Transsphenoidal surgery is a type of surgery in which an endoscope and/or surgical instruments are inserted into part of the brain by going through the nose and the sphenoid bone (a butterfly-shaped bone forming the anterior inferior portion of the brain case) into the sphenoidal sinus cavity. Transsphenoidal surgery is used to remove tumors of the pituitary gland. (Such tumours, although within the skull, are outside the brain itself).
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Transsphenoidal surgery Wikipedia(Text) CC BY-SA