Cystic fibrosis is named after cysts, yet involves none
A cyst is a sealed pouch whose wall is built from cells that look and behave unlike their neighbours. It may hold air, fluid or something semi-solid, and it can vanish on its own. Confusingly, some famous medical terms built on the same Greek root have nothing to do with cysts.
What separates a cyst from a random lump is its lining: a distinct envelope of abnormal cells, rather like a bubble with its own skin. A pocket of pus is an abscess, not a cyst. A pseudocyst also holds fluid but lacks that epithelial lining, and a syrinx, a fluid channel in the spinal cord or brainstem, is sometimes wrongly given the label. Size vocabulary runs from microcysts, visible only under magnification, to unusually large macrocysts.
Cysts turn up almost anywhere. A Baker's cyst bulges behind the knee, ganglion cysts sit on hand and foot joints, a pilonidal cyst forms near the tailbone, and dermoid cysts can appear from the head down. Some come from parasites: hydatid cysts grow in the liver or elsewhere from the larval stage of the tapeworm Echinococcus granulosus. Adrenal cysts are rare, showing up in roughly 0.06 to 0.18 percent of autopsy studies, and about 7 percent of them can be malignant.
Some cysts are tumours, known as cystic tumours, while many others arise from abnormal but non-cancerous growth. One account describes the body walling off rapidly dividing cells inside a capsule; if those cells later develop their own blood supply, the barrier stops working and the growth may progress.
Treatment ranges from watching and waiting, since some resolve without help, through scraping out the contents to full surgical removal. The word itself comes from a Greek root meaning a fluid-filled sac, which also crops up in terms for the bladder and gallbladder. Cystic fibrosis, described in 1938, takes its name from that root yet is a genetic disorder that does not involve cysts at all.
Source: Cyst
