1/"You can put this diagnosis in the differential as many times as you want in your life, but you will only be right once," I told my fellow.
A🧵about a dx you hear about but are rarely lucky enough to see #medtwitter#FOAMed#FOAMrad#medstudent#neurorad#radres#neurosurgery
2/Pt had a calcified lesion in the posterior fossa found incidentally on a trauma CT, that was now enlarging. It had very coarse, stippled appearing calcifications, like grains of sand or dirt
3/It also had very jagged, irregular margins, almost as if the grains of calcium had just been piled up together haphazardly
4/On MRI, it was very T2 dark (from the calcs) & demonstrated mild enhancement. It was extraaxial, but didn't appear to arise from the meninges. Rather, it was in the lateral cerebellomedullary cistern, where CN 9-11 arise.
5/So went back to the CT--left SCM & trapezius atrophy but no cord palsy! This means it's a CN11 lesion--not just affecting it from mass effect, then it would affect 10 also. Calcified schwannomas are rare. CN11 schwannomas are rare. Calcified CN11 schwannomas likely don't exist
6/Googling "calcified lesion CN11" gave us CAPNON--a rare, non-neoplastic, reactive process. It affects CNs & when it does, usually 11.We were right! So I've had my 1 time to be right about this. If you haven't, now you know what to look for to make this dx a feather in your CAP!
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@TheAJNR 2/Since the prehistoric days of medicine (1979!), we knew that some brain tumor patients treated w/radiation (XRT) initially declined, but then get better.
Today, we see this on imaging, where it looks worse early, but then gets better.
Now we call this pseudoprogression.
@TheAJNR 3/Why does this happen?
XRT induces a lot of inflammatory changes—from initiating the complement cascade to opening the blood brain barrier (BBB)
It’s these inflammatory changes that make the imaging look worse.