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