Clin Med - Neuroradio Flashcards
Define Computed tomography (CT)
a diagnostic imaging tool that uses X-rays to provides a three dimensional scan.
CT is based on…
the density of the tissue passed by the X-ray beam.
CT is measured in…
The Hounsfield unit (HU): a quantity which is commonly used by radiologists to express CT numbers in a standardized and convenient form.
Which tissues are hypodense?
Air and fat
Which tissues are isodense?
Pure water and CSF
Which tissues are hyperdense?
White & gray matter, blood, bone
Advantages of CT
- Inexpensive
- Widely available
- Allows relatively quick assessment
- Very sensitive to acute hemorrhage and calcification
Disadvantages of CT
-Craniocerebral trauma (short exam time, well
demonstrated hemorrhage and skull fracture)
-Intracranial hemorrhage
-Infarction (infarct itself not seen well on CT, but looking for cause of infarct: hemorrhage/tumor)
-Seizures (in the ER setting to screen for underlying cause)
CT interpretation
-3 aspects
- orientation
- contrast vs. non-contrast
- general review
CT orientation
- view
- slices
The CT slice is regarded as being viewed from the patient’s feet, so the left side of the picture as you view it is the right side of the patient.
There are 3 slices:
- axial
- sagittal
- coronal
CT with IV contrast
Does not cross the normal blood brain barrier and is used if there is a suspicion of tumor, infection (e.g. abscess)
When should you use contrast?
- in stroke patients
- concerned about infection/abscess
- concerned about a tumor
Which feature of the brain should always be visualized on CT?
Sulci - if you cannot see it, that’s a sign there’s something in it (blood or inflammation)!
CT interpretation mnemonic
Blood Can (cisterns) Be (brain) Very (ventricles) Bad (bone)
How does acute hemorrhage appear on CT?
Acute hemorrhage absorbs X-rays and appears hyperdense (white) on CT scans
What happens as clot retracts and becomes acute?
it becomes isodense (same color) with brain over the following 1-4 weeks and finally hypodense (darker) compared with brain over the subsequent 4-6 weeks.
2 normal calcifications of the brain
- choroid plexus
- pineal gland
Define dystrophic calcification
calcification occurring in degenerated or necrotic tissue
What are the 3 intracerebral hemorrhages?
- intraparenchymal cerebral hemorrhage
- intraventricular hemorrhage
- extracerebral hemorrhage
Intraparenchymal cerebral hemorrhage
- definition
- etiologies
- acute accumulation of blood in the parenchyma of the brain
- HTN, trauma, hemorrhagic transformation of an ischemic stroke, or venous infarct
What is the first imaging modality for hemorrhage?
CT without contrast - always!!
When would you order CT angiography?
concern for a vascular underlying cause
When would you order MRI?
if an underlying tumor/abscess is suspected
Intraventricular hemorrhage
- definition
- etiology
- The present of blood within the brain ventricular systems
- Primary etiologies include HTN, vascular malformations, anticoagulation, tumors
-Secondary etiologies include trauma or extension from
other intracerebral hemorrhages
Extracerebral hemorrhage
-definition
occurring within the skull, but outside the brain
Subdural hematoma
-5 features
- between the dura and arachnoid
- venous blood (bridging veins MC)
- +/- fracture
- concave shape
- does cross suture lines
Epidural hematoma
-5 features
- between the inner surface of the skull and outer layer of the dura
- arterial blood (middle meningeal A is MC)
- ALWAYS associated with fracture
- convex shape
- does NOT cross suture lines
Subarachnoid hemorrhage
-3 features
- hemorrhage into CSF and cisterns (blood on spinal tap)
- etiologies: aneurysms, trauma, AVMs
Cisterns
- collections of CSF, which surround and protect the brain
- look for evidence of effacement, asymmetry, presence of blood
Steps to CT interpretation of brain matter
- compare the sulci pattern for effacement (squishing closed) and volume asymmetry
- look for midline shift secondary to mass effect
- look for inconsistencies in the gray-white
differentiation (evolving stroke?) - identify hyperdense (white/bright) regions: blood, IV contrast, calcification
- identify hypodense (dark) regions: air, fat ischemia, tumor
CT interpretation of ventricles
Ventricles
-Examine lateral, 3rd, and 4th ventricles: asymmetry, dilation, effacement, and hemorrhage
CT interpretation of bone
Cortical bone has the highest density on the CT scan and is best viewed on separate bony windows when looking for evidence of fractures or tumors.
MRI advantages
- No ionizing radiation
- Various thickness in any plan
- Excellent discrimination between gray and white matter
- Excellent soft-tissue contrast
MRI indications
- Congenital anomalies
- Vascular Malformations
- Infarct (infarct itself seen better on MRI, but usually CT is done first to look for secondary cause)
- Brain tumors (contrast-enhanced)
- Infection (contrast-enhanced)
- Neurodegenerative diseases
- Anything spinal cord related
MRI interpretation
- 3 planes: axial, sagittal, coronal
- T1 and T2 weighted (most brain MRIs use both, hint to tell which one: T1= fluid is dark/T2=fluid is very bright)
- bone and air are dark
- you can use contrast
Cerebral angiography (CTA/MRA) advantages
***gold standard for assessing vascular abnormalities (vasculitis, aneurysm, malformations)
CTA disadvantages
- Expensive
- Invasive procedure (main issue)
- Risk of stroke
CTA indications
- Aneurysm (CTA)
- Infarct (reveal the extent/location of vessel occlusion, volume/severity, predict final infarct size)
- Cerebral vascular malformations
CTA procedure
Contrast material is injected into the desired vessel via a small catheter, which has been introduced into the body through the femoral or brachial artery
What information does CTA record?
Information about the arterial, capillary, or venous circulation of the brain is recorded on serial plain films or digitized (MC)
Indication for CTA
- aneurysms
- acute ischemic stroke
- vascular abnormalities (arteriovenous malformation, arteriovenous fistula or caroticocavernous fistula)
