<prompt> Choose the appropriate lettered structure in this MRI scan showing a sagittal section through the head and neck. A tumor of which structure can be removed through the transsphenoidal approach following the septum of the nose through the body of the sphenoid?ABCD  <response>: a The pituitary gland can be reached through the transsphenoidal approach following the septum of the nose through the body of the sphenoid. 