Pilonidal Cysts
Adolescents and young adults can develop a painful swelling at the end of the spine near the tail bone.  This is often caused by a cyst that contains hair giving it the name pilonidal cyst from "pilo" meaning hair and "nidal" meaning nest. 
There is some controversy on whether these cysts are present at birth (congenital) or whether they develop from an ingrown hair (acquired).  The typical age of presentation, the constant connection with the surface of the sacral bone and other features tend to point more toward the congenital theory. 
These cysts can become infected and require an incision to drain pus, however, incision and drainage is not a cure.  After an infection, it is necessary to wait 8 to 12 weeks to allow the inflammation to subside before excising (cutting out) the entire cyst with all its branches and roots. 
The wound that is left after this excision can be quite large.  It often heals by “second intention” which is from the inside out through daily packings.  On occasion some reconstructive surgery or a wound vac (a dressing with a vacuum system that helps promote healing of an open wound) is needed.

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