acute abdomen

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Acute abdominal pain is a common acute presentation in clinical practice. It encompasses a very broad range of possible etiologies 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 approximately 5% presentations to a typical emergency department are for acute abdominal pain .

Clinical presentation

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

Pathology

Etiology

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
bowel obstruction
- small bowel obstruction
- large bowel obstruction
bowel ischemia
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
pregnancy: sometimes it maybe 'concealed', i.e. patient may not even be aware!

Less common causes

Gynecological

Trauma

penetrating abdominal injury
blunt abdominal injury

Iatrogenic

post-operative
medications
radiotherapy

Medical causes

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

thoracic
infection
- gastroenteritis: many organisms
- acute hepatitis
- intestinal anthrax
- pneumococcal peritonitis
- shingles (herpes zoster)
- urinary tract infection (UTI)
- tuberculosis
- malaria
- typhoid fever
- cholera
- tabes dorsalis
- infectious mononucleosis: splenic rupture
endocrine
- diabetes mellitus
- pheochromocytoma
- 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)
miscellaneous
- sickle cell disease: acute crisis
- lead toxicity
- opiate withdrawal: classically heroin
- porphyria
- selenosis

Functional GI disorders

functional dyspepsia
irritable bowel syndrome (IBS)
functional abdominal pain syndrome
functional gallbladder disorder
opioid bowel syndrome

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 favor 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.