ABC ofEmergency Radiology

THE ABDOMEN I

D A Nicholson, P A Driscoll

Plain radiographs remain the best method ofdetecting intestinal obstruction orperforation

Patients with abdominal symptoms account for a large proportion of peoplepresenting as emergencies. Despite the development of other investigationsplain film radiographs are still performed in most cases to look for intestinalobstruction or perforation. This article describes a systematic approach tothe evaluation of abdominal radiographs and the next article will describethe different conditions commonly encountered.

Important anatomical considerations

A thin layer of extraperitoneal fat lies in the lateral abdominal wall betweenthe inner muscle layer (transverse abdominal muscle) and the parietalperitoneum. This produces a lucent shadow called the properitoneal line

The abdominal radiograph lacks symmetry (flank stripe), which can extend from above the lateral margin of the liver toand has a wide variation in normal below the iliac crest. Similarly a thin layer of adipose tissue is often seenappearances, which makes interpretationdifficult. Careful systematic interpretation is between the dome of the bladder and the pelvic perltoneum as a lucent line.therefore essential These lines are not usually seen in infants or elderly patients because of

scant adipose tissue. Normally the serosal surface of the ascending anddescending colon is next to the parietal peritoneum, with a potential space(the paracolic gutter) between.

FIG 1-Normal supine abdominal radiograph and line diagram. A large amount of bowel gas is seen in the non-dilated small and largebowel because of air swallowing. The properitoneal fat line is clear on the right continuing lateral to the liver edge.

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Types of view

Routine Additional The supine abdominal radiograph is theSupine Erect standard projection.Erect chest radiograph Left lateral decubitus

Erect chest radiograph-The erect chest radiograph is a fundamental partof the examination of the acute abdomen as it is the most sensitive

Causes of heart disease mimicking radiograph for detecting a small pneumoperitoneum. In addition, manyintrathoracic conditions can mimic an acute abdominal emergency andelderly people may have coexisting chest disease.

Myocardial infarctionPulmonary embolismPneumoniaDissecting aortic aneurysmOesophageal disease The erect abdominal radiograph adds little diagnostic information to the

standard supine abdominal radiograph and erect chest radiograph and hasbeen abandoned in many centres. It is occasionally needed to show thepresence of air-fluid levels (see later). It must be remembered, however,that fluid levels are not pathognomonic of obstruction. A left lateraldecubitus radiograph taken with a horizontal x ray beam is sometimes

useful as an alternative to the erect abdominal radiograph in patients whoare unfit to sit or stand.~~~~~~~~~~~~~~~~~~~~~~~.....,-.......

_ -~~~~~~~~~~~~~Causes0g~~~~~~~~~~~erect

>-E-? ::---a ~~~~~ObstructionI -X X ~~~~~~~~~~~~Gastroe

l l P ; | I~~~~~~~~~~~~schaemia

l -- l ~~~~~~~~~~~~Hypokalaemia

_ 1l ;< ~~~~~~~~~~~~Normal(<2.5 cm in length)

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FiG 2-Erect abdominal radiograph showing free air

under both hemidiaphragms (pneumoperitoneum).

Radiological assessment of supine abdominal radiograph

Check the adequacy and quality of the radiographThe radiograph should include the area from the diaphragm to the

hernial orifices. Laterally the proportional line should be evident.

Check alignment of bonesExamination of the lumbar spine will be covered in the article on the

thoracolumbar spine.

Check bone margins and densityThe abdominal radiograph shows many portions of the skeleton that

can be injured after blunt or penetrating trauma. The lower ribs and lumbartransverse processes must be examined carefully. If fractures ofthese bones are seen consider associated soft tissue injury to the liver,spleen, or kidney.

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Check the cartilage andjoints

FIG 3-Perforated duodenal ulcer with a large amount C

air overlying the liver.

See the article on the pelvis for details (9 October, pp 927-3 1).

Check soft tissuesBowel gas patter-Gas and faecal matter in the gastrointestinal tract

delineate the distribution of the bowel as well as indirectly identify intra-abdominal organs. Almost all patients in distress with abdominal painswallow air, which rapidly passes through the bowel (fig 1). The stomach isoften partly filled with air and it can be located by the characteristicappearance of the gastric rugae. A small amount of gas is often seen in theduodenal bulb and in various parts ofnormal small bowel, which does notexceed 2 5 cm in diameter. The valvulae conniventes appear relativelythick. The amount of gas in the normal colon is extremely variable but theupper limit ofnormal for the air-fluid level in the colon is 5-5 cm.

Free air and air in biliary tree or portal vein-Pneumoperitoneum is a result ofperforation of a

viscus, unless the patient has recently had a

laparotomy. The commonest cause is perforatedpeptic ulcer, but free air is evident in only 70-80%ofsuch cases (figs 2 and 3). On a supine radiographintraperitoneal air collects under the inferiorsurface of the liver or hepatorenal recess(Morison's pouch). Small triangular collectionsof air may also be evident between adjacent loopsofbowel. Larger collections rise to lie under thecentral tendon of the diaphragm (capula sign) oroutline the falciform ligament. Visibility ofbothsides of the bowel wall (Rigler's sign; fig 4) isimportant but may be misleading when two loopsof air filled bowel are in apposition. Occasionallyair is seen outlining the gall bladder or urinarybladder in diabetic patients with emphysematous

f free infections.

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FIG 4-Pneumoperitoneum as shown by Rigler's sign-both sides of the bowel wall can be seen. There aremultiple dilated small bowel loops and gall stones in tigall bladder.

.. .' ... ... ...

FIG 5-Air in biiiary tree from previous endoscopic

sphincterotomy. The patient has also had a bowel

resection for carcinoma-note surgical sutures to

the right of L4/5 disc space. Only a little gas is seen in

the pelvis where there is increased soft tissue

density because of localised ascites.

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Assessing cartilage and jointsPubic symphysis-Widening or overlappingof boneSacroileac joint-Widening or overlapping ofbone, defects in cortical surfaceAcetabulum-Check for fractures

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FIG 6--Right paracolic abscess showing increaseddensity in the right flank and displacement of thecolonic gas medially. A few locules of extraluminalgas are seen within the abscess cavity, overlying theright 1 1th rib.

FIG 7-Soft tissue density mass in mid-abdomen withcurvilinear calcification. This represents largeabdominal aortic aneurysm.

Check size of organsIdentification of the organs within the

abdomen depends on knowledge of theiranatomical position, helped by the tissue-fatinterfaces and the adjacent bowel, which containsgas, fluid, and food residue. The soft tissuedensity of the liver, spleen, and kidneys canusually be seen on this view (fig 1).

The size and shape of the liver is extremelyvariable and its posterior edge can extenddown to the region of the iliac crest (Riedel'slobe). With severe hepatomegaly the hepaticflexure, transverse colon, or stomach is usuallydisplaced with a raised right hemidiaphragm.The pancreas cannot be seen on plain abdominalfilms unless it is calcified.

Check fat and soft tissue interfacesThe borders of the kidneys, psoas muscles,

bladder, and properitoneal line can usually beseen on an abdominal radiograph because of theinterface between these structures and thesurrounding retroperitoneal fat (fig 1).Remember, however, that their visibility andappearance is not consistent. The right psoasoutline is not seen in a fifth of the normalpopulation.

The visibility of the psoas shadow alsodepends on overlying normal structures suchas bowel contents, as well as on pathologicalconditions (retroperitoneal haemorrhage inkidney trauma, fractures of the vertebral spinousprocesses, or psoas haematoma). Fluid within theparacolic gutter causes displacement of the colonmedially, increasing the width of the soft tissuedensity between the properitoneal line and theintraluminal colonic contents (fig 6).

Check for abnormal calcificationThe commonest calcified structures seen on

the abdominal radiograph are pelvic phlebolithsdue to pelvic vein thrombosis and lymph nodes.About 85% of renal stones are radio-opaque,compared with only 15% of gall stones. Renalstones can be suspected by the presence ofa stone overlying the renal outline or ureter(fig 8). Occasionally punctate pancreaticcalcification is seen in patients with chronicpancreatitis.

FIG 8-A small ureteric calculus is projected overthe left L3 transverse process.

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Catches to avoid

Conditions simulating air under thediaphragmChilaiditi syndrome (fig 9)-Interposition of hepatic flexure between liverand diaphragmSubphrenic abscessSubdiaphragmatic fatBasal curvilinear atelectasis

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FIG O-Chilaiditi syndrome-interposition of colonbetween liver and diaphragm. Air is seen underthe right hemidiaphragm but bowel markingsare evident.

The properitoneal line adjacent to the lateral margin of the livercan be mistaken for a pneumoperitoneum in a left lateral decubitus view.Air in the biliary tree can be due to previous sphincterotomy orsurgery (fig 5). Pelvic phleboliths can often be differentiated from distalureteric stones by their characteristic appearance; they are round witha radio-opaque halo surrounding a small central lucent nidus.

SummaryDiagnostic qualityAlignment of bonesBone margins and densityCartilage and jointsSoft tissuesBowel gas patternPneumoperitoneumAir in the biliary tree or portal veinSize of organsFat-tissue interfacesAbnormal calcification

D A Nicholson is consultant radiologist and P A Driscoll is senior lecturer in emergencymedicine at Hope Hospital, Salford.The line drawings were prepared by Mary Harrison, medical illustrator.The ABC of Emergency Radiology has been edited by David Nicholson and

Peter Driscoll.

Minimally Invasive Surgery

Advanced techniques in abdominal surgery

John RT Monson

Almost every abdominal organ is now amenable tolaparoscopic surgery. Laparoscopic appendicec-tomy is a routine procedure which also permitsidentification of other conditions initially confusedwith an inflamed appendix. However, assessment ofappendiceal inflammation is more difficult. Almostall colonic procedures can be performed laparo-scopically, at least partly, though resection forcolonic cancer is still controversial. For simplepatch repair of perforated duodenal ulcers laparo-scopy is ideal, and inguinal groin hernia can berepaired satisfactorily with a patch of syntheticmesh. Many upper abdominal procedures, however,still take more time than the open operations. Thesetechniques reduce postoperative pain and theincidence of wound infections and allow a muchearlier return to normal activity compared with opensurgery. They have also brought new disciplines:surgeons must learn different hand-eye coordination,meticulous haemostasis is needed to maintainpicture quality, and delivery of specimens may

be problematic. The widespread introduction oflaparoscopic techniques has emphasised the needfor adequate training (operations that were straight-forward open procedures may require considerablelaparoscopic expertise) and has raised questionsabout trainee surgeons acquliring adequate experi-ence ofopen procedures.

At the end of the 1980s, when the first laparoscopictechniques were described, few could have predictedthe developments that have occurred since then. Farfrom being limited to the removal of uninflamedgallbladders, laparoscopic techniques have beenapplied to almost every abdominal organ: oesophagus,stomach, duodenum, small and large bowel, liver,spleen, kidney, ureters, and pancreas have all beeneither resected or repaired.The development of high quality video imaging

systems has been the single biggest advance in recentyears that has allowed many of these new proceduresto be developed. For practising surgeons, however,

This is the second in a series ofarticles on minimally invasivesurgery

Academic Surgical Unit,St Mary's Hospital andImperial College ofScience, Technology andMedicine, LondonW2 INYJohn RT Monson, assistantdirector

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