2 Lightbulb momenta moment of sudden inspiration, revelation, or recognition
3 Approach to AXR Bowel gas pattern Extraluminal air Soft tissue masses Calcifications
4 Normal AXR Gas in stomach Liver Splenic flexure 11th rib T12 Psoas marginLeft kidneyHepatic flexureTransverse colonIliac crestGas in sigmoidSacrumGas in caecumSI jointBladderFemoral head
5 Gas pattern What is normal? Stomach Small bowel Large bowel Almost always air in stomachSmall bowelUsually small amount of air in2 or 3 loopsLarge bowelAlmost always air in rectumand sigmoidVarying amount of gas in rest of large bowel
6 Normal fluid levels Stomach Small bowel Large bowel Always (upright, decub)Small bowelTwo or three levelsacceptable (upright, decub)Large bowelNone normally(functions to remove fluid)
7 Large vs small bowel Large bowel Small bowel Peripheral (except RUQ occupied by liver)Haustral markings don’t extend from wall to wallSmall bowelCentralValvulae conniventes extend across lumen and are spaced closer together
8 Radiographic principles Series of films for acute abdomenObstruction series/ Acute abdominal series/ Complete abdominal seriesSupine (almost always)Upright or left decubitus (almost always)Prone or lateral rectum (variable)Chest, upright or supine (variable)
9 Acute abdominal series What to look for VIEWLOOK FORSUPINE ABDOMENBowel gas patternCalcificationsMassesPRONE ABDOMENGas in rectosigmoidGas in ascending and descending colonUPRIGHT ABDOMENFree air, air-fluid levelsUPRIGHT CHESTFree air, lung pathology secondary to intraabdominal processLung pathology – pacreatitis assoc with left pleural effusion, ovarian tumour assoc with right or bilateral effusion, subphrenic abscess assoc with right pleural effusionSubstitutes: Prone Lateral rectumUpright Left lateral decubUpright chest Supine chest
10 Obtaining viewsSupinePatient on back, x ray beam directed vertically downward, casette posterior, x-ray tube anterior (AP)PronePatient on abdomen, x-ray beam directed vertically downward, cassette anterior, x-ray tube posterior (PA)UprightPatient stands or sits, x-ray beam directed horizontally, cassette posterior, x-ray tube anterior (AP)Upright chestPatient stands or sits, horizontal x-ray beam, cassette anterior, x-ray tube posterior (PA)1900s X-Ray-based fluoroscopy machine in which radiation is shot directly through the patient and into the doctor’s face.
11 Abnormal Gas Patterns Functional ileus Mechanical obstruction One or more bowel loops become aperistaltic usually due to local irritation or inflammationLocalised “sentinel loops” (one or two loops)Generalised (all loops of large and small bowel)Mechanical obstructionIntraluminal or extraluminalSmall bowel obstructionLarge bowel obstruction
12 3, 6, 9 RULE Maximum Normal Diameter of bowel Small bowel 3cm Large bowel 6cmCaecum 9cm
13 Localised ileus Key features One or two persistently dilated loops of small or large bowel (multiple views)Often air-fluid levels in sentinel loopsLocal irritation, ileus in same anatomical region as pathologyGas in rectum or sigmoidMay resemble early SBO
14 Causes of Localised Ileus by location SITE OF DILATED LOOPSCAUSERight upper quadrantCholecystitisLeft upper quadrantPancreatitisRight lower quadrantAppendicitisLeft lower quadrantDiverticulitisMid-abdomenUlcer or kidney/ureteric calculi
15 Colon cut off signAbrupt cutoff of colonic gas column at the splenic flexure (arrow). The colon is usually decompressed beyond this point.Explanation:Inflammatory exudate in acute pancreatitis extends into the phrenicocolic ligament via lateral attachment of the transverse mesocolonInfiltration of the phrenicocolic ligament results in functional spasm and/or mechanical narrowing of the splenic flexure at the level where the colon returns to the retroperitoneum.
16 Generalised ileus Key features Entire bowel aperistaltic/hypoperistalticDilated small bowel and large bowel to rectum (with LBO no gas in rectum/sigmoid)Long air-fluid levelsCAUSEREMARK*PostoperativeUsually abdominal surgeryElectrolyte imbalanceDiabetic ketoacidosis* almost always
17 Generalised adynamic ileus The large andsmall bowel are extensively airfilled but not dilated.small bowel "look the same".
18 Mechanical SBO Dilated small bowel Fighting loops (visible loops, lying transversely, with air-fluid levels at different levels)Little gas in colon, especially rectum
28 Mechanical LBO Colon dilates from point of obstruction backwards Little/no air fluid levels (colon reabsorbs water)Little or no air in rectum/sigmoid
29 Large bowel obstruction Bowel loops tend not to overlap therefore possible to identify site of obstructionLittle or no gas in small bowel if ileocaecal valve remains competent** If incompetent, large bowel decompresses into small bowel, may look like SBO
30 Causes of Mechanical LBO TUMOURVOLVULUSHERNIADIVERTICULITISINTUSSUSCEPTION
31 Note on volvulusSigmoid colon has its own mesentry therefore prone to twistingCaecum usually retroperitoneal and not prone to twisting; 20% people have defect in peritoneum that covers the caecum resulting in a mobile caecum
32 VolvulusA volvulus always extends away from the area of twist. Sigmoid volvulus can only move upwards and usuallygoes to the right upper quadrant. Caecal volvuluscan go almost anywhere.
34 Lateral decubitus of value HerniaLateral decubitus of valueThe advantage is that there may be a greater chance of air entering the herniated bowel because it is the least dependent part of the bowel in the supine position.
35 Apple core signRadiologic manifestation of a focal stricture of the bowel usually at contrast material enema examination. The stricture demonstrates shouldered margins and resembles the core of an apple that has been partially eaten. The most common cause is an annular carcinoma of the colon.
36 ThumbprintingThe distance between loops of bowel is increased due to thickening of the bowel wall.The haustral folds are very thick, leading to a sign known as 'thumbprinting.'
37 Lead pipe colon Shortening of colon secondary to fibrosis Loss of haustrationUlcerative colitis
38 Extraluminal air TYPES Pneumoperitoneum/free air/intraperitoneal air Retroperintoneal airAir in the bowel wall (pneumatosis intestinalis)Air in the biliary system (pneumobilia)
39 Upright film bestThe patient should be positioned sitting upright for minutes prior to acquiring the erect chest X-ray image.This allows any free intra-abdominal gas to rise up, forming a crescent beneath the diaphragm. It is said that as little as 1ml of gas can be detected in this way.
40 Free Air Causes Rupture of a hollow viscus Perforated peptic ulcerTraumaPerforated diverticulitis (usually seals off)Perforated carcinomaPost-op 5-7 days normal, should get less with successive studies *NOT ruptured appendix (seals off)
41 Signs of free air Crescent sign Chilaiditis sign Riglers (and False Rigler’s)Football signFalciform ligament signTriangle signCupola signLesser sac sign
42 Crescent Sign II Free air under the diaphragm Best demonstrated on upright chest x rays or left lat decubEasier to see under right diaphragm
43 Chilaiditis sign May mimic air under the diaphragm Look for haustral foldsGet left lat decub to confirmIn patients who have cirrhosis or flattened diaphragms due to lung hyperinflation, a void is created within the upper abdomen above the liver. This space may be filled by bowel. If this bowel is air filled then it may mimic free gas.
44 Rigler’s SignBowel wall visualised on both sides due to intra and extraluminal airUsually large amounts of free airMay be confused with overlapping loops of bowel, confirm with upright view
45 False Rigler’s SignThe Rigler sign can sometimes be simulated by contiguous loops of bowel, whereby intraluminal air in one loop of bowel may appear to outline the wall of an adjacent loop, which results in a misdiagnosis of free air.Measure distance of interface if unsure
46 Football SIgn Seen with massive pneumoperitoneum Most often in children with necrotising enterocolitisIn supine position air collects anterior to abdominal visceraPaediatricAdult
47 Falciform ligament sign Normally invisible.Supine film, free air rises over anterior surface of liver
48 Other patterns of air around liver Doge’s Cap Sign
49 Inverted V signOn the supine radiograph, an inverted "V" may be seen over the pelvis in a patient with pneumoperitoneum.While in infants this is produced by the umbilical arteries, in adults it appears to be created by the inferior epigastric vessels
50 Continuous diaphragm sign Sufficient free air, left and right hemi- diaphragmsappear continous
51 Lesser sac Sign Cupola Sign (white arrows)Lesser sac sign(black arrows)The lesser sac is positioned posterior to the stomach and is usually a potential space. There is free connection between the lesser sac and the greater sac through the foramen of WinslowAir superior to left lobe of liverDouble Bubble Sign
52 Cupola SignAir beneath the central tendon of the diaphragmThe term cupola comes from a dome such as this famous dome of the Duomo in Florence.
53 Triangle SignThe triangle sign refers to small triangles of free gas that can typically be positioned between the large bowel and the flank
54 Retroperitoneal Air Recognised by: May outline: Streaky, linear appearance outlining retroperitoneal structuresMottled, blotchy appearanceRelatively fixed positionMay outline:Psoas musclesKidneys, ureters, bladderAorta or IVCSubphrenic spaces
55 Causes of retroperitoneal air Bowel perforation (appendix, ileum, colon)Trauma (blunt or penetrating)IatrogenicForeign bodyGas producing infection
56 Pneumoretroperitoneum This patient has free air in the retroperitoneal space. The air is seen surrounding the lateral border of the right kidney (white arrow). There is other evidence of free gas including Rigler's sign.If you are not confident that the appearance is pneumoretroperitoneum, you can try an erect and decubitus view to see if the gas moves. If the gas is seen to move, it's not in the retroperitoneum.
57 Air in the bowel wall Signs Best seen in profile producing a linear lucency that parallels the bowelAir en face has a mottled appearance resembling gas mixed with faeculent material
58 Causes of air in bowel wall Primary Pneumatosis cystoides intestinalis (rare)usually affects left colonProduces cyst-like collections of air in the submucosa or serosaSecondaryDiseases with bowel wall necrosisObstructing lesions of the bowel that raise intraluminal pressureComplicationsRupture into peritoneal cavityDissection of air into portal venous system
59 Pneumatosis intestinalis Intramural air, best appreciated in profile
60 Air in the biliary treeOne or two tube-like branching lucencies in the RUQ, conform to location of major bile ducts
61 Causes “Normal” if Sphincter of Oddi incompetence Previous surgery including sphincterotomy or transplantation of CBDPathology (uncommon)Gallstone ileus: gallstone erodes through wall of GB into the duodenum producing a fistula between the bowel and the biliary system.Stone impacts in small bowel = mechanical SBO. “ileus” misnomer
62 Biliary vs Portal Venous Air Portal venous air usually associated with bowel necrosisAir is peripheral rather than centralNumerous branching structures
63 Soft tissue masses Organomegaly Know normal landmarks 2 ways to identify soft tissue masses/organs:Direct visualisation of edges of structureIndirect by displacement of bowelCT, US and MRI have essentially replaced conventional radiography in the assessment of organomegaly and soft tissue masses
67 Rim-likeCalcification that has occurred in the wall of a hollow viscusCystsrenal, splenic, hepaticAneurysmsaortic, splenic, renal arterySaccular organsGallbladderUrinary bladderCalcified hydatid cysts
68 Linear/Track Calcification in walls of tubular structures Arteries Fallopian tubesVas deferensUreterAortoiliac calcification
71 Floccular, Amorphous, Popcorn Formed in solid organ or tumourPancreas (chronic pancreatitis)Leiomyomas of uterusOvarian cystadenomasLymph nodesAdenocarcinomas of stomach, ovary, colonMetastasesSoft tissue (previous trauma, crystal deposition)
76 Staghorn Calcification Renal stones are often small, but if large can fill the renal pelvis or a calyx, taking on its shape which is likened to a staghorn.Tubular
77 Renal calculi Parenchymal calcification Nephrocalcinosis Uncommonly the renal parenchyma can become calcified.This is known as nephrocalcinosis, a condition found in disease entities such as medullary sponge kidney or hyperparathyroidism.Flocculent
78 Putty Kidney "Putty kidney" – sacs of casseous, necrotic material (TB) Autonephrectomy – small, shrunken kidney with dystrophic calcificationFlocculent
80 ConclusionApproach to AXR should include gas pattern, extraluminal air, soft tissue and calcificationsNamed radiological signs are a useful way of remembering, identifying and reporting on films
81 References Herring, W. Learning Radiology 2nd Ed, 2012 Begg, J. Abdominal X-rays Made Easy, 1999Roche, C et al. Radiographics: Selections from the buffet of food signs in Radiology. Nov 2002, RG, 22,Young, L. Radiology Cases in Paediatric Emergency Medicine. Vol 1 Ca 2. The Target, Crescent and Absent Liver Edge Signs.Raymond, B et al. Radiographics: Classic signs in uroradiology. RSN 2004Radiology Teaching Site. Introduction to abdominal radiographyMussin, R. Postgrad Med J 2011: 87: Gas patterns on plain abdominal radiographsMettler: Essentials of Radiology, 2nd Ed, 2005Muharram Food signs in radiology. International Journal of Health Sciences Vol 1 No 1. Jan 2007.
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