Download - Approach to PFA Interpretation
Approaching the PFADavid Murphy FRCR, FFRRCSI
Radiology SpRSt Vincent’s University Hospital
Dublin, Ireland
Terminology
PFA=Plain Film of the Abdomen
AXR=Abdominal X-Ray
Terminology
PFA=Plain Film of the Abdomen
AXR=Abdominal X-Ray
These terms are interchangeable!
Technique
Nearly all PFAs are now acquired as supine antero-posterior (AP) radiographs
Erect PFAs are not routinely performed anymore in adults
Lateral decubitus (patient lying on their side) abdominal x-rays are rarely performed in adults-occasionally in children
Radiation Dose
Average radiation dose for a PFA is 0.7mSv (Sieverts).
Approximately 35 times the dose of a standard chest x-ray (CXR), which is 0.02mSv.
Portable PFAs are not routinely performed due to the problem of radiation dose to surrounding patients
Indications
Suspected bowel obstruction
Suspected bowel perforation (along with an erect CXR)
Suspected abdominal mass
Ingested foreign body
Evaluation of possible toxic megacolon
Follow up of renal tract calculi
PFA is not routinely indicated in…
Vague abdominal pain
Constipation
Uncomplicated appendicitis
Gastroenteritis
Haematemesis
Normal Structures Visible on PFA
Gas in stomach, colon, rectum +/- small bowel
Renal outlines
Outline of right lobe of liver
+/- outline of spleen
Psoas shadows
Costal margin, lumbar vertebrae, pelvic bones
Bowel gas pattern
Any part of the bowel will be visible if it contains gas in the lumen
Upper limit of normal for bowel diameter -3/6/9 rule
1. 3cm - Small Bowel
2. 6cm - Large Bowel
3. 9cm - Caecum
Stomach
May be visible if it contains gas/fluid
Usually visible in the left upper quadrant
Can cross the midline
May see pattern of gastric rugae
Rugae
Small bowel
Usually central in the abdomen
Has valvulae conniventes (arrows) that cross the entire width of the small bowel
Normally <3cm in diameter
Large Bowel
Peripheral position
Has incomplete transverse folds called haustra (arrow)
Contains faeces
Large bowel should be <6cm, caecum <9cm
Liver
Lies in the RUQ
Superior portion forms the right hemidiaphragm contour
Gallbladder not usually visible (can see gallstones if calcified, 10-20% of cases)
Kidneys
Often visible on PFA
Lie at T12-L3
Lateral to psoas muscles
Right kidney slightly lower due to liver
T12
L1
L2
L3
Psoasoutline
Normal Bones Visible
Sacrum
Iliacbone
Femoral head
T12
L1
L2
L3
L4
L5
11th and 12th ribs
Acetabulum
Superior pubic ramus
Normal PFA
Normal PFA-Liver & Spleen
Normal PFA-Kidneys
Normal PFA- Psoas shadows
Normal PFA-Colon
Interpretation
Major areas to assess on the PFA:
1. Bowel gas pattern
2. Soft tissues
3. Bones
4. Calcifications
10 practice casesRead the history, look at the PFA and try and
formulate a differential diagnosis before clicking ahead
Case 160 year old man with abdominal pain,
distension and vomiting
1. Mechanical Small bowel obstruction
Multiple air filled dilated loops of bowel in the center of the abdomen with valvulae conniventes
1. Mechanical Small bowel obstruction
Coronal CT confirms mechanical small bowel obstruction.
1. Mechanical Small bowel obstruction
Coronal CT confirms mechanical small bowel obstruction.
Axial CT shows the site of obstruction (zone of transition, arrow) in the right iliac fossa.
Obstruction caused by ileal stricture from Crohn’s disease.
Case 278 year old man with sudden onset severe
abdominal pain
2. Perforation
Multiple dilated loops of large bowel
Generalised central lucency in the abdomen
Air underneath the liver, outlining the falciform ligament (arrow)
2. Perforation
Zoomed up image of the right upper quadrant shows air outlining both sides of the bowel wall (arrows)
Allows for exact deliniation of the bowel wall
Called Rigler’s sign-very sensitive for perforated large or small bowel
CT confirmed perforation due to a colonic tumour
Case 380 year old woman with
abdominal pain and distension
3. Sigmoid Volvulus
Large dilate loop of large bowel centered in the pelvis
Has an inverted U configuration, with its axis pointed towards the right upper quadrant (arrow)
Dilated loops of large bowel are seen in the left upper quadrant
Also note the EVAR stent
3. Sigmoid Volvulus
This appearance is often called the coffee bean appearance and is typical for a sigmoid volulus
3. Sigmoid Volvulus
Coronal CT shows the swirled sigmoid mesentery around which the sigmoid colon has twisted (arrows)
This is called the whirlpool sign
Case 450 year old man with painless abdominal
swelling and a history of alcohol excess
4. Ascites
General paucity of aerated bowel loops
Homogenous increased density throughout the abdomen
Visible bowel loops tend to be in the centre of the abdomen (imagine them floating!)
4. Ascites
CT shows a shrunken, nodular liver consistent with cirrhosis with large volume ascites
Note the calcified gallstones (arrow)-Did you spot them on the PFA?
Case 580 year old woman with a
painless, pulsatile abdominal mass
5. Abdominal Aortic Aneurysm
There is round structure in the lower abdominal midline with faint peripheral calcification (arrows)
Classical appearance of an abdominal aortic aneurysm (AAA) on PFA with mural calcification
5. Abdominal Aortic Aneurysm
CT angiogram confirms the presence of the large infrarenal AAA (arrows)
Significant amount of thrombus (low density material) within the aneurysm sac
5. Abdominal Aortic Aneurysm
3D reconstructions shows the relationship of the aneurysm to the kidneys and can help with operative planning
Case 660 year old man with
difficulty urinating and severe back pain
6. Bone Metastases
There is a generalised increased density of the pelvic bones and lumbar spine (compare the density to the previous PFAs)
Appearances are those of diffuse sclerotic bone metastases
6. Bone Metastases
Sagittal whole spine CT confirmed diffuse bone sclerosis
Classical appearance of prostate cancer with diffuse sclerotic osseous metastases
Always check the bones on a PFA!
Case 770 year old woman with severe abdominal pain
7. Bowel ischaemia
Generalised increase in lucency with positive Rigler’s sign in the RUQ and free air under the right hemidiaphragm consistent with perforation
7. Bowel ischaemia
Close up of large bowel loops in the RIF shows bubbles of gas within the bowel wall (arrows), known as pneumatosis
7. Bowel ischaemia
Close up of large bowel loops in the RIF shows bubbles of gas within the bowel wall (arrows), known as pneumatosis
Pneumatosis is highly suggestive of ischaemic bowel
7. Bowel ischaemia
CT abdomen on lung windows (to look for air) shows bubbles of gas within the bowel wall, confirming pneumatosis.
Bowel ischaemia was confirmed at surgery.
Case 865 year old woman with
altered bowel habit
Case 8
Nonspecific bowel gas pattern
No cause for the patient’s acute symptoms is identified
8. Splenic Artery Aneurysms
Did you spot the several peripherally calcified lesions in the left upper quadrant? (arrow)
This appearance is typical of multiple splenic artery aneurysms
8. Splenic Artery Aneurysms
CT confirmed the presence of multiple peripherally calcified splenic artery aneurysms at the splenic hilum
Important diagnosis as they are prone to rupture, especially during pregnancy.
Case 950 year old man with
chronic lower back pain
9. Sacral tumour
There is a large lytic, expansile, destructive abnormality in the sacrum (arrow) consistent with a tumour.
The foreign body in the left lower quadrant is a spinal cord stimulator to help treat chronic pain
9. Sacral tumour
Coronal CT abdomen on bone windows confirms the large destructive soft tissue mass in the sacrum (arrow)
Biopsy confirmed a primary bone tumour
Case 1060 year old woman with
abdominal pain and reduced mobility
Case 10
At first look this PFA looks normal
Do you spot any abnormality?
Case 10
Always look at the edge of the film
10. Displaced Left Femoral Fracture
The left femoral shaft is in an abnormal position
10. Displaced Left Femoral Fracture
Pelvic X-ray shows an old non-united left femoral neck fracture with superior migration of the left femoral shaft (arrow).
Always look at the edge of the x-ray for ‘hidden’ abnormalities, especially in exams!
Summary
Major areas to look at on the PFA:1. Bowel gas pattern (3/6/9 rule)
2. Soft tissues
3. Bones
4. Calcifications
Always look at the edges of an x-ray for ‘hidden’ abnormalities
svuhradiology.ieDavid Murphy FRCR, FFRRCSI
Radiology SpRSt Vincent’s University Hospital
Dublin, Ireland