A cyst or fluid-filled sac located in or near the head region.
From Greek 'kephale' (head) + 'kystis' (bladder, sac). Medical term combining location with the structure of an enclosed fluid cavity.
Parasitic tapeworms can form cephalocysts in the brain—the organism's head (or scolex) gets trapped inside a protective sac, which sounds like science fiction but is actually a real and serious medical condition.
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