2/Some believe that the peaked, mountain like appearance of the frontal lobes is a critical sign of a life-threatening complication & should be called & reported. Others believe it is too non-specific, is commonly seen when there isn’t tension & should be retired. Who’s right?
3/First, let’s clarify about what the Mt Fuji sign actually is. Most are familiar with the fact that large collections of pneumocephalus can compress the frontal lobes—making them look like the slopes of a mountain. But this isn’t actually enough to call Mt Fuji.
4/You also need to see frontal lobe separation. This means the subdural air tension is greater than CSF surface tension between the frontal lobes--one of the highest liquid surface tensions—so you know pressure is high. This little V is why it looks like Mt Fuji, not any mountain
5/Why do we get tension pneumocephalus? 3 main ways. (1) Upside down coke bottle effect w/a CSF leak. As liquid drips out w/a CSF leak, nature abhors a vacuum, so air rushes in to replace it. If outside pressure is higher than CSF pressure, more air will come in & create tension
6/Here’s a skullbase CSF leak creating pneumocephalus. As CSF leaks out, air replaces it. If air pressure is higher than intracranial pressure, more air will come in. The worst tension pneumocephalus I ever saw was a pt w/an unknown sphenoid sinus skullbase leak they put on CPAP!
7/Next mechanism is the ball valve mechanism. Air gets in through a defect (from trauma, surgery, etc). Increased pressure eventually pushes down on the brain, causing the brain to close the defect so the air can’t escape. This is the same mechanism seen w/tension pneumothorax.
8/Final mechanism is use of nitrous oxide in neuroanesthesia. If the pt has a subdural collection (usually w/air in the operative setting), nitrous oxide enters the subdural 34 times faster than it diffuses out as nitrogen into the blood stream—creating increased pressure/tension
9/This is why nitrous oxide is no longer commonly used in neuroanesthesia. Decreased use of nitrous oxide is also why tension pneumocephalus is less common in the post-operative setting now than it was in the past.
10/So how helpful is the Mt Fuji sign for determining tension pneumocephalus post-operatively (a time when pneumocephalus is common)? Well it turns out, the sign can be seen in 1/3 pts without a neurosurgical emergency. So it is not very specific and can cause overcalling
11/More importantly is how the pt is doing clinically. Significant pneumocephalus can be seen post op—but if the pt is not declining, even large amounts of pneumocephalus can be managed by putting the pt on 100% O2--just like w/a pneumothorax--w/good results.
12/So remember it isn’t just one sign—it is the whole picture of how the pt is doing clinically. Don’t lose sight of the forest for the mountain!
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1/Do you get a Broca’s aphasia trying remember the location of Broca's area?
Does trying to remember inferior frontal gyrus anatomy leave you speechless?
Don't be at a loss for words when it comes to Broca's area
Here’s a 🧵to help you remember the anatomy of this key region!
2/Anatomy of the inferior frontal gyrus (IFG) is best seen on the sagittal images, where it looks like the McDonald’s arches.
So, to find this area on MR, I open the sagittal images & scroll until I see the arches. When it comes to this method of finding the IFG, i’m lovin it.
3/Inferior frontal gyrus also looks like a sideways 3, if you prefer. This 3 is helpful bc the inferior frontal gyrus has 3 parts—called pars
1/Need help reading spine imaging? I’ve got your back!
It’s as easy as ABC!
A thread about an easy mnemonic you can use on every single spine study you see to increase your speed & make sure you never miss a thing!
2/A is for alignment
Look for: (1) Unstable injuries
(2) Malalignment that causes early degenerative change. Abnormal motion causes spinal elements to abnormally move against each other, like grinding teeth wears down teeth—this wears down the spine
3/B is for bones.
On CT, the most important thing to look for w/bones is fractures. You may see focal bony lesions, but you may not
On MR, it is the opposite—you can see marrow lesions easily but you may or may not see edema associated w/fractures if the fracture is subtle
@TheAJNR 2/Vascular cognitive impairment, or its most serious form, vascular dementia, used to be called multi-infarct dementia.
It was thought dementia directly resulted from brain volume loss from infarcts, w/the thought that 50-100cc of infarcted related volume loss caused dementia
@TheAJNR 3/But that’s now outdated. We now know vascular dementia results from diverse pathologies that all share a common vascular origin.
It’s possible to lose little volume from infarct & still result in dementia.
So if infarcts are common—which contribute to vascular dementia?