Article about the acute abdomen
Essentials
The term ‘acute abdomen’ is commonly used to describe abdominal pain of recent onset requiring urgent surgical assessment. Most cases of acute abdominal pain present in the community and are managed by family practitioners, with only a few presenting to a hospital. Those cases that do present to hospital are usually referred to the general surgeons. In a third of cases, no specific diagnosis is made, although many will subsequently re-present with identifiable pathology.
Only a few patients with an acute abdomen present directly to medical specialities or occur in patients already on a medical ward. These patients are often older, and the acute abdomen may present on a background of other comorbidities; hence a patient with known ischaemic heart disease who presents with upper abdominal pain from biliary colic or reflux may be misdiagnosed with cardiac chest pain. In addition, the disorders most commonly causing an acute abdomen in a medical patient differ from those occurring in the community and referred to surgeons, since the more obvious causes are likely to have been identified and referred appropriately. In elderly medical patients vascular events and intestinal obstruction due to malignancy are much more common than the appendicitis seen in the typical ‘surgical’ patient.
Management of the acute abdomen in medical patients can be extremely difficult: there is no substitute for an experienced and vigilant physician working together with a thoughtful surgeon and radiologist. The key question is, ‘Does this patient need an operation?’, a decision which depends on (1) symptoms, e.g. severe pain; (2) findings on examination, e.g. a rigid abdomen; (3) findings on investigation, e.g. subdiaphragmatic air; (4) excluding nonoperative diagnoses, e.g. pancreatitis; and (5) the presumed diagnosis, e.g. appendicitis as opposed to Crohn’s ileitis. But it must be remembered that in very sick patients it may be necessary to proceed straight to surgery without any supportive imaging.
Assessment
Principles of management
Unlike the management of a medical condition, where achieving a precise diagnosis is often essential before treatment can be initiated, the management of the acute abdomen is more generic but no less imperative. The principle of management is to answer the question: ‘Does this patient need an operation?’ If the answer is yes, then the surgeon must decide the optimal timing of surgical intervention.
The surgical assessment of any patient with abdominal pain should be undertaken with this point in mind, and the decision to undertake surgical intervention is generally based upon the following:
- ◆ Symptoms, e.g. severe pain
- ◆ Findings on examination, e.g. a rigid abdomen
- ◆ Findings on investigation, e.g. subdiaphragmatic air
- ◆ Excluding nonoperative diagnoses, e.g. pancreatitis
- ◆ The presumed diagnosis, e.g. appendicitis as opposed to Crohn’s ileitis
In very sick patients it may be necessary to proceed straight to surgery without any supportive imaging. The best place for a patient with acute abdominal pain radiating into the back, a palpable abdominal aortic aneurysm and an unrecordable blood pressure is in an operating theatre and not a CT scanner. Nevertheless, in most patients urgent imaging and laboratory investigations can be undertaken and a definitive diagnosis made.
There are two further management principles that are worthy of discussion at this stage:
- ◆ In a patient with an acute abdomen, administration of analgesia may affect the findings on clinical examination, but there is good evidence to suggest that it does not prevent the appropriate management being undertaken. There is therefore no justification in withholding analgesia from patients in pain with an acute abdomen. However, repeated administration of opiate analgesia without appropriate surgical review is unwise.
- ◆ Antimicrobial treatment can influence the course of an acute abdomen and may confuse the clinical findings. It should be withheld until a diagnosis is made, at which point appropriately targeted therapy may be commenced.
History
The common causes of the acute abdomen can usually be diagnosed by careful history taking. See Table 1 below
Pain
The hallmark of the acute abdomen is abdominal pain, and ascertaining the tempo of onset is important. Pain of sudden onset (coming on in seconds) suggests rupture of an abdominal viscus or sudden intra-abdominal bleeding (and occasionally torsion of an ovary or testis). Rapid onset pain, reaching maximum intensity within an hour, is typical of acute pancreatitis whereas other inflammatory conditions have a slower onset pain. Loss of consciousness when the pain starts is suggestive of abrupt blood loss as in a ruptured aneurysm.
Colicky pain, described as gripes or cramping by patients, comes and goes in waves and originates from a muscular-walled hollow viscus, such as the intestine or ureter. It also occurs during parturition, with a tubal ectopic pregnancy, and in acute urinary retention. Colicky pain typically makes patients restless; the pain of peritonitis is exacerbated by movement so the patient lies still.
Biliary colic typically is a sustained pain lasting 2 to 3 h coming on a couple of hours after a fatty meal; unless a stone is stuck in the sphincter of Oddi, colicky pain is not a feature. The marked intensity of this pain, lack of fever, and minimal abdominal tenderness may result in such patients being misdiagnosed with cardiac pain. The true diagnosis is suggested by pain radiating round to the inferior angle of the right scapula.
Other symptoms
Nausea and vomiting often occur in patients with an acute abdomen, and are typical of appendicitis and obstruction. Retching is suggestive of pancreatitis and typically the patient sits forward to relieve pain. Changes in bowel habit, particularly absence of flatus and faeces, distension (‘bloating’), and a history of previous abdominal surgery should be sought. Similarly urinary symptoms, such as haematuria, dysuria, and frequency are important in indicating the cause of pain.
Examination
A thorough clinical examination should confirm the diagnosis, and will go a long way to indicating whether immediate surgery is required. A patient who is walking about or eating food is unlikely to be in need of urgent operative intervention. In contrast, the patient who lies still for fear of exacerbating the pain, is dehydrated from vomiting, and has a foetor is much more likely to have serious abdominal mischief. Adequate exposure for a thorough clinical examination is important. The common missed diagnoses are in the groins (e.g. femoral hernia) and scrotum (e.g. testicular torsion) and these must be exposed, as should the upper abdomen up to the nipples. Not infrequently breast cancer is diagnosed on clinical examination, and may explain jaundice, lymphadenopathy, and back pain (all a result of secondary deposits).
| Table 1 Common causes of an acute abdomen |
|---|
| Cause | Approximate incidence (%) |
| Nonspecific abdominal pain | 35 |
| Infection, e.g. viral or bacterial gastroenteritis | |
| Irritable bowel syndrome | |
| Psychosomatic pain | |
| Abdominal wall pain, e.g. herpes zoster, rectus sheath haematoma | |
| Acute appendicitis | 20 |
| Intestinal obstruction | 15 |
| Adhesions from previous surgery (60%) | |
| Hernia (20%) | |
| Cancer—colon/small intestine | |
| Volvulus ± malrotation | |
| Intussusception | |
| Crohn’s disease | |
| Congenital bands | |
| Gallstone ileus | |
| Biliary pain | 10 |
| Acute cholecystitis | |
| Biliary colic | |
| Urological causes | 6 |
| Renal colic | |
| Testicular torsion | |
| Acute pyelonephritis | |
| Acute colonic diverticulitis | 3 |
| Perforation | 2 |
| Peptic ulcer | |
| Colonic diverticulum | |
| Carcinoma of colon | |
| Ulcerative colitis | |
| Pancreatitis | 2 |
| Ruptured abdominal aneurysm | <1 |
| Aortic, iliac, mesenteric arteries | |
| Mesenteric ischaemia | <1 |
| Arterial embolus or thrombosis | |
| Venous thrombosis | |
| Aortic dissection | |
| Gynaecological emergencies | <1 |
| Salpingitis | |
| Ovarian torsion | |
| Ruptured ectopic pregnancy | |
| Cause | Approximate incidence (%) |
| Miscellaneous examples | |
| Primary peritonitis (streptococcal infection) | |
| Torted appendix epiploica | |
| Omental torsion | |
| Meckel’s diverticulitis | |
| Jejunal diverticulitis | |
Asking the patient to cough, upon which the patient experiences severe pain, indicates peritonitis. Palpation should seek features of peritonitis, such as guarding (increased resistance to increased palpation) and rigidity; eliciting rebound tenderness is unnecessary and cruel where coughing has been demonstrated to cause pain and other features are present—gentle percussion usually suffices. In more equivocal cases, the absence of rebound tenderness is reassuring. Abdominal aortic aneurysms are palpated by placing the flat of the hand just above the umbilicus (which is where the aorta bifurcates); once ruptured, the presence of a large retroperitoneal haematoma and hypotension will make them difficult to palpate. The hernial orifices (inguinal and femoral canals) should always be examined carefully—obstructed hernias are one of the first things a surgeon looks for on a patient on a medical ward, and it is surprising how often a previously unnoticed hernia is identified. Similarly, remember that testicular torsion may present with abdominal pain and vomiting, and unless the testes are palpated the diagnosis is missed, as is the opportunity to avoid the need for an orchidectomy.
Auscultation may confirm absence of bowel sounds, indicating generalized peritonitis; but their presence does not exclude a localized peritoneal reaction as is present in appendicitis, for example.
Finally, the value of a digital rectal examination should not be underestimated. In the jaundiced patient it could reveal the abscess that caused the portal pyaemia or the primary tumour that has metastasized to the liver; in the patient with diarrhoea and vomiting, or dysuria and pyuria, it may reveal peritoneal irritation due to a pelvic appendicitis.
Investigations
The laboratory investigation of patients with an acute abdomen usually contributes little to diagnosis, with the exception of serum amylase, which can be diagnostic and could avoid an inappropriate laparotomy. Raised concentrations of inflammatory markers such as C-reactive protein, or a moderate leucocytosis (up to 20 × 109/litre) are nonspecific, although a very high leucocyte count (>30 × 109/litre) is suggestive of mesenteric ischaemia.
Imaging
The contribution of radiology in the assessment of the acute abdomen has changed in recent years, particularly with the enhanced resolution of modern helical CT, and it is now common for patients with undiagnosed pain to have an emergency CT. Table 2 details the appropriate investigations and their limitations.
Initial management
Patients with an acute abdomen are usually volume depleted and require fluid resuscitation. The fluid losses in vomiting and third space losses in intestinal obstruction are usually underestimated, and regular review of volume status is required to ensure adequate replacement. Since many patients will require urgent surgery they should be kept nil by mouth. Nasogastric suction is indicated in the presence of continued vomiting and suspected intestinal obstruction. Decompressing the stomach with a wide-bore tube may later prevent aspiration on induction of anaesthesia.
Common causes of an acute abdomen
Acute appendicitis
Appendicitis, the most common surgical cause of the acute abdomen, typically starts with a central periumbilical pain which migrates to the right iliac fossa over the course of 3 to 12 h, during which nausea and vomiting are common. Although common in children and young adults it can occur at any age, and is usually missed in older people in whom the mortality is around 3%. Laparoscopic appendicectomy has become standard practice, permitting confirmation of the diagnosis (particularly in young women in whom gynaecological pathology is common), as well as facilitating rapid recovery after surgery.
Intestinal obstruction
This is suggested by a history of colicky pain and distension, with vomiting or constipation. Any patient presenting with a history of vomiting should be examined to exclude an occult hernia, and obstruction considered as a possibility. Conservative treatment with nasogastric aspiration and intravenous fluid replacement is only indicated in patients with a history of previous abdominal surgery, when adhesive small-bowel obstruction is a likely diagnosis and surgery is withheld; for other causes of small-bowel obstruction, surgery is usually inevitable. The timing of surgery depends whether there is evidence that the blood supply of the bowel is compromised, so called strangulating obstruction. Features suggestive of strangulation include colicky pain that becomes constant, a pyrexia (>37.5°C) and a tachycardia, together with features of peritonitis and leucocytosis. Strangulation is an indication for urgent surgery.
Perforated viscus
Acute perforation is usually associated with a sudden onset of severe abdominal pain. When a peptic ulcer perforates the patient suffers a chemical irritative peritonitis, and is seldom septic. In contrast, faecal peritonitis that follows perforation of a colonic diverticulum is associated with profound sepsis, in addition to pain. The mortality from faecal peritonitis is high, and increases with increasing age.
| Table 2 Preferred investigations for the acute abdomen |
|---|
| Condition | Investigation | Comments |
| Right lower quadrant pain | CT | Reasonably sensitive in confirming appendicitis or other causes of right iliac fossa pain |
| Intestinal obstruction | Supine abdominal radiograph | Shows dilated small or large bowel, but seldom indicates cause |
| CT | Demonstrates obstruction and may indicate cause, particularly if it is a hernia missed on clinical examination or in an unusual place (e.g. obturator hernia). In cases of malignancy CT may also reveal liver metastases that could alter surgical approach | |
| Acute gallbladder disease | Ultrasonography | Identifies gallstones, thickened gallbladder wall (suggesting inflammation), dilated bile duct (suggesting biliary obstruction/stones in bile duct). Does not reliably detect stones in bile duct. Also identifies liver metastases which may present with right upper quadrant pain. Murphy’s sign elicited by the ultrasound probe when the abdominal wall is indented into the gallbladder is diagnostic of acute cholecystitis. |
| CT | Better to detect complications of cholecystitis, (e.g. emphysematous cholecystitis and gallbladder perforation). Not so sensitive for gallstones | |
| Pancreatitis | Amylase | Typically very high (>1000 units) in pancreatitis, but goes down within a few days. Nonspecific—also very high in inflammation of salivary glands, perforation of peptic ulcer, ruptured aortic aneurysm, and in patients with macroamylasaemia. Moderately raised (300 to 1000 units) in many other causes of acute abdomen including biliary colic, cholecystitis, mesenteric ischaemia. Also said to be raised in renal failure |
| CT | Best for detecting pancreatitis in patients presenting late where amylase not very high, as well as assessing severity and complications of pancreatitis | |
| Perforated viscus | Erect chest radiograph | The patient needs to have been sitting up for some time to optimize the chances of picking up subdiaphragmatic air. Misses 10% of perforations |
| CT | Most sensitive in detection of free air, and may also indicate what has perforated | |
| Mesenteric ischaemia | CT | Readily available and noninvasive compared to angiography, but reported sensitivity varying from 40 to 80%. Nonspecific features include bowel dilatation, bowel wall thickening, and abnormal wall enhancement. Occlusion of mesenteric vessels may be seen after contrast. In addition infarction (nonperfusion) of other abdominal organs suggests multiple emboli. In many cases imaging is not diagnostic, and if suspicion is high laparotomy is indicated, although the chances of successful outcome are limited |
| Left iliac fossa pain (presumed diverticulitis) | CT | Barium enema and colonoscopy are contraindicated due to risk of converting inflammation into perforation. CT is sensitive in confirming diverticulitis, and will confirm complications such as abscess and perforation. It also detects other causes of left iliac fossa pain, including ruptured aneurysms. It is underused in patients thought to have diverticulitis, in whom left iliac fossa peritonitis is too frequently assumed to be diagnostic of uncomplicated colonic diverticulitis |
| Renal colic | Supine abdominal radiograph | Traditionally the investigation of choice, it is now been superseded by CT |
| CT | Thin slice CT reliably detects stones. Will exclude abdominal aortic aneurysm where confusion exists | |
| Gynaecological | Transvaginal ultrasonography | Not advisable if a high suspicion of a ruptured ectopic pregnancy due to risk of precipitating further haemorrhage. Should detect ovarian abnormalities |
Diverticulitis
Often a label given to any left iliac fossa pain, acute colonic diverticulitis is a gradual onset lower abdominal pain that locates to the left iliac fossa, although it may cause suprapubic or right iliac fossa pain if the sigmoid colon is very mobile. It is similar to a left-sided appendicitis, and like appendicitis can result in abscess formation or perforation. Following initial cultures, antimicrobial therapy is commenced; if the pain does not improve over the next 24 h, or if there are other features suggesting that this is a complicated diverticulitis, an urgent CT should be performed.
The acute abdomen on the medical ward - for hospital doctors
Acute pseudo-obstruction (adynamic ileus)
Originally described by Ogilivie in two patients with retroperitoneal malignancy, colonic pseudo-obstruction is common in hospitalized patients with acute infections, metabolic disorders (including electrolyte disorders), and following orthopaedic and pelvic surgery; drugs, particularly anticholinergics, are also associated. It is believed to arise from an imbalance in autonomic innervation of the colon, with a relative excess of sympathetic stimulation and reduction in parasympathetic activity. This results in an atonic distal colon, while the small bowel continues normal peristalsis. The ensuing features are typical of large-bowel obstruction, with vague central colicky abdominal pain, distension, and vomiting. Rectal examination reveals a capacious rectum, and imaging confirms a dilated large bowel with no obstructing cause seen on contrast enema. Left untreated the colon, in particular the caecum, distends and becomes ischaemic leading to necrosis and perforation. Treatment involves correcting any identifiable cause, such as electrolyte imbalances. Infusion of neostigmine (a cholinesterase inhibitor) or colonoscopic decompression are effective treatments. Surgery is indicated when perforation has occurred. Laxatives should be avoided since they worsen the distension and precipitate perforation. Prokinetic agents, such as erythromycin which stimulates the motilin receptor, have been reported to be effective.
The acute abdomen in older patients
Acute abdominal pain is common in older people, but tends to present less dramatically, such that severe mesenteric ischaemia or diverticular perforation might be associated with surprisingly few physical signs. The pain may be nonspecific, and pyrexia maybe absent in spite of intra-abdominal sepsis. On occasion the acute abdomen may precipitate an acute confusional state, so a thorough abdominal examination is important in all such patients. The pattern of disease also changes in older people. Diverticular disease and colonic cancer are common, as is biliary disease, alcohol use and, in consequence, acute pancreatitis. Obstruction due to adhesions and hernias is also more common, the hernias often being overlooked by patient and physician alike. Comorbidity is routine, so the morbidity and mortality from the acute abdomen are higher.
The acute abdomen in immunosuppressed patients
In immunosuppressed patients, as in older people, the typical presentation and course of an acute abdomen may alter. In addition the presence of immunosuppression might make other diagnoses more likely, particularly lymphoma and viral diseases such as cytomegalovirus. Immunosuppression often reduces the inflammatory response to the abdominal pathology, so signs of peritonitis might be much less impressive than in the nonimmunosuppressed; but such patients tolerate the untreated acute abdomen badly. For this reason urgent imaging and early surgery are appropriate. Likewise a less ambitious surgical approach is required, such that exteriorization of the bowel should be considered routine rather than risking a primary anastomosis. An early leak from an anastomotic disruption could be fatal in an immunosuppressed patient, but is obviated if the bowel is defunctioned.
The acute abdomen with peritoneal dialysis
The peritonitis that occurs in patients on peritoneal dialysis is commonly due to skin organisms such as Staphylococcus epidermidis and Staph. aureus. In addition to abdominal pain and tenderness the peritoneal dialysis fluid is cloudy with a high cell count. Culture of the fluid usually confirms the causative organism, and systemic and intraperitoneal antibiotics usually treat the infection completely. The presence of gut organisms in the fluid, particularly where more than one organism is identified, suggests a bowel perforation, as does the presence of free intraperitoneal air (best seen on CT). Although peritoneal dialysis exchanges can result in free intraperitoneal air, in the context of abdominal pain a perforation is more likely. Perforations are usually of diverticular origin, and can be very difficult to find at laparotomy because of the effective irrigation that the peritoneal dialysis provides and the small size of an early perforation. A negative laparotomy should therefore not be taken as eliminating perforation as a diagnosis, and continued pain is an indication for a second look, even within 48 h of the original laparotomy.
The acute abdomen in chronic liver disease
In cirrhotic patients with ascites, translocation of gut flora, or haematogenous seeding of bacteria, can result in bacterial infection of the fluid, a condition referred to as spontaneous bacterial peritonitis. This is diagnosed by a high white cell count (>250 cells/mm3) on aspiration, and is treated by systemic antibiotics even where culture is negative. Culture is negative in over one-half of the cases, although sensitivity of culture can be increased by direct inoculation into culture bottles at the bedside. Where the liver disease is advanced it often precipitates encephalopathy or renal failure and there is some evidence to suggest it may precipitate variceal haemorrhage. Surgery is not usually necessary, and if undertaken in this setting is associated with a high mortality due to decompensated liver disease.
The iatrogenic acute abdomen
Modern investigation and minimally invasive treatments carry risks, including the precipitation of an acute abdomen. These should be borne in mind by anyone reviewing a patient in pain in the following circumstances.
- ◆ Angiography/angioplasty—dislodged plaque fragments may result in mesenteric or renal ischaemia. Angioplasty to a branch of the aorta, such as a renal artery or mesenteric artery may cause in situ thrombosis. Since mesenteric ischaemia is difficult to diagnose, a high index of suspicion is necessary.
- ◆ Percutaneous drainage, be it under radiological guidance or unguided drainage of ascites, runs the risk of bowel perforation. Typical presentation as following a perforation of any aetiology, with the added diagnostic aid being the colour and nature of the fluid being drained.
- ◆ Liver procedures, such as transjugular portosystemic shunt formation, percutaneous transhepatic cholangiography, or endoscopic retrograde cholangiopancreatography may result in a bile leak and biliary peritonitis. Liver biopsy and percutaneous transhepatic cholangiography may also result in intraperitoneal haemorrhage.
- ◆ Endoscopic retrograde cholangiopancreatography is occasionally associated with acute pancreatitis. It may also cause a retroperitoneal perforation.
- ◆ Endoscopic investigation and treatment, whether upper or lower gastrointestinal tract—perforation of the bowel is recognized. Typically patients present with acute abdominal pain if the perforation is intraperitoneal; occasional retroperitoneal perforations may result in local abscess formation and be difficult to diagnose without cross-sectional imaging.
Medical causes of an acute abdomen
While the keen student will recount the acute abdomen that results from porphyria or sickle crisis, or in association with tabetic crises, it should be borne in mind that common things are common and that applies particularly to the acute abdomen. Nevertheless some nonsurgical causes are important to note:
- ◆ Diabetic ketoacidosis is associated with abdominal pain; it might also be precipitated by intra-abdominal pathology such as appendicitis and ectopic pregnancy.
- ◆ Herpes zoster often presents with a prodromal pain a few days before the rash appears. Its unilateral nature may result in diagnoses of diverticulitis or cholecystitis being made.
- ◆ Pneumonia—particularly in young people and older people, lower lobe pneumonia can present with upper abdominal pain. A careful history, chest examination, and radiology should provide the correct diagnosis. Occasionally the pneumonia is secondary to upper abdominal pathology which has resulted in reduced respiratory effort.
- ◆ Gastroenteritis can present with colicky pain followed by diarrhoea and/or vomiting. The history of exposure to a potential infective source, as well as contacts with similar symptoms is usually helpful. Stool cultures should be taken, and the patient nursed appropriately.
- ◆ Constipation can often cause concern, particularly in patients with Parkinson’s disease where both disease and treatment contribute. Constipation may present with colicky pain and distension, and may be the first manifestation of a colonic carcinoma. Occasionally chronic constipation might result in sigmoid volvulus, diagnosed radiologically and treated sigmoidoscopically.
- ◆ Acute porphyria causes abdominal pain and other features of neurovisceral manifestations. It is a disease that is worthy of consideration since specific treatment with haem arginate and avoidance of precipitating factors such as drugs, starvation, surgical procedures, and anaesthetics is often life-saving. A characteristic feature of acute porphyria is the distress that accompanies the pain and the associated hypertension and tachycardia: a notable aspect is the lack of tenderness. The diagnosis is based on history, family history, and specific urinary tests.
Further reading
Burnand KG et al. (eds) (2005). The acute abdomen, Chapter 25 in The new Aird’s companion in surgical studies, 3rd edition. Churchill Livingstone, Edinburgh.
Flasar MH, Goldberg E (2006). Acute abdominal pain. Med Clin N Am, 90, 481–503. [Acute abdominal pain for physicians, with an American flavour.]
Ranji SR et al. (2006). Do opiates affect the clinical evaluation of patients with acute abdominal pain? JAMA, 296, 1764–74. [Evidence that opiates do not alter the outcome in acute abdominal pain, although they may increase the time to diagnosis.]
Saunders MD, Kimmey MB (2005). Systematic review: acute colonic pseudo-obstruction. Aliment Pharmacol Ther, 22, 917–25. [A review of the aetiology and treatment of pseudo-obstruction.]