AXR Interpretation

Question 1

LITFL

Answer 1

https://litfl.com/axr-interpretation/

Question 2

What are the indications for AXR?

Answer 2

Only for certain defined pathology e.g. ‘gases, masses, bones and stones’
- Often times, CT/MRI is preferred, but may not be as readily available

Useful for investigating preliminary diagnoses of:

• Toxic megacolon (colon <6cm)
• Bowel obstruction (50% sensitive)
• Perforation of viscus with abdominal free air - would want it to be erect, and an erect CXR too; but ultimately USS = higher sensitivity/specificity
• KUB for renal stones - 80-90% sensitive if radioopaque stone >3mm - but first line is CTKUB
• Foreign body including penetrating injury
• Bowel ischaemia

NOT for constipation

Question 3

What are some medically ingested radio-opaque items?

Answer 3

Radio-dense tablets:

• Iron
• KCl

Metals:
- Mercury

Contrast:
- Barium

(also ‘body packers’ = wrapped drugs)

Question 4

What do you look for when assessing ‘gasses’?

normal in SB and LB and some key pathology

Answer 4

Look for normal or abnormal intraluminal and extraluminal gas distribution

Small bowel:

• Intraluminal gas usually minimal, centrally located within numerous tight loops of small diameter (2.5-3.5cm)
• Distinguished by valvulae conniventes/plique circularis/’stack of coins’ stretching across whole bowel diameter

Large bowel:

• Has a mixture of gas and faeces
• Located within larger loops (3-5cm) around the periphery
• Haustra - mucosal folds stretching part way across bowel loops

Abnormal findings and possible causes:

• Dilated loops of small or large bowel = obstruction, ileus, inflammation
• Air-fluid levels on erect AXR - >5 fluid levels, greater than 2.5cm in length = obstruction, ileus, ischaemia, gastroenteritis
• Intramural gas/pneumatosis intestinalis - hazy/bubbly appearance over darker hollow viscus = ischaemic colitis, NEC, obstruction, trauma
• Intraperitoneal gas - perforated viscus or penetrating injury (best confirmed with erect CXR)
• Extraperitoneal gas e.g. in soft tissues, retroperitoneal structures or chest = infection or trauma

Question 5

What do you look for when assessing ‘masses’?

Answer 5

Look for the size and position of the solid organ shadows of the liver, spleen, kidneys and bladder

Identify retroperitoneal shadow of psoas muscle

Abnormal findings:

• Bulging or lateral margin or obliteration of psoas muscle = retroperitoneal pathology
• Dilated calcified sac of a ruptured AAA

Question 6

What do you look for when assessing ‘bones’?

Answer 6

Look for abnormalities of the ribs, spine, sacrum, pelvis

• Fractures
• Scoliosis
• Degenerative disease
• Tumours
• Metastatic deposition

Question 7

What do you look for when assessing ‘stones’?

Answer 7

Trace the course of the ureter from the pelvis of the kidney, along the tips of the lumbar spine transverse processes, over the SI joint, down to the ischial spine and medially to the bladder

Look for renal, ureteric, and bladder stones/calcification

• 80-90% are opaque
• Non-contrast CT or USS to confirm

Look at RUQ and transpyloric plane at the level of L1:

• Look for gallstones (15% radio-opaque)
• Pancreatic calcification
• Confirm with CT/USS

Question 8

What is the ABDO-X structure for assessment?

Answer 8

Air - where it should and shouldn’t be

Bowel - diameter etc

Densities - bones, stones, radio-opaque drugs

Organs - very poorly assessed on AXR, but try and visualise anatomy when looking

External objects - medical devices, foreign bodies

Present findings according to this structure
- Then suggest differentials or key causes of the picture, then follow up with further investigations and initial management

Question 9

What is the 369 rule?

Answer 9

Upper limit of normal width in cm in SBO, LBO and caecum respectively

Question 10

What is thumbprinting?

Answer 10

Mucosal wall oedema

Looks like someone has put their thumb on the bowel wall bilaterally

Acute

Question 11

What is lead pipe bowel?

Answer 11

Chronic

Question 12

What happens to SI joints in some IBD?

Answer 12

They can fuse - cracks disappear

Question 13

How does sigmoid volvulus present?

Answer 13

‘Coffee bean’ sign

• Massive dilated loop of large bowel
• • also dilatation of descending colon

Happens as is not retroperitoneal and thus liable to twisting in its mesentery

Question 14

How does caecal volvulus present?

Answer 14

Dilated loops of small bowel without large bowel

Much less common than sigmoid

Tends to be in younger people; previous surgery; improper fixation to mesentery

Question 15

How does perforation present on AXR?

Answer 15

Rigler sign***

• Double wall sign = free intraperitoneal air
• When normal, the external wall of bowel typically just blends with external abdominal cavity; in this sign, you can ‘clearly’ see free bowel gas, bowel margin then normal bowel gas again.

Copolar sign
- Air under the central tendon of the diaphragm - an obvious arching lucency

Always do a CXR>AXR if you’re thinking someone has perforated

Question 16

What organs are retroperitoneal? And how does this relate to retroperitoneal perforation?

Answer 16

SADPUCKER
Spleen
Abdominal aorta 
Duodenum - from the 2nd part onwards 
P
Ureters 
Colon - ascending and descending 
Kidneys 
(o)Esophagus 
R

So perforation leading to retroperitoneal air MUST come from:

• D2-D4 or AC or DC
• Due to duodenal ulcer, endoscopy, ERCP, AC/DC cancer or diverticulitis, trauma

Question 17

What is a staghorn calculi?

Answer 17

Struvite stones = most common
- Caused themselves by infection with urease producing bacteria (Protease, klebsiella_ - which raise pH increasing stone formation

Very large radiolucency, filling whole renal pelvis

Question 18

What are the signs of gallstone ileus?

Answer 18

Rigler’s triad:

• SBO
• Ectopic calcified gallstone, usually impacted at the ileocaecal valve
• Pneumobilia i.e. air in the biliary tree (from the lumen)

Question 19

What is the ‘satisfaction of search’ error in radiology?

Answer 19

Getting hung up early on in your assessment on a key finding and failing to complete your whole search