Neuroimaging Flashcards
Indications for skull xray?
- when they are not otherwise getting a CT scan (A&Ox3, GCS 15) and:
you suspect skull fracture, sinusitis, facial bone tumors, nose pathology, fb - eval for fractures of mandible and maxilla
- eval of skull for lytic lesions: MM
- scalp has full thickness laceration or boggy hematoma (looking for skull fracture)
- to eval for scalp fbs such as glass
What are the drawbacks to skull X-rays?
- lack detail
- no reassurance if negative in setting of trauma as unable to eval in intracranial contents
- unable to see fractures in skull base, if *basilar skull fracture suspected - get CT
Difference b/t vessels and fractures on skull xray?
- vascular indentations branch and taper, and are curvy, and fractures are usually straight and don’t branch
What is a CT?
uses X-rays to create images with the aid of compute to generate cross sectional views of anatomy
- iodine contrast is sometimes used (may cause acute tubular necrosis in pts with compromised renal fxn)
- fast
Indications for CT?
- eval of skull and skull base, vertebrae (trauma, bone lesions)
- eval of ventricles (hydrocephalus, shunt placement)
- suspicion of intracranial mass, mass effects (HA, N/V, visual sxs) - not as detailed as MRI, just a screening test
- looking for acute hemorrhage, ischemia: stroke, mental status change (ischemia isn’t evident on CT until 24 hrs post onset of sxs)
Why should you get a CT scan when a pt is having a stroke?
- to differentiate b/t hemorrhagic and ischemic
- if hemorrhagic - bleeding will show up on CT
When do you use a CT w/o contrast?
- trauma
- r/o stroke
- r/o hemorrhage
- hydrocephalus
- dementia
- epilepsy
- congenital malformations
When should you order a CT w/ contrast?
- neoplasm (neovascularization)
- infection
- vascular disease
- inflammatory disease
What are the main things you should look at in a CT?
- fluid
- mass
- shift
- at each side, and compare
Difference windows on CT?
- Brain (detailed image of brain) vs Bone (brain detail taken out, focus on bone)
The density of the tissue related to the brightness on CT?
- more dense the tissue - brighter it is on CT
- any calcified structure (bone) - bright
- new hemorrhage is also bright
- water (CSF) will be dark
Difference in location of hemorrhage?
- subarachnoid hemorrhage: arterial bleeding on surface of brain, b/t pia mater and arachnoid mater (layer out over brain)
- subdural hematoma: venous bleeding b/t arachnoid and dura mater (contained bleed)
- epidural hematoma: dural artery or venous sinus bleeding b/t skull and dura, assoc with skull fracture (usually trauma involved)
Subarachnoid hemorrhage, causes?
- injury of small arteries or veins on surface of brain, ruptured vessel bleeds into space b/t pia and arachnoid mater
- usually arterial (circle of willis)
- causes: trauma (most common), ruptured cerebral aneurysm
- show up bright (high density blood)
- no respect for anything, going into fissures and sulci and sella (death-star)
- ACUTE presentation
What is a subdural hematoma?
- tearing of bridging veins from deceleration and acceleration or rotational forces
- blood collects in space b/t arachnoid mater and dura mater
- below dura, doesn’t respect suture lines
- low force trauma
- ** Venous (venous plexus)
- may be insidious (worsening HA over days)
- crescent shaped
- ex: old person falling
Characteristics of a subdural hematoma on CT?
- crescent shaped
- hyperdense, may contain hypodense foci due to serum, CSF, or active bleeding
- doesn’t cross dural reflections
- if it is subacute - hematoma may not be as bright on CT (old blood)
- if chronic: will be darker due to reabsorbtion of hemorrhage over time
Epidural hematoma, causes?
- usually assoc with skull fracture
- fractured bone lacerates a dural artery or venous sinus
- blood from ruptured vessel collects b/t skull and dura
- above dura, respects suture lines
- high force trauma
- arterial blood (commonly middle meningeal artery)
- acute presentation
What will epidural hematoma look like on CT?
- hematoma forms hyperdense bioconvex mass (lens shaped)
- usually uniformly high density but may contain hypodense foci due to active bleeding
Indications for CT angiography?
- atherosclerosis
- thromboembolism
- vascular dissection
- aneurysms
- vascular malformations
- penetrating trauma
- eval of carotids (for stenting)
What is an MRI? Advantage?
- images internal structures of body and brain using magnetism, radio waves and a compute
- image and resolution of structures and soft tissue is very detailed
- MRI is painless and has advantage of avoiding radiation exposure
- risk of dislodging tissue with imbedded metal (CI: welding, metal FB)
Most common types of MRIs?
- T1: useful to look at normal anatomy of brain
- T2: useful to look at abnormal processes (or pathology) in the brain
- difference b/t 2 are diff pulse sequences
What shows up bright and dark on T1 MRI?
- fat is bright
- white matter (inner part) is brighter than gray matter (cortex - outer part)
- water: CSF is dark
WHat is bright and dark on T2 MRI?
- water = bright
- blood = bright
- white matter is darker than gray matter
Indications for MRI?
- subacute and chronic hemorrhages
- cerebral infarct (stroke)
- primary and metastatic brain tumors***
- intracranial abscess and other demyelinating diseases
- new onset or refractory seizures
- vasculitis
When is MRI more superior to CT, when is it not?
- more superior to CT for every pathology except skull fracture and acute subarachnoid hemorrhage
- much more superior for edema, contusions, hematomas, and posterior fossa lesions
- less advantageous:
speed of study and cost
improved data doesn’t impact clinical care
CT advantages to MRI? Disadvantages?
- simpler, cheaper, more accessible
- tolerateed by claustrophobics
- no absolute CIs
- fewer pitfalls in interpretation
- better than MR for bone detail
- CT disadvantages: IV contrast complications, ionizing radiation
MRI advantages compared to CT? Disadvantages?
- much broader palette of tissue contrasts (includes fxnl and molecular), yield greater anatomic detail and more comprehensive anaylsis of pathology
- no ionizing radiation
- IV contrast better tolerated
- better for tumor eval!!
- disadvantages:
higher cost, limited access
difficult for unstable pts
several absolute CIs: pacer, some aneurysm clips - claustrophobics may need sedation
- imaging interpretation more challenging
- lacks bone detail
- MRI is preferred over CT but ct is suitable to exclude mass lesion, hemorrhage or stroke if MRI unavailable
When is a MR angiography helpful?
- useful for eval of intracerebral vessels
use of cerebral angiography?
- GOLD STD for imaging carotid arteries and evaluating cerebral aneurysms after subarachnoid hemorrhage
- cerebral vasculitis
- small aneurysms
- AVMs
- intrarterial tx of cerebral vasospasm
- tx of aneurysm or AVMs
What imaging study is most approp for acute stroke? Limitations of this study?
- CT
- can’t see immed ischemia
what imaging study is most appropriate in pt with full thickness scalp laceration and a GCS of 15?
- skull XR
If there is concern for a tumor what is most approp study?
- MRI
If there is a concern for an aneurysm what is the most appr study to order?
- MRI
In a pt with new onset seizures what is dx TOC and what is initial TOC?
- CT: initally, with new onset seizure disorder - always going to follow up with MRI
- Dx TOC: MRI
