Session 10 Flashcards
When to request an abdominal x-ray?
Acute abdominal pain
Small or large bowel obstruction
Acute exacerbation of IBD
Renal colic - CT now first line investigation
How is an abdominal x-ray projected and why is the radiation dosage higher when compared to a chest x-ray?
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.
Features of an AXR
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
What is a bowel gas pattern?
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)
Small bowel compared to large bowel on x-ray
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
Abnormal Gas Patterns to recognise
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)
Small Bowel Obstruction
Presentation:
Vomiting (early)
Distension (mild)
Absolute constipation (late)
Colicky pain
Causes:
Adhesions (most common)
Hernias - Inguinal/Femoral/Incisional
Tumours
Inflammation
Large Bowel Obstruction
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
Volvulus
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
AXR to see inflammation and Infection of GI
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
Toxic Megacolon
Acute deterioration with UC or colitis
Colonic dilatation
Oedema
Pseudopolyps
Toxic implies patient unwell
Lead Pipe Colon
Featureless colon
Loss of haustra
Ulcerative colitis
Chronic inflammation
Thumb printing on abdominal x-ray?
Oedematous thickened haustra, thickened wall from active inflammation
Often ulcerative colitis
supposed to look like thumb printing
Soft tissues and bones seen in AXR
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
Other abnormalities seen in AXR
Stones
Organs/masses
Calcification
Pancreatitis
Vascular
Nodes
Bones
Artefact
Foreign body
What might cause a perforation in the GI system and what is the imaging of choice?
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
Fluoroscopic Contrast Studies
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
Abdominal CT
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.
Anatomical planes
Section/plane
Transverse/axial (transversus = across)
Sagittal (sagitta = arrow)
Coronal (corona = crown)
Risk of intraenous contrast?
Small risk of allergy
Most adverse events are mild.
Major life-threatening contrast reaction is rare.
Also contrast Induced Nephropathy
Contrast Induced Nephropathy
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
Why is intravenous contrast important?
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.
Abdominal MRI
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
Abdominal Ultrasound
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).
GI CT Angiography
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.
Calcification
Calcification is visible on an abdominal x-ray. Renal calculi, vascular calcification and the calcification of the pancreas following chronic inflammation are all visible.
Risk of using radiation imaging
Why is abdominal xray higher dose of radiation than chest x-ray?
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
SBO vs ileus
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.
Importance of seeing psoas major on an abdominal x-ray?
If we have lost it, it is akin to the silhouette sign meaning thereis a mass in the retroperitoneal space, usually an aortic aneurysm.
