31st July 2023

Acute Abdominal Pathology

The Acute Abdomen

Abdominal pain is a common symptom and is ranked in the top 3 acute presentations in emergency medicine and primary care. However, only a small proportion will have what is termed ‘an acute abdomen’.

An acute abdomen is the sudden onset of generalised severe abdominal pain, secondary to abdominal or pelvic pathology. It may be caused by an infection, inflammation, vascular occlusion or obstruction. Acute abdomens may be life-threatening, and hence require prompt diagnosis and management. A mainstay of management is to use the ABCDE approach, as in any acutely unwell patient.

The differential diagnosis of abdominal pain is vast. Reaching a definitive diagnosis is often difficult as there are many different peritoneal organs within the peritoneal cavity, and referred pain is common. A thorough assessment is therefore needed, in order to determine the most likely causes in any given case.

Pathophysiology

There are different mechanisms underlying the pain associated with an acute abdomen.

Visceral pain relates to the organs of the abdominal cavity (i.e. the viscera). Autonomic nerve fibres respond to distension and muscle contraction to produce a pain, which is characteristically poorly localised, dull in nature, and often associated with nausea. The location of the pain roughly corresponds to the embryonic origin of the affected structure, i.e:

• Foregut structures (stomach, duodenum, liver and pancreas) cause upper abdominal pain
• Midgut structures (small bowel, proximal colon and appendix) cause periumbilical pain
• Hindgut structures (distal colon and genitourinary tract) cause lower abdominal pain.

Somatic pain is due to irritation of the parietal lining of the peritoneum, which is innervated by somatic nerve fibres. Irritation is caused by infectious, chemical or inflammatory processes. The associated pain is sharp in nature and well localised.

Referred pain is pain that is perceived distant from its source, and is due to the way nerve fibres converge in the spinal cord. For example, groin pain due to renal colic, shoulder tip pain due to diaphragmatic irritation, and scapular pain due to biliary colic. You should therefore be vigilant that pain in these areas may correspond to a different location of pathology.

Causes 

A useful way to categorise and learn the different causes of an acute abdomen is through the pathologies associated with different sites. This will enable you to formulate differential diagnoses based on the location of the pain, which can be seen in the table below.

Table 1: Classification of causes according to site of pain

Common pathologies

The following section features brief summaries of the clinical features, investigations, and management for some of the most common causes of an acute abdomen. More detailed background on certain conditions can also be found in the other topics in the Gastroenterology and Hepatology section.

Peptic ulcer disease

Includes both duodenal and gastric ulcers. Commonly present with epigastric pain, dyspepsia, bloating, nausea, and vomiting. Coffee ground vomitus and melaena suggest bleeding peptic ulcers, which is a medical emergency.

Symptoms are generally related to meals; gastric ulcers will generally feel worse after eating, and duodenal ulcers improved. Risk factors include NSAIDs, alcohol, smoking, and spicy foods. Unless complicated by peritonitis, examination findings will most likely consist of a soft abdomen but with epigastric tenderness.

Associated with microcytic anaemia. If Helicobacter pylori is suspected then a urea breath test or a stool antigen test should be done. Endoscopy can be performed if diagnosis is uncertain from clinical history.

Treatment depends on the cause:

• Lifestyle factor modification is generally first line  – i.e. smoking cessation, reducing alcohol intake, avoiding trigger foods, weight loss if BMI is high
• NSAIDs should be avoided
• Proton pump inhibitors are first line medical treatment
• H. pylori eradication therapy, if required

Appendicitis

Typically seen in younger patients. Characteristic presentation of pain that starts in the periumbilical region and then radiates to the right iliac fossa (RIF). Associated with fever, nausea and vomiting, and diarrhoea. On examination, patients will be tender in the RIF, especially at McBurney’s point (which correlates with the location of the appendix). Other findings include guarding, rebound tenderness, and Rovsing’s sign (palpation in the left iliac fossa will produce pain in the right).

It can be diagnosed clinically. CT abdomen is done for confirmation. It can be managed conservatively with antibiotics and monitoring, or surgically with an appendectomy.

Diverticulitis

Generally presents in the middle aged and elderly, and the most common location of pain is in the left iliac fossa (LIF). Associated with a history of low fibre diet and constipation.

Diverticular disease refers to the chronic condition, and diverticulitis refers to the infective flare-ups, as well as acute pain, also associated with PR bleeding, fever, and diarrhoea. Can be diagnosed with CT abdomen. Management consists of antibiotics and supportive treatments, i.e. fluids and analgesia. Long term, dietary modification should be advised.

Acute mesenteric ischaemia

A life-threatening condition in which the blood supply to the bowel is disrupted, most commonly due to thromboembolic disease obstructing the superior mesenteric artery. Risk factors include age and atrial fibrillation.

Presets with severe pain, but generally a soft abdomen. “Pain out of proportion to examination” is a typical feature. Diagnosis is with CT abdomen or mesenteric artery angiogram.

Initial management is supportive: nil by mouth, IV fluids, analgesia, and NG tube. If there is no bowel infarct, then it can be treated through revascularisation. If there is an established infarct, then bowel resection is the treatment of choice to remove the diseased tissue.

Ischaemic colitis

Similar to acute mesenteric ischemia, but is less severe, as disruption of blood supply is temporary. Presents with generally left-sided cramping abdominal pain, followed by dark red rectal bleeding, nausea and vomiting. Risk factors include atrial fibrillation and cocaine use (in younger patients).

The diagnostic scan of choice is a CT abdomen +/- angiography. An X-ray can demonstrate the characteristic ‘thumbprinting’ sign. Endoscopy would show a variable appearance, from mild reddening to gangrene. Histology shows intramucosal haemorrhage, fibrosis, hemosiderin.

Initial management is conservative with bowel rest, IV fluids and broad-spectrum antibiotics. In rare cases, conservative management fails, in which case, laparotomy may be required.

Bowel obstruction

Medical emergency. Presents with severe abdominal pain and distension, associated with nausea and vomiting (which may be faeculant). In complete bowel obstruction, there will be constipation and the absence of flatus. On examination, the abdomen is generally tender and distended. In small bowel obstruction may hear ‘tinkling’ bowel sounds but may also be normal.

An abdominal x-ray can be done as the first line investigation, which will show distended bowel loops proximal to the point of obstruction. CT abdomen is then done to establish the cause. Gastrografin studies can be done in small bowel obstruction.

Management is colloquially referred to as ‘drip and suck’. Patients are made nil by mouth to rest the bowel and prepare for potential surgery, with the ‘drip’ referring to IV fluids, and ‘suck’ a wide bore NG tube, which can be used for drainage. If it does not resolve with this period of bowel rest, or if there are signs of developing ischemia or perforation, then surgical management is required, which may involve bowel resection and stoma creation.

Pyelonephritis

May also be considered as an ‘upper UTI’. Pyelonephritis typically presents with a triad of loin pain, fever and rigors. It may be associated with lower urinary tract symptoms, such as frequency, urgency, and dysuria. On examination, there is generally tenderness in the renal angle and loin.

Urinalysis will be positive for leukocytes and nitrites. A urine sample should be sent for cultures and sensitivities, and an ultrasound scan of the renal tract to assess for any underlying urinary tract abnormality or the development of associated abscesses.

Management consists of antibiotics (commonly ciprofloxacin) and analgesia. Admission for IV antibiotics and IV fluids may be necessary, especially due to the associated risk of AKI.

Renal colic

Due to obstruction within the urinary tract, due to calculi. Presents with acute onset of excruciating ‘loin to groin’ pain, associated with nausea, vomiting, and the inability to lie flat. The abdomen is typically soft, but tender in the renal angle.

Urinalysis may be normal, but often positive for leukocytes, red cells, and protein. Gold standard investigation is a non-contrast CT of the urinary tract (CT-KUB).

First line management is analgesia and IV fluids. PR diclofenac is highly efficacious, and recommended as the first line analgesic. If an infection is suspected, then antibiotics are indicated.

Patients should be referred to urology, who may manage as an inpatient or outpatient. Ureteric stents or nephrostomies may be indicated, if the stone is leading to obstruction and hydronephrosis.

Biliary tract disease

Encompasses several different pathologies, which are summarised in the table below.

Table 2: Biliary tract disease

Acute pancreatitis

Classically presents with severe epigastric pain radiating to the back, which is relieved by sitting forward. Associated with nausea and vomiting. Risk factors include gallstones, alcohol, recent ERCP, and hypertriglyceridemia.

On examination, patients commonly have epigastric tenderness, and may be tachycardic and hypotensive. In more significant cases can see jaundice (indicating obstruction). The Grey-Turner sign (flank bruising) and Cullen sign (periumbilical bruising) are suggestive of haemorrhagic pancreatitis.

Supportive blood results include a raised amylase and lipase, and deranged LFTs. Diagnosis is generally made clinically, but a CT abdomen can be done if there is any uncertainty.

Management is supportive with analgesia, IV fluids, and fluid balance chart. Often made nil by mouth when vomiting. Once the cause is established, and the patient is stable, this should also be treated. Antibiotics are only indicated if there is evidence of an associated infection.

Patients can deteriorate quickly; ITU should be involved early if there is clinical concern. The APACHE II and Glasgrow-Imrie criteria are used as risk stratification tools.

Budd-Chiari syndrome

A rare condition in which the hepatic veins become obstructed. This is usually due to hepatic vein thrombosis but may be due to external compression (i.e. tumours). Risk factors are those associated with thrombo-embolic disease, e.g. pregnancy, oral contraceptives, thrombophilic diseases like protein C and protein S deficiency, and Factor V Leiden. Also a strong association with polycythaemia vera.

Characteristic triad of abdominal pain, hepatomegaly and ascites. Also associated with nausea and vomiting, pruritus, peripheral oedema, and distended abdominal veins. Typical blood findings include deranged LFTs and polycythaemia (if this is the underlying cause).

First line diagnostic investigation is a Doppler ultrasound scan, followed by CT or MRI. Thrombophilia screens should be performed, as well as screening for the JAK2 mutation (indicative of myeloproliferative disorders).

Management includes:

• Treatment of underlying cause
• Anticoagulation  – first line medical treatment
• Interventional radiology  – i.e. hepatic vein dilation and stent insertion
• Transjugular intrahepatic portosystemic shunt (TIPSS)
• Treatment of consequences of portal hypertension  – i.e. diuretics, ascitic tap, beta blockers/variceal band ligation for variceal bleeding prophylaxis

Liver abscess

Generally occurs as a consequence of hepatitis or due to an intra-abdominal infection that is disseminated to the liver via the hepatic vein.

Presents with abdominal pain, fever, rigors, jaundice, anorexia, and bloating. Examination findings include tenderness in the RUQ, with or without hepatomegaly. Rupture of the abscess can lead to cardiorespiratory collapse.

Blood tests show raised inflammatory markers, deranged LFTs (especially ALP). Investigations should also include blood cultures and ultrasound as the first line imaging, followed by a CT abdomen with contrast.

Management is with IV antibiotics and ultrasound-guided aspiration of the abscess. If the abscess has ruptured or persists despite drainage and antibiotics, then surgery may be required.

Ruptured abdominal aortic aneurysm

‘Triple A’ or ‘AAA’. A medical emergency. Characteristic severe generalised abdominal pain, radiated to the back, associated with collapse. On examination, the abdomen will likely be peritonitic, a pulsatile abdominal mass will be felt, and the patient likely in shock.

Elderly and male patients are at higher risk, especially those with a known aneurysm.

The most immediate investigation is a bedside ultrasound scan of the abdomen (known as Point of Care Ultrasound Scan, or POCUS). CT angiogram is the best imaging modality, if the patient is stable.

Management follows an ABCDE approach; resuscitation and the massive haemorrhagic protocol may be required. Early surgical team involvement, as urgent open repair or endovascular aneurysm repair is the definitive, and potentially life-saving treatment. ‘Permissive hypotension’ is allowed to maintain a blood pressure in which more than 100 mmHg is acceptable, to reduce the risk of further bleeding.

Ectopic pregnancy

Implantation of a fertilised egg outside of the uterus, generally in the Fallopian tube. If it ruptures, this is a life-threatening medical emergency.

Presents with severe unilateral pelvic pain, typically around 6-8 weeks into pregnancy. It may also cause referred shoulder tip pain and be associated with PV bleeding. On examination, there will be tenderness in the iliac fossa with guarding. Internal examination may show cervical excitation and adnexal tenderness, with or without a mass.

An ectopic pregnancy must be ruled out in any person with a uterus of childbearing age, presenting with acute abdominal pain or PV bleeding.

Investigations include urinary pregnancy tests and serial serum β-hCG levels to measure trend. First line imaging is a transvaginal ultrasound scan.

If β-hCG is stable and the patient is not acutely unwell, then methotrexate can be used as management (i.e. medical abortion).

Any haemodynamically unstable patient should first be appropriately resuscitated, followed by urgent surgical intervention once stabilised, which would either be a laparoscopic salpingectomy or salpingostomy.

Pelvic inflammatory disease

Infection of the upper female reproductive organs, i.e. the uterus, Fallopian tubes or ovaries. Generally secondary to STI.

Presents with gradual onset bilateral pelvic pain, vaginal discharge, dyspareunia, dysmenorrhoea and PV bleeding (may include post-coital bleeding and intermenstrual bleeding). On examination, there will likely be suprapubic tenderness, vaginal discharge, cervical excitation, and fever.

As well as standard investigations, high vaginal swabs should also be done to assess for any causative STIs.

Management is with broad-spectrum antibiotics as aetiology, generally polymicrobial. If any STIs are diagnosed, then contact tracing should also be done.

Rupture or torsion of ovarian cysts

Associated with a past medical history of polycystic ovaries. Ruptured cysts present with sudden unilateral pelvic pain (very severe if also torsion), nausea and vomiting, fever, and PV bleeding. On examination, there will be iliac fossa tenderness with associated guarding, and adnexal tenderness with or without mass on internal examination. An ectopic must first be ruled out; a transvaginal ultrasound scan is the diagnostic investigation of choice.

Definitive management is surgical, either laparoscopic ovarian cystectomy with detorsion or open laparotomy.

Testicular torsion

A medical emergency, as if untreated, ischaemia could lead to loss of the affected testicle. Occurs when the testicle rotates, causing twisting of the spermatic cord and an obstruction of blood supply.

Presents with severe sudden onset unilateral testicular pain, associated with nausea and vomiting. Most common between the ages of 12 and 18, and rare outside of adolescence. Characteristic examination findings are exquisite tenderness and swelling (often without erythema), a high-lying testicle, absent cremasteric reflex, and negative Prehn’s sign (elevation of testicle will not relieve pain, unlike in epididymo-orchitis).

If suspected, then an urgent referral to urology should be made for prompt surgical exploration. The diagnostic investigation of choice is a Doppler ultrasound scan, but this should not delay surgical referral.

Assessment 

Initial assessment of a patient presenting with an acute abdomen should follow the ABCDE approach to establish the severity of their condition and ensure appropriate steps are taken to stabilise them.

Alongside a focused history and thorough abdominal examination, which is generally what yields the key information that guides diagnosis and further management, the following investigations may also be employed:

• Blood tests  – FBC, U&Es, LFTs, CRP/ESR, amylase, blood glucose as routine
• Blood cultures if suspicion of sepsis
• Urinalysis and urine sample for microscopy, culture and sensitivity
• Urinary pregnancy test (and β-hCG, if necessary)  – essential in any person with a uterus of childbearing age to rule out an ectopic pregnancy
• Venous blood gas (or arterial blood gas)  – lactate is a key readout, as indicates tissue hypoperfusion and ischaemia; acidosis or alkalosis associated with certain pathologies
• Abdominal x-ray  – relatively limited, but first line for a suspected bowel obstruction as it can be arranged more quickly than a CT scan
• Chest x-ray  – to assess for bowel perforation (i.e. pneumoperitoneum), generally done as standard in any patient presenting with an acute abdomen
• Ultrasound:
  • POCUS  – in suspected ruptured AAAs
  • Abdomen and pelvis  – especially for liver and gynaecological pathology
  • Testes  – if testicular torsion is suspected
  • Urinary tract  – less accurate than CT, but can be used to assess for stones, obstruction, hydronephrosis, and urinary tract abnormalities which may underlie pathology
• CT imaging:
  • Abdomen  – gold standard for an acute abdomen
  • Urinary tract  – gold standard for suspected renal colic, can reveal stones, as well as assess for obstruction and hydronephrosis
  • Angiogram  – gold standard for aortic pathology, providing the patient is stable
• ERCP/MRCP  – used in the investigation of pancreaticobiliary disease, but generally only when the patient is stable
• Endoscopy  – upper GI endoscopy is done acutely in patients with suspected upper GI bleeds (i.e. perforated ulcers, oesophageal varices)
  • Colonoscopy and other forms of scopes are generally not done acutely, but may be important if bowel pathology is suspected, once the patient has stabilised

Management 

Focused management depends on the underlying cause, as outlined above.

Immediate management follows the ABCDE approach, as patients with an acute abdomen are often acutely unwell and may be haemodynamically unstable.

The key aspects of management may include:

• Oxygen, titrated as required
• Fluid resuscitation with IV fluids  – patients with blood loss or acute pancreatitis may need aggressive fluid resuscitation
• Blood products  – group and save/cross matches should be immediately sent in patients at risk of blood loss/actively bleeding, and massive haemorrhage protocol may be required
• Analgesia  – including the use of parenteral opioids
• Antiemetics  – often needs to be given IV
• Antibiotics  – depending on underlying cause
• Nasogastric tube  – especially if severe vomiting or suspicion of bowel obstruction

Generally, definitive management is surgical. Any patient presenting with an acute abdomen should therefore be urgently referred to the surgical or gynaecological team, as appropriate, once the most likely diagnosis is established. Any patient presenting with an acute abdomen should be kept nil by mouth until review by the specialty team, in case emergency surgery is required.

Peritonitis

Peritonitis refers to inflammation of the peritoneal cavity. It can either be localised or generalised, the latter of which is much more serious, as it can lead to life-threatening sepsis.

Causes of peritonitis include:

• Bowel perforation
• Any abdominal pathology that causes marked inflammation, i.e. appendicitis, diverticulitis, strangulating intestinal obstruction, acute pancreatitis.
• Irritation from intraperitoneal blood from any source, i.e. ruptured aortic aneurysm, ruptured ectopic pregnancy, ruptured spleen, trauma.
• Infectious peritonitis from peritoneal-systemic shunts, drains and dialysis catheters in the peritoneal cavity.
• Spontaneous bacterial peritonitis (SBP) occurs when there is no obvious infective trigger, but widespread inflammation (specifically of the ascitic fluid) occurs, and the causative organisms are generally bowel flora. Particularly associated as a complication of chronic liver disease.

Generalised peritonitis presents as severe generalised abdominal pain. Common signs include a firm abdomen, and lack of abdominal movement with respiration, guarding, rebound tenderness, severe pain to light palpation, and percussion tenderness (all of which are indicative of a ‘peritonitic’ abdomen). It is also associated with shock.

Management and treatment are of the acute abdomen, as above.

If an abdomen is peritonitic, then a bowel perforation should be suspected, and an erect chest x-ray should be performed to assess for pneumoperitoneum. A CT abdomen is the gold standard imaging investigation, as it will help to determine the cause. If fit for surgical intervention, then a bowel perforation needs urgent surgical repair.

Generalised peritonitis leads to severe dehydration and electrolyte disturbances, due to the fluid shifts between the peritoneal cavity and the bowel. Other complications include acute respiratory distress syndrome, renal failure, liver failure and disseminated intravascular coagulation. These complications are life-threatening; hence, any patient with a peritonitic abdomen requires urgent treatment.