1. Abdominal X-ray Radiological Signs
Suzanne O’Hagan

2. Lightbulb moment
a 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 margin
Left kidney
Hepatic flexure
Transverse colon
Iliac crest
Gas in sigmoid
Sacrum
Gas in caecum
SI joint
Bladder
Femoral head

5. Gas pattern What is normal? Stomach Small bowel Large bowel
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

6. Normal fluid levels Stomach Small bowel Large bowel
Always (upright, decub)
Small bowel
Two or three levels
acceptable (upright, decub)
Large bowel
None 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 wall
Small bowel
Central
Valvulae conniventes extend across lumen and are spaced closer together

8. 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)

9. Acute abdominal series What to look for
VIEW
LOOK FOR
SUPINE ABDOMEN
Bowel gas pattern
Calcifications
Masses
PRONE ABDOMEN
Gas in rectosigmoid
Gas in ascending and descending colon
UPRIGHT ABDOMEN
Free air, air-fluid levels
UPRIGHT CHEST
Free air, lung pathology secondary to intraabdominal process
Lung pathology – pacreatitis assoc with left pleural effusion, ovarian tumour assoc with right or bilateral effusion, subphrenic abscess assoc with right pleural effusion
Substitutes: Prone Lateral rectum
Upright Left lateral decub
Upright chest Supine chest

10. 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.

11. Abnormal Gas Patterns Functional ileus Mechanical obstruction
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

12. 3, 6, 9 RULE Maximum Normal Diameter of bowel Small bowel 3cm
Large bowel 6cm
Caecum 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 loops
Local irritation, ileus in same anatomical region as pathology
Gas in rectum or sigmoid
May resemble early SBO

14. Causes of Localised Ileus by location
SITE OF DILATED LOOPS
CAUSE
Right upper quadrant
Cholecystitis
Left upper quadrant
Pancreatitis
Right lower quadrant
Appendicitis
Left lower quadrant
Diverticulitis
Mid-abdomen
Ulcer or kidney/ureteric calculi

15. Colon cut off sign
Abrupt 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 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.

16. 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
CAUSE
REMARK
*Postoperative
Usually abdominal surgery
Electrolyte imbalance
Diabetic ketoacidosis
* almost always

17. Generalised adynamic ileus
The large and
small 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

19. SBO Erect
SBO Supine
Air fluid levels

20. Causes of Mechanical SBO
* May be visible on AXR
Adhesions
Hernia*
Malignancy
Gallstone ileus*
Intussesception
Inflammatory bowel disease

21. Step ladder appearance
Loops arrange themselves from left upper to right lower quadrant in distal SBO

22. Coil spring sign

23. 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.

24. Stretch/slit sign
Slit of air caught in a valvulae, characteristic of SBO

25. 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

26. Crescent Sign Caused by: LUQ Soft tissue mass OR
Head of intussusception in distal transverse colon

27. Double Bubble Sign
Duodenal Atresia

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 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

30. Causes of Mechanical LBO
TUMOUR
VOLVULUS
HERNIA
DIVERTICULITIS
INTUSSUSCEPTION

31. 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

32. 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.

33. Coffee Bean Sign Sigmoid volvulus
Massively dilated sigmoid loop

34. Lateral decubitus of value
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.

35. 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.

36. 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.'

37. Lead pipe colon Shortening of colon secondary to fibrosis
Loss of haustration
Ulcerative colitis

38. Extraluminal air TYPES Pneumoperitoneum/free air/intraperitoneal air
Retroperintoneal air
Air in the bowel wall (pneumatosis intestinalis)
Air in the biliary system (pneumobilia)

39. 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.

40. 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)

41. 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

42. 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

43. 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.

44. 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

45. 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

46. Football SIgn Seen with massive pneumoperitoneum
Most often in children with necrotising enterocolitis
In supine position air collects anterior to abdominal viscera
Paediatric
Adult

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 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

50. Continuous diaphragm sign
Sufficient free air, left and right hemi- diaphragms
appear 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 Winslow
Air superior to left lobe of liver
Double Bubble Sign

52. Cupola Sign
Air beneath the central tendon of the diaphragm
The term cupola comes from a dome such as this famous dome of the Duomo in Florence.

53. Triangle Sign
The 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 structures
Mottled, blotchy appearance
Relatively fixed position
May outline:
Psoas muscles
Kidneys, ureters, bladder
Aorta or IVC
Subphrenic spaces

55. Causes of retroperitoneal air
Bowel perforation (appendix, ileum, colon)
Trauma (blunt or penetrating)
Iatrogenic
Foreign body
Gas 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 bowel
Air 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 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

59. Pneumatosis intestinalis
Intramural air, best appreciated in profile

60. Air in the biliary tree
One 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 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

62. Biliary vs Portal Venous Air
Portal venous air usually associated with bowel necrosis
Air is peripheral rather than central
Numerous branching structures

63. 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

64. Abdominal Calcifications
Location Pattern

65. First exclude artefact
Kim Kardashian’s butt – real or artefact?

66. Location Vascular Liver Gallbladder Spleen Pancreas Lymph nodes
Adrenals
Kidneys
Ureters
Bladder
Prostate

67. Rim-like
Calcification that has occurred in the wall of a hollow viscus
Cysts
renal, splenic, hepatic
Aneurysms
aortic, splenic, renal artery
Saccular organs
Gallbladder
Urinary bladder
Calcified hydatid cysts

68. Linear/Track Calcification in walls of tubular structures Arteries
Fallopian tubes
Vas deferens
Ureter
Aortoiliac calcification

69. Chinese Dragon Sign
Calcified splenic artery

70. Calcified vas deferens

71. Floccular, Amorphous, Popcorn
Formed in solid organ or tumour
Pancreas (chronic pancreatitis)
Leiomyomas of uterus
Ovarian cystadenomas
Lymph nodes
Adenocarcinomas of stomach, ovary, colon
Metastases
Soft tissue (previous trauma, crystal deposition)

72. Calcified enteric lymph nodes
Calcified fibroids
Calcified enteric lymph nodes
Calcified pancreas
Floccular

73. 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

74. Bladder calculi
Lamellar

75. Renal calculi
Pelvicalyceal calcifications

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 calcification
Flocculent

79. Calcified gallstones
Lamellar

80. 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

81. References Herring, W. Learning Radiology 2nd Ed, 2012
Begg, J. Abdominal X-rays Made Easy, 1999
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 2004
Radiology Teaching Site. Introduction to abdominal radiography
Mussin, R. Postgrad Med J 2011: 87: Gas patterns on plain abdominal radiographs
Mettler: Essentials of Radiology, 2nd Ed, 2005
Muharram Food signs in radiology. International Journal of Health Sciences Vol 1 No 1. Jan 2007.

82. THANK YOU