Contrast Reactions/Emergencies
Memorize basic protocols for contrast reactions, you shouldn’t have to be looking these up when there is an emergency.
Know the difference between IM and IV forms of epinephrine
Know how to recognize and treat vasovagal reactions.
BRAIN
Subdural Hemorrhage
Q: What is the rationale for using subdural windows?
A: Hemorrhage can blend in with the bone on a brain window. Hemorrhage can blend in with the brain on a bone window.
Q: What are the values of the subdural window?
A: We use Window 170 HU, Level 70 HU (as of 10/2022)
https://radiopaedia.org/articles/subdural-haemorrhage?lang=us
Q: What is White Matter buckling
A: This finding is useful for detecting a lesion that is isodense to gray matter (isodense subdural or some meningiomas) Since the border of the isodense subdural with the gray matter is impossible to see, one uses the gray white matter junction to infer the size of the extra-axial lesion.
References:
described by Ajax George from NYU from AJR 1980, the year NK graduated from college (remember Call Me - Blondie, Rock with You -Michael Jackson, Brass in Pocket - Pretenders?)
http://www.ajronline.org/doi/pdf/10.2214/ajr.135.5.1031
nice example from Radiopeadia
http://radiopaedia.org/cases/subdural-haematoma-isodense-bilateral
Acute Subdural Effusion
Q:Why should this be on a pre-call list, i.e. so what?
A: Acute hygromas stretch bridging veins and could result in hematomas
Q: What is the differential dx of a low attenuation collection?
A: While many times this finding may represent chronic hygroma or a chronic prominent CSF space, one must consider urgent entities such as subdural empyema, hyperacute hemorrhage, or acute hygroma as noted above.
The relevant DDx is pulsatile tinnitus with a vascular mass in the middle ear:
Aberrant ICA
Glomus tympanicum
Case in Point (2/23/2007)
http://3s.acr.org/CIP/ArchiveCaseView.aspx?CaseId=BF4Th0RkFDs%3d
Dehiscent jugular bulb
Glomus jugulotympanicum
Persistent stapedial artery
Case in Point (8/2/2006)
http://3s.acr.org/CIP/ArchiveCaseView.aspx?CaseId=gxioKFgDF5Y%3d
Aberrant ICA
if this diagnosis is not made and surgery is done a 3) pseudoaneurysm can result
glomus tympanicum / glomus jugulotympanicum
This is what happens when the carotid is biopsied during an ENT procedure
https://twitter.com/TheJNS/status/1089243755776016384/video/1
Reference:
a classic reference by Lo et. al
https://pubs.rsna.org/doi/abs/10.1148/radiographics.5.6.3880011
AVM
Q: What does an AVM look like on a noncontrast CT?
A: Can be hyperdense to parenchyma (unclotted blood). Use the sagittal sinus and vein of Galen as a control. May see an enlarged vessel
Superior Sagital Sinus Thrombosis
Q: What are the findings associated with superior sinus thrombosis?
A: Hyperdense sagittal sinus (denser than Vein of Galen)
Q: What is the treatment?
A: Get stroke team involved, systemic heparinization, possible neurointerventional thrombolysis
Q: How could a delay in diagnosis affect patient outcome?
A: If there is a delay in heparinization and the patient develops an infarct or hemorrhagic complications , we would never know if prompt diagnosis and treatment would have prevented these complications.
References:
Case-in-point 1.24.06
http://3s.acr.org/CIP/SearchCaseView.aspx?CaseId=o5gljr%2blgpg%3d
Case-in-point 7.28.11
http://3s.acr.org/CIP/CaseView.aspx?CaseId=GCtey8BalRo%3d
Companion case
Case-in-point 8.10.11
http://3s.acr.org/CIP/CaseView.aspx?CaseId=%2bjvcs0mZRts%3d
Third (Oculomotor) Nerve Palsy
Q: Why is this entity on this list?
A: Because the differential that must be excluded on an urgent basis is expanding popsterior communicating artery aneurysm with risk of imminent rupture/fatal SAH.
Q: What is the mechanism of the third nerve palsy?
A; The aneurysm compresses the third n. against the dura. (see image attached below)
Q: Is there dilitation of the pupil (blown pupil)? Why or why not?
A: Yes. The parasympathetic fibers are peripheral and are the first to be involved with pressure on the nerve. Sympathetics then dominate and dilate the pupil.
see diagram at this link
https://timroot.com/super-cranial-nerve-palsies-video/
Q: What are other causes of CN III palsy.
A: One of the more common causes is ischemic neuropathy. Also MS
Q: What other aneurysms can cause this?
A: Posterior communicating artery and less commonly distal basilar. (Remember that the third nerve passes between the superior cerebellar artery and the posterior cerebral artery.) Knowing this, the radiologist can direct his/her search pattern on noninvasive imaging, as well as the angiographic protocol during emergency procedures.
covered by Kagetsu Neurovascular conference
Our protocol is to do a Brain MRA as well as a brain/orbit MRI (without and with contrast)
Reference
J Neurosurg. 2006 Aug;105(2):228-34.
Kupersmith MJ1, Heller G, Cox TA.
https://www.ncbi.nlm.nih.gov/pubmed/17219827
Q: Is Lyme Disease part of the differential of third nerve palsy?
A: While Lyme disease can present with isolated third n. palsy, this is not typical (There is a case report describing this occurence.) http://www.springerlink.com/content/ntyjnvgkyjnukb9a/ The interested resident should review the Case in Point from 6.30.11. http://3s.acr.org/CIP/CaseView.aspx?CaseId=I7jjF%2bp4S6M%3d
Subarachnoid Hemorrhage (SAH)
Q: What is a caveat for the detection of SAH with CT?
A: There is marked decreased sensitivity for detecting SAH beyond 6 hours after the onset of headache, i.e. CT can not reliably exclude SAH. (see discussion below.)
Q: Why is this entity on this list?
A: Because the differential that must be excluded on an urgent basis is aneurysmal SAH. The aneurysm could rerupture (rebleed) with resulting fatal SAH before the next morning. The patients that could benefit the most from emergent surgery (low Hunt-Hess Score) are also the most likely to be sent out of the emergency department.
Q: FLAIR is more sensitive for detecting hemorrhage (ex vivo studies have shown this), so why don't we use MR for detection of SAH
A: While more sensitive, FLAIR is not specific at all. Pulsation artifact often causes CSF to have signal that would be diffucult to differentiate from SAH.
Anatomy
Identify the interpeduncular cistern. This is important since it may be the only place SAH collects.
Q: What structure arises from the interpeduncular cisterm
A: Third nerve.
Q: Isn’t vasospasm a concern.
A: While vasospasm is certainly a concern, it typically occurs in the 4-10 day timeframe and is therefore less important for emergency management. Spasm could result in ischemia/infarct.
Reference
Case in Point 5.5.06 http://3s.acr.org/CIP/SearchCaseView.aspx?CaseId=j0vtg9/APnc=
AHRQ Case (Agency for Healthcare Research and Quality) (your tax dollars at work)
Please review the case described at the following link:
http://webmm.ahrq.gov/case.aspx?caseID=69
Some say that the time cut off should be 6 hours after onset of headache. (i.e. LP should be done) (See BMJ reference attached below.)
Infarct (call)
What findings on head CT are contraindications for TPA administration?
1) Hemorrhage.
2) An infarct larger than 1/3 of the MCA territory is a relative contraindication (increased chance of hemorrhage).
3) Mass lesion
That is why we state:
“No evidence of hemorrhage, acute infarct, or mass lesion on this noncontrast CT.”
Q: Is a dense MCA sign a contraindication for giving TPA?
A: No
Reference:
http://www.ncbi.nlm.nih.gov/pubmed/19235441
Q: What is the CT criteria for calling an infarct hemorrhagic?
A: There should be areas denser than gray matter.
Why do we image patients who present with TIA?
a) You want to exclude clinical mimics of TIA/stroke that may have a surgical treatment algorithm (e.g. subdural hemorrhage)
b) Some patients who have a transient deficit actually have an infarct.
Know:
"loss of the insular ribbon"
Use this phrase to imply that you are familiar with this reference from 1990.
Reference:
http://www.ncbi.nlm.nih.gov/pubmed/2389039
“obscuration of the lentiform nucleus”
Use this phrase to imply that you are familiar with this reference from 1988.
Reference:
http://pubs.rsna.org/doi/abs/10.1148/radiology.168.2.3393665
new vs. old infarct.
Old infarcts are lower in attenuation (can even approach CSF attenuation) Recent infarcts have mass effect. The larger the infarct, the easier it is to identify the mass effect. The smaller the infarct, the harder it is to differentiate recent from old infarcts. Using attenuation alone will lead to errors. Of course you could always get a diffusion MRI. If you try to describe the age, avoid the term like subacute or phrase "stroke in evolution". I recommend the term recent infarct (usually something that will be bright on diffusion MRI images.)
Q: How do you differentiate a lacune from a prominent perivascular space in the basal ganglia?
A: If the lucency is in the inferior third of the lentiform nucleus the default dx is perivascular space.
Anatomy
Know the ACA, MCA, and PCA territories.
Posterior temporal branch
Superior Cerebellar
AICA (Anterior Infererior Cerebellar)
PICA (Posterior Inferior Cerebellar)
http://myradnotes.wordpress.com/category/vascular-territories/
Reference:
Radiographics: Nontraumatic Neurologic Emergencies
http://radiographics.rsna.org/content/19/5/1323.full.pdf
Colloid Cyst
Can cause acute obstructive hydrocephalus, sudden death
Reference
case in point 10.19.05 http://3s.acr.org/CIP/SearchCaseView.aspx?CaseId=INpNrauCXmw%3d
http://www.ajnr.org/content/19/5/875.full.pdf
Q: Where do they come from?
A: Believed to be derived from neuroepithelium, including ependyma and choroid plexus. Same as Rathke Cleft cyst, just different location.
http://www.ajnr.org/content/21/8/1470.full
HEAD AND NECK
Orbital Cellulitis
Prevertebral soft tissue swelling on plain film.
DDX:
In addition to possible c-spine injury, consider retropharyngeal of prevertebral phlegmon/abscess.
Nice slides and diagrams of prevetebral and retropharyngeal spaces can be found at:
http://www.slideshare.net/Bahnassy/neck-spaces-anatomy-and-infections
SPINE
Occipital condyle fracture
References:
Noble and Smoker
“Sir Charles Bell’s patient sustained his fracture by falling backward off a wall. When the
patient was leaving the hospital, he turned to thank the physicians and nurses and suddenly
dropped dead. This, rather vividly, demonstrates the potential instability of these fractures.”
http://www.ajnr.org/content/17/3/507.full.pdf
Harborview AJR
http://www.ajronline.org/content/163/1/193.full.pdf
October 5, 2012 Case in Point (thanks to Sagar Patel)
http://3s.acr.org/CIP/CaseView.aspx?CaseId=IrYGA0M0fo8=
1) Epidermoid
can rupture leading to chemical meningitis, infarcts
2) Alar meningocele/ethmoid meningocele
I these go undiagnosed and the pt gets surgery for "sinus disease", the ENT surgeon will enter the meningocele with resulting CSF leak, possible meningitis/death!
Workstation skills (call)
Can you post process a perfusion CT?
Can you make MIP images from source CTA images?
Q: Why are overlapping MIP slabs important when reviewing CTAs?
A: If slabs do not overlap, it may be impossible to determine if a vessel is narrowed. We typically have a slab interval that is half the slab thickness for this reason.
Q: How you tell if the MIP was done properly.
A: One should see segment of vessels that overlap on sequential MIP images. (for vessels that course more or less parallel to the slab)