Location and migration

Whether abdominal pain is generalised or localised to an abdominal segment is the most important piece of information to obtain first. Migration of abdominal pain also often assists in diagnosis (Fig 7.1). Central or generalised abdominal pain is a common initial symptom of many diseases (appendicitis, bowel obstruction, visceral perforation). Persisting severe generalised abdominal pain suggests generalised peritonitis. Epigastric or right upper quadrant pain extending in a band around the abdomen suggests a biliary origin (‘colic’). Migration of central pain to the right iliac fossa over the course of several hours indicates appendicitis. This is an example of visceral pain evolving into a somatic pattern as local peritonitis develops with pathological progression of appendicitis. Another example of this phenomenon is migration of pain from the left iliac fossa to the whole abdomen may be associated with initial sigmoid diverticulitis with subsequent perforation and the development of generalised peritonitis.

Figure 7.1 Migration of pain in common abdominal conditions

A: biliary pain — migration to below the top of the right scapula (‘wing sign’); B: perforated ulcer — down the right paracolic gutter; C: acute appendicitis — to the right iliac fossa; D: perforated diverticulitis — over the abdomen starting from the left iliac fossa; E: renal colic — from loin to groin

Onset and duration

The time, pattern and character of onset and the duration of symptoms are elicited. Acute abdominal pain that persists for six or more hours suggests the presence of a surgical abdomen; so does a history of awakening at night with the pain, especially if pain precedes other symptoms such as vomiting or diarrhoea. A sudden and dramatic onset of pain suggests rupture of a previously intact structure (e.g. duodenum, colonic diverticulum, splenic capsule, aortic aneurysm). A gradual onset, progressively worsening over hours or days, correlates with inflammation. The onset after excessive alcohol intake suggests pancreatitis. A history of abdominal injury may be of importance. A latent period can exist between the time of trauma and presentation, as is seen with delayed rupture of the spleen. A latent period can also be seen in other acute abdominal conditions such as perforated peptic ulcer, intussusception, large bowel obstruction, gallstone ileus and intestinal infarction. Sometimes such a latent period gives the illusion of resolution of the problem and can delay or obscure diagnosis.

Type and intensity

The character of the pain is subjective. Patients often relate pain to previous or imagined occurrences (‘stabbed by a knife’, ‘struck by lightning’, ‘burning’). It is important to establish whether the pain has been constant and unremitting since onset or is periodic. If periodic, is it a true colic? Colic causes a spasmodic, gripping abdominal pain that returns every few minutes with a crescendo rise and fall in intensity often described by women as similar to labour pains. Colic associated with an urge to defaecate or pass flatus and with abdominal borborygmi is pathognomonic of intestinal colic due to obstruction or irritation. The colicky pain of obstruction is usually more severe than is found with gastroenteritis. Severe colicky pain that becomes constant suggests ischaemic bowel. Constant pain often varies in severity during the course of the illness, but careful questioning will distinguish this from a true colic. The need for narcotics to control upper abdominal pain is suggestive of renal or biliary pain. Severe pain persisting without relief requires hospital admission.

Severity is also subjective and best assessed by the effect of pain on the patient, the response to the suggestion that an operation may be necessary and the necessity for and whether relief from analgesics already administered has occurred. Inability to sleep because of pain suggests a surgical problem.

Severe unremitting pain may be due to localised peritonitis because of appendicitis, cholecystitis or diverticulitis, or due to widespread peritonitis from visceral rupture or mesenteric ischemia. Biliary pain tends to plateau, after a gradual onset; it is continuous but fluctuates in severity. Acute renal pain is a very severe and constant pain. Neither is a true colic.

Radiation

Radiation or referral is extension of the pain to another site while the initial pain persists. Occasionally the site of referral may be dominant and simulate disease in another organ. Biliary pain may be felt primarily in the back or in the precordium, simulating angina. Pain from a penetrating duodenal ulcer (or from pancreatitis) and from carcinoma of the pancreas often pass directly through to the back. Renal pain radiates from the flank (loin) to groin, testis or thigh. Conversely, the pain of testicular torsion may sometimes be referred to the hypogastric region. Segmental nerve root pain is referred to the appropriate dermatome. Shoulder pain can be referred from the mediastinum or result from diaphragmatic irritation from an abdominal cause — for example, blood or intestinal contents beneath the diaphragm.

Associated symptoms

Nausea, vomiting and anorexia often precede pain of non-surgical origin: profuse vomiting as a main feature suggests upper small bowel obstruction; persistent anorexia following pain favours an organic cause; persistent vomiting from any cause can occasionally give haematemesis from a Mallory-Weiss tear in the lower oesophagus.

Nausea, diarrhoea and vomiting preceding colicky pain is a feature of gastroenteritis; diarrhoea may be due to pelvic appendicitis or abscess.

An association with menstrual disorders often indicates gynaecological disease. Abnormal menstrual loss before pain suggests abortion, or after pain suggests ectopic pregnancy. A missed period implies the possibility of a complication of pregnancy. Intermenstrual pain and bleeding may be associated with ovarian problems and vaginal discharge with salpingitis. Urinary symptoms such as frequency, scalding or haematuria suggest pyelonephritis, cystitis or stone. Chills and rigors hint at significant infective conditions such as pyelonephritis, salpingitis or viral gastroenteritis.

Offsetting factors

The factors that relieve pain may clarify the diagnosis. Relief of pain by food and alkali suggests peptic ulceration. Certain movements can relieve pain; the pain of pancreatitis may be relieved by sitting forward. A hot-water bottle is often used for biliary pain and nonsteroidal anti-inflammatory agents commonly relieve musculoskeletal pain. Relief of pain by vomiting indicates possible ulcer disease and relief of pain by defaecation or passage of flatus suggests gastroenteritis or functional bowel disease. Biliary and renal pain often require analgesic injection for relief.

Factors that worsen pain, such as movement, may indicate that the pain is musculoskeletal in origin. However, the pain of peritonitis is worsened by abdominal movement, deep breathing or coughing, as is pain from diaphragmatic irritation. If food worsens the pain, conditions such as benign or malignant gastric ulceration need consideration.

Past history

Previous episodes of pain, previous abdominal operations, a history of previous trauma, past and current drug treatment and alcohol intake are commonly relevant to the assessment of the current presentation of abdominal pain.

Examination of the periphery

The hands are examined. Nail changes include clubbing, which may be found in a number of gastrointestinal conditions, chronic liver disease, inflammatory bowel disease and malabsorption. Other changes such as leuconychia, indicating malnutrition and hypoproteinaemia, or koilonychia, suggesting iron deficiency, may be present. Palmar erythema, spider naevi and Dupuytren’s disease (palmar nodules, bands, contractures, pits and sinuses and knuckle pads) suggest alcoholic liver disease (Fig 7.2). Asterixis is a flapping tremor best seen with the hands in extension and is found in patients with portal systemic encephalopathy.

The head and neck are then examined for abnormal pigmentation, spider naevi, xanthelasma of the eyelids, scleral jaundice or pallor and parotid enlargement. The neck is examined for cervical lymphadenopathy, especially left supraclavicular nodal enlargement (Troisier’s sign) as a sign of metastatic node involvement from carcinoma of the stomach.

The mouth is then examined for the smell of fetor hepaticus suggesting encephalopathy, mucosal thickening and ulceration, atrophy or erythema, gingivitis and angular stomatitis. A ketotic breath and coated tongue is suggestive of appendicitis or related conditions. Angular stomatitis (‘perlèche’) is seen frequently in patients with iron deficiency and malnutrition. Glossitis occurs in patients with iron, folate and vitamin B12 deficiency. Mouth ulceration may be present. The hydration status (i.e. skin turgor and moistness of mucous membranes) should be assessed at this time, especially in the acute setting.

Abdominal examination

The patient lies supine with arms by the side and with groin and hernial orifices exposed. The examination should be performed in a good light. The abdomen is inspected for abnormal contour, either distension or scaphoid appearance, for generalised or localised distension, for scars, discolouration, pigmentation or striae, for distended veins radiating from the umbilicus (caput medusae) and for visible pulsations or peristalsis. The patient is then asked to breathe deeply in and out through the mouth, to see if the contour changes or if a mass moves or becomes more obvious and to see if respiratory movement is painful. The patient is asked to cough and scars and the hernial orifices are watched to detect an expansile impulse. The patient is asked to lift the legs or shoulders from the bed and similar observations are made for an impulse. With this manoeuvre a visible mass, if subcutaneous, will become more prominent, an intra-abdominal mass less so.

Figures 7.3 and 7.4 depict anterior and posterior surface markings of the abdominal viscera.

Figure 7.3 Anterior surface markings of upper abdominal viscera

Figure 7.4 Posterior surface markings of abdominal viscera

A: lung; B: pleura; C: kidney; D: pancreas; E: spleen

After inspection, the patient is asked if there is any tenderness and, if there is, its site. Palpation is started gently with the hand flat, at a site away from the site of maximal tenderness and then in all quadrants (Fig 7.5).

Figure 7.5 Region of the abdomen

A: epigastrium; B: right hypochondrium; C: lumbar region; D: periumbilical region; E: right iliac fossa; F: hypogastrium

Then the abdomen is palpated more deeply using the flexor surface of the fingers — the use of two hands often helps to define masses (Fig 7.6).

Figure 7.6 Method of palpating the spleen

The hernial orifices and genitalia are examined. It is important to distinguish normally palpable structures from abnormal masses (Fig 7.7).

Figure 7.7 Palpable normal abdominal structures

1: xiphoid process; 2: liver; 3: edge of rectus abdominis; 4: lower pole of right kidney; 5: caecum; 6: aorta; 7: ala of sacrum; 8: pregnant uterus; 9: full bladder; 10: sigmoid colon; 11: faecal loading

Routine examination for ascites is essential in the distended abdomen, by eliciting shifting dullness or a fluid thrill. Shifting dullness is shown to be present by rotating the patient about the long axis and demonstrating a change in the ‘Plimsoll line’ or transition line of dullness to percussion (Fig 7.8). Fluid thrill is detected by flicking the side of the abdomen and palpating for a transmitted impulse on the other side. Transmission of the impulse via the abdominal wall is blocked by another hand placed on the midabdomen.

Figure 7.8 Shifting dullness

Area 1 is resonant when supine and dull in lateral position. Area 2 is dull when supine and resonant in lateral position.

Based on Burkitt, 2007

The following physical signs are sought: tenderness or resistance on palpation (voluntary or involuntary guarding); rigidity (extreme guarding); and rebound tenderness (best assessed by gentle percussion). A full description of any detected mass is often most usefully recorded as a simple schematic sketch in the medical record. The edge of a mass may be best delineated by deep palpation during inspiration (liver and spleen) or by percussion (Table 7.1). The site and depth of a mass are very important diagnostic features. Other important features include shape and consistency and whether the mass is mobile or fixed. Faecal masses are indentable.

Anorectal examination

Anorectal examination is usually performed on patients in the left lateral position if there are appropriate symptoms requiring this to assess the clinical problem. It is not required as part of all abdominal examinations. The spine and hips are fully flexed; the knees are flexed to a little less than 90° to obtain better access for sigmoidoscopy. The equipment required is a good light, examination gloves, lubricating jelly and paper tissues to clean the anus after examination. Proctoscopy (anoscopy) and sigmoidoscopy (rectoscopy) should be part of a routine office or outpatient examination by appropriately trained practitioners. The proctoscope permits visualisation of the anal canal up to 10 cm; the standard rigid sigmoidoscope up to 30 cm. The flexible sigmoidoscope is a specialist instrument, visualising up to 50 cm from the anal verge. Long biopsy forceps are also necessary should sampling for histology be necessary. Neither form of sigmoidoscopy is part of a standard non-specialist examination. Bowel preparation is not usually necessary for routine anorectal examination.

Initial inspection may reveal prolapsed haemorrhoids, perianal haematomas, external openings of fistulas and the dry or moist skin changes of pruritus. Examination of the anus during straining will be necessary to reveal prolapsing haemorrhoids or rectal prolapse. Anal fissures are normally not initially obvious on inspection, as they are located above the anal verge. Most fissures are seen in the midline posteriorly. Laterally placed fissures suggest an association with inflammatory bowel disease. Gentle retraction of the anal verge will usually expose the lower edge of a posterior fissure. Rectal examination (Fig 7.10) and proctoscopy may not be possible in such instances because of painful anal spasm. Palpation commences using the pulp of the index finger introduced slowly into the anorectum. The finger will usually reach 10 cm with a little pressure on the perineum or with the assistance of bimanual compression of the lower abdomen. As the finger is withdrawn the whole circumference of the rectum is examined. The indurated, elevated and ulcerated lesion of a carcinoma is characteristic. The capacity of the rectum should be noted. Masses outside the rectum in the pouch of Douglas may be palpable anteriorly. Anteriorly in the male the normal prostate is a firm rubbery bilobed structure about 3 cm in diameter. A shallow central sulcus may be palpated and the mucosa over the prostate should be freely mobile. In the male it is difficult to define anatomical structures above the base of the prostate. The prostate feels larger on examination if performed while the patient has a full bladder. In the female the cervix of the uterus or a vaginal tampon may be palpable anteriorly and should not be mistaken for a mobile extrarectal tumour. Faecal pellets in an intrapelvic sigmoid colon can simulate abnormal extrarectal lumps but faeces are regular and indentable. The glove should be examined for blood after completion of the digital examination.

Figure 7.10 Rectal examination

Digital detection of a carcinoma of the rectum at about 10 cm from the anal verge. The characteristics on palpation are induration, elevation and ulceration. Blood may be seen on the glove after completion of the examination.

Figure 7.9 Anatomy of the anorectum

The anal canal extends from the anorectal ring, which is formed by the puborectalis, down to the anal verge, a distance of about 3 cm. 1: puborectalis muscle 2: inferior haemorrhoidal plexus or cushion; 3: anal crypt; 4: dentate line; 5: interhaemorrhoidal groove; 6: anal verge; 7: external haemorrhoidal plexus; 8: external haemorrhoidal artery; 9: internal sphincter; 10: external sphincter

Proctoscopy is the best method of diagnosing haemorrhoids, as these lesions are impalpable on digital examination unless thrombosed. Proctoscopy also provides a means of close viewing of tumours in the lower third of the rectum for biopsy and for the office treatment of haemorrhoids.

1. Acute appendicitis with perforation (see also acute right iliac fossa pain)

Perforation, with presentation as an acute abdomen, is seen most frequently in the young, the old and in patients with diabetes. In many series, perforation at the time of appendicectomy has occurred in almost half those patients under 10 years and over 50 years. It is unusual for the acutely inflamed appendix to perforate within the first 12 hours. Pain in appendicitis is often initially central and diffuse, followed by a shift to the right iliac fossa within a few hours. Pain is deep-seated, continuous and gradually increases in intensity. Nausea and vomiting are common, but vomiting is rarely pronounced or persistent and is rarely the first symptom. Diarrhoea is also rarely the first symptom (Table 7.2). Its presence suggests pelvic appendicitis. The development of perforation is accompanied by more severe generalised abdominal pain and higher fever.

Table 7.2 Comparison of clinical features of perforated pelvic appendicitis and gastroenteritis

Signs. With general peritonitis, there is diffuse abdominal tenderness with guarding, which is often maximal in the right iliac fossa. The degree of guarding depends upon the rapidity of onset of the peritonitis. Bowel sounds often persist for some time. If untreated the abdomen becomes silent and progressively distends, with diminution of tenderness as exudate accumulates. High fever, toxicity and eventually septic shock develop. A tender local mass may be felt in the right iliac fossa suggesting abscess formation. In such a case the patient is usually toxic and febrile due to irritation of the rectum. In pelvic appendicitis, abdominal signs are often delayed or less marked but rectal examination may reveal the presence of pelvic tenderness and peritonitis.

2. Severe acute (haemorrhagic) pancreatitis

A small but important proportion of patients with severe acute pancreatitis present with an acute abdomen. The remaining patients with less severe disease present with localised acute upper abdominal pain (Ch 7.3). The most severe haemorrhagic form of the disease is associated with collapse and shock.

The onset of symptoms is occasionally explosive and can mimic a visceral perforation. Usually, however, increasingly severe pain develops over a period of several hours and spreads from the epigastrium throughout the whole abdomen and through to the back. Progressive dyspnoea and prostration (shock) are common. Persistent vomiting is often a feature of the illness (Table 7.3). Change of posture may aggravate or relieve the pain. Fever is variable.

Table 7.3 Comparison of perforated duodenal ulcer with acute pancreatitis

Signs. Signs of generalised peritonitis are present. There is often a ‘doughy’ feel to the abdomen and the signs of peritonitis and muscle rigidity are less than one would expect from the severity of the pain and the degree of prostration (an important point of differentiation from perforated ulcer). Disparity between the signs of peritonitis and the severity of pain is sometimes a feature of bowel ischaemia.

Prostration and shock, dyspnoea, ventilatory insufficiency and cyanosis indicate a severe attack with poorer prognosis. Extraperitoneal fluid and blood extravasation may be indicated by staining in the flanks (Grey-Turner’s sign) or around the umbilicus (Cullen’s sign).These signs are typically delayed in onset and may not be present at the initial presentation. The common predisposing causes of severe pancreatitis are gallstones and alcohol. In alcoholic pancreatitis the patient may be agitated and confused, indicating imminent delirium tremens.

3. Perforated peptic ulcer

The history is usually typical, with a sudden onset of very severe abdominal pain spreading from the epigastrium to the whole abdomen; radiation to the back and shoulder is less common. The patient is anxious, grey, sweaty and still. Movement and coughing exacerbate the pain. Breathing is shallow and is inhibited by pain. Many patients have a past history of peptic ulcer.

Signs. The clinical signs are usually unmistakable. Generalised peritonitis is present, with board-like rigidity in the epigastrium and elsewhere. The term is very appropriate and, once felt, is difficult to confuse with anything else. The abdomen is silent and loss of liver dullness to percussion may be elicited. Pulse, temperature and blood pressure are all likely to be normal. Shock does not develop until a late stage. The delayed ‘stage of reaction’ or of ‘masked’ peritonitis takes several hours to develop. This should not confuse the careful observer, as rigidity and ileus persist. More difficulty is found with a localised duodenal leak when the history is less typical and the abdominal signs are restricted to local tenderness in the upper abdomen (Ch 7.3).

4. Diverticulitis with perforation

Acute abdomen from diverticulitis results usually from the rupture of a pericolic abscess. Sometimes faecal peritonitis results from sudden rupture of an uninflamed diverticulum. Thus the onset may be without warning or after a recent history of acute diverticulitis. In many cases, a long history of bowel upset and episodic lower abdominal distension and discomfort precedes the acute attack. Very severe widespread pain originating from the left iliac fossa with prostration suggests perforated diverticulitis.

Signs. General peritonitis is present with maximum tenderness and guarding in the left iliac fossa. A tender mass due to a peridiverticular phlegmon or abscess may be palpable. Fever and toxicity are common associated features: they suggest a septic cause for the acute abdomen and help to distinguish diverticulitis from perforated ulcer.

5. Strangulating intestinal obstruction

Simple intestinal obstruction is usually readily diagnosed on clinical assessment and a plain X-ray film of the abdomen and is discussed in more detail in Chapter 7.9. Strangulating obstruction is a complication of simple obstruction; it can be notoriously difficult to diagnose and is lethal without prompt surgery. In simple small bowel obstruction the abdominal pain is colicky and periumbilical. If the pain becomes continuous, strangulation should be suspected.

Obstruction with ischaemia or strangulation is also seen in the large bowel. In an important minority of patients with malignant large bowel obstruction, the ileocaecal valve is competent and prevents regurgitation into the small bowel and decompression of the large bowel so that a ‘closed loop’ obstruction develops. The main danger is then progressive distension and perforation of the caecum. Such patients may present with right-sided pain and tenderness with distension and will require urgent surgical treatment to prevent caecal perforation and the consequent faecal peritonitis. Sigmoid or caecal volvulus is of more abrupt onset with severe constant pain due to early ischaemia and rapid massive distension and imminent perforation.

In malignant large bowel obstruction, a history of altered bowel habit often precedes complete constipation for faeces and flatus. This is often due to left-sided colonic stenotic lesions. Pain is often late and is felt in the lower abdomen or back. Nausea is common, but vomiting is generally a late feature.

Signs. Although certain clinical features can create a suspicion that strangulation is present (Box 7.1), no clinical or laboratory findings exist that exclude with certainty the possibility of strangulation. In small bowel obstruction the bowel sounds are hyperactive. Signs of local peritonitis and a palpable mass strongly suggest strangulation. A strangulated external hernia (femoral, inguinal, umbilical or incisional) will be tense, tender, irreducible and will have lost the cough impulse. Always search for a hernia, even in the patient who has had previous abdominal operations. Signs of interstitial fluid and blood volume depletion will be present when bowel obstruction has persisted for one or more days. Early shock or poor response to resuscitation suggests the presence of strangulation.

In large bowel obstruction, distension is particularly marked in the flanks and in the right iliac fossa. Signs of fluid depletion are late. The distension is predominantly gaseous and signs of shock or peritonitis suggest that perforation has occurred. Careful sigmoidoscopy may reveal the cause of the obstruction.

6. Vascular catastrophes

Ruptured aortic aneurysm usually presents in elderly men with the sudden onset of central abdominal pain radiating to the back and/or groin, associated with collapse, pallor and severe shock. There may be previous knowledge of a pulsatile abdominal swelling. The patient with ruptured aortic aneurysm is pale and sweating with collapsed veins, the signs of haemorrhagic shock. The majority of patients have ‘contained retroperitoneal haematoma’ rather than a free intraperitoneal rupture. A poorly defined pulsatile upper abdominal swelling is present in the epigastrium to the left of the midline. Femoral pulses may be weak or absent, but this is not diagnostic. Ruptured visceral artery aneurysms should be considered as well in patients with hypotension and severe sudden upper abdominal pain.

Aortic dissection presents with sudden severe tearing pain felt in the interscapular region or lower chest, radiating to the back and abdomen. Signs of distal vascular insufficiency in the limbs with absent or diminished peripheral pulses may be present, depending on the anatomy of the dissection, with possible anuria and with mild general abdominal tenderness. The patient is not always elderly in contrast to most patients with ruptured abdominal aortic aneurysms.

Acute mesenteric ischemia is typified by the presence of generalised severe, continuous abdominal pain of sudden with surprisingly few abdominal signs initially. The development of peritonism and mental confusion, associated with gross prostration and often dark rectal bleeding is usually associated with a grave outcome. Often evidence of an underlying embolic focus exists — such as atrial fibrillation or a recent myocardial infarct. The triad of pain, rectal bleeding and prostration in an elderly patient with fibrillation is suggestive of the diagnosis.

7. Ruptured ectopic pregnancy

Acute lower abdominal and shoulder-tip pain associated with pallor, prostration or fainting in a woman of child-bearing age is the characteristic presentation. Gastrointestinal symptoms are unusual. Rupture usually occurs between six and eight weeks’ gestation, so a missed period is common but not invariable. Death of the embryo causes the pain to be followed by dark, withdrawal vaginal bleeding in most but not all cases. This contrasts with the acute, bright, copious bleeding of abortion that often precedes pain. Acute abdomen from a ruptured ectopic pregnancy usually results from the rupture of isthmial implantations — in contrast to the problem of acute pelvic pain seen with a leak from an ampullary implantation.

Signs. The patient is pale and shocked, with a tender silent lower abdomen that may be mildly distended. There are usually no obvious signs of pregnancy such as breast enlargement but vaginal examination shows a soft cervix that is exquisitely tender to palpation. A tender pelvic mass may be present in one or other fornix.

8. Gastroenteritis

This non-surgical cause of an acute abdomen presents a problem in diagnosis, particularly in general practice. The main difficulty is the exclusion of appendicitis (particularly in infants), pelvic appendicitis and intestinal obstruction (in adults). In gastroenteritis, nausea, vomiting or diarrhoea precede the pain in contrast to the sequence of events in appendicitis, for example. The pain is less severe (though it may be colicky) than with obstruction. Early high fever is more suggestive of a viral illness, as are the presence of diffuse myalgias, photophobia and headache.

Signs. Abdominal tenderness tends to be poorly localised and diffuse. Abdominal guarding is not a feature of the illness and bowel sounds are hyperactive. Early high fever is a feature. As well as the common viral aetiology, enteritis may be caused by bacteria such as Yersinia, Salmonella or Campylobacter.

9. Less common causes

Primary peritonitis is now mainly found in association with alcoholic liver disease and ascites and can lead to a ‘negative’ laparotomy or laparoscopy. Foreign body perforation is not rare and may be difficult to locate at laparotomy. Periodic peritonitis (familial Mediterranean fever), gonococcal peritonitis, tuberculous peritonitis and granulomatous peritonitis, are other causes to be considered in the differential diagnosis of the acute abdomen. Complications of inflammatory bowel disease need to be considered.

The pain of renal infection can mimic an acute abdomen. Associated urinary frequency, dysuria and pyuria usually suggest the diagnosis. Rupture of an inferior epigastric vessel may be associated or follow treatment with oral anticoagulants. Rectus sheath haematoma may be spontaneous or precipitated by minor trauma and can mimic an acute abdomen or appendicitis. Similarly, ‘spontaneous’ retroperitoneal haematoma can occur in anticoagulated patients and present with lateralised abdominal or flank pain.

Medical conditions do not usually simulate an acute abdomen to the degree where surgical intervention is necessary. Basal pneumonia, however, can present difficulties. In these patients respiratory signs may be minimal, although respiratory distress is often the clue that suggests the diagnosis. Myocardial infarction is rarely a cause of an acute abdomen, but the initial pain may be in the epigastric region. Acute painful hepatic engorgement secondary to acute right ventricular failure may give rise to diagnostic confusion such as occurs in large pulmonary embolism. Acute porphyria, precipitated by barbiturates and diabetic ketosis with abdominal pain and vomiting, are occasionally problems in diagnosis, especially when associated with collapse and a confused mental state.

Urine examination

All patients should have a dipstick test on admission. Haematuria may accompany renal colic. Proteinuria, pus cells and organisms on microscopy suggest urinary infection. Urinary polymorphs may also accompany retrocaecal or pelvic appendicitis. Bile suggests acute cholecystitis or pancreatitis. Urinary glucose testing will detect the undiagnosed diabetic. The additional presence of acetone makes diabetic ketosis a possible cause of abdominal pain. Urine osmolality may be useful in assessing fluid depletion. A specific urine β-HCG should be done in all female patients of reproductive age.

Haematological examination

Haemoglobin and white cell count are often useful. Anaemia suggests that peritonitis may be due to blood in the peritoneal cavity or that there is underlying malignant or benign ulceration of the gastrointestinal tract. Leucocytosis (greater than 11 × 10∧9 per litre) suggests sepsis or inflammation. If very high (over 20) an abscess is likely. High white cell count suggests also the possibility of strangulated bowel and makes a diagnosis of perforated ulcer, pancreatitis and gastroenteritis less likely. Leucopenia may occur with severe sepsis. Blood culture is indicated for any patient with a suspected septic cause.

An elevated haemoglobin or haematocrit level is indicative of plasma volume depletion. Diminished levels indicate pre-existing anaemia or blood loss.

Biochemistry

Few tests are specifically helpful in making a diagnosis but several are useful in monitoring the treatment of metabolic and ventilatory disturbances.

Serum lipase levels over 100 iu/L are very suggestive of pancreatitis. Lipase is much more specific for pancreatitis than serum amylase where moderate elevations up to 1000 iu/L may occur with intestinal obstruction, strangulation or perforation. Serum electrolyte, urea and creatinine levels help assess fluid and electrolyte requirements. Urea elevation is commonly due to isotonic extracellular fluid (‘saline’) depletion.

Arterial blood gas analysis is important in monitoring shocked patients, those with ventilatory problems or with pancreatitis. Serum lactate levels are often disproportionately high in mesenteric vascular occlusion. Liver function tests rarely influence early operative management but are useful baselines in jaundiced patients and in alcoholics.

Imaging techniques

These include plain radiology, ultrasound, contrast and computed tomography (CT scan) and are very often valuable. Erect chest X-ray (Fig 7.11), together with erect and supine films of the abdomen, are indicated in nearly all patients. (For patients too moribund to undergo an erect chest X-ray, a lateral decubitus film may be requested.) These X-rays may show primary chest pathology (pneumonia) or basal changes secondary to a subdiaphragmatic condition such as pancreatitis. Free gas under the diaphragm indicates a perforated viscus, usually a perforated ulcer or perforated diverticulitis. A grossly dilated stomach may be seen in patients in diabetic coma, falsely suggesting the possibility of a surgical condition.

Figure 7.11 Chest X-ray with gas under the diaphragm

Based on Burkitt, 2007

If small bowel obstruction is suspected, erect and supine views show significant distension of the small bowel with gas fluid levels and a ladder pattern (Fig 7.12). In large bowel obstruction, the colon is distended down to the site of obstruction and small bowel dilatation may coexist. If the ileocaecal valve is incompetent specific causes such as sigmoid or caecal volvulus may show localised distended large bowel loops. Gastroenteritis can be associated with small gas–fluid levels with moderate intestinal distension. Air swallowing in association with severe pain and recent injury may cause confusion. The absence of free gas does not exclude perforated viscus, nor does the absence of fluid levels in the bowel exclude strangulation. Free gas is seen in only about two-thirds of cases of perforated peptic ulcer. In appendicitis, distended bowel with fluid levels on plain X-ray often indicates a localised ileus in the right iliac fossa. Pancreatic calcification or lithiasis or a sentinel small bowel loop in the region of the pancreas or a colonic ‘cut-off’ sign may be seen in pancreatitis. More commonly, generalised ileus is present, with evidence of ascites. Distended, gas-filled, small and large bowel loops with fluid levels are present and large bowel gas extends to the rectum. Mesenteric infarction causes a diffuse small bowel ileus. In ruptured aortic aneurysm a rim of calcium may be seen in the aneurysm, particularly in the lateral decubitus films. Radio-opaque gallstones may be seen in cholecystitis (20%); urinary calculi are usually visible (80%).

Figure 7.12 Films of small bowel obstruction

A: supine abdominal X-ray with dilated small bowel loops; B: erect abdominal X-ray with multiple air fluid levels (arrowed); C: typical ’ladder’ pattern (arrowed) on supine abdominal X-ray

From Feldman, 2006

Contrast-enhanced X-rays may be required in special instances to diagnose bowel leakage. A gastrografin meal or enema will not damage the peritoneum and can be very useful, especially if combined with a CT scan at the same time. A limited contrast enema is often used to confirm the diagnosis and the site of a large bowel obstruction prior to operation.

Ultrasound is the investigation of first choice in the diagnosis of gallstones and hepatobiliary conditions.

Aortic aneurysms are readily diagnosed with ultrasound and CT angiography may be useful in diagnosis of ruptured aortic aneurysm or dissecting aneurysm if the diagnosis is not clear, the patient is stable and renal function known to be satisfactory. When a focus of infection is suspected, CT scan with oral contrast can both facilitate the diagnosis and direct interventional or surgical treatment. Ascites may be seen in pancreatitis — aspiration and amylase level on the fluid may be diagnostic.

Catheter angiography is rarely required, apart from the context of mesenteric vascular insufficiency.

Peritoneal tap and lavage

Peritoneal tap or lavage is much less commonly used to assess the acute abdomen than in assessing blunt abdominal trauma. Abdominal distension and previous incisions are contraindications. False negative results can mislead and most surgeons prefer to explore the abdomen by laparoscopy or laparotomy if a surgical cause cannot be excluded by other means.