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/Have MULTIPLE questions about the new criteria for MULTIPLE sclerosis?
ECTRIMS 2024 just came out w/proposed new changes to the McDonald criteria for multiple sclerosis.
The changes are complex, but here is a thread w/the basics that you NEED to know!
2/The 2017 criteria were complex as well, but the basic theme was that they required dissemination in both time & space.
So you needed lesions in multiple locations and of multiple different ages.
3/Proposed new criteria bring a paradigm shift from relying on a combination of dissemination in both space in time, to relying on other factors that can replace dissemination in time
It also proposes that new imaging features specific to MS can be used in diagnosis as well
How back pain radiates can tell you where the lesion is—if you know where to look!
Do YOU know where to look?
Here’s how to remember the lumbar radicular pain distributions!
2/Why is it important to know the radicular pain distributions?
Most times patients have many POSSIBLE sources of pain--and when you are looking at an MRI, it's your job to decide which finding is the most LIKELY source of pain
These pain distributions can help you do that!
3/Let’s start with L1. L1 radiates to the groin.
I remember that b/c the number 1 is, well, um…phallic.
1/Hate it when one radiologist called the stenosis mild, the next one said moderate--but it was unchanged?!
How do you grade it?
Do you estimate? Measure? Guess???
Here’s a thread about a lumbar grading system that’s easy, reproducible & evidence-based!
2/Lumbar stenosis has always been controversial.
In 2012, they tried to survey spine experts to get a consensus as to what are the most important criteria for canal & foraminal stenosis.
And the consensus was…that there was no consensus
So what should you use to call it?
3/Well, you don’t want just gestalt it—that is a recipe for inconsistency & disagreement
But you don’t want to measure everything either—measurements are not only cumbersome, they introduce reader variability & absolute measurements don’t mean the same thing in every patient.