cannot discern diaphragmatic tears, pancreatic injury, bowel perforation, and small amounts of free fluid (<500 mL). The sensitivity of eFAST is also limited. The main objective of eFAST is to decrease the number of people who require a CT scan, thereby shortening their time to surgery.

In case eFAST detects intraabdominal free fluid, the patient has likely suffered large injuries which require surgery, and so the patient should be taken to emergency laparotomy.

In case eFAST does not detect any pathology, an abdominal CT scan should be performed if the risk for intra-abdominal injury isn’t low. If the abdominal CT shows injury, emergency laparotomy should be performed.