Emergency Imaging : Chest, Abdomen And Neuro Flashcards
What are the leading imaging modalities in emergency chest imaging?
- CT angiography
- DSA (coronography)
- Chest X Ray
- MRI (only if we have time)
What is a triple rule out CT?
Protocol that assesses 3 different problems at the same time : coronary artery disease, aortic dissection and pulmonary embolism
Absolute contraindication of using iodine contrast agent
Documented previous severe reaction to iodinated contrast media
Relative contraindication to using iodine contrast agent
- Mild reactions
- Renal impairment / failure (GFR under 30)
- Risk factors for adverse reaction like hyperthyroidism, allergy, asthma
What is the CT angio sign of PE?
Hypodense filling defect in primary and secondary pulmonary arterial vessels
How to tell difference between chronic and acute PE in CT angi?
As it gets older, the thrombus will shrink and won’t fill the whole lumen
What additional examination needs to be done in PE after CT?
Doppler US of the lower extremities to exclude deep vein thrombosis
Imaging modalities in suspected PE
- Chest X-Ray
- CTA with IV contrast
- CT chest with IV contrast
- Tc99m V/Q scan lung
- US doppler scan of lower extremities
Imaging modalities in suspected aortic aneurysm
- US of aorta / abdomen
- CT(A) of abdomen with IV contrast
- MRA abdomen without and with IV contrast (alternative to CT if there’s a contraindication)
- DSA
What does DSA stand for?
Digital substraction angiography
How can aortic dissection cause ischemia?
- If an artery arises from the false lumen, which has less oxygenated blood
- The flap can cause obstruction
Types of aortic dissections
- Stanford type A : absolute emergency, involves aortic arch +/- more
- Stanford type B : can be treated conservatively, doesn’t involve the arch
Treatment of aortic dissection
Stent implantation
Imaging recommendations for aortic dissection
- Chest XRAY
- CTA chest and abdomen, with IV contrast
- MRA chest and abdomen +/- IV contrast
(MRA can replace CTA in hemodynamically stable patients, if available)
What are some life threatening acute abdomen situation?
- Aortic aneurysm rupture
- Pancreatitis
- Bowel Ischemia
- Perforation
X RAY signs of bowel obstruction
- Bowel distension
- Multiple air / fluid levels
How to prepare patient for abdominal US?
- Fasting for 6 hours (so air doesn’t obstruct visibility and gallbladder isn’t constructed)
- Patient can drink still water only
What is US used for in the abdomen?
- Assesment of pelvis
- Ascitis
- Fluid collection (abscess)
- Parenchymal organs (kidney, liver, spleen)
- Biliary system (gallbladder is best seen in US)
Limitations of US in abdomen
- Meteoristic patient
- Obesity
- Postoperative bandage and drains
When is CT the first option in abdominal pain?
When there is suspected aortic occlusion, ischemia - emergency situation
Why would US be prefered to XRAY in acute appendicitis?
Because of the risk of perforation and air that would be a problem on X RAY but is not visible on ultrasound
Signs of inflammed appendix on US
- Periappendiceal fluid or abscess (hypogenic)
- Increased vascularisation in doppler
- Diameter over 6mm
Acute appendix on CT morphology
- Peri appendicular fat can be inflammed (brighter)
- Thickened appendix
Imaging modalities for right upper quadrant pain (usually suspected biliary disease)
- US abdomen
- CT abdomen with IV contrast
- MRI abdomen
What are the advantages of CT compared to US in right upper quadrant pain?
CT is more sensitive than US in the depiction of pericholecystic abscesses, gas and stones in the biliary tract
Sign of biliary disorders on US
- Highly reflective echogenic gallstone
- Thickened gallbladder wall with increased vascularization
- Sonographic Murphy sign
When is MRI used in biliary issues?
- Pregnant patients
- To get more precise depiction than CT, especially in chronic biliary disorders and stones (because can’t see non calcified stones on CT)
What do stones look like on T2W MRI?
Gallstones are dark, with no signal
Do we need contrast MR for biliary system?
No, in T2W the fluid structures are easily visible and bright
How can we differenciate blood vessels from bililary ducts on US
When we use doppler, there won’t be a signal in the ducts
Limitation of CT on cholecysto-pancreatography
CT cannot see stones that don’t contain calcium
What is the first imaging modality in suspected bowel loop, ileus…
Abdominal XRAY to confirm dilated bowel
How to tell if it’s small or large bowel obstruction on XRAY?
- Location : if it’s in the center, it’s the small bowel. If it’s peripheral it’s large bowel
- Wall of bowel : kerkring folds and haustrae
What is the next step after XRAY in bowel obstruction?
Contrast enhanced CT to localize and determine the underlying cause
Signs of bowel wall necrosis on CT
- Distended bowels because of edema
- No contrast enhancement
Most common causes of small and large bowel obstruction
Small : adhesions, Crohn, herniation, tumors
Large : colorectal adenocarcinoma, diverticulitis, herniation, volvulus (in children)
How can we tell if the bowel obstruction if recent or not?
When the bowel has been obstructed for a long time, it cannot constrict (because of the blockage) so it will increase secretions of fluid
When can we use US in bowel obstruction?
In very advanced obstruction, when there is a lot of fluid (because if it’s just air then US can’t see it)
What is the use of small bowel follow through?
- can offer additional information regarding degree and level of obstruction (ie ileus if contrast doesn’t reach large bowels in 3 hours)
- can have therapeutic effect (pushes bowel, has a diarrhea effect)
Limitations of small bowel follow through
- Takes 6-24 hours
- Inability to drink in case of severely ill patients
Important questions for imaging of bowel obstruction?
- Mechanical or functional?
- Small or large bowel?
- Cause of ileus?
- Necrosis? Perforation?
When is imaging necessary in pancreatitis?
- CT to rule out complications (abscess, thrombosis, necrosis)
- US to detect biliary stone or duct dilation in early phae
(But usually we mostly rely on lab results)
Imaging modalities for kidney stones
- Low dose enhanced CT : gold standard, very specific and sensitive
- US : can visualize stones in the pelvis, calyxes
- XRAY : high false negatives
Neurological reasons for imaging
- Vascular (stroke, aneurysm)
- Trauma (risk of bleeding)
- Tumor
- Infections (encephalitis, abscess)
- Spine (trauma, disc herniation)
What are the 2 types of strokes
- Ischaemic (85%)
- Hemorrhagic (15%)
Early signs of brain infarct on CT
- Hyperdense sign (Gacs sign) for MCA
- Loss of gray/white matter differentiation
- Less visible sulci because of edema
-> but changes are barely visible in the acute phase on CT
What MRI is used for showing infarcts?
Diffusion weighed imaging (DWI) will have high signal intensity areas in ischemia
Why is diffusion perfusion mismatch useful in strokes?
The mismatch on the fusion image of diffusion and perfusion shows the parts of the brain that can still be saved
What is an acute epidural hematoma?
An absolute emergency, bleeding between dura and skull, usually due to meningeal artery rupture after trauma
How do hematomas change on CT over time?
Start as hyperdense (compared to cortex), and become hypodense after 10-14 days
What is a subdural hematoma?
Less urgent bleeding in between the dura and the arachnoid space, often due to tearing of bridging cortical veins
Which imaging modality can accurately determine age / stage of hemorrhage?
MRI
What is brain herniation?
Life threatening emergency most probably due to space occupying lesions and / or increased intracranial pressure.
What is the most dangerous brain herniation that needs to be ruled out?
Tonsillar herniation
Why is MRI necessary for diagnosis of encephalitis?
Because of the very good soft tissue resolution (CT wouldn’t work)
Signs of encephalitis on MRI
T2W, ADC, FLAIR : edema, restricted diffusion in temporal lobe - looks hyperdense
