Lightbulb moment a moment of sudden inspiration, revelation, or recognition
Approach to AXR Bowel gas pattern Extraluminal air Soft tissue masses Calcifications
Normal AXR 11 th rib Hepatic flexure Gas in stomach T12 Gas in caecum Iliac crest Femoral head SI joint Gas in sigmoid Transverse colon Splenic flexure Psoas margin Sacrum Left kidney Liver Bladder
Gas pattern Stomach – Almost always air in stomach Small bowel – Usually small amount of air in 2 or 3 loops Large bowel – Almost always air in rectum and sigmoid – Varying amount of gas in rest of large bowel What is normal?
Normal fluid levels Stomach – Always (upright, decub) Small bowel – Two or three levels acceptable (upright, decub) Large bowel – None normally (functions to remove fluid)
Large vs small bowel Large bowel – Peripheral (except RUQ occupied by liver) – Haustral markings don’t extend from wall to wall Small bowel – Central – Valvulae conniventes extend across lumen and are spaced closer together
Radiographic principles Series of films for acute abdomen Obstruction series/ Acute abdominal series/ Complete abdominal series – Supine (almost always) – Upright or left decubitus (almost always) – Prone or lateral rectum (variable) – Chest, upright or supine (variable)
VIEWLOOK FOR SUPINE ABDOMENBowel gas pattern Calcifications Masses PRONE ABDOMENGas in rectosigmoid Gas in ascending and descending colon UPRIGHT ABDOMENFree air, air-fluid levels UPRIGHT CHESTFree air, lung pathology secondary to intraabdominal process Acute abdominal series What to look for Substitutes: Prone Lateral rectum Upright Left lateral decub Upright chest Supine chest
Obtaining views Supine – Patient on back, x ray beam directed vertically downward, casette posterior, x-ray tube anterior (AP) Prone – Patient on abdomen, x-ray beam directed vertically downward, cassette anterior, x-ray tube posterior (PA) Upright – Patient stands or sits, x-ray beam directed horizontally, cassette posterior, x-ray tube anterior (AP) Upright chest – Patient 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.
Abnormal Gas Patterns Functional ileus – One or more bowel loops become aperistaltic usually due to local irritation or inflammation Localised “sentinel loops” (one or two loops) Generalised (all loops of large and small bowel) Mechanical obstruction – Intraluminal or extraluminal Small bowel obstruction Large bowel obstruction
3, 6, 9 RULE Maximum Normal Diameter of bowel Small bowel 3cm Large bowel6cm Caecum9cm
Localised ileus Key features One or two persistently dilated loops of small or large bowel (multiple views) Often air-fluid levels in sentinel loops Local irritation, ileus in same anatomical region as pathology Gas in rectum or sigmoid May resemble early SBO
Causes of Localised Ileus by location SITE OF DILATED LOOPSCAUSE Right upper quadrantCholecystitis Left upper quadrantPancreatitis Right lower quadrantAppendicitis Left lower quadrantDiverticulitis Mid-abdomenUlcer or kidney/ureteric calculi
Colon cut off sign Explanation: Inflammatory exudate in acute pancreatitis extends into the phrenicocolic ligament via lateral attachment of the transverse mesocolon Infiltration 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. Abrupt cutoff of colonic gas column at the splenic flexure (arrow). The colon is usually decompressed beyond this point.
Generalised ileus Key features Entire bowel aperistaltic/hypoperistaltic Dilated small bowel and large bowel to rectum (with LBO no gas in rectum/sigmoid) Long air-fluid levels CAUSEREMARK *PostoperativeUsually abdominal surgery Electrolyte imbalanceDiabetic ketoacidosis * almost always
Generalised adynamic ileus The large and small bowel are extensively airfilled but not dilated. The large and small bowel "look the same".
Mechanical SBO Dilated small bowel Fighting loops (visible loops, lying transversely, with air-fluid levels at different levels) Little gas in colon, especially rectum
SBO ErectSBO Supine Air fluid levels
Causes of Mechanical SBO * May be visible on AXR Adhesions Hernia* Malignancy Gallstone ileus* Intussesception Inflammatory bowel disease
Step ladder appearance Loops arrange themselves from left upper to right lower quadrant in distal SBO
Coil spring sign
String of pearls sign Considered diagnostic of obstruction (as opposed to ileus) and is caused by small bubbles of air trapped in the valvulae of the small bowel.
Stretch/slit sign Slit of air caught in a valvulae, characteristic of SBO
Closed loop obstruction Two points of same loop of bowel obstructed at a single location Forms a C or a U shape – Term applies to small bowel, usually caused by adhesions – Large bowel, called a volvulus
Crescent Sign Caused by: LUQ Soft tissue mass OR Head of intussusception in distal transverse colon
Double Bubble Sign Duodenal Atresia
Mechanical LBO Colon dilates from point of obstruction backwards Little/no air fluid levels (colon reabsorbs water) Little or no air in rectum/sigmoid
Large bowel obstruction Bowel loops tend not to overlap therefore possible to identify site of obstruction Little or no gas in small bowel if ileocaecal valve remains competent* * If incompetent, large bowel decompresses into small bowel, may look like SBO
Causes of Mechanical LBO TUMOUR VOLVULUS HERNIA DIVERTICULITIS INTUSSUSCEPTION
Note on volvulus Sigmoid colon has its own mesentry therefore prone to twisting Caecum usually retroperitoneal and not prone to twisting; 20% people have defect in peritoneum that covers the caecum resulting in a mobile caecum
Volvulus A volvulus always extends away from the area of twist. Sigmoid volvulus can only move upwards and usually goes to the right upper quadrant. Caecal volvulus can go almost anywhere.
Hernia Lateral decubitus of value The 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.
Apple core sign Radiologic 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.
Thumbprinting The 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.'
Lead pipe colon Shortening of colon secondary to fibrosis Loss of haustration Ulcerative colitis
Extraluminal air TYPES – Pneumoperitoneum/free air/intraperitoneal air – Retroperintoneal air – Air in the bowel wall (pneumatosis intestinalis) – Air in the biliary system (pneumobilia)
Upright film best The 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.
Free Air Causes Rupture of a hollow viscus – Perforated peptic ulcer – Trauma – Perforated diverticulitis (usually seals off) – Perforated carcinoma Post-op 5-7 days normal, should get less with successive studies *NOT ruptured appendix (seals off)
Signs of free air Crescent sign Chilaiditis sign Riglers (and False Rigler’s) Football sign Falciform ligament sign Triangle sign Cupola sign Lesser sac sign
Crescent Sign II Free air under the diaphragm Best demonstrated on upright chest x rays or left lat decub Easier to see under right diaphragm
Chilaiditis sign May mimic air under the diaphragm Look for haustral folds Get left lat decub to confirm In 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.
Rigler’s Sign Bowel wall visualised on both sides due to intra and extraluminal air Usually large amounts of free air May be confused with overlapping loops of bowel, confirm with upright view
False Rigler’s Sign The 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
Football SIgn Seen with massive pneumoperitoneum Most often in children with necrotising enterocolitis Paediatric Adult In supine position air collects anterior to abdominal viscera
Falciform ligament sign Normally invisible. Supine film, free air rises over anterior surface of liver
Other patterns of air around liver Doge’s Cap Sign
Inverted V sign On 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
Continuous diaphragm sign Sufficient free air, left and right hemi- diaphragms appear continous
Lesser sac Sign Cupola Sign 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 Winslow Cupola sign – (white arrows) Air superior to left lobe of liver Double Bubble Sign
Cupola Sign The term cupola comes from a dome such as this famous dome of the Duomo in Florence. Air beneath the central tendon of the diaphragm
Triangle Sign The triangle sign refers to small triangles of free gas that can typically be positioned between the large bowel and the flank
Retroperitoneal Air Recognised by: – Streaky, linear appearance outlining retroperitoneal structures – Mottled, blotchy appearance – Relatively fixed position May outline: – Psoas muscles – Kidneys, ureters, bladder – Aorta or IVC – Subphrenic spaces
Causes of retroperitoneal air Bowel perforation (appendix, ileum, colon) Trauma (blunt or penetrating) Iatrogenic Foreign body Gas producing infection
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.
Air in the bowel wall Signs – Best seen in profile producing a linear lucency that parallels the bowel – Air en face has a mottled appearance resembling gas mixed with faeculent material
Causes of air in bowel wall Primary Pneumatosis cystoides intestinalis (rare) – usually affects left colon – Produces cyst-like collections of air in the submucosa or serosa Secondary – Diseases with bowel wall necrosis – Obstructing lesions of the bowel that raise intraluminal pressure Complications – Rupture into peritoneal cavity – Dissection of air into portal venous system
Pneumatosis intestinalis Intramural air, best appreciated in profile
Air in the biliary tree One or two tube-like branching lucencies in the RUQ, conform to location of major bile ducts
Causes “Normal” if Sphincter of Oddi incompetence Previous surgery including sphincterotomy or transplantation of CBD Pathology (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
Biliary vs Portal Venous Air Portal venous air usually associated with bowel necrosis Air is peripheral rather than central Numerous branching structures
Soft tissue masses Organomegaly – Know normal landmarks 2 ways to identify soft tissue masses/organs: – Direct visualisation of edges of structure – Indirect by displacement of bowel CT, US and MRI have essentially replaced conventional radiography in the assessment of organomegaly and soft tissue masses
LocationPattern Abdominal Calcifications
First exclude artefact Kim Kardashian’s butt – real or artefact?
Lamellar or laminar Formed around a nidus inside hollow lumen Concentric layers due to prolonged movement of stone inside hollow viscus – Renal stones – Gallstones – Bladder stones
Bladder calculi Lamellar
Renal calculi Pelvicalyceal calcifications
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
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. Renal calculi Parenchymal calcification Flocculent
Putty Kidney "Putty kidney" – sacs of casseous, necrotic material (TB) Autonephrectomy – small, shrunken kidney with dystrophic calcification Flocculent
Calcified gallstones Lamellar
Conclusion Approach to AXR should include gas pattern, extraluminal air, soft tissue and calcifications Named radiological signs are a useful way of remembering, identifying and reporting on films
References Herring, W. Learning Radiology 2 nd Ed, 2012 Begg, J. Abdominal X-rays Made Easy, Roche, 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 Radiology Teaching Site. Introduction to abdominal radiography Mussin, R. Postgrad Med J 2011: 87: Gas patterns on plain abdominal radiographs Mettler: Essentials of Radiology, 2 nd Ed, Muharram Food signs in radiology. International Journal of Health Sciences Vol 1 No 1. Jan 2007.