Pituitary stalk agenesis: magnetic resonance imaging of 'ectopic posterior lobe' with surgical correlation.

A patient with anterior pituitary deficiencies, without diabetes insipidus, was found to have a retrochiasmatic mass in association with a large middle fossa cyst on CT and MRI scans, and no tissue in the sella ('empty sella'). At surgery, the pituitary stalk was absent. The retrochiasmatic mass was biopsied and shown to be consistent with pituitary stalk. Recent descriptions of MR visualization of an 'ectopic' posterior pituitary lobe are discussed in relation to this case of agenesis of the pituitary stalk and posterior lobe.