Session 10

Question 1

When to request an abdominal x-ray?

Answer 1

Acute abdominal pain

Small or large bowel obstruction

Acute exacerbation of IBD

Renal colic - CT now first line investigation

Question 2

How is an abdominal x-ray projected and why is the radiation dosage higher when compared to a chest x-ray?

Answer 2

Anterior to posterior, more structures in the abdomen that are more dense too so more radiation is absorbed whereas theres lots air in the chest cavity.

Question 3

Features of an AXR

Answer 3

Bowel gas pattern 

Soft tissue structures 

A = air/gas 

B = bowel 

C = calcification and stones 

D = dem bones 

E = everything else

Or

ABDO X - Air, Bowel, Dense structures, Organs and soft tissue, External

Question 4

What is a bowel gas pattern?

Answer 4

Any part of hollow tube visible if: 

Gas filled or Gas and Fluid filled 

Low density gas acts as a contrast 

Fully fluid filled NOT visible 

Transit time 

Slow = Colon (faeces +/-gas) 

Medium = stomach (fluid + lots of gas) 

Fast = small bowel (fluid)

Question 5

Small bowel compared to large bowel on x-ray

Answer 5

Small Bowel: 

Central position 

Often don’t see gas in it due to fast transit time 

Valvulae conniventes/plicae circulares - Cross entire wall -Thin

Large bowel:

Peripheral position 

Haustra 

Faeces and gas due slow transit time 

Remember:

Transverse colon and hang down to pelvis (more common in women)

Sigmoid colon can loop and be long

Question 6

Abnormal Gas Patterns to recognise

Answer 6

Small bowel obstruction (>3 cm) 

Large bowel obstruction (>6 cm) 

Competent ileocaecal valve (caecum >9 cm) / Incompetent ileocaecal valve, wont distend as much 

Paralytic Ileus 

Volvulus 

Toxic Megacolon Rule of 3s (3/6/9)

Question 7

Small Bowel Obstruction

Answer 7

Presentation: 

Vomiting (early) 

Distension (mild) 

Absolute constipation (late) 

Colicky pain 

Causes: 

Adhesions (most common)

Hernias - Inguinal/Femoral/Incisional 

Tumours 

Inflammation

Question 8

Large Bowel Obstruction

Answer 8

Presentation 

Vomiting (late, faeculant) 

Distension (significant) 

Pain 

Absolute constipation 

Causes: 

Colorectal carcinoma 

Diverticular stricture 

Hernia 

Volvulus 

Pseudo-obstruction

What next in an adult – likely CT Abdomen and pelvis with contrast

Perforation is important complication

Question 9

Volvulus

Answer 9

Twisting around mesentery 

Enclosed bowel loop -Dilates leading to Perforation and Ischaemia

Sigmoid volvulus common as its not attached

Caecal uncommon – anatomical defect - attached normally but can be detached in defect - normally seen in younger people

Sigmoid Volvulus - Starts in LIF - Coffee bean sign - pain moves towards RUQ - Dilatation of proximal bowel - Obstructed

Question 10

AXR to see inflammation and Infection of GI

Answer 10

AXR not the gold-standard 

Dont want to do too many as patients with chronic illnesses like Crohn’s will need many scans so want least amount as possible to reduce radiation exposure.

May see acute or chronic changes such as Mucosal thickening, Featureless colon, Bowel wall oedema

Question 11

Toxic Megacolon

Answer 11

Acute deterioration with UC or colitis 

Colonic dilatation 

Oedema 

Pseudopolyps

Toxic implies patient unwell

Question 12

Lead Pipe Colon

Answer 12

Featureless colon 

Loss of haustra 

Ulcerative colitis 

Chronic inflammation

Question 13

Thumb printing on abdominal x-ray?

Answer 13

Oedematous thickened haustra, thickened wall from active inflammation

Often ulcerative colitis

supposed to look like thumb printing

Question 14

Soft tissues and bones seen in AXR

Answer 14

Organs: Liver, Spleen, Kidneys, Bladder, Lung bases 

Musculature - psoas major important as if we lost it, it’s akin to silhouette sign

Bones: Pelvis, Sacrum, Coccyx, Lumbar spine, Lower thoracic spine, Lower ribs

Question 15

Other abnormalities seen in AXR

Answer 15

Stones 

Organs/masses 

Calcification 

Pancreatitis 

Vascular 

Nodes 

Bones 

Artefact 

Foreign body

Question 16

What might cause a perforation in the GI system and what is the imaging of choice?

Answer 16

Peptic ulcer 

Diverticular 

Tumour 

Obstruction 

Trauma 

Iatrogenic

Can be determined from an erect chest x-ray. It will show free gas under the diaphragm.

CT scan can also be used

Question 17

Fluoroscopic Contrast Studies

Answer 17

Contrast used to define hollow viscera - mucosa - using barium or dense water soluble substance

Common GI contrast studies - Swallow(look at larync, pharynx and oesophagus), Meal (looks at stomach and stomach ulcers (not done as much anymore)), Follow through (looks at small bowel), Enema (looks at large bowel)

Often dynamic real time

OGD often used instead

Question 18

Abdominal CT

Answer 18

Computerised axial tomography 

First clinical CT head scan

High dose radiation 

Good spatial resolution (poor contrast resolution vs MRI) 

Use of IV or oral/rectal contrast

Dose reduction techniques available and being developed

Individual images from a CT scan can be reformatted and combined to produce a 3D representation of the scanned anatomy. Eg a virtual colonoscopy.

Question 19

Anatomical planes

Answer 19

Section/plane 

Transverse/axial (transversus = across) 

Sagittal (sagitta = arrow) 

Coronal (corona = crown)

Question 20

Risk of intraenous contrast?

Answer 20

Small risk of allergy

Most adverse events are mild. 

Major life-threatening contrast reaction is rare. 

Also contrast Induced Nephropathy

Question 21

Contrast Induced Nephropathy

Answer 21

Contrast-induced nephropathy (CIN) is defined as the impairment of renal function—measured as either a 25% increase in serum creatinine (SCr) from baseline or a 0.5 mg/dL (44 µmol/L) increase in absolute SCr value—within 48-72 hours after intravenous contrast administration

For risk stratification using eGFR: 

very low risk: >60 mL/min 

low risk: 45-59 mL/min 

moderate: 30-45 mL/min 

high risk: <30 mL/min

Diabetes, multiple myeloma congestive cardiac failure, cirrhosis, nephrotic syndrome, sepsis lowers risk boundaries 

low risk: >60 mL/min 

moderate: 45-59 mL/min 

High risk: <45 mL/min

Renal transplant 

moderate: normal renal function 
high: <60 mL/min

Question 22

Why is intravenous contrast important?

Answer 22

Can give detail to scans where if we had not given contrast we wouldnt be able to see the pathology. Only time we really don’t use contrast is when looking for calcuili.

Question 23

Abdominal MRI

Answer 23

Abdominal MRI gives detailed and high contrast images of the abdomen without using any radiation. It is however a very time consuming process. It can also be used with contrast to enhance images.

Good spatial and contrast resolution

Good to use on patients who will need a lot of imaging

Question 24

Abdominal Ultrasound

Answer 24

Use of sound waves to generate image 

Frequency above audible range of human hearing

Cheap compared to CT and MRI 

Portable (FAST scanning) 

Highly user dependant

Can be used to guide biopsies too.

Abdominal ultrasound is commonly used to visualise the biliary tree (for gallstones and dilated bile ducts).

Question 25

GI CT Angiography

Answer 25

During the exam, contrast material is injected through a small catheter placed in a vein of the arm or groin.

Test then uses X-rays to provide detailed pictures of the contrast in bloodvessels.

Question 26

Calcification

Answer 26

Calcification is visible on an abdominal x-ray. Renal calculi, vascular calcification and the calcification of the pancreas following chronic inflammation are all visible.

Question 27

Risk of using radiation imaging

Why is abdominal xray higher dose of radiation than chest x-ray?

Answer 27

Carcinogenesis

Genetic

Developmental risk to foetus

High dose of radiation from CT scan

More structures to pass through in abdominal x-ray whereas lungs mainly compromised of air so chest x-ray has lower dosage

Question 28

SBO vs ileus

Answer 28

SBO vs ileus:

An ileus and an intestinal obstruction have similarities, but an ileus results from muscle or nerve problems that stop peristalsis while an obstruction is a physical blockage in the digestive tract. However, a type of ileus known as paralytic ileus can cause a physical block due to a buildup of food in the intestines.

ileus is suggested by hypoactive bowel sounds whereas small bowel obstruction is described with rushes and bowel sounds consistent with peristalsis against the obstruction.

Question 29

Importance of seeing psoas major on an abdominal x-ray?

Answer 29

If we have lost it, it is akin to the silhouette sign meaning thereis a mass in the retroperitoneal space, usually an aortic aneurysm.