Imaging the Abdomen Flashcards
For what 3 reasons may the abdomen be imaged?
- to confirm a clinical diagnosis / suspicion
- to rule out important diagnoses / pathologies
- to guide or evaluate management / treatment
What are the following structures on AXR?
What do the pink lines represent?
- the pink lines represent the lateral margin of the psoas muscle
- this can be seen as there is a change in density - soft tissue with fat next to it
- if this lateral border cannot be seen, there may be an abnormality (e.g. collection of fluid)
- the faeces appear speckled in appearance as they contain air
What are the limited number of indications for when an AXR might be performed?
- suspected perforation (of a hollow organ / viscus i.e. bowel, gallbladder, bladder)
- an erect CXR would be performed for suspected pneumoperitoneum
- small or large bowel obstruction
- toxic megacolon (in ulcerative colitis exacerbations and C-diff infection)
- foreign body ingestion
- renal calculus (but AXR has been superseded by other imaging modalities)
What is Rigler’s sign?
When might this be seen?
- it is the “double-wall sign” as gas is outlining both sides of the bowel wall
- there is gas present within the bowel lumen and within the peritoneal cavity
- this is present in pneumoperitoneum where there is >1000ml gas
What is shown in this AXR?
small bowel obstruction
- the small bowel is dilated as diameter >3cm
- it is small bowel as valvulae connvientes are visible across the full width of the bowel and it is positioned more centrally within the abdomen
- the prominent valvulae conniventes produce a “coiled spring” appearance
What are 3 possible causes of small bowel obstruction?
What symptoms would this present with?
Causes:
- adhesions following previous abdominal surgery
-
IBD can cause strictures than narrow the lumen of the bowel
- this does not cause obstruction, but the narrower lumen means obstruction is more likely
- direct and indirect abdominal hernias
Symptoms:
- colicky abdominal pain
- vomiting
What is shown in this AXR?
large bowel obstruction
- the large bowel is dilated (>6cm for colon and >9cm for caecum)
- haustra are visible that do not completely traverse the bowel and faeces can be seen within it (speckled appearance)
What are the 2 main causes of large bowel obstruction?
What is the main symptom and why is it an emergency?
Causes:
- it can be caused by cancerous tumours (rectal carcinoma)
- it can be caused by twisting of the bowel (volvulus)
Symptoms:
- there is an inability to pass flatus as the bowel is not opening
- this is an emergency due to the risk of rupture leading to faecal peritonitis
What are the 2 most common types of volvulus?
Why can this only happen in certain locations?
- volvulus describes twisting of the bowel, and in order for the bowel to twist, it needs to have a mesentery
- the majority of the large bowel is retroperitoneal and unable to move
- the only parts that can twist are the parts on a mesentery - the sigmoid colon and caecum
How does sigmoid volvulus present?
In what age group is this more common and why?
- twisting of the sigmoid colon presents with the “coffee bean sign” that tends to point towards the upper abdomen
- the sigmoid colon stretches with age and becomes redundant, and so the likelihood of volvulus increases with age
- this is an emergency as there is a high risk of bowel perforation and/or ischaemia secondary to vascular compromise
What is meant by “thumb-printing” on AXR?
- this describes thumb-shaped, nodular, indentations at regular intervals in the bowel wall
- it occurs when there is thickening of the large bowel wall
- this is usually caused by oedema (infective / inflammatory process), but can also be a sign of bowel ischaemia
- the haustra become thickened at regular intervals to resemble “thumb-prints”
What is shown in this AXR and how can you tell?
pneumoperitoneum
-
Rigler’s sign is present as the bowel wall appears nicely delineated
- free air in the abdomen means that both sides of the bowel wall become visible
- there is free air present under the diaphragm
- be aware that there is often air present underneath the left hemidiaphragm due to the presence of the stomach - not pathological
What is shown in these images?
What is the drawback of using AXR to identify this pathology?
- most renal calculi are radio-opaque, but some will be missed
- the calculus is visible on AXR, but the AXR reveals nothing about the effect that the stone is having on the kidney
- i.e. is there any renal impairment or hydronephrosis?
What is shown in this image?
medullary sponge kidney
- instead of a stone in the hilum, there is calcification of the medulla producing fuzzy, patchy calcification
What is shown in this image?
Double J stents
- these are used for urinary tract obstruction
Often AXR can be unremarkable in cases of serious pathology.
When might there be a serious cause of abdominal pain and a normal AXR?
- appendicitis
- pancreatitis
- leaking AAA
- ruptured ectopic pregnancy
- mesenteric ischaemia / infarct
- diverticulitis
What are the drawbacks of AXR?
- it is only likely to be beneficial in specifc cases, but can be falsely reassuring when there is underlying serious pathology
- it may not reveal underlying pathology
- no functional information can be obtained
- further imaging will still be required if AXR is inconclusive
What abdominal structures can be imaged well on USS?
What structures cannot be imaged well?
- USS is very good for delineating fluid, air and soft tissue
Structures that can be imaged well:
- gallbladder and biliary tree
- liver
- aorta
- kidneys
Structures that CANNOT be imaged well:
- pancreas
- gas-filled structures (if there is overlying bowel containing gas then this obscures structures so they can no longer be seen)
What are the advantages of using USS?
- cheap
- portable - can be used in A&E if patient is too unstable for CT
- non-invasive - can be used to guide interventions such as drains and biopsies
- non-ionising radiation
^^ these factors make USS an attractive option for screening when possible
- it allows good visualisation of hollow viscera, stones and fluid-filled structures
- it can be used to demonstrate free fluid in the abdomen
What are the disadvantages of using USS?
- interpretation of images requires considerable skill / training
- it is user / operator dependent
- it is difficult in overweight/obese patients or if a patient has abdominal pain
- may not give a definitive diagnosis
- may not show other pathology
- not adequate for detailed surgical planning
In what 5 scenarios is CT abdomen indicated?
- when a definitive diagnosis is needed
- to exclude life-threatening pathologies
- e.g. to rule out AAA as the cause of abdominal pain in patients presenting with a history of “renal colic”
- for staging in malignancy as CT can reveal metastatic disease (e.g. in the liver)
- for surgical planning in malignancy, IBD and vascular surgery
- for monitoring disease progression in malignancy and IBD
When is CT scanning of the abdomen used in the acute setting?
- suspected ruptured AAA
-
trauma patients
- if there is direct / obvious abdominal trauma
- OR mechanism of injury is severe enough to warrant whole body CT
- suspected mesenteric ischaemia / bowel infarction
- acute pancreatitis
- bowel obstruction - to determine the site and cause
What is the most important factor to consider before taking a CT scan of the abdomen?
Timing
- CT scans of the abdomen and pelvis can be performed in many different ways depending on the question being answered
What are the advantages of CT scanning the abdomen?
- it provides a definitive diagnosis
- it allows for excellent visualisation of the anatomy, which allows for surgical planning
-
other pathologies may be demonstrated
- e.g. hepatic metastases in the case of bowel obstruction due to cancer
- it can be used with contrast if required
- e.g. CT angiogram for abdominal vessels
What are the disadvantages of CT scanning the abdomen?
- it requires the patient to be transferred to CT - they need to be stable enough
- image interpretation may take longer and you need to wait for the radiologists report
- it uses ionising radiation, which is increased further if contrast is used
- the patient needs to lie still in the scanner
What type of scan is this and what pathology does it demonstrate?
- this is fluoroscopy (barium studies of the GI tract)
- this shows a barium swallow, as barium has entered the lumen of hollow structures
- it demonstrates a stricture in the cervical oesophagus
What type of scan is this and what pathology does it demonstrate?
- this is a barium enema
- the patient has an incompetent ileocaecal valve as the contrast has passed through the large bowel and entered the small bowel
What is fluoroscopy?
How is it performed and what type of information can be obtained?
- fluoroscopy uses X-rays and contrast agent to acquire “real time” images
- static images can also be obtained
- it allows for functional and dynamic information to be obtained
- it can be used to guide interventional procedures
What types of pathology is fluoroscopy good for investigating?
- pharyngeal pouches
- oesophageal strictures - benign or malignant
- small bowel lesions - ulceration, inflammation, erosions (Crohn’s/UC)
- large bowel pathologies - diverticulitis, malignancy, polyps
What needs to be considered prior to fluoroscopy?
- it has a high ionising radiation dose (300x that of a CXR)
- the patient must be able to swallow contrast
- adequate bowel prep is required
What interventional procedures may be performed on the abdomen using imaging?
- image guided biopsies
- percutaneous drains
- stenting - GI tract / biliary tree
- percutaneous PEG & JEG
What are the benefits of MRI scanning of the abdomen and when may it be performed?
When is it not appropriate?
- it provides excellent visualisation of all tissues, including soft tissues
- it can be used if detailed visualisation of the GI tract is needed
- it is not** appropriate for the **acute setting / acute abdominal pain
- it is only used for targeted problem solving (not a “fishing trip”)
What are the 5 major uses of MRI scanning in abdomino-pelvic imaging?
- MRCP in jaundice / to look for retained stones post-op
- MRI adrenal, renal and liver - to characterise lesions found on CT/US
- in inflammatory bowel disease to assess wall thickness / enhancement
- for staging in colorectal cancer
- for diagnosing and staging prostate cancer (and with US for targeted biopsy)
