Image Originally from Peru this individual was noted on MRI to have curved slivers of low (air) density just within the perimeter of his hydatid.What is this sign and what does it indicate?
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Image  It has been called the "air crescent" sign, and, for some, its presence is a sensitive indicator that the cyst is an hydatid and not a simple cyst. However it has also been reported in aspergillomas. It's prognostic value for risk of perforation is still unexplored as far as I can see. This hydatid in fact had an air fluid level (indicating a leak) seen on the chest x-ray at the time the "air crescent" was visualized on the MRI. (see image)

  Dec 1, 2003