Acute abdominal pain is a common acute presentation in clinical practice. It encompasses a very broad range of possible aetiologies and diagnoses, and imaging is routinely employed as the primary investigative tool in its modern management.

Terminology

A subgroup of patients with acute abdominal pain will have a so-called acute abdomen (also known as an acute surgical abdomen). This is restricted to those with an acute presentation of abdominal pain coupled with serious morbidity, a tender abdomen and marked rigidity (a.k.a. involuntary guarding) on abdominal physical examination.

Epidemiology

It is estimated that ~5% of presentations to a typical emergency department are for acute abdominal pain ¹.

Clinical presentation

Acute abdominal pain includes a wide spectrum of severity and differing character, with qualifying descriptors, such as sharp, colicky, dull, etc.

Pathology

Aetiology

The list of causes of acute abdominal pain is extremely long and can be subdivided in a multiplicity of ways.

Common causes

• acute visceral inflammation

  • acute appendicitis

  • acute cholecystitis

  • acute pancreatitis

• bowel obstruction

  • small bowel obstruction

  • large bowel obstruction

• bowel ischaemia

• acute diverticulitis

• biliary colic

• renal colic

• pyelonephritis

• peptic ulcer disease: gastric or duodenal ulcer

• abdominal aortic aneurysm (AAA)

• inflammatory bowel disease

  • Crohn disease

  • ulcerative colitis

• mesenteric adenitis: common differential for appendicitis in young

• pregnancy: sometimes it maybe 'concealed', i.e. patient may not even be aware

Less common causes

• Meckel diverticulitis

• psoas abscess

• rectus sheath haematoma

• spontaneous splenic rupture

• intraperitoneal focal fat infarction

  • epiploic appendagitis

  • omental infarction

• mesenteric panniculitis

• Mondor disease (abdominal wall) ⁷

Gynaecological

• ovarian torsion

• salpingitis

• tubo-ovarian abscess

• ruptured ectopic pregnancy

• uterine rupture

• uterine perforation

• endometriosis

Trauma

• abdominal trauma

Iatrogenic

• post-operative

• medications

• radiotherapy

Medical causes

Many medical conditions can present with acute abdominal pain. In some cases it may be an atypical presentation of a common condition (e.g. myocardial ischaemia), or a typical presentation of a rare condition (e.g. porphyria). This list is not exhaustive (in medicine they rarely are!).

• thoracic

  • myocardial infarction

  • angina pectoris

  • pneumonia

  • Bornholm disease

• infection

  • gastroenteritis: many organisms

  • acute hepatitis

  • COVID-19

  • intestinal anthrax

  • pneumococcal peritonitis

  • shingles (herpes zoster)

  • urinary tract infection (UTI)

  • tuberculosis

  • malaria

  • typhoid fever

  • cholera

  • tabes dorsalis

  • infectious mononucleosis: splenic rupture

  • tetanus: very rare ⁵

• endocrine

  • adrenal crisis

  • diabetes mellitus including acute hypoglycaemia

  • phaeochromocytoma

  • thyrotoxic crisis (thyroid storm)

• musculoskeletal

  • epidemic myalgia

  • abdominal muscle injury e.g. rectus abdominis muscle strain

  • Cyriax syndrome

• vasculitis

  • Henoch-Schonlein purpura (HSP)

  • polyarteritis nodosa (PAN)

• toxins ⁶

  • arsenic toxicity

  • lead toxicity

  • selenosis

  • vinyl chloride (and PVC) exposure

  • opiate withdrawal: classically heroin

  • latrodectism: envenomation by Latrodectus (black widow spiders)

• miscellaneous

  • sickle cell disease: acute crisis

  • porphyria

  • intestinal angioedema ⁸

Functional GI disorders

• functional dyspepsia

• irritable bowel syndrome (IBS)

• functional abdominal pain syndrome

• functional gallbladder disorder

• opioid bowel syndrome ³

Radiographic features

CT of the abdomen and pelvis is the first-line investigation for many presentations of acute abdominal pain. Traditionally, the plain abdominal radiograph was the initial investigation but has fallen out of favour due to its poor sensitivity and specificity for many of the causes of abdominal pain. 

Plain radiograph

Historically the plain abdominal radiograph was mandatory in every patient presenting with an acute abdomen. 

CT/US/MRI

to be completed

Treatment and prognosis

In the pre-CT era, patients with an acute abdomen were often sent for urgent surgery. Contemporaneously, with the virtually ubiquitous availability of CT, some of these patients will not be operated on at all. Conversely, some patients who do not meet the traditional criteria for an "acute abdomen" will be diagnosed on imaging with conditions, such as acute appendicitis, and be sent for surgery.

Practical approach

A pragmatic approach needs to be taken by clinicians/radiologists when considering the potential causes of an acute abdomen and a surgical sieve may be helpful as a starting point. 

Beware of a normal abdominal radiograph providing a false sense of security. Emergent pathologies including bowel obstruction and perforation may not produce a radiographic abnormality.