Changes

==== External links ====

==== External links ====

* [http://www.nlm.nih.gov/medlineplus/ency/article/001310.htm Medical encyclopædia entry (as mirrored on nih.gov)]

* [http://www.nlm.nih.gov/medlineplus/ency/article/001310.htm Medical encyclopedia entry (as mirrored on nih.gov)]